{"id":190,"date":"2021-07-23T09:19:13","date_gmt":"2021-07-23T13:19:13","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/aperrott\/chapter\/classifying-chemical-reactions\/"},"modified":"2022-06-22T09:44:03","modified_gmt":"2022-06-22T13:44:03","slug":"classifying-chemical-reactions","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/aperrott\/chapter\/classifying-chemical-reactions\/","title":{"raw":"4.2 Classifying Chemical Reactions","rendered":"4.2 Classifying Chemical Reactions"},"content":{"raw":"<strong><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.602em;background-color: #cbd4b6;color: #000000\">Learning Objectives<\/span><\/strong>\r\n<div class=\"textbox textbox--learning-objectives\">\r\n\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Define three common types of chemical reactions (precipitation, acid-base, and oxidation-reduction)<\/li>\r\n \t<li>Classify chemical reactions as one of these three types given appropriate descriptions or chemical equations<\/li>\r\n \t<li>Identify common acids and bases<\/li>\r\n \t<li>Predict the solubility of common inorganic compounds by using solubility rules<\/li>\r\n \t<li>Compute the oxidation states for elements in compounds<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idp140132627979408\">Humans interact with one another in various and complex ways, and we classify these interactions according to common patterns of behavior. When two humans exchange information, we say they are communicating. When they exchange blows with their fists or feet, we say they are fighting. Faced with a wide range of varied interactions between chemical substances, scientists have likewise found it convenient (or even necessary) to classify chemical interactions by identifying common patterns of reactivity. This module will provide an introduction to three of the most prevalent types of chemical reactions: precipitation, acid-base, and oxidation-reduction.<\/p>\r\n\r\n<div id=\"fs-idp140132627979792\" class=\"bc-section section\" data-depth=\"1\">\r\n<h3 data-type=\"title\"><strong>Precipitation Reactions and Solubility Rules<\/strong><\/h3>\r\n<p id=\"fs-idp140132618169728\">A <span data-type=\"term\">precipitation reaction<\/span> is one in which dissolved substances react to form one (or more) solid products. Many reactions of this type involve the exchange of ions between ionic compounds in aqueous solution and are sometimes referred to as <em data-effect=\"italics\">double displacement<\/em>, <em data-effect=\"italics\">double replacement<\/em>, or <em data-effect=\"italics\">metathesis<\/em> reactions. These reactions are common in nature and are responsible for the formation of coral reefs in ocean waters and kidney stones in animals. They are used widely in industry for production of a number of commodity and specialty chemicals. Precipitation reactions also play a central role in many chemical analysis techniques, including spot tests used to identify metal ions and <em data-effect=\"italics\">gravimetric methods<\/em> for determining the composition of matter.<\/p>\r\n<p id=\"fs-idp140132617792992\">The extent to which a substance may be dissolved in water, or any solvent, is quantitatively expressed as its <strong>solubility<\/strong>, defined as the maximum concentration of a substance that can be achieved under specified conditions. Substances with relatively large solubilities are said to be <strong>soluble<\/strong>. A substance will <strong>precipitate <\/strong>when solution conditions are such that its concentration exceeds its solubility. Substances with relatively low solubilities are said to be <strong>insoluble<\/strong>, and these are the substances that readily precipitate from solution. More information on these important concepts is provided in a later chapter on solutions. For purposes of predicting the identities of solids formed by precipitation reactions, one may simply refer to patterns of solubility that have been observed for many ionic compounds (<a class=\"autogenerated-content\" href=\"#fs-idp140132617697568\">(Figure)<\/a>).<\/p>\r\n<img class=\"alignnone wp-image-1166\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-263x300.png\" alt=\"\" width=\"600\" height=\"684\" \/>\r\n<p id=\"fs-idm63476864\">A vivid example of precipitation is observed when solutions of potassium iodide and lead nitrate are mixed, resulting in the formation of solid lead iodide:<\/p>\r\n\r\n<div id=\"fs-idp98445312\" style=\"text-align: center\" data-type=\"equation\">2KI(<em>aq<\/em>) + Pb(NO<sub>3<\/sub>)<sub>2<\/sub>(<em>aq<\/em>) \u27f6 PbI<sub>2<\/sub>(<em>s<\/em>) + 2KNO<sub>3<\/sub>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idp24544224\">This observation is consistent with the solubility guidelines: The only insoluble compound among all those involved is lead iodide, one of the exceptions to the general solubility of iodide salts.<\/p>\r\n<p id=\"fs-idp30939280\">The net ionic equation representing this reaction is:<\/p>\r\n\r\n<div id=\"fs-idp31365696\" style=\"text-align: center\" data-type=\"equation\">Pb<sup>2+<\/sup>(<em>aq<\/em>) + 2I<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 PbI<sub>2<\/sub>(<em>s<\/em>)<\/div>\r\n<p id=\"fs-idm52098368\">Lead iodide is a bright yellow solid that was formerly used as an artist\u2019s pigment known as iodine yellow (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_LeadIodide\">(Figure)<\/a>). The properties of pure PbI<sub>2<\/sub> crystals make them useful for fabrication of X-ray and gamma ray detectors.<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_04_02_LeadIodide\" class=\"scaled-down\">\r\n<div class=\"bc-figcaption figcaption\">A precipitate of PbI<sub>2<\/sub> forms when solutions containing Pb<sup>2+<\/sup> and I<sup>\u2212<\/sup> are mixed. (credit: Der Kreole\/Wikimedia Commons)<\/div>\r\n<span id=\"fs-idp29197296\" data-type=\"media\" data-alt=\"A photograph is shown of a yellow green opaque substance swirled through a clear, colorless liquid in a test tube.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_LeadIodide-1.jpg\" alt=\"A photograph is shown of a yellow green opaque substance swirled through a clear, colorless liquid in a test tube.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<p id=\"fs-idp157312304\">The solubility guidelines in the table above may be used to predict whether a precipitation reaction will occur when solutions of soluble ionic compounds are mixed together. One merely needs to identify all the ions present in the solution and then consider if possible cation\/anion pairing could result in an insoluble compound. For example, mixing solutions of silver nitrate and sodium chloride will yield a solution containing Ag<sup>+<\/sup>, NO<sub>3<\/sub><sup>-<\/sup>, Na<sup>+<\/sup>, and Cl<sup>\u2212<\/sup> ions. Aside from the two ionic compounds originally present in the solutions, AgNO<sub>3<\/sub> and NaCl, two additional ionic compounds may be derived from this collection of ions: NaNO<sub>3<\/sub> and AgCl. The solubility guidelines indicate all nitrate salts are soluble but that AgCl is one of the exceptions to the general solubility of chloride salts. A precipitation reaction, therefore, is predicted to occur, as described by the following equations:<\/p>\r\n\r\n<div id=\"fs-idm4746128\" style=\"text-align: center\" data-type=\"equation\">NaCl(<em>aq<\/em>) + AgNO<sub>3<\/sub>(<em>aq<\/em>) \u27f6 AgCl(<em>s<\/em>) + NaNO<sub>3<\/sub>(<em>aq<\/em>)\u00a0 \u00a0 \u00a0 \u00a0(molecular)<\/div>\r\n<div style=\"text-align: center\" data-type=\"equation\">Ag<sup>+<\/sup>(<em>aq<\/em>) + Cl<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 AgCl(<em>s<\/em>)\u00a0 \u00a0 \u00a0 (net ionic)<\/div>\r\n<div id=\"fs-idp3608096\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idm5664816\"><strong>Predicting Precipitation Reactions:<\/strong><\/p>\r\nPredict the result of mixing reasonably concentrated solutions of the following ionic compounds. If precipitation is expected, write a balanced net ionic equation for the reaction.\r\n<p id=\"fs-idp8541200\">(a) potassium sulfate and barium nitrate<\/p>\r\n<p id=\"fs-idm5793440\">(b) lithium chloride and silver acetate<\/p>\r\n<p id=\"fs-idm605024\">(c) lead nitrate and ammonium carbonate<\/p>\r\n<p id=\"fs-idp65557120\"><strong>Solution:<\/strong><\/p>\r\n(a) The two possible products for this combination are KNO<sub>3<\/sub> and BaSO<sub>4<\/sub>. The solubility guidelines indicate BaSO<sub>4<\/sub> is insoluble, and so a precipitation reaction is expected. The net ionic equation for this reaction, derived in the manner detailed in the previous module, is\r\n<div id=\"eip-799\" style=\"text-align: center\" data-type=\"equation\">Ba<sup>2+<\/sup>(<em>aq<\/em>) + SO<sub>4<\/sub><sup>2-<\/sup>(<em>aq<\/em>) \u27f6 BaSO<sub>4<\/sub>(<em>s<\/em>)<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idm27273344\">(b) The two possible products for this combination are LiC<sub>2<\/sub>H<sub>3<\/sub>O<sub>2<\/sub> and AgCl. The solubility guidelines indicate AgCl is insoluble, and so a precipitation reaction is expected. The net ionic equation for this reaction, derived in the manner detailed in the previous module, is<\/p>\r\n\r\n<div id=\"fs-idm70392576\" style=\"text-align: center\" data-type=\"equation\">Ag<sup>+<\/sup>(<em>aq<\/em>) + Cl<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 AgCl(<em>s<\/em>)<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idm5437216\">(c) The two possible products for this combination are PbCO<sub>3<\/sub> and NH<sub>4<\/sub>NO<sub>3<\/sub>. The solubility guidelines indicate PbCO<sub>3<\/sub> is insoluble, and so a precipitation reaction is expected. The net ionic equation for this reaction, derived in the manner detailed in the previous module, is<\/p>\r\n\r\n<div id=\"eip-767\" style=\"text-align: center\" data-type=\"equation\">Pb<sup>2+<\/sup>(<em>aq<\/em>) + CO<sub>3<\/sub><sup>2-<\/sup>(<em>aq<\/em>) \u27f6 PbCO<sub>3<\/sub>(<em>s<\/em>)<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idm72085968\"><strong>Check Your Learning :<\/strong><\/p>\r\nWhich solution could be used to precipitate the barium ion, Ba<sup>2+<\/sup>, in a water sample: sodium chloride, sodium hydroxide, or sodium sulfate? What is the formula for the expected precipitate?\r\n<div id=\"fs-idp24003520\" data-type=\"note\">\r\n<div data-type=\"title\"><\/div>\r\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\r\n<p id=\"fs-idp153308448\">sodium sulfate, BaSO<sub>4<\/sub><\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp128853312\" class=\"bc-section section\" data-depth=\"1\">\r\n<h3 data-type=\"title\"><strong>Acid-Base Reactions<\/strong><\/h3>\r\n<p id=\"fs-idm1255344\">An<strong> acid-base reaction<\/strong> is one in which a hydrogen ion, H<sup>+<\/sup>, is transferred from one chemical species to another. Such reactions are of central importance to numerous natural and technological processes, ranging from the chemical transformations that take place within cells and the lakes and oceans, to the industrial-scale production of fertilizers, pharmaceuticals, and other substances essential to society. The subject of acid-base chemistry, therefore, is worthy of thorough discussion, and a full chapter is devoted to this topic later in the text.<\/p>\r\n<p id=\"fs-idp89436016\">For purposes of this brief introduction, we will consider only the more common types of acid-base reactions that take place in aqueous solutions. In this context, an <strong>acid <\/strong>is a substance that will dissolve in water to yield hydronium ions, H<sub>3<\/sub>O<sup>+<\/sup>. As an example, consider the equation shown here:<\/p>\r\n\r\n<div id=\"fs-idm54028336\" style=\"text-align: center\" data-type=\"equation\">HCl(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>aq<\/em>) \u27f6 Cl<sup>\u2212<\/sup>(<em>aq<\/em>) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idm10390992\">The process represented by this equation confirms that hydrogen chloride is an acid. When dissolved in water, H<sub>3<\/sub>O<sup>+<\/sup> ions are produced by a chemical reaction in which H<sup>+<\/sup> ions are transferred from HCl molecules to H<sub>2<\/sub>O molecules (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_HClsoln\">(Figure)<\/a>).<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_04_02_HClsoln\" class=\"scaled-down\">\r\n<div class=\"bc-figcaption figcaption\">When hydrogen chloride gas dissolves in water, (a) it reacts as an acid, transferring protons to water molecules to yield (b) hydronium ions (and solvated chloride ions).<\/div>\r\n<span id=\"fs-idp103294384\" data-type=\"media\" data-alt=\"This figure shows two flasks, labeled a and b. The flasks are both sealed with stoppers and are nearly three-quarters full of a liquid. Flask a is labeled H C l followed by g in parentheses. In the liquid there are approximately twenty space-filling molecular models composed of one red sphere and two smaller attached white spheres. The label H subscript 2 O followed by a q in parentheses is connected with a line to one of these models. In the space above the liquid in the flask, four space filling molecular models composed of one larger green sphere to which a smaller white sphere is bonded are shown. To one of these models, the label H C l followed by g in parentheses is attached with a line segment. An arrow is drawn from the space above the liquid pointing down into the liquid below. Flask b is labeled H subscript 3 O superscript positive sign followed by a q in parentheses. This is followed by a plus sign and C l superscript negative sign which is also followed by a q in parentheses. In this flask, no molecules are shown in the open space above the liquid. A label, C l superscript negative sign followed by a q in parentheses, is connected with a line segment to a green sphere. This sphere is surrounded by four molecules composed each of one red sphere and two white smaller spheres. A few of these same molecules appear separate from the green spheres in the liquid. A line segment connects one of them to the label H subscript 2 O which is followed by l in parentheses. There are a few molecules formed from one central larger red sphere to which three smaller white spheres are bonded. A line segment is drawn from one of these to the label H subscript 3 O superscript positive sign, followed by a q in parentheses.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_HClsoln-1.jpg\" alt=\"This figure shows two flasks, labeled a and b. The flasks are both sealed with stoppers and are nearly three-quarters full of a liquid. Flask a is labeled H C l followed by g in parentheses. In the liquid there are approximately twenty space-filling molecular models composed of one red sphere and two smaller attached white spheres. The label H subscript 2 O followed by a q in parentheses is connected with a line to one of these models. In the space above the liquid in the flask, four space filling molecular models composed of one larger green sphere to which a smaller white sphere is bonded are shown. To one of these models, the label H C l followed by g in parentheses is attached with a line segment. An arrow is drawn from the space above the liquid pointing down into the liquid below. Flask b is labeled H subscript 3 O superscript positive sign followed by a q in parentheses. This is followed by a plus sign and C l superscript negative sign which is also followed by a q in parentheses. In this flask, no molecules are shown in the open space above the liquid. A label, C l superscript negative sign followed by a q in parentheses, is connected with a line segment to a green sphere. This sphere is surrounded by four molecules composed each of one red sphere and two white smaller spheres. A few of these same molecules appear separate from the green spheres in the liquid. A line segment connects one of them to the label H subscript 2 O which is followed by l in parentheses. There are a few molecules formed from one central larger red sphere to which three smaller white spheres are bonded. A line segment is drawn from one of these to the label H subscript 3 O superscript positive sign, followed by a q in parentheses.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<p id=\"fs-idm57695504\">The nature of HCl is such that its reaction with water as just described is essentially 100% efficient: Virtually every HCl molecule that dissolves in water will undergo this reaction. Acids that completely react in this fashion are called <strong>strong acids<\/strong>, and HCl is one among just a handful of common acid compounds that are classified as strong (<a class=\"autogenerated-content\" href=\"#fs-idp55395904\">(Figure)<\/a>). A far greater number of compounds behave as <strong>weak acids<\/strong> and only partially react with water, leaving a large majority of dissolved molecules in their original form and generating a relatively small amount of hydronium ions. Weak acids are commonly encountered in nature, being the substances partly responsible for the tangy taste of citrus fruits, the stinging sensation of insect bites, and the unpleasant smells associated with body odor. A familiar example of a weak acid is acetic acid, the main ingredient in food vinegars:<\/p>\r\n\r\n<div id=\"fs-idp23273024\" style=\"text-align: center\" data-type=\"equation\">CH<sub>3<\/sub>CO<sub>2<\/sub>H(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc CH<sub>3<\/sub>CO<sub>2<\/sub><sup>\u2212<\/sup>(<em>aq<\/em>) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idm23363712\">When dissolved in water under typical conditions, only about 1% of acetic acid molecules are present in the ionized form, CH<sub>3<\/sub>CO<sub>2<\/sub><sup>-<\/sup> (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_Citrus\">(Figure)<\/a>). (The use of a double-arrow in the equation above denotes the partial reaction aspect of this process, a concept addressed fully in the chapters on chemical equilibrium.)<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_04_02_Citrus\" class=\"scaled-down\">\r\n<div class=\"bc-figcaption figcaption\">(a) Fruits such as oranges, lemons, and grapefruit contain the weak acid citric acid. (b) Vinegars contain the weak acid acetic acid. (credit a: modification of work by Scott Bauer; credit b: modification of work by Br\u00fccke-Osteuropa\/Wikimedia Commons)<\/div>\r\n<span id=\"fs-idp185890880\" data-type=\"media\" data-alt=\"This figure contains two images, each with an associated structural formula provided in the lower left corner of the image. The first image is a photograph of a variety of thinly sliced, circular cross sections of citrus fruits ranging in color for green to yellow, to orange and reddish-orange. The slices are closely packed on a white background. The structural formula with this picture shows a central chain of five C atoms. The leftmost C atom has an O atom double bonded above and to the left and a singly bonded O atom below and to the left. This single bonded O atom has an H atom indicated in red on its left side which is highlighted in pink. The second C atom moving to the right has H atoms bonded above and below. The third C atom has a single bonded O atom above which has an H atom on its right. This third C atom has a C atom bonded below it which has an O atom double bonded below and to the left and a singly bonded O atom below and to the right. An H atom appears in red and is highlighted in pink to the right of the singly bonded O atom. The fourth C atom has H atoms bonded above and below. The fifth C atom is at the right end of the structure. It has an O atom double bonded above and to the right and a singly bonded O atom below and to the right. This single bonded O atom has a red H atom on its right side which is highlighted in pink. The second image is a photograph of bottles of vinegar. The bottles are labeled, \u201cBalsamic Vinegar,\u201d and appear to be clear and colorless. The liquid in this bottle appears to be brown. The structural formula that appears with this image shows a chain of two C atoms. The leftmost C atom has H atoms bonded above, below, and to the left. The C atom on the right has a doubly bonded O atom above and to the right and a singly bonded O atom below and to the right. This O atom has an H atom bonded to its right which is highlighted in pink.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_Citrus-1.jpg\" alt=\"This figure contains two images, each with an associated structural formula provided in the lower left corner of the image. The first image is a photograph of a variety of thinly sliced, circular cross sections of citrus fruits ranging in color for green to yellow, to orange and reddish-orange. The slices are closely packed on a white background. The structural formula with this picture shows a central chain of five C atoms. The leftmost C atom has an O atom double bonded above and to the left and a singly bonded O atom below and to the left. This single bonded O atom has an H atom indicated in red on its left side which is highlighted in pink. The second C atom moving to the right has H atoms bonded above and below. The third C atom has a single bonded O atom above which has an H atom on its right. This third C atom has a C atom bonded below it which has an O atom double bonded below and to the left and a singly bonded O atom below and to the right. An H atom appears in red and is highlighted in pink to the right of the singly bonded O atom. The fourth C atom has H atoms bonded above and below. The fifth C atom is at the right end of the structure. It has an O atom double bonded above and to the right and a singly bonded O atom below and to the right. This single bonded O atom has a red H atom on its right side which is highlighted in pink. The second image is a photograph of bottles of vinegar. The bottles are labeled, \u201cBalsamic Vinegar,\u201d and appear to be clear and colorless. The liquid in this bottle appears to be brown. The structural formula that appears with this image shows a chain of two C atoms. The leftmost C atom has H atoms bonded above, below, and to the left. The C atom on the right has a doubly bonded O atom above and to the right and a singly bonded O atom below and to the right. This O atom has an H atom bonded to its right which is highlighted in pink.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<table id=\"fs-idp55395904\" class=\"top-titled\" summary=\"This table contains two columns and seven rows. The columns are labeled, \u201cCompound Formula,\u201d and, \u201cName in Aqueous Solution.\u201d Under the column, \u201cCompound Formula,\u201d are: \u201cH B r,\u201d \u201cH C l,\u201d \u201cH I,\u201d \u201cH N O subscript 3,\u201d \u201cH C l O subscript 4,\u201d and, \u201cH subscript 2 S O subscript 4.\u201d Under the column, \u201cName in Aqueous Solution,\u201d are: \u201chydrobromic acid,\u201d \u201chydrochloric acid,\u201d \u201chydroiodic acid,\u201d \u201cnitric acid,\u201d \u201cperchloric acid,\u201d and, \u201csulfuric acid.\u201d\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"3\" data-align=\"center\">Common Strong Acids<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th data-align=\"left\">Compound Formula<\/th>\r\n<th data-align=\"left\">Name in Aqueous Solution<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">HBr<\/td>\r\n<td data-align=\"left\">hydrobromic acid<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">HCl<\/td>\r\n<td data-align=\"left\">hydrochloric acid<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">HI<\/td>\r\n<td data-align=\"left\">hydroiodic acid<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">HNO<sub>3<\/sub><\/td>\r\n<td data-align=\"left\">nitric acid<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">HClO<sub>4<\/sub><\/td>\r\n<td data-align=\"left\">perchloric acid<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">H<sub>2<\/sub>SO<sub>4<\/sub><\/td>\r\n<td data-align=\"left\">sulfuric acid<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<p id=\"fs-idp2912576\">A <strong>base <\/strong>is a substance that will dissolve in water to yield hydroxide ions, OH<sup>\u2212<\/sup>. The most common bases are ionic compounds composed of alkali or alkaline earth metal cations (groups 1 and 2) combined with the hydroxide ion\u2014for example, NaOH and Ca(OH)<sub>2<\/sub>. Unlike the acid compounds discussed previously, these compounds do not react chemically with water; instead they dissolve and dissociate, releasing hydroxide ions directly into the solution. For example, KOH and Ba(OH)<sub>2<\/sub> dissolve in water and dissociate completely to produce cations (K<sup>+<\/sup> and Ba<sup>2+<\/sup>, respectively) and hydroxide ions, OH<sup>\u2212<\/sup>. These bases, along with other hydroxides that completely dissociate in water, are considered<strong> strong bases<\/strong>.<\/p>\r\n<p id=\"fs-idp74282160\">Consider as an example the dissolution of lye (sodium hydroxide) in water:<\/p>\r\n\r\n<div id=\"fs-idm62931696\" style=\"text-align: center\" data-type=\"equation\">NaOH(<em>s<\/em>) \u27f6 Na<sup>+<\/sup>(<em>aq<\/em>) + OH<sup>\u2212<\/sup>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idp8724736\">This equation confirms that sodium hydroxide is a base. When dissolved in water, NaOH dissociates to yield Na<sup>+<\/sup> and OH<sup>\u2212<\/sup> ions. This is also true for any other ionic compound containing hydroxide ions. Since the dissociation process is essentially complete when ionic compounds dissolve in water under typical conditions, NaOH and other ionic hydroxides are all classified as strong bases.<\/p>\r\n<p id=\"fs-idm50199792\">Unlike ionic hydroxides, some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and so are classified as <strong>weak bases<\/strong>. These types of compounds are also abundant in nature and important commodities in various technologies. For example, global production of the weak base ammonia is typically well over 100 metric tons annually, being widely used as an agricultural fertilizer, a raw material for chemical synthesis of other compounds, and an active ingredient in household cleaners (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_ammonia\">(Figure)<\/a>). When dissolved in water, ammonia reacts partially to yield hydroxide ions, as shown here:<\/p>\r\n\r\n<div id=\"fs-idm9327664\" style=\"text-align: center\" data-type=\"equation\">NH<sub>3<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc NH<sub>4<\/sub><sup>+<\/sup>(<em>aq<\/em>) + OH<sup>\u2212<\/sup>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idm73811808\">This is, by definition, an acid-base reaction, in this case involving the transfer of H<sup>+<\/sup> ions from water molecules to ammonia molecules. Under typical conditions, only about 1% of the dissolved ammonia is present as NH<sub>4<\/sub><sup>+<\/sup>\u00a0ions.<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_04_02_ammonia\" class=\"scaled-down\">\r\n<div class=\"bc-figcaption figcaption\">Ammonia is a weak base used in a variety of applications. (a) Pure ammonia is commonly applied as an agricultural fertilizer. (b) Dilute solutions of ammonia are effective household cleansers. (credit a: modification of work by National Resources Conservation Service; credit b: modification of work by pat00139)<\/div>\r\n<span id=\"fs-idm1349584\" data-type=\"media\" data-alt=\"This photograph shows a large agricultural tractor in a field pulling a field sprayer and a large, white cylindrical tank which is labeled \u201cCaution Ammonia.\u201d\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_ammonia-1.jpg\" alt=\"This photograph shows a large agricultural tractor in a field pulling a field sprayer and a large, white cylindrical tank which is labeled \u201cCaution Ammonia.\u201d\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<p id=\"fs-idp101951952\">A <span data-type=\"term\"><strong>neutralization<\/strong> reaction<\/span> is a specific type of acid-base reaction in which the reactants are an acid and a base (but not water), and the products are often (but not always!) a <span data-type=\"term\">salt<\/span> and water:<\/p>\r\n\r\n<div id=\"fs-idm49357376\" style=\"text-align: center\" data-type=\"equation\">acid + base \u27f6 salt + water<\/div>\r\n<p id=\"fs-idm21828864\">To illustrate a neutralization reaction, consider what happens when a typical antacid such as milk of magnesia (an aqueous suspension of solid Mg(OH)<sub>2<\/sub>) is ingested to ease symptoms associated with excess stomach acid (HCl):<\/p>\r\n\r\n<div id=\"fs-idm8492448\" style=\"text-align: center\" data-type=\"equation\">Mg(OH)<sub>2<\/sub>(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 MgCl<sub>2<\/sub>(<em>aq<\/em>)+ 2H<sub>2<\/sub>O(<em>l<\/em>)<\/div>\r\n<p id=\"fs-idm52053696\">Note that in addition to water, this reaction produces a salt, magnesium chloride.<\/p>\r\n\r\n<div id=\"fs-idm49295040\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idm22209232\"><strong>Writing Equations for Acid-Base Reactions:<\/strong><\/p>\r\nWrite balanced chemical equations for the acid-base reactions described here:\r\n<p id=\"fs-idp55337856\">(a) hypochlorous acid reacts with water<\/p>\r\n<p id=\"fs-idm22923872\">(b) a solution of barium hydroxide is neutralized with a solution of nitric acid<\/p>\r\n<p id=\"fs-idp20180224\"><strong>Solution:<\/strong><\/p>\r\n(a) The two reactants are provided, HOCl and H<sub>2<\/sub>O. Since the substance is an acid, its reaction with water will involve the transfer of H<sup>+<\/sup> from HOCl to H<sub>2<\/sub>O to generate hydronium ions, H<sub>3<\/sub>O<sup>+<\/sup> and hypochlorite ions, OCl<sup>\u2212<\/sup>.\r\n<div id=\"fs-idm141852368\" style=\"text-align: center\" data-type=\"equation\">HOCl(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc OCl<sup>\u2212<\/sup>(<em>aq<\/em>) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idp73299936\">A double-arrow is appropriate in this equation because it indicates the HOCl is a weak acid that has not reacted completely.<\/p>\r\n<p id=\"fs-idm23237280\">(b) The two reactants are provided, Ba(OH)<sub>2<\/sub> and HNO<sub>3<\/sub>. Since this is a neutralization reaction, the two products will be water and a salt composed of the cation of the ionic hydroxide (Ba<sup>2+<\/sup>) and the anion generated when the acid transfers its hydrogen ion (NO<sub>3<\/sub><sup>\u2212<\/sup>).<\/p>\r\n\r\n<div id=\"fs-idp42762464\" style=\"text-align: center\" data-type=\"equation\">Ba(OH)<sub>2<\/sub>(<em>aq<\/em>) + 2HNO<sub>3<\/sub>(<em>aq<\/em>) \u27f6 Ba(NO<sub>3<\/sub>)<sub>2<\/sub>(<em>aq<\/em>) + 2H<sub>2<\/sub>O(<em>l<\/em>)<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idm20270192\"><strong>Check Your Learning:<\/strong><\/p>\r\nWrite the net ionic equation representing the neutralization of any strong acid with an ionic hydroxide. (Hint: Consider the ions produced when a strong acid is dissolved in water.)\r\n\r\n&nbsp;\r\n<div id=\"fs-idp218691008\" data-type=\"note\">\r\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\r\nH<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>) + OH<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 2H<sub>2<\/sub>O(<em>l<\/em>)\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm119690112\" class=\"chemistry everyday-life\" data-type=\"note\">\r\n<div data-type=\"title\"><\/div>\r\n<div data-type=\"title\"><strong>Stomach Antacids<\/strong><\/div>\r\n<p id=\"fs-idm55572160\">Our stomachs contain a solution of roughly 0.03 <em data-effect=\"italics\">M<\/em> HCl, which helps us digest the food we eat. The burning sensation associated with heartburn is a result of the acid of the stomach leaking through the muscular valve at the top of the stomach into the lower reaches of the esophagus. The lining of the esophagus is not protected from the corrosive effects of stomach acid the way the lining of the stomach is, and the results can be very painful. When we have heartburn, it feels better if we reduce the excess acid in the esophagus by taking an antacid. As you may have guessed, antacids are bases. One of the most common antacids is calcium carbonate, CaCO<sub>3<\/sub>. The reaction,<\/p>\r\n\r\n<div id=\"fs-idm156299504\" style=\"text-align: center\" data-type=\"equation\">CaCO<sub>3<\/sub>(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 CaCl<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) + CO<sub>2<\/sub>(<em>g<\/em>)<\/div>\r\n<p id=\"fs-idp31618928\">not only neutralizes stomach acid, it also produces CO<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>), which may result in a satisfying belch.<\/p>\r\n<p id=\"fs-idm158365360\">Milk of Magnesia is a suspension of the sparingly soluble base magnesium hydroxide, Mg(OH)<sub>2<\/sub>. It works according to the reaction:<\/p>\r\n\r\n<div id=\"fs-idp1457888\" style=\"text-align: center\" data-type=\"equation\">Mg(OH)<sub>2<\/sub>(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 MgCl<sub>2<\/sub>(<em>aq<\/em>) + 2H<sub>2<\/sub>O(<em>l<\/em>)<\/div>\r\n<div id=\"fs-idp51950320\" data-type=\"equation\"><\/div>\r\n<p id=\"fs-idp39159216\">This reaction does not produce carbon dioxide, but magnesium-containing antacids can have a laxative effect. Several antacids have aluminum hydroxide, Al(OH)<sub>3<\/sub>, as an active ingredient. The aluminum hydroxide tends to cause constipation, and some antacids use aluminum hydroxide in concert with magnesium hydroxide to balance the side effects of the two substances.<\/p>\r\n&nbsp;\r\n\r\n<\/div>\r\n<div id=\"fs-idm116223344\" class=\"chemistry everyday-life\" data-type=\"note\">\r\n<div data-type=\"title\"><strong>Culinary Aspects of Chemistry<\/strong><\/div>\r\n<p id=\"fs-idm118182736\">Examples of acid-base chemistry are abundant in the culinary world. One example is the use of baking soda, or sodium\u00a0 hydrogen carbonate in baking. NaHCO<sub>3<\/sub> is a base. When it reacts with a\u00a0 acid such as lemon juice, buttermilk, or sour cream in a batter, bubbles of carbon dioxide gas are formed from decomposition of the resulting carbonic acid, and the batter \u201crises.\u201d Baking powder is a combination of sodium hydrogen carbonate, and one or more acid salts that react when the two chemicals come in contact with water in the batter.<\/p>\r\n<p id=\"fs-idp3959248\">Many people like to put lemon juice or vinegar, both of which are acids, on cooked fish (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_03_FishLemon\">(Figure)<\/a>). It turns out that fish have volatile amines (bases) in their systems, which are neutralized by the acids to yield involatile ammonium salts. This reduces the odor of the fish, and also adds a \u201csour\u201d taste that we seem to enjoy.<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_14_03_FishLemon\" class=\"bc-figure figure\">\r\n<div class=\"bc-figcaption figcaption\">A neutralization reaction takes place between citric acid in lemons or acetic acid in vinegar, and the bases in the flesh of fish.<\/div>\r\n<span id=\"fs-idm122004144\" data-type=\"media\" data-alt=\"An image is shown of two fish with heads removed and skin on with lemon slices placed in the body cavity. The first line of an equation below the image reads C H subscript 3 C O O H plus N H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2 arrow C H subscript 3 C O O superscript negative sign plus N H subscript 3 superscript positive sign C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2. The second line of the equation reads Acetic acid plus sign Putrescine arrow Acetate ion plus sign Putrescinium ion.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_03_FishLemon-1.jpg\" alt=\"An image is shown of two fish with heads removed and skin on with lemon slices placed in the body cavity. The first line of an equation below the image reads C H subscript 3 C O O H plus N H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2 arrow C H subscript 3 C O O superscript negative sign plus N H subscript 3 superscript positive sign C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2. The second line of the equation reads Acetic acid plus sign Putrescine arrow Acetate ion plus sign Putrescinium ion.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<p id=\"fs-idm117278880\">Pickling is a method used to preserve vegetables using a naturally produced acidic environment. The vegetable, such as a cucumber, is placed in a sealed jar submerged in a brine solution. The brine solution favors the growth of beneficial bacteria and suppresses the growth of harmful bacteria. The beneficial bacteria feed on starches in the cucumber and produce lactic acid as a waste product in a process called fermentation. The lactic acid eventually increases the acidity of the brine to a level that kills any harmful bacteria, which require a basic environment. Without the harmful bacteria consuming the cucumbers they are able to last much longer than if they were unprotected. A byproduct of the pickling process changes the flavor of the vegetables with the acid making them taste sour.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idp164722352\" class=\"chemistry link-to-learning\" data-type=\"note\">\r\n<p id=\"fs-idm40317104\">Explore the microscopic <a href=\"http:\/\/openstaxcollege.org\/l\/16AcidsBases\">view<\/a> of strong and weak acids and bases.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm48520656\" class=\"bc-section section\" data-depth=\"1\">\r\n<h3 data-type=\"title\"><strong>Oxidation-Reduction Reactions<\/strong><\/h3>\r\n<p id=\"fs-idp3801440\">Earth\u2019s atmosphere contains about 20% molecular oxygen, O<sub>2<\/sub>, a chemically reactive gas that plays an essential role in the metabolism of aerobic organisms and in many environmental processes that shape the world. The term <strong>oxidation <\/strong>was originally used to describe chemical reactions involving O<sub>2<\/sub>, but its meaning has evolved to refer to a broad and important reaction class known as <em data-effect=\"italics\">oxidation-reduction (redox) reactions<\/em>. A few examples of such reactions will be used to develop a clear picture of this classification.<\/p>\r\n<p id=\"fs-idm49954608\">Some redox reactions involve the transfer of electrons between reactant species to yield ionic products, such as the reaction between sodium and chlorine to yield sodium chloride:<\/p>\r\n\r\n<div id=\"fs-idm5657872\" style=\"text-align: center\" data-type=\"equation\">2Na(<em>s<\/em>) + Cl<sub>2<\/sub>(<em>g<\/em>) \u27f6 2NaCl(<em>s<\/em>)<\/div>\r\n<p id=\"fs-idm102441680\">It is helpful to view the process with regard to each individual reactant, that is, to represent the fate of each reactant in the form of an equation called a <strong>half-reaction<\/strong>:<\/p>\r\n\r\n<div id=\"fs-idp15924368\" style=\"text-align: center\" data-type=\"equation\">2Na(<em>s<\/em>) \u27f6 2Na<sup>+<\/sup>(<em>s<\/em>) + 2e<sup>-<\/sup><\/div>\r\n<div style=\"text-align: center\" data-type=\"equation\">Cl<sub>2<\/sub>(<em>g<\/em>) + 2e<sup>-<\/sup> \u27f6 2Cl<sup>\u2212<\/sup>(<em>s<\/em>)<\/div>\r\n<p id=\"fs-idp97564400\">These equations show that Na atoms <em data-effect=\"italics\">lose electrons<\/em> while Cl atoms (in the Cl<sub>2<\/sub> molecule) <em data-effect=\"italics\">gain electrons<\/em>, the \u201c<em data-effect=\"italics\">s<\/em>\u201d subscripts for the resulting ions signifying they are present in the form of a solid ionic compound. For redox reactions of this sort, the loss and gain of electrons define the complementary processes that occur:<\/p>\r\n\r\n<div id=\"fs-idp61672384\" style=\"text-align: center\" data-type=\"equation\"><strong>oxidation<\/strong> = loss of electrons<\/div>\r\n<div style=\"text-align: center\" data-type=\"equation\"><strong>reduction<\/strong> = gain of electrons<\/div>\r\n<p id=\"fs-idp6686448\">In this reaction, then, sodium is <em data-effect=\"italics\">oxidized<\/em> and chlorine undergoes <strong>reduction<\/strong>. Viewed from a more active perspective, sodium functions as a <span data-type=\"term\"><strong>reducing agent<\/strong> (reductant)<\/span>, since it provides electrons to (or reduces) chlorine. Likewise, chlorine functions as an <span data-type=\"term\"><strong>oxidizing agent<\/strong> (oxidant)<\/span>, as it effectively removes electrons from (oxidizes) sodium.<\/p>\r\n\r\n<div id=\"fs-idm29833328\" style=\"text-align: center\" data-type=\"equation\"><strong>reducing agent<\/strong> = species that is oxidized<\/div>\r\n<div style=\"text-align: center\" data-type=\"equation\"><strong>oxidizing agent<\/strong> = species that is reduced<\/div>\r\n<p id=\"fs-idp108466096\">Consider another reaction:<\/p>\r\n\r\n<div id=\"fs-idp37282464\" style=\"text-align: center\" data-type=\"equation\">H<sub>2<\/sub>(<em>g<\/em>) +\u00a0 Cl<sub>2<\/sub>(<em>g<\/em>) \u27f6 2HCl(<em>g<\/em>)<\/div>\r\n<p id=\"fs-idp168168224\">The product of this reaction is a covalent compound (it is in the gaseous, not aqueous, state), so transfer of electrons in the explicit sense is not involved. To clarify the similarity of this reaction to the previous one and permit an unambiguous definition of redox reactions, a property called <em data-effect=\"italics\">oxidation number<\/em> has been defined. The <strong>oxidation number <\/strong>(or <span data-type=\"term\">oxidation state<\/span>) of an element in a compound is the charge its atoms would possess <em data-effect=\"italics\">if the compound was ionic<\/em>. The following guidelines are used to assign oxidation numbers to each element in a molecule or ion.<\/p>\r\n\r\n<ol id=\"fs-idp29396208\" type=\"1\">\r\n \t<li>The oxidation number of an atom in an elemental substance is zero.<\/li>\r\n \t<li>The oxidation number of a monatomic ion is equal to the ion\u2019s charge.<\/li>\r\n \t<li>Oxidation numbers for common nonmetals are usually assigned as follows:\r\n<ul id=\"fs-idm48186672\" data-bullet-style=\"bullet\">\r\n \t<li>Hydrogen: +1 when combined with nonmetals, \u22121 when combined with metals<\/li>\r\n \t<li>Oxygen: \u22122 in most compounds<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>The sum of oxidation numbers for all atoms in a molecule or polyatomic ion equals the charge on the molecule or ion.<\/li>\r\n<\/ol>\r\n<p id=\"fs-idm72440048\">Note: The proper convention for reporting charge is to write the number first, followed by the sign (e.g., 2+), while oxidation number is written with the reversed sequence, sign followed by number (e.g., +2). This convention aims to emphasize the distinction between these two related properties.<\/p>\r\n\r\n<div id=\"fs-idm24634320\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idm73523056\"><strong>Assigning Oxidation Numbers:<\/strong><\/p>\r\nFollow the guidelines in this section of the text to assign oxidation numbers to all the elements in the following species:\r\n<p id=\"fs-idp9372816\">(a) H<sub>2<\/sub>S<\/p>\r\n<p id=\"fs-idp5671152\">(b) SO<sub>3<\/sub><sup>2-<\/sup><\/p>\r\n<p id=\"fs-idp109909120\">(c) Na<sub>2<\/sub>SO<sub>4<\/sub><\/p>\r\n<p id=\"fs-idp203498912\"><strong>Solution:<\/strong><\/p>\r\n(a) According to guideline 3, the oxidation number for H is +1.\r\n<p id=\"fs-idm32134656\">Using this oxidation number and the compound\u2019s formula, guideline 4 may then be used to calculate the oxidation number for sulfur:<\/p>\r\n&nbsp;\r\n<div id=\"fs-idm58489232\" data-type=\"equation\">charge on H<sub>2<\/sub>S = 0 = (2 \u00d7 +1) + (1 \u00d7 <em>x<\/em>)<\/div>\r\n<div data-type=\"equation\"><em>x<\/em> = 0 - (2 \u00d7 +1) = - 2<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idm1965888\">(b) Guideline 3 suggests the oxidation number for oxygen is \u22122.<\/p>\r\n<p id=\"fs-idp181502096\">Using this oxidation number and the ion\u2019s formula, guideline 4 may then be used to calculate the oxidation number for sulfur:<\/p>\r\n&nbsp;\r\n<div id=\"fs-idm22135232\" data-type=\"equation\">\r\n<div id=\"fs-idm58489232\" data-type=\"equation\">charge on SO<sub>3<\/sub><sup>2-<\/sup> = -2 = <em>x<\/em> + (3 \u00d7 -2)<\/div>\r\n<div data-type=\"equation\"><em>x<\/em> = -2 - (3 \u00d7 -2) = +4<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<\/div>\r\n<p id=\"fs-idp180932672\">(c) For ionic compounds, it\u2019s convenient to assign oxidation numbers for the cation and anion separately.<\/p>\r\n<p id=\"fs-idp50986592\">According to guideline 2, the oxidation number for sodium is +1.<\/p>\r\n<p id=\"fs-idm60591184\">Assuming the usual oxidation number for oxygen (\u22122 per guideline 3), the oxidation number for sulfur is calculated as directed by guideline 4:<\/p>\r\n&nbsp;\r\n<div id=\"fs-idp6634688\" data-type=\"equation\">\r\n<div id=\"fs-idm58489232\" data-type=\"equation\">charge on SO<sub>4<\/sub><sup>2-<\/sup> = -2 = <em>x<\/em> + (4 \u00d7 -2)<\/div>\r\n<div data-type=\"equation\"><em>x<\/em> = -2 - (4 \u00d7 -2) = +6<\/div>\r\n<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idp108038048\"><strong>Check Your Learning:<\/strong><\/p>\r\nAssign oxidation states to the elements whose atoms are underlined in each of the following compounds or ions:\r\n<p id=\"fs-idp34225952\">(a) K<u data-effect=\"underline\">N<\/u>O<sub>3<\/sub><\/p>\r\n<p id=\"fs-idp31054592\">(b) <u data-effect=\"underline\">Al<\/u>H<sub>3<\/sub><\/p>\r\n<p id=\"fs-idm64889152\">(c) <span style=\"text-decoration: underline\">N<\/span>H<sub>4<\/sub><sup>+<\/sup><\/p>\r\n<p id=\"fs-idp214214448\">(d) H<sub>2<\/sub><span style=\"text-decoration: underline\">P<\/span>O<sub>4<\/sub><sup>-<\/sup><\/p>\r\n<strong>Answer:<\/strong>\r\n<div id=\"fs-idm9084576\" data-type=\"note\">\r\n<p id=\"fs-idm24741776\">(a) N, +5; (b) Al, +3; (c) N, \u22123; (d) P, +5<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<p id=\"fs-idp45838960\">Using the oxidation number concept, an all-inclusive definition of redox reaction has been established. <strong>Oxidation-reduction (redox) reactions<\/strong> are those in which one or more elements involved undergo a change in oxidation number. (While the vast majority of redox reactions involve changes in oxidation number for two or more elements, a few interesting exceptions to this rule do exist <a class=\"autogenerated-content\" href=\"#fs-idp180799104\">(Figure)<\/a>.) Definitions for the complementary processes of this reaction class are correspondingly revised as shown here:<\/p>\r\n\r\n<div id=\"fs-idp231200304\" style=\"text-align: center\" data-type=\"equation\"><strong>oxidation<\/strong> = increase in oxidation number<\/div>\r\n<div style=\"text-align: center\" data-type=\"equation\"><strong>reduction<\/strong> = decrease in oxidation number<\/div>\r\n<p id=\"fs-idm1410784\">Returning to the reactions used to introduce this topic, they may now both be identified as redox processes. In the reaction between sodium and chlorine to yield sodium chloride, sodium is oxidized (its oxidation number increases from 0 in Na to +1 in NaCl) and chlorine is reduced (its oxidation number decreases from 0 in Cl<sub>2<\/sub> to \u22121 in NaCl). In the reaction between molecular hydrogen and chlorine, hydrogen is oxidized (its oxidation number increases from 0 in H<sub>2<\/sub> to +1 in HCl) and chlorine is reduced (its oxidation number decreases from 0 in Cl<sub>2<\/sub> to \u22121 in HCl).<\/p>\r\n<p id=\"fs-idp112552240\">Several subclasses of redox reactions are recognized, including <strong>combustion reactions<\/strong> in which the reductant (also called a <em data-effect=\"italics\">fuel<\/em>) and oxidant (often, but not necessarily, molecular oxygen) react vigorously and produce significant amounts of heat, and often light, in the form of a flame. Solid rocket-fuel reactions are combustion processes. A typical propellant reaction in which solid aluminum is oxidized by ammonium perchlorate is represented by this equation:<\/p>\r\n\r\n<div id=\"fs-idp91244624\" style=\"text-align: center\" data-type=\"equation\">10Al(<em>s<\/em>) + 6NH<sub>4<\/sub>ClO<sub>4<\/sub>(<em>s<\/em>)\u00a0 \u27f6 4Al<sub>2<\/sub>O<sub>3<\/sub>(<em>s<\/em>) + 2AlCl<sub>3<\/sub>(<em>s<\/em>) + 12H<sub>2<\/sub>O(<em>g<\/em>) + 3N<sub>2<\/sub>(<em>g<\/em>)<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<div id=\"fs-idp4633776\" class=\"chemistry link-to-learning\" data-type=\"note\">\r\n<p id=\"fs-idm5712736\">Watch a brief <a href=\"http:\/\/openstaxcollege.org\/l\/16hybridrocket\">video<\/a> showing the test firing of a small-scale, prototype, hybrid rocket engine planned for use in the new Space Launch System being developed by NASA. The first engines firing at<span data-type=\"newline\">\r\n<\/span>3 s (green flame) use a liquid fuel\/oxidant mixture, and the second, more powerful engines firing at 4 s (yellow flame) use a solid mixture.<\/p>\r\n\r\n<\/div>\r\n<p id=\"fs-idm580304\"><strong>Single-displacement (replacement) reactions<\/strong> are redox reactions in which an ion in solution is displaced (or replaced) via the oxidation of a metallic element. One common example of this type of reaction is the acid oxidation of certain metals:<\/p>\r\n\r\n<div id=\"fs-idp4619296\" style=\"text-align: center\" data-type=\"equation\">Zn(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 ZnCl<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>(<em>g<\/em>)<\/div>\r\n<p id=\"fs-idm50858768\">Metallic elements may also be oxidized by solutions of other metal salts; for example:<\/p>\r\n\r\n<div id=\"fs-idm10324592\" style=\"text-align: center\" data-type=\"equation\">Cu(<em>s<\/em>) + 2AgNO<sub>3<\/sub>(<em>aq<\/em>) \u27f6 Cu(NO<sub>3<\/sub>)<sub>2<\/sub>(<em>aq<\/em>) + 2Ag(<em>s<\/em>)<\/div>\r\n<p id=\"fs-idm10678768\">This reaction may be observed by placing copper wire in a solution containing a dissolved silver salt. Silver ions in solution are reduced to elemental silver at the surface of the copper wire, and the resulting Cu<sup>2+<\/sup> ions dissolve in the solution to yield a characteristic blue color (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_CuAgNO3\">(Figure)<\/a>).<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_04_02_CuAgNO3\" class=\"scaled-down\">\r\n<div class=\"bc-figcaption figcaption\">(a) A copper wire is shown next to a solution containing silver(I) ions. (b) Displacement of dissolved silver ions by copper ions results in (c) accumulation of gray-colored silver metal on the wire and development of a blue color in the solution, due to dissolved copper ions. (credit: modification of work by Mark Ott)<\/div>\r\n<span id=\"fs-idm51046320\" data-type=\"media\" data-alt=\"This figure contains three photographs. In a, a coiled copper wire is shown beside a test tube filled with a clear, colorless liquid. In b, the wire has been inserted into the test tube with the clear, colorless liquid. In c, the test tube contains a light blue liquid and the coiled wire appears to have a fuzzy silver gray coating.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_04_CuAgNO3-1.jpg\" alt=\"This figure contains three photographs. In a, a coiled copper wire is shown beside a test tube filled with a clear, colorless liquid. In b, the wire has been inserted into the test tube with the clear, colorless liquid. In c, the test tube contains a light blue liquid and the coiled wire appears to have a fuzzy silver gray coating.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<div id=\"fs-idp180799104\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idm59303872\"><strong>Describing Redox Reactions:<\/strong><\/p>\r\nIdentify which equations represent redox reactions, providing a name for the reaction if appropriate. For those reactions identified as redox, name the oxidant and reductant.\r\n<p id=\"fs-idm23437408\">(a) ZnCO<sub>3<\/sub>(<em>s<\/em>) \u27f6 ZnO(<em>s<\/em>) + CO<sub>2<\/sub>(<em>g<\/em>)<\/p>\r\n<p id=\"fs-idm32376704\">(b) 2Ga(<em>l<\/em>) + 3Br<sub>2<\/sub>(<em>l<\/em>) \u27f6 2GaBr<sub>3<\/sub>(<em>s<\/em>)<\/p>\r\n<p id=\"fs-idp65112704\">(c) 2H<sub>2<\/sub>O<sub>2<\/sub>(<em>aq<\/em>) \u27f6 2H<sub>2<\/sub>O(<em>l<\/em>) + O<sub>2<\/sub>(<em>g<\/em>)<\/p>\r\n<p id=\"fs-idp65830752\">(d) BaCl<sub>2<\/sub>(<em>aq<\/em>) + K<sub>2<\/sub>SO<sub>4<\/sub>(<em>aq<\/em>) \u27f6 BaSO<sub>4<\/sub>(<em>s<\/em>) + 2KCl(<em>aq<\/em>)<\/p>\r\n<p id=\"fs-idp64660848\">(e) C<sub>2<\/sub>H<sub>4<\/sub>(<em>g<\/em>) + 3O<sub>2<\/sub>(<em>g<\/em>) \u27f6 2CO<sub>2<\/sub>(<em>g<\/em>) + 2H<sub>2<\/sub>O(<em>l<\/em>)<\/p>\r\n<p id=\"fs-idp502896\"><strong>Solution:<\/strong><\/p>\r\nRedox reactions are identified per definition if one or more elements undergo a change in oxidation number.\r\n<p id=\"fs-idp31047840\">(a) This is not a redox reaction, since oxidation numbers remain unchanged for all elements.<\/p>\r\n<p id=\"fs-idp218627312\">(b) This is a redox reaction. Gallium is oxidized, its oxidation number increasing from 0 in Ga(<em data-effect=\"italics\">l<\/em>) to +3 in GaBr<sub>3<\/sub>(<em data-effect=\"italics\">s<\/em>). The reducing agent is Ga(<em data-effect=\"italics\">l<\/em>). Bromine is reduced, its oxidation number decreasing from 0 in Br<sub>2<\/sub>(<em data-effect=\"italics\">l<\/em>) to \u22121 in GaBr<sub>3<\/sub>(<em data-effect=\"italics\">s<\/em>). The oxidizing agent is Br<sub>2<\/sub>(<em data-effect=\"italics\">l<\/em>).<\/p>\r\n<p id=\"fs-idp223712368\">(c) This is a redox reaction. It is a particularly interesting process, as it involves the same element, oxygen, undergoing both oxidation and reduction (a so-called <em data-effect=\"italics\">disproportionation reaction)<\/em>. Oxygen is oxidized, its oxidation number increasing from \u22121 in H<sub>2<\/sub>O<sub>2<\/sub>(<em data-effect=\"italics\">aq<\/em>) to 0 in O<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>). Oxygen is also reduced, its oxidation number decreasing from \u22121 in H<sub>2<\/sub>O<sub>2<\/sub>(<em data-effect=\"italics\">aq<\/em>) to \u22122 in H<sub>2<\/sub>O(<em data-effect=\"italics\">l<\/em>). For disproportionation reactions, the same substance functions as an oxidant and a reductant.<\/p>\r\n<p id=\"fs-idm40215792\">(d) This is not a redox reaction, since oxidation numbers remain unchanged for all elements.<\/p>\r\n<p id=\"fs-idm55300832\">(e) This is a redox reaction (combustion). Carbon is oxidized, its oxidation number increasing from \u22122 in C<sub>2<\/sub>H<sub>4<\/sub>(<em data-effect=\"italics\">g<\/em>) to +4 in CO<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>). The reducing agent (fuel) is C<sub>2<\/sub>H<sub>4<\/sub>(<em data-effect=\"italics\">g<\/em>). Oxygen is reduced, its oxidation number decreasing from 0 in O<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>) to \u22122 in H<sub>2<\/sub>O(<em data-effect=\"italics\">l<\/em>). The oxidizing agent is O<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>).<\/p>\r\n<p id=\"fs-idm9371232\"><strong>Check Your Learning:<\/strong><\/p>\r\nThis equation describes the production of tin(II) chloride:\r\n<div id=\"fs-idm73301872\" style=\"text-align: center\" data-type=\"equation\">Sn(<em>s<\/em>) + 2HCl(<em>g<\/em>) \u27f6 SnCl<sub>2<\/sub>(<em>s<\/em>) + H<sub>2<\/sub>(<em>g<\/em>)<\/div>\r\n<p id=\"fs-idp98112752\">Is this a redox reaction? If so, provide a more specific name for the reaction if appropriate, and identify the oxidant and reductant.<\/p>\r\n\r\n<div id=\"fs-idp105853680\" data-type=\"note\">\r\n<div data-type=\"title\"><\/div>\r\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\r\n<p id=\"fs-idm50940704\">Yes, a single-replacement reaction. Sn(<em data-effect=\"italics\">s<\/em>) is the reductant, HCl(<em data-effect=\"italics\">g<\/em>) is the oxidant.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp98840016\" class=\"bc-section section\" data-depth=\"2\">\r\n<h4 data-type=\"title\"><strong>Balancing Redox Reactions via the Half-Reaction Method<\/strong><\/h4>\r\n<p id=\"fs-idm141853312\">Redox reactions that take place in aqueous media often involve water, hydronium ions, and hydroxide ions as reactants or products. Although these species are not oxidized or reduced, they do participate in chemical change in other ways (e.g., by providing the elements required to form oxyanions). Equations representing these reactions are sometimes very difficult to balance by inspection, so systematic approaches have been developed to assist in the process. One very useful approach is to use the method of half-reactions, which involves the following steps:<\/p>\r\n<p id=\"fs-idm64885712\">1. Write the two half-reactions representing the redox process.<\/p>\r\n<p id=\"fs-idm219773632\">2. Balance all elements except oxygen and hydrogen.<\/p>\r\n<p id=\"fs-idm339557376\">3. Balance oxygen atoms by adding H<sub>2<\/sub>O molecules.<\/p>\r\n<p id=\"fs-idm161858496\">4. Balance hydrogen atoms by adding H<sup>+<\/sup> ions.<\/p>\r\n<p id=\"fs-idm218459968\">5. Balance charge by adding electrons.<\/p>\r\n<p id=\"fs-idm31626864\">6. If necessary, multiply each half-reaction\u2019s coefficients by the smallest possible integers to yield equal numbers of electrons in each.<\/p>\r\n<p id=\"fs-idm241499680\">7. Add the balanced half-reactions together and simplify by removing species that appear on both sides of the equation.<\/p>\r\n<p id=\"fs-idm228573904\">8. For reactions occurring in basic media (excess hydroxide ions), carry out these additional steps:<\/p>\r\n\r\n<ol id=\"fs-idp48488192\" type=\"a\" data-mark-prefix=\"(\" data-mark-suffix=\")\">\r\n \t<li>Add OH<sup>\u2212<\/sup> ions to both sides of the equation in numbers equal to the number of H<sup>+<\/sup> ions.<\/li>\r\n \t<li>On the side of the equation containing both H<sup>+<\/sup> and OH<sup>\u2212<\/sup> ions, combine these ions to yield water molecules.<\/li>\r\n \t<li>Simplify the equation by removing any redundant water molecules.<\/li>\r\n<\/ol>\r\n<p id=\"fs-idm268418480\">9. Finally, check to see that both the number of atoms and the total charges<sup data-type=\"footnote-number\"><a href=\"#footnote1\" data-type=\"footnote-link\">1<\/a><\/sup> are balanced.<\/p>\r\n\r\n<div id=\"fs-idm53644080\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idp164751888\"><strong>Balancing Redox Reactions in Acidic Solution:<\/strong><\/p>\r\nWrite a balanced equation for the reaction between dichromate ion and iron(II) to yield iron(III) and chromium(III) in acidic solution.\r\n<div id=\"fs-idm59837744\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + Fe<sup>2+<\/sup> \u27f6 Cr<sup>3+<\/sup> + Fe<sup>3+<\/sup><\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idp3143536\"><strong>Solution<\/strong><\/p>\r\n\r\n<ol id=\"fs-idp34895184\" class=\"stepwise\" type=\"1\">\r\n \t<li>\r\n<p id=\"fs-idp218612096\"><em data-effect=\"italics\">Write the two half-reactions<\/em>.<\/p>\r\n<p id=\"fs-idm9107808\">Each half-reaction will contain one reactant and one product with one element in common.<\/p>\r\n\r\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\r\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> \u27f6 Cr<sup>3+<\/sup><\/div><\/li>\r\n \t<li>\r\n<p id=\"fs-idm63161856\"><em data-effect=\"italics\">Balance all elements except oxygen and hydrogen<\/em>. The iron half-reaction is already balanced, but the chromium half-reaction shows two Cr atoms on the left and one Cr atom on the right. Changing the coefficient on the right side of the equation to 2 achieves balance with regard to Cr atoms.<\/p>\r\n\r\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\r\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> \u27f6 2Cr<sup>3+<\/sup><\/div><\/li>\r\n \t<li>\r\n<p id=\"fs-idm39730544\"><em data-effect=\"italics\">Balance oxygen atoms by adding<\/em> H<sub>2<\/sub>O <em data-effect=\"italics\">molecules<\/em>. The iron half-reaction does not contain O atoms. The chromium half-reaction shows seven O atoms on the left and none on the right, so seven water molecules are added to the right side.<\/p>\r\n\r\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\r\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div><\/li>\r\n \t<li><em data-effect=\"italics\">Balance hydrogen atoms by adding<\/em> H<sup>+<\/sup><em data-effect=\"italics\">ions<\/em>. The iron half-reaction does not contain H atoms. The chromium half-reaction shows 14 H atoms on the right and none on the left, so 14 hydrogen ions are added to the left side.\r\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\r\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div><\/li>\r\n \t<li>\r\n<p id=\"fs-idp23619040\"><em data-effect=\"italics\">Balance charge by adding electrons<\/em>. The iron half-reaction shows a total charge of 2+ on the left side (1 Fe<sup>2+<\/sup> ion) and 3+ on the right side (1 Fe<sup>3+<\/sup> ion). Adding one electron to the right side brings that side\u2019s total charge to (3+) + (1\u2212) = 2+, and charge balance is achieved.<\/p>\r\n<p id=\"fs-idm52131936\">The chromium half-reaction shows a total charge of (1 \u00d7 2\u2212) + (14 \u00d7 1+) = 12+ on the left side (1 Cr<sub>2<\/sub>O<sub>7<\/sub>}<sup>2\u2212<\/sup> ion and 14 H<sup>+<\/sup> ions). The total charge on the right side is (2 \u00d7 3+) = 6 + (2 Cr<sup>3+<\/sup> ions). Adding six electrons to the left side will bring that side\u2019s total charge to (12+ + 6\u2212) = 6+, and charge balance is achieved.<\/p>\r\n\r\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup> + e<sup>-<\/sup><\/div>\r\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> + 6e<sup>-<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div><\/li>\r\n \t<li>\r\n<p id=\"fs-idp2921088\"><em data-effect=\"italics\">Multiply the two half-reactions so the number of electrons in one reaction equals the number of electrons in the other reaction<\/em>. To be consistent with mass conservation, and the idea that redox reactions involve the transfer (not creation or destruction) of electrons, the iron half-reaction\u2019s coefficient must be multiplied by 6.<\/p>\r\n\r\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">6Fe<sup>2+<\/sup> \u27f6 6Fe<sup>3+<\/sup> + 6e<sup>-<\/sup><\/div>\r\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> + 6e<sup>-<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div><\/li>\r\n \t<li>\r\n<p style=\"text-align: center\"><em data-effect=\"italics\">Add the balanced half-reactions and cancel species that appear on both sides of the equation<\/em>.<\/p>\r\n<\/li>\r\n<\/ol>\r\n<p style=\"text-align: center\">6Fe<sup>2+<\/sup> + Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> + 6e<sup>-<\/sup> \u27f6 6Fe<sup>3+<\/sup> + 6e<sup>-<\/sup> + 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/p>\r\n\r\n<div id=\"fs-idm208390896\" data-type=\"equation\"><\/div>\r\n<p id=\"fs-idp66154720\">\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Only the six electrons are redundant species. Removing them from each side of the equation yields the simplified, balanced equation here:<\/p>\r\n\r\n<div style=\"text-align: center\" data-type=\"equation\">6Fe<sup>2+<\/sup> + Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> \u27f6 6Fe<sup>3+<\/sup> + 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div>\r\n<p id=\"fs-idm59483360\">A final check of atom and charge balance confirms the equation is balanced.<\/p>\r\n\r\n<table id=\"fs-idp8525760\" class=\"medium unnumbered\" summary=\"This table has three columns and six rows. The first column is unlabeled but the second and third columns are labeled, \u201cReactants,\u201d and \u201cProducts.\u201d Under the first column are the following: \u201cF e,\u201d \u201cC r,\u201d \u201cO,\u201d \u201cH,\u201d and, \u201ccharge.\u201d Under the \u201cReactants\u201d column are the numbers: 6, 2, 7, 14, 24 plus sign. Under the \u201cProducts\u201d column are the numbers: 6, 2, 7, 14 and 24 plus sign.\" data-label=\"\">\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\"><\/td>\r\n<td data-align=\"left\">Reactants<\/td>\r\n<td data-align=\"left\">Products<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">Fe<\/td>\r\n<td data-align=\"left\">6<\/td>\r\n<td data-align=\"left\">6<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">Cr<\/td>\r\n<td data-align=\"left\">2<\/td>\r\n<td data-align=\"left\">2<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">O<\/td>\r\n<td data-align=\"left\">7<\/td>\r\n<td data-align=\"left\">7<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">H<\/td>\r\n<td data-align=\"left\">14<\/td>\r\n<td data-align=\"left\">14<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"left\">charge<\/td>\r\n<td data-align=\"left\">24+<\/td>\r\n<td data-align=\"left\">24+<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<p id=\"fs-idp193051584\"><strong>Check Your Learning:<\/strong><\/p>\r\nIn basic solution, molecular chlorine, Cl<sub>2<\/sub>, reacts with hydroxide ions, OH<sup>\u2212<\/sup>, to yield chloride ions, Cl<sup>\u2212<\/sup>. and chlorate ions, ClO<sub>4<\/sub><sup>\u2212<\/sup>. HINT: This is a <em data-effect=\"italics\">disproportionation reaction<\/em> in which the element chlorine is both oxidized and reduced. Write a balanced equation for this reaction.\r\n\r\n&nbsp;\r\n<div id=\"fs-idm39281984\" data-type=\"note\">\r\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\r\n<p style=\"text-align: center\">3Cl<sub>2<\/sub>(<em>aq<\/em>) + 6OH<sup>-<\/sup>(<em>aq<\/em>) \u27f6 5Cl<sup>-<\/sup>(<em>aq<\/em>) + ClO<sub>3<\/sub><sup>-<\/sup>(<em>aq<\/em>) + 3H<sub>2<\/sub>O(<em>l<\/em>)<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm51820592\" class=\"summary\" data-depth=\"1\">\r\n<h3 data-type=\"title\"><strong>Key Concepts and Summary<\/strong><\/h3>\r\n<p id=\"fs-idp62302320\">Chemical reactions are classified according to similar patterns of behavior. A large number of important reactions are included in three categories: precipitation, acid-base, and oxidation-reduction (redox). Precipitation reactions involve the formation of one or more insoluble products. Acid-base reactions involve the transfer of hydrogen ions between reactants. Redox reactions involve a change in oxidation number for one or more reactant elements. Writing balanced equations for some redox reactions that occur in aqueous solutions is simplified by using a systematic approach called the half-reaction method.<\/p>\r\n\r\n<\/div>\r\n<div data-type=\"footnote-refs\">\r\n<h3 data-type=\"footnote-refs-title\"><strong>Footnotes<\/strong><\/h3>\r\n<ul data-list-type=\"bulleted\" data-bullet-style=\"none\">\r\n \t<li data-type=\"footnote-ref\"><a href=\"#footnote-ref1\" data-type=\"footnote-ref-link\">1<\/a><span data-type=\"footnote-ref-content\">The requirement of \u201ccharge balance\u201d is just a specific type of \u201cmass balance\u201d in which the species in question are electrons. An equation must represent equal numbers of electrons on the reactant and product sides, and so both atoms and charges must be balanced.<\/span><\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox shaded\" data-type=\"glossary\">\r\n<h3 data-type=\"glossary-title\"><strong>Glossary<\/strong><\/h3>\r\n<dl id=\"fs-idm39846352\">\r\n \t<dt>acid<\/dt>\r\n \t<dd id=\"fs-idm39845712\">substance that produces H<sub>3<\/sub>O<sup>+<\/sup> when dissolved in water<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm54009824\">\r\n \t<dt>acid-base reaction<\/dt>\r\n \t<dd id=\"fs-idm54009184\">reaction involving the transfer of a hydrogen ion between reactant species<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm54008672\">\r\n \t<dt>base<\/dt>\r\n \t<dd id=\"fs-idm54008032\">substance that produces OH<sup>\u2212<\/sup> when dissolved in water<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm54007136\">\r\n \t<dt>combustion reaction<\/dt>\r\n \t<dd id=\"fs-idm28946480\">vigorous redox reaction producing significant amounts of energy in the form of heat and, sometimes, light<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm28945840\">\r\n \t<dt>half-reaction<\/dt>\r\n \t<dd id=\"fs-idm28945200\">an equation that shows whether each reactant loses or gains electrons in a reaction.<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm28944688\">\r\n \t<dt>insoluble<\/dt>\r\n \t<dd id=\"fs-idm28944048\">of relatively low solubility; dissolving only to a slight extent<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm73914400\">\r\n \t<dt>oxidation<\/dt>\r\n \t<dd id=\"fs-idm73913760\">process in which an element\u2019s oxidation number is increased by loss of electrons<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm73913072\">\r\n \t<dt>oxidation-reduction reaction<\/dt>\r\n \t<dd id=\"fs-idm73912432\">(also, redox reaction) reaction involving a change in oxidation number for one or more reactant elements<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp57129632\">\r\n \t<dt>oxidation number<\/dt>\r\n \t<dd id=\"fs-idp57130272\">(also, oxidation state) the charge each atom of an element would have in a compound if the compound were ionic<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp57130912\">\r\n \t<dt>oxidizing agent<\/dt>\r\n \t<dd id=\"fs-idp57131552\">(also, oxidant) substance that brings about the oxidation of another substance, and in the process becomes reduced<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp57132192\">\r\n \t<dt>precipitate<\/dt>\r\n \t<dd id=\"fs-idp57132832\">insoluble product that forms from reaction of soluble reactants<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp55089136\">\r\n \t<dt>precipitation reaction<\/dt>\r\n \t<dd id=\"fs-idp55089776\">reaction that produces one or more insoluble products; when reactants are ionic compounds, sometimes called double-displacement or metathesis<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp55090448\">\r\n \t<dt>reduction<\/dt>\r\n \t<dd id=\"fs-idp55091088\">process in which an element\u2019s oxidation number is decreased by gain of electrons<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp55091776\">\r\n \t<dt>reducing agent<\/dt>\r\n \t<dd id=\"fs-idp55092416\">(also, reductant) substance that brings about the reduction of another substance, and in the process becomes oxidized<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp64227344\">\r\n \t<dt>single-displacement reaction<\/dt>\r\n \t<dd id=\"fs-idp64227984\">(also, replacement) redox reaction involving the oxidation of an elemental substance by an ionic species<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp64228624\">\r\n \t<dt>soluble<\/dt>\r\n \t<dd id=\"fs-idp67578576\">of relatively high solubility; dissolving to a relatively large extent<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp67579088\">\r\n \t<dt>solubility<\/dt>\r\n \t<dd id=\"fs-idp67579728\">the extent to which a substance may be dissolved in water, or any solvent<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp67580240\">\r\n \t<dt>strong acid<\/dt>\r\n \t<dd id=\"fs-idp67580880\">acid that reacts completely when dissolved in water to yield hydronium ions<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp67581392\">\r\n \t<dt>strong base<\/dt>\r\n \t<dd id=\"fs-idm4239184\">base that reacts completely when dissolved in water to yield hydroxide ions<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm4238672\">\r\n \t<dt>weak acid<\/dt>\r\n \t<dd id=\"fs-idm4238032\">acid that reacts only to a slight extent when dissolved in water to yield hydronium ions<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm4237408\">\r\n \t<dt>weak base<\/dt>\r\n \t<dd id=\"fs-idm4236768\">base that reacts only to a slight extent when dissolved in water to yield hydroxide ions<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<p><strong><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.602em;background-color: #cbd4b6;color: #000000\">Learning Objectives<\/span><\/strong><\/p>\n<div class=\"textbox textbox--learning-objectives\">\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Define three common types of chemical reactions (precipitation, acid-base, and oxidation-reduction)<\/li>\n<li>Classify chemical reactions as one of these three types given appropriate descriptions or chemical equations<\/li>\n<li>Identify common acids and bases<\/li>\n<li>Predict the solubility of common inorganic compounds by using solubility rules<\/li>\n<li>Compute the oxidation states for elements in compounds<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idp140132627979408\">Humans interact with one another in various and complex ways, and we classify these interactions according to common patterns of behavior. When two humans exchange information, we say they are communicating. When they exchange blows with their fists or feet, we say they are fighting. Faced with a wide range of varied interactions between chemical substances, scientists have likewise found it convenient (or even necessary) to classify chemical interactions by identifying common patterns of reactivity. This module will provide an introduction to three of the most prevalent types of chemical reactions: precipitation, acid-base, and oxidation-reduction.<\/p>\n<div id=\"fs-idp140132627979792\" class=\"bc-section section\" data-depth=\"1\">\n<h3 data-type=\"title\"><strong>Precipitation Reactions and Solubility Rules<\/strong><\/h3>\n<p id=\"fs-idp140132618169728\">A <span data-type=\"term\">precipitation reaction<\/span> is one in which dissolved substances react to form one (or more) solid products. Many reactions of this type involve the exchange of ions between ionic compounds in aqueous solution and are sometimes referred to as <em data-effect=\"italics\">double displacement<\/em>, <em data-effect=\"italics\">double replacement<\/em>, or <em data-effect=\"italics\">metathesis<\/em> reactions. These reactions are common in nature and are responsible for the formation of coral reefs in ocean waters and kidney stones in animals. They are used widely in industry for production of a number of commodity and specialty chemicals. Precipitation reactions also play a central role in many chemical analysis techniques, including spot tests used to identify metal ions and <em data-effect=\"italics\">gravimetric methods<\/em> for determining the composition of matter.<\/p>\n<p id=\"fs-idp140132617792992\">The extent to which a substance may be dissolved in water, or any solvent, is quantitatively expressed as its <strong>solubility<\/strong>, defined as the maximum concentration of a substance that can be achieved under specified conditions. Substances with relatively large solubilities are said to be <strong>soluble<\/strong>. A substance will <strong>precipitate <\/strong>when solution conditions are such that its concentration exceeds its solubility. Substances with relatively low solubilities are said to be <strong>insoluble<\/strong>, and these are the substances that readily precipitate from solution. More information on these important concepts is provided in a later chapter on solutions. For purposes of predicting the identities of solids formed by precipitation reactions, one may simply refer to patterns of solubility that have been observed for many ionic compounds (<a class=\"autogenerated-content\" href=\"#fs-idp140132617697568\">(Figure)<\/a>).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1166\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-263x300.png\" alt=\"\" width=\"600\" height=\"684\" srcset=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-263x300.png 263w, https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-897x1024.png 897w, https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-768x877.png 768w, https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-65x74.png 65w, https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-225x257.png 225w, https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a-350x400.png 350w, https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/4.2a.png 1120w\" sizes=\"auto, (max-width: 600px) 100vw, 600px\" \/><\/p>\n<p id=\"fs-idm63476864\">A vivid example of precipitation is observed when solutions of potassium iodide and lead nitrate are mixed, resulting in the formation of solid lead iodide:<\/p>\n<div id=\"fs-idp98445312\" style=\"text-align: center\" data-type=\"equation\">2KI(<em>aq<\/em>) + Pb(NO<sub>3<\/sub>)<sub>2<\/sub>(<em>aq<\/em>) \u27f6 PbI<sub>2<\/sub>(<em>s<\/em>) + 2KNO<sub>3<\/sub>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idp24544224\">This observation is consistent with the solubility guidelines: The only insoluble compound among all those involved is lead iodide, one of the exceptions to the general solubility of iodide salts.<\/p>\n<p id=\"fs-idp30939280\">The net ionic equation representing this reaction is:<\/p>\n<div id=\"fs-idp31365696\" style=\"text-align: center\" data-type=\"equation\">Pb<sup>2+<\/sup>(<em>aq<\/em>) + 2I<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 PbI<sub>2<\/sub>(<em>s<\/em>)<\/div>\n<p id=\"fs-idm52098368\">Lead iodide is a bright yellow solid that was formerly used as an artist\u2019s pigment known as iodine yellow (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_LeadIodide\">(Figure)<\/a>). The properties of pure PbI<sub>2<\/sub> crystals make them useful for fabrication of X-ray and gamma ray detectors.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_04_02_LeadIodide\" class=\"scaled-down\">\n<div class=\"bc-figcaption figcaption\">A precipitate of PbI<sub>2<\/sub> forms when solutions containing Pb<sup>2+<\/sup> and I<sup>\u2212<\/sup> are mixed. (credit: Der Kreole\/Wikimedia Commons)<\/div>\n<p><span id=\"fs-idp29197296\" data-type=\"media\" data-alt=\"A photograph is shown of a yellow green opaque substance swirled through a clear, colorless liquid in a test tube.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_LeadIodide-1.jpg\" alt=\"A photograph is shown of a yellow green opaque substance swirled through a clear, colorless liquid in a test tube.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<p id=\"fs-idp157312304\">The solubility guidelines in the table above may be used to predict whether a precipitation reaction will occur when solutions of soluble ionic compounds are mixed together. One merely needs to identify all the ions present in the solution and then consider if possible cation\/anion pairing could result in an insoluble compound. For example, mixing solutions of silver nitrate and sodium chloride will yield a solution containing Ag<sup>+<\/sup>, NO<sub>3<\/sub><sup>&#8211;<\/sup>, Na<sup>+<\/sup>, and Cl<sup>\u2212<\/sup> ions. Aside from the two ionic compounds originally present in the solutions, AgNO<sub>3<\/sub> and NaCl, two additional ionic compounds may be derived from this collection of ions: NaNO<sub>3<\/sub> and AgCl. The solubility guidelines indicate all nitrate salts are soluble but that AgCl is one of the exceptions to the general solubility of chloride salts. A precipitation reaction, therefore, is predicted to occur, as described by the following equations:<\/p>\n<div id=\"fs-idm4746128\" style=\"text-align: center\" data-type=\"equation\">NaCl(<em>aq<\/em>) + AgNO<sub>3<\/sub>(<em>aq<\/em>) \u27f6 AgCl(<em>s<\/em>) + NaNO<sub>3<\/sub>(<em>aq<\/em>)\u00a0 \u00a0 \u00a0 \u00a0(molecular)<\/div>\n<div style=\"text-align: center\" data-type=\"equation\">Ag<sup>+<\/sup>(<em>aq<\/em>) + Cl<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 AgCl(<em>s<\/em>)\u00a0 \u00a0 \u00a0 (net ionic)<\/div>\n<div id=\"fs-idp3608096\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idm5664816\"><strong>Predicting Precipitation Reactions:<\/strong><\/p>\n<p>Predict the result of mixing reasonably concentrated solutions of the following ionic compounds. If precipitation is expected, write a balanced net ionic equation for the reaction.<\/p>\n<p id=\"fs-idp8541200\">(a) potassium sulfate and barium nitrate<\/p>\n<p id=\"fs-idm5793440\">(b) lithium chloride and silver acetate<\/p>\n<p id=\"fs-idm605024\">(c) lead nitrate and ammonium carbonate<\/p>\n<p id=\"fs-idp65557120\"><strong>Solution:<\/strong><\/p>\n<p>(a) The two possible products for this combination are KNO<sub>3<\/sub> and BaSO<sub>4<\/sub>. The solubility guidelines indicate BaSO<sub>4<\/sub> is insoluble, and so a precipitation reaction is expected. The net ionic equation for this reaction, derived in the manner detailed in the previous module, is<\/p>\n<div id=\"eip-799\" style=\"text-align: center\" data-type=\"equation\">Ba<sup>2+<\/sup>(<em>aq<\/em>) + SO<sub>4<\/sub><sup>2-<\/sup>(<em>aq<\/em>) \u27f6 BaSO<sub>4<\/sub>(<em>s<\/em>)<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idm27273344\">(b) The two possible products for this combination are LiC<sub>2<\/sub>H<sub>3<\/sub>O<sub>2<\/sub> and AgCl. The solubility guidelines indicate AgCl is insoluble, and so a precipitation reaction is expected. The net ionic equation for this reaction, derived in the manner detailed in the previous module, is<\/p>\n<div id=\"fs-idm70392576\" style=\"text-align: center\" data-type=\"equation\">Ag<sup>+<\/sup>(<em>aq<\/em>) + Cl<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 AgCl(<em>s<\/em>)<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idm5437216\">(c) The two possible products for this combination are PbCO<sub>3<\/sub> and NH<sub>4<\/sub>NO<sub>3<\/sub>. The solubility guidelines indicate PbCO<sub>3<\/sub> is insoluble, and so a precipitation reaction is expected. The net ionic equation for this reaction, derived in the manner detailed in the previous module, is<\/p>\n<div id=\"eip-767\" style=\"text-align: center\" data-type=\"equation\">Pb<sup>2+<\/sup>(<em>aq<\/em>) + CO<sub>3<\/sub><sup>2-<\/sup>(<em>aq<\/em>) \u27f6 PbCO<sub>3<\/sub>(<em>s<\/em>)<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idm72085968\"><strong>Check Your Learning :<\/strong><\/p>\n<p>Which solution could be used to precipitate the barium ion, Ba<sup>2+<\/sup>, in a water sample: sodium chloride, sodium hydroxide, or sodium sulfate? What is the formula for the expected precipitate?<\/p>\n<div id=\"fs-idp24003520\" data-type=\"note\">\n<div data-type=\"title\"><\/div>\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\n<p id=\"fs-idp153308448\">sodium sulfate, BaSO<sub>4<\/sub><\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp128853312\" class=\"bc-section section\" data-depth=\"1\">\n<h3 data-type=\"title\"><strong>Acid-Base Reactions<\/strong><\/h3>\n<p id=\"fs-idm1255344\">An<strong> acid-base reaction<\/strong> is one in which a hydrogen ion, H<sup>+<\/sup>, is transferred from one chemical species to another. Such reactions are of central importance to numerous natural and technological processes, ranging from the chemical transformations that take place within cells and the lakes and oceans, to the industrial-scale production of fertilizers, pharmaceuticals, and other substances essential to society. The subject of acid-base chemistry, therefore, is worthy of thorough discussion, and a full chapter is devoted to this topic later in the text.<\/p>\n<p id=\"fs-idp89436016\">For purposes of this brief introduction, we will consider only the more common types of acid-base reactions that take place in aqueous solutions. In this context, an <strong>acid <\/strong>is a substance that will dissolve in water to yield hydronium ions, H<sub>3<\/sub>O<sup>+<\/sup>. As an example, consider the equation shown here:<\/p>\n<div id=\"fs-idm54028336\" style=\"text-align: center\" data-type=\"equation\">HCl(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>aq<\/em>) \u27f6 Cl<sup>\u2212<\/sup>(<em>aq<\/em>) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idm10390992\">The process represented by this equation confirms that hydrogen chloride is an acid. When dissolved in water, H<sub>3<\/sub>O<sup>+<\/sup> ions are produced by a chemical reaction in which H<sup>+<\/sup> ions are transferred from HCl molecules to H<sub>2<\/sub>O molecules (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_HClsoln\">(Figure)<\/a>).<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_04_02_HClsoln\" class=\"scaled-down\">\n<div class=\"bc-figcaption figcaption\">When hydrogen chloride gas dissolves in water, (a) it reacts as an acid, transferring protons to water molecules to yield (b) hydronium ions (and solvated chloride ions).<\/div>\n<p><span id=\"fs-idp103294384\" data-type=\"media\" data-alt=\"This figure shows two flasks, labeled a and b. The flasks are both sealed with stoppers and are nearly three-quarters full of a liquid. Flask a is labeled H C l followed by g in parentheses. In the liquid there are approximately twenty space-filling molecular models composed of one red sphere and two smaller attached white spheres. The label H subscript 2 O followed by a q in parentheses is connected with a line to one of these models. In the space above the liquid in the flask, four space filling molecular models composed of one larger green sphere to which a smaller white sphere is bonded are shown. To one of these models, the label H C l followed by g in parentheses is attached with a line segment. An arrow is drawn from the space above the liquid pointing down into the liquid below. Flask b is labeled H subscript 3 O superscript positive sign followed by a q in parentheses. This is followed by a plus sign and C l superscript negative sign which is also followed by a q in parentheses. In this flask, no molecules are shown in the open space above the liquid. A label, C l superscript negative sign followed by a q in parentheses, is connected with a line segment to a green sphere. This sphere is surrounded by four molecules composed each of one red sphere and two white smaller spheres. A few of these same molecules appear separate from the green spheres in the liquid. A line segment connects one of them to the label H subscript 2 O which is followed by l in parentheses. There are a few molecules formed from one central larger red sphere to which three smaller white spheres are bonded. A line segment is drawn from one of these to the label H subscript 3 O superscript positive sign, followed by a q in parentheses.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_HClsoln-1.jpg\" alt=\"This figure shows two flasks, labeled a and b. The flasks are both sealed with stoppers and are nearly three-quarters full of a liquid. Flask a is labeled H C l followed by g in parentheses. In the liquid there are approximately twenty space-filling molecular models composed of one red sphere and two smaller attached white spheres. The label H subscript 2 O followed by a q in parentheses is connected with a line to one of these models. In the space above the liquid in the flask, four space filling molecular models composed of one larger green sphere to which a smaller white sphere is bonded are shown. To one of these models, the label H C l followed by g in parentheses is attached with a line segment. An arrow is drawn from the space above the liquid pointing down into the liquid below. Flask b is labeled H subscript 3 O superscript positive sign followed by a q in parentheses. This is followed by a plus sign and C l superscript negative sign which is also followed by a q in parentheses. In this flask, no molecules are shown in the open space above the liquid. A label, C l superscript negative sign followed by a q in parentheses, is connected with a line segment to a green sphere. This sphere is surrounded by four molecules composed each of one red sphere and two white smaller spheres. A few of these same molecules appear separate from the green spheres in the liquid. A line segment connects one of them to the label H subscript 2 O which is followed by l in parentheses. There are a few molecules formed from one central larger red sphere to which three smaller white spheres are bonded. A line segment is drawn from one of these to the label H subscript 3 O superscript positive sign, followed by a q in parentheses.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<p id=\"fs-idm57695504\">The nature of HCl is such that its reaction with water as just described is essentially 100% efficient: Virtually every HCl molecule that dissolves in water will undergo this reaction. Acids that completely react in this fashion are called <strong>strong acids<\/strong>, and HCl is one among just a handful of common acid compounds that are classified as strong (<a class=\"autogenerated-content\" href=\"#fs-idp55395904\">(Figure)<\/a>). A far greater number of compounds behave as <strong>weak acids<\/strong> and only partially react with water, leaving a large majority of dissolved molecules in their original form and generating a relatively small amount of hydronium ions. Weak acids are commonly encountered in nature, being the substances partly responsible for the tangy taste of citrus fruits, the stinging sensation of insect bites, and the unpleasant smells associated with body odor. A familiar example of a weak acid is acetic acid, the main ingredient in food vinegars:<\/p>\n<div id=\"fs-idp23273024\" style=\"text-align: center\" data-type=\"equation\">CH<sub>3<\/sub>CO<sub>2<\/sub>H(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc CH<sub>3<\/sub>CO<sub>2<\/sub><sup>\u2212<\/sup>(<em>aq<\/em>) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idm23363712\">When dissolved in water under typical conditions, only about 1% of acetic acid molecules are present in the ionized form, CH<sub>3<\/sub>CO<sub>2<\/sub><sup>&#8211;<\/sup> (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_Citrus\">(Figure)<\/a>). (The use of a double-arrow in the equation above denotes the partial reaction aspect of this process, a concept addressed fully in the chapters on chemical equilibrium.)<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_04_02_Citrus\" class=\"scaled-down\">\n<div class=\"bc-figcaption figcaption\">(a) Fruits such as oranges, lemons, and grapefruit contain the weak acid citric acid. (b) Vinegars contain the weak acid acetic acid. (credit a: modification of work by Scott Bauer; credit b: modification of work by Br\u00fccke-Osteuropa\/Wikimedia Commons)<\/div>\n<p><span id=\"fs-idp185890880\" data-type=\"media\" data-alt=\"This figure contains two images, each with an associated structural formula provided in the lower left corner of the image. The first image is a photograph of a variety of thinly sliced, circular cross sections of citrus fruits ranging in color for green to yellow, to orange and reddish-orange. The slices are closely packed on a white background. The structural formula with this picture shows a central chain of five C atoms. The leftmost C atom has an O atom double bonded above and to the left and a singly bonded O atom below and to the left. This single bonded O atom has an H atom indicated in red on its left side which is highlighted in pink. The second C atom moving to the right has H atoms bonded above and below. The third C atom has a single bonded O atom above which has an H atom on its right. This third C atom has a C atom bonded below it which has an O atom double bonded below and to the left and a singly bonded O atom below and to the right. An H atom appears in red and is highlighted in pink to the right of the singly bonded O atom. The fourth C atom has H atoms bonded above and below. The fifth C atom is at the right end of the structure. It has an O atom double bonded above and to the right and a singly bonded O atom below and to the right. This single bonded O atom has a red H atom on its right side which is highlighted in pink. The second image is a photograph of bottles of vinegar. The bottles are labeled, \u201cBalsamic Vinegar,\u201d and appear to be clear and colorless. The liquid in this bottle appears to be brown. The structural formula that appears with this image shows a chain of two C atoms. The leftmost C atom has H atoms bonded above, below, and to the left. The C atom on the right has a doubly bonded O atom above and to the right and a singly bonded O atom below and to the right. This O atom has an H atom bonded to its right which is highlighted in pink.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_Citrus-1.jpg\" alt=\"This figure contains two images, each with an associated structural formula provided in the lower left corner of the image. The first image is a photograph of a variety of thinly sliced, circular cross sections of citrus fruits ranging in color for green to yellow, to orange and reddish-orange. The slices are closely packed on a white background. The structural formula with this picture shows a central chain of five C atoms. The leftmost C atom has an O atom double bonded above and to the left and a singly bonded O atom below and to the left. This single bonded O atom has an H atom indicated in red on its left side which is highlighted in pink. The second C atom moving to the right has H atoms bonded above and below. The third C atom has a single bonded O atom above which has an H atom on its right. This third C atom has a C atom bonded below it which has an O atom double bonded below and to the left and a singly bonded O atom below and to the right. An H atom appears in red and is highlighted in pink to the right of the singly bonded O atom. The fourth C atom has H atoms bonded above and below. The fifth C atom is at the right end of the structure. It has an O atom double bonded above and to the right and a singly bonded O atom below and to the right. This single bonded O atom has a red H atom on its right side which is highlighted in pink. The second image is a photograph of bottles of vinegar. The bottles are labeled, \u201cBalsamic Vinegar,\u201d and appear to be clear and colorless. The liquid in this bottle appears to be brown. The structural formula that appears with this image shows a chain of two C atoms. The leftmost C atom has H atoms bonded above, below, and to the left. The C atom on the right has a doubly bonded O atom above and to the right and a singly bonded O atom below and to the right. This O atom has an H atom bonded to its right which is highlighted in pink.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<table id=\"fs-idp55395904\" class=\"top-titled\" summary=\"This table contains two columns and seven rows. The columns are labeled, \u201cCompound Formula,\u201d and, \u201cName in Aqueous Solution.\u201d Under the column, \u201cCompound Formula,\u201d are: \u201cH B r,\u201d \u201cH C l,\u201d \u201cH I,\u201d \u201cH N O subscript 3,\u201d \u201cH C l O subscript 4,\u201d and, \u201cH subscript 2 S O subscript 4.\u201d Under the column, \u201cName in Aqueous Solution,\u201d are: \u201chydrobromic acid,\u201d \u201chydrochloric acid,\u201d \u201chydroiodic acid,\u201d \u201cnitric acid,\u201d \u201cperchloric acid,\u201d and, \u201csulfuric acid.\u201d\">\n<thead>\n<tr>\n<th colspan=\"3\" data-align=\"center\">Common Strong Acids<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th data-align=\"left\">Compound Formula<\/th>\n<th data-align=\"left\">Name in Aqueous Solution<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td data-align=\"left\">HBr<\/td>\n<td data-align=\"left\">hydrobromic acid<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">HCl<\/td>\n<td data-align=\"left\">hydrochloric acid<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">HI<\/td>\n<td data-align=\"left\">hydroiodic acid<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">HNO<sub>3<\/sub><\/td>\n<td data-align=\"left\">nitric acid<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">HClO<sub>4<\/sub><\/td>\n<td data-align=\"left\">perchloric acid<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">H<sub>2<\/sub>SO<sub>4<\/sub><\/td>\n<td data-align=\"left\">sulfuric acid<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p id=\"fs-idp2912576\">A <strong>base <\/strong>is a substance that will dissolve in water to yield hydroxide ions, OH<sup>\u2212<\/sup>. The most common bases are ionic compounds composed of alkali or alkaline earth metal cations (groups 1 and 2) combined with the hydroxide ion\u2014for example, NaOH and Ca(OH)<sub>2<\/sub>. Unlike the acid compounds discussed previously, these compounds do not react chemically with water; instead they dissolve and dissociate, releasing hydroxide ions directly into the solution. For example, KOH and Ba(OH)<sub>2<\/sub> dissolve in water and dissociate completely to produce cations (K<sup>+<\/sup> and Ba<sup>2+<\/sup>, respectively) and hydroxide ions, OH<sup>\u2212<\/sup>. These bases, along with other hydroxides that completely dissociate in water, are considered<strong> strong bases<\/strong>.<\/p>\n<p id=\"fs-idp74282160\">Consider as an example the dissolution of lye (sodium hydroxide) in water:<\/p>\n<div id=\"fs-idm62931696\" style=\"text-align: center\" data-type=\"equation\">NaOH(<em>s<\/em>) \u27f6 Na<sup>+<\/sup>(<em>aq<\/em>) + OH<sup>\u2212<\/sup>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idp8724736\">This equation confirms that sodium hydroxide is a base. When dissolved in water, NaOH dissociates to yield Na<sup>+<\/sup> and OH<sup>\u2212<\/sup> ions. This is also true for any other ionic compound containing hydroxide ions. Since the dissociation process is essentially complete when ionic compounds dissolve in water under typical conditions, NaOH and other ionic hydroxides are all classified as strong bases.<\/p>\n<p id=\"fs-idm50199792\">Unlike ionic hydroxides, some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and so are classified as <strong>weak bases<\/strong>. These types of compounds are also abundant in nature and important commodities in various technologies. For example, global production of the weak base ammonia is typically well over 100 metric tons annually, being widely used as an agricultural fertilizer, a raw material for chemical synthesis of other compounds, and an active ingredient in household cleaners (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_ammonia\">(Figure)<\/a>). When dissolved in water, ammonia reacts partially to yield hydroxide ions, as shown here:<\/p>\n<div id=\"fs-idm9327664\" style=\"text-align: center\" data-type=\"equation\">NH<sub>3<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc NH<sub>4<\/sub><sup>+<\/sup>(<em>aq<\/em>) + OH<sup>\u2212<\/sup>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idm73811808\">This is, by definition, an acid-base reaction, in this case involving the transfer of H<sup>+<\/sup> ions from water molecules to ammonia molecules. Under typical conditions, only about 1% of the dissolved ammonia is present as NH<sub>4<\/sub><sup>+<\/sup>\u00a0ions.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_04_02_ammonia\" class=\"scaled-down\">\n<div class=\"bc-figcaption figcaption\">Ammonia is a weak base used in a variety of applications. (a) Pure ammonia is commonly applied as an agricultural fertilizer. (b) Dilute solutions of ammonia are effective household cleansers. (credit a: modification of work by National Resources Conservation Service; credit b: modification of work by pat00139)<\/div>\n<p><span id=\"fs-idm1349584\" data-type=\"media\" data-alt=\"This photograph shows a large agricultural tractor in a field pulling a field sprayer and a large, white cylindrical tank which is labeled \u201cCaution Ammonia.\u201d\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_02_ammonia-1.jpg\" alt=\"This photograph shows a large agricultural tractor in a field pulling a field sprayer and a large, white cylindrical tank which is labeled \u201cCaution Ammonia.\u201d\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<p id=\"fs-idp101951952\">A <span data-type=\"term\"><strong>neutralization<\/strong> reaction<\/span> is a specific type of acid-base reaction in which the reactants are an acid and a base (but not water), and the products are often (but not always!) a <span data-type=\"term\">salt<\/span> and water:<\/p>\n<div id=\"fs-idm49357376\" style=\"text-align: center\" data-type=\"equation\">acid + base \u27f6 salt + water<\/div>\n<p id=\"fs-idm21828864\">To illustrate a neutralization reaction, consider what happens when a typical antacid such as milk of magnesia (an aqueous suspension of solid Mg(OH)<sub>2<\/sub>) is ingested to ease symptoms associated with excess stomach acid (HCl):<\/p>\n<div id=\"fs-idm8492448\" style=\"text-align: center\" data-type=\"equation\">Mg(OH)<sub>2<\/sub>(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 MgCl<sub>2<\/sub>(<em>aq<\/em>)+ 2H<sub>2<\/sub>O(<em>l<\/em>)<\/div>\n<p id=\"fs-idm52053696\">Note that in addition to water, this reaction produces a salt, magnesium chloride.<\/p>\n<div id=\"fs-idm49295040\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idm22209232\"><strong>Writing Equations for Acid-Base Reactions:<\/strong><\/p>\n<p>Write balanced chemical equations for the acid-base reactions described here:<\/p>\n<p id=\"fs-idp55337856\">(a) hypochlorous acid reacts with water<\/p>\n<p id=\"fs-idm22923872\">(b) a solution of barium hydroxide is neutralized with a solution of nitric acid<\/p>\n<p id=\"fs-idp20180224\"><strong>Solution:<\/strong><\/p>\n<p>(a) The two reactants are provided, HOCl and H<sub>2<\/sub>O. Since the substance is an acid, its reaction with water will involve the transfer of H<sup>+<\/sup> from HOCl to H<sub>2<\/sub>O to generate hydronium ions, H<sub>3<\/sub>O<sup>+<\/sup> and hypochlorite ions, OCl<sup>\u2212<\/sup>.<\/p>\n<div id=\"fs-idm141852368\" style=\"text-align: center\" data-type=\"equation\">HOCl(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc OCl<sup>\u2212<\/sup>(<em>aq<\/em>) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idp73299936\">A double-arrow is appropriate in this equation because it indicates the HOCl is a weak acid that has not reacted completely.<\/p>\n<p id=\"fs-idm23237280\">(b) The two reactants are provided, Ba(OH)<sub>2<\/sub> and HNO<sub>3<\/sub>. Since this is a neutralization reaction, the two products will be water and a salt composed of the cation of the ionic hydroxide (Ba<sup>2+<\/sup>) and the anion generated when the acid transfers its hydrogen ion (NO<sub>3<\/sub><sup>\u2212<\/sup>).<\/p>\n<div id=\"fs-idp42762464\" style=\"text-align: center\" data-type=\"equation\">Ba(OH)<sub>2<\/sub>(<em>aq<\/em>) + 2HNO<sub>3<\/sub>(<em>aq<\/em>) \u27f6 Ba(NO<sub>3<\/sub>)<sub>2<\/sub>(<em>aq<\/em>) + 2H<sub>2<\/sub>O(<em>l<\/em>)<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idm20270192\"><strong>Check Your Learning:<\/strong><\/p>\n<p>Write the net ionic equation representing the neutralization of any strong acid with an ionic hydroxide. (Hint: Consider the ions produced when a strong acid is dissolved in water.)<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idp218691008\" data-type=\"note\">\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\n<p>H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>) + OH<sup>\u2212<\/sup>(<em>aq<\/em>) \u27f6 2H<sub>2<\/sub>O(<em>l<\/em>)<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idm119690112\" class=\"chemistry everyday-life\" data-type=\"note\">\n<div data-type=\"title\"><\/div>\n<div data-type=\"title\"><strong>Stomach Antacids<\/strong><\/div>\n<p id=\"fs-idm55572160\">Our stomachs contain a solution of roughly 0.03 <em data-effect=\"italics\">M<\/em> HCl, which helps us digest the food we eat. The burning sensation associated with heartburn is a result of the acid of the stomach leaking through the muscular valve at the top of the stomach into the lower reaches of the esophagus. The lining of the esophagus is not protected from the corrosive effects of stomach acid the way the lining of the stomach is, and the results can be very painful. When we have heartburn, it feels better if we reduce the excess acid in the esophagus by taking an antacid. As you may have guessed, antacids are bases. One of the most common antacids is calcium carbonate, CaCO<sub>3<\/sub>. The reaction,<\/p>\n<div id=\"fs-idm156299504\" style=\"text-align: center\" data-type=\"equation\">CaCO<sub>3<\/sub>(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 CaCl<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) + CO<sub>2<\/sub>(<em>g<\/em>)<\/div>\n<p id=\"fs-idp31618928\">not only neutralizes stomach acid, it also produces CO<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>), which may result in a satisfying belch.<\/p>\n<p id=\"fs-idm158365360\">Milk of Magnesia is a suspension of the sparingly soluble base magnesium hydroxide, Mg(OH)<sub>2<\/sub>. It works according to the reaction:<\/p>\n<div id=\"fs-idp1457888\" style=\"text-align: center\" data-type=\"equation\">Mg(OH)<sub>2<\/sub>(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 MgCl<sub>2<\/sub>(<em>aq<\/em>) + 2H<sub>2<\/sub>O(<em>l<\/em>)<\/div>\n<div id=\"fs-idp51950320\" data-type=\"equation\"><\/div>\n<p id=\"fs-idp39159216\">This reaction does not produce carbon dioxide, but magnesium-containing antacids can have a laxative effect. Several antacids have aluminum hydroxide, Al(OH)<sub>3<\/sub>, as an active ingredient. The aluminum hydroxide tends to cause constipation, and some antacids use aluminum hydroxide in concert with magnesium hydroxide to balance the side effects of the two substances.<\/p>\n<p>&nbsp;<\/p>\n<\/div>\n<div id=\"fs-idm116223344\" class=\"chemistry everyday-life\" data-type=\"note\">\n<div data-type=\"title\"><strong>Culinary Aspects of Chemistry<\/strong><\/div>\n<p id=\"fs-idm118182736\">Examples of acid-base chemistry are abundant in the culinary world. One example is the use of baking soda, or sodium\u00a0 hydrogen carbonate in baking. NaHCO<sub>3<\/sub> is a base. When it reacts with a\u00a0 acid such as lemon juice, buttermilk, or sour cream in a batter, bubbles of carbon dioxide gas are formed from decomposition of the resulting carbonic acid, and the batter \u201crises.\u201d Baking powder is a combination of sodium hydrogen carbonate, and one or more acid salts that react when the two chemicals come in contact with water in the batter.<\/p>\n<p id=\"fs-idp3959248\">Many people like to put lemon juice or vinegar, both of which are acids, on cooked fish (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_03_FishLemon\">(Figure)<\/a>). It turns out that fish have volatile amines (bases) in their systems, which are neutralized by the acids to yield involatile ammonium salts. This reduces the odor of the fish, and also adds a \u201csour\u201d taste that we seem to enjoy.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_14_03_FishLemon\" class=\"bc-figure figure\">\n<div class=\"bc-figcaption figcaption\">A neutralization reaction takes place between citric acid in lemons or acetic acid in vinegar, and the bases in the flesh of fish.<\/div>\n<p><span id=\"fs-idm122004144\" data-type=\"media\" data-alt=\"An image is shown of two fish with heads removed and skin on with lemon slices placed in the body cavity. The first line of an equation below the image reads C H subscript 3 C O O H plus N H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2 arrow C H subscript 3 C O O superscript negative sign plus N H subscript 3 superscript positive sign C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2. The second line of the equation reads Acetic acid plus sign Putrescine arrow Acetate ion plus sign Putrescinium ion.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_03_FishLemon-1.jpg\" alt=\"An image is shown of two fish with heads removed and skin on with lemon slices placed in the body cavity. The first line of an equation below the image reads C H subscript 3 C O O H plus N H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2 arrow C H subscript 3 C O O superscript negative sign plus N H subscript 3 superscript positive sign C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 2 N H subscript 2. The second line of the equation reads Acetic acid plus sign Putrescine arrow Acetate ion plus sign Putrescinium ion.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<p id=\"fs-idm117278880\">Pickling is a method used to preserve vegetables using a naturally produced acidic environment. The vegetable, such as a cucumber, is placed in a sealed jar submerged in a brine solution. The brine solution favors the growth of beneficial bacteria and suppresses the growth of harmful bacteria. The beneficial bacteria feed on starches in the cucumber and produce lactic acid as a waste product in a process called fermentation. The lactic acid eventually increases the acidity of the brine to a level that kills any harmful bacteria, which require a basic environment. Without the harmful bacteria consuming the cucumbers they are able to last much longer than if they were unprotected. A byproduct of the pickling process changes the flavor of the vegetables with the acid making them taste sour.<\/p>\n<\/div>\n<div id=\"fs-idp164722352\" class=\"chemistry link-to-learning\" data-type=\"note\">\n<p id=\"fs-idm40317104\">Explore the microscopic <a href=\"http:\/\/openstaxcollege.org\/l\/16AcidsBases\">view<\/a> of strong and weak acids and bases.<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idm48520656\" class=\"bc-section section\" data-depth=\"1\">\n<h3 data-type=\"title\"><strong>Oxidation-Reduction Reactions<\/strong><\/h3>\n<p id=\"fs-idp3801440\">Earth\u2019s atmosphere contains about 20% molecular oxygen, O<sub>2<\/sub>, a chemically reactive gas that plays an essential role in the metabolism of aerobic organisms and in many environmental processes that shape the world. The term <strong>oxidation <\/strong>was originally used to describe chemical reactions involving O<sub>2<\/sub>, but its meaning has evolved to refer to a broad and important reaction class known as <em data-effect=\"italics\">oxidation-reduction (redox) reactions<\/em>. A few examples of such reactions will be used to develop a clear picture of this classification.<\/p>\n<p id=\"fs-idm49954608\">Some redox reactions involve the transfer of electrons between reactant species to yield ionic products, such as the reaction between sodium and chlorine to yield sodium chloride:<\/p>\n<div id=\"fs-idm5657872\" style=\"text-align: center\" data-type=\"equation\">2Na(<em>s<\/em>) + Cl<sub>2<\/sub>(<em>g<\/em>) \u27f6 2NaCl(<em>s<\/em>)<\/div>\n<p id=\"fs-idm102441680\">It is helpful to view the process with regard to each individual reactant, that is, to represent the fate of each reactant in the form of an equation called a <strong>half-reaction<\/strong>:<\/p>\n<div id=\"fs-idp15924368\" style=\"text-align: center\" data-type=\"equation\">2Na(<em>s<\/em>) \u27f6 2Na<sup>+<\/sup>(<em>s<\/em>) + 2e<sup>&#8211;<\/sup><\/div>\n<div style=\"text-align: center\" data-type=\"equation\">Cl<sub>2<\/sub>(<em>g<\/em>) + 2e<sup>&#8211;<\/sup> \u27f6 2Cl<sup>\u2212<\/sup>(<em>s<\/em>)<\/div>\n<p id=\"fs-idp97564400\">These equations show that Na atoms <em data-effect=\"italics\">lose electrons<\/em> while Cl atoms (in the Cl<sub>2<\/sub> molecule) <em data-effect=\"italics\">gain electrons<\/em>, the \u201c<em data-effect=\"italics\">s<\/em>\u201d subscripts for the resulting ions signifying they are present in the form of a solid ionic compound. For redox reactions of this sort, the loss and gain of electrons define the complementary processes that occur:<\/p>\n<div id=\"fs-idp61672384\" style=\"text-align: center\" data-type=\"equation\"><strong>oxidation<\/strong> = loss of electrons<\/div>\n<div style=\"text-align: center\" data-type=\"equation\"><strong>reduction<\/strong> = gain of electrons<\/div>\n<p id=\"fs-idp6686448\">In this reaction, then, sodium is <em data-effect=\"italics\">oxidized<\/em> and chlorine undergoes <strong>reduction<\/strong>. Viewed from a more active perspective, sodium functions as a <span data-type=\"term\"><strong>reducing agent<\/strong> (reductant)<\/span>, since it provides electrons to (or reduces) chlorine. Likewise, chlorine functions as an <span data-type=\"term\"><strong>oxidizing agent<\/strong> (oxidant)<\/span>, as it effectively removes electrons from (oxidizes) sodium.<\/p>\n<div id=\"fs-idm29833328\" style=\"text-align: center\" data-type=\"equation\"><strong>reducing agent<\/strong> = species that is oxidized<\/div>\n<div style=\"text-align: center\" data-type=\"equation\"><strong>oxidizing agent<\/strong> = species that is reduced<\/div>\n<p id=\"fs-idp108466096\">Consider another reaction:<\/p>\n<div id=\"fs-idp37282464\" style=\"text-align: center\" data-type=\"equation\">H<sub>2<\/sub>(<em>g<\/em>) +\u00a0 Cl<sub>2<\/sub>(<em>g<\/em>) \u27f6 2HCl(<em>g<\/em>)<\/div>\n<p id=\"fs-idp168168224\">The product of this reaction is a covalent compound (it is in the gaseous, not aqueous, state), so transfer of electrons in the explicit sense is not involved. To clarify the similarity of this reaction to the previous one and permit an unambiguous definition of redox reactions, a property called <em data-effect=\"italics\">oxidation number<\/em> has been defined. The <strong>oxidation number <\/strong>(or <span data-type=\"term\">oxidation state<\/span>) of an element in a compound is the charge its atoms would possess <em data-effect=\"italics\">if the compound was ionic<\/em>. The following guidelines are used to assign oxidation numbers to each element in a molecule or ion.<\/p>\n<ol id=\"fs-idp29396208\" type=\"1\">\n<li>The oxidation number of an atom in an elemental substance is zero.<\/li>\n<li>The oxidation number of a monatomic ion is equal to the ion\u2019s charge.<\/li>\n<li>Oxidation numbers for common nonmetals are usually assigned as follows:\n<ul id=\"fs-idm48186672\" data-bullet-style=\"bullet\">\n<li>Hydrogen: +1 when combined with nonmetals, \u22121 when combined with metals<\/li>\n<li>Oxygen: \u22122 in most compounds<\/li>\n<\/ul>\n<\/li>\n<li>The sum of oxidation numbers for all atoms in a molecule or polyatomic ion equals the charge on the molecule or ion.<\/li>\n<\/ol>\n<p id=\"fs-idm72440048\">Note: The proper convention for reporting charge is to write the number first, followed by the sign (e.g., 2+), while oxidation number is written with the reversed sequence, sign followed by number (e.g., +2). This convention aims to emphasize the distinction between these two related properties.<\/p>\n<div id=\"fs-idm24634320\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idm73523056\"><strong>Assigning Oxidation Numbers:<\/strong><\/p>\n<p>Follow the guidelines in this section of the text to assign oxidation numbers to all the elements in the following species:<\/p>\n<p id=\"fs-idp9372816\">(a) H<sub>2<\/sub>S<\/p>\n<p id=\"fs-idp5671152\">(b) SO<sub>3<\/sub><sup>2-<\/sup><\/p>\n<p id=\"fs-idp109909120\">(c) Na<sub>2<\/sub>SO<sub>4<\/sub><\/p>\n<p id=\"fs-idp203498912\"><strong>Solution:<\/strong><\/p>\n<p>(a) According to guideline 3, the oxidation number for H is +1.<\/p>\n<p id=\"fs-idm32134656\">Using this oxidation number and the compound\u2019s formula, guideline 4 may then be used to calculate the oxidation number for sulfur:<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idm58489232\" data-type=\"equation\">charge on H<sub>2<\/sub>S = 0 = (2 \u00d7 +1) + (1 \u00d7 <em>x<\/em>)<\/div>\n<div data-type=\"equation\"><em>x<\/em> = 0 &#8211; (2 \u00d7 +1) = &#8211; 2<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idm1965888\">(b) Guideline 3 suggests the oxidation number for oxygen is \u22122.<\/p>\n<p id=\"fs-idp181502096\">Using this oxidation number and the ion\u2019s formula, guideline 4 may then be used to calculate the oxidation number for sulfur:<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idm22135232\" data-type=\"equation\">\n<div id=\"fs-idm58489232\" data-type=\"equation\">charge on SO<sub>3<\/sub><sup>2-<\/sup> = -2 = <em>x<\/em> + (3 \u00d7 -2)<\/div>\n<div data-type=\"equation\"><em>x<\/em> = -2 &#8211; (3 \u00d7 -2) = +4<\/div>\n<div data-type=\"equation\"><\/div>\n<\/div>\n<p id=\"fs-idp180932672\">(c) For ionic compounds, it\u2019s convenient to assign oxidation numbers for the cation and anion separately.<\/p>\n<p id=\"fs-idp50986592\">According to guideline 2, the oxidation number for sodium is +1.<\/p>\n<p id=\"fs-idm60591184\">Assuming the usual oxidation number for oxygen (\u22122 per guideline 3), the oxidation number for sulfur is calculated as directed by guideline 4:<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idp6634688\" data-type=\"equation\">\n<div id=\"fs-idm58489232\" data-type=\"equation\">charge on SO<sub>4<\/sub><sup>2-<\/sup> = -2 = <em>x<\/em> + (4 \u00d7 -2)<\/div>\n<div data-type=\"equation\"><em>x<\/em> = -2 &#8211; (4 \u00d7 -2) = +6<\/div>\n<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idp108038048\"><strong>Check Your Learning:<\/strong><\/p>\n<p>Assign oxidation states to the elements whose atoms are underlined in each of the following compounds or ions:<\/p>\n<p id=\"fs-idp34225952\">(a) K<u data-effect=\"underline\">N<\/u>O<sub>3<\/sub><\/p>\n<p id=\"fs-idp31054592\">(b) <u data-effect=\"underline\">Al<\/u>H<sub>3<\/sub><\/p>\n<p id=\"fs-idm64889152\">(c) <span style=\"text-decoration: underline\">N<\/span>H<sub>4<\/sub><sup>+<\/sup><\/p>\n<p id=\"fs-idp214214448\">(d) H<sub>2<\/sub><span style=\"text-decoration: underline\">P<\/span>O<sub>4<\/sub><sup>&#8211;<\/sup><\/p>\n<p><strong>Answer:<\/strong><\/p>\n<div id=\"fs-idm9084576\" data-type=\"note\">\n<p id=\"fs-idm24741776\">(a) N, +5; (b) Al, +3; (c) N, \u22123; (d) P, +5<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idp45838960\">Using the oxidation number concept, an all-inclusive definition of redox reaction has been established. <strong>Oxidation-reduction (redox) reactions<\/strong> are those in which one or more elements involved undergo a change in oxidation number. (While the vast majority of redox reactions involve changes in oxidation number for two or more elements, a few interesting exceptions to this rule do exist <a class=\"autogenerated-content\" href=\"#fs-idp180799104\">(Figure)<\/a>.) Definitions for the complementary processes of this reaction class are correspondingly revised as shown here:<\/p>\n<div id=\"fs-idp231200304\" style=\"text-align: center\" data-type=\"equation\"><strong>oxidation<\/strong> = increase in oxidation number<\/div>\n<div style=\"text-align: center\" data-type=\"equation\"><strong>reduction<\/strong> = decrease in oxidation number<\/div>\n<p id=\"fs-idm1410784\">Returning to the reactions used to introduce this topic, they may now both be identified as redox processes. In the reaction between sodium and chlorine to yield sodium chloride, sodium is oxidized (its oxidation number increases from 0 in Na to +1 in NaCl) and chlorine is reduced (its oxidation number decreases from 0 in Cl<sub>2<\/sub> to \u22121 in NaCl). In the reaction between molecular hydrogen and chlorine, hydrogen is oxidized (its oxidation number increases from 0 in H<sub>2<\/sub> to +1 in HCl) and chlorine is reduced (its oxidation number decreases from 0 in Cl<sub>2<\/sub> to \u22121 in HCl).<\/p>\n<p id=\"fs-idp112552240\">Several subclasses of redox reactions are recognized, including <strong>combustion reactions<\/strong> in which the reductant (also called a <em data-effect=\"italics\">fuel<\/em>) and oxidant (often, but not necessarily, molecular oxygen) react vigorously and produce significant amounts of heat, and often light, in the form of a flame. Solid rocket-fuel reactions are combustion processes. A typical propellant reaction in which solid aluminum is oxidized by ammonium perchlorate is represented by this equation:<\/p>\n<div id=\"fs-idp91244624\" style=\"text-align: center\" data-type=\"equation\">10Al(<em>s<\/em>) + 6NH<sub>4<\/sub>ClO<sub>4<\/sub>(<em>s<\/em>)\u00a0 \u27f6 4Al<sub>2<\/sub>O<sub>3<\/sub>(<em>s<\/em>) + 2AlCl<sub>3<\/sub>(<em>s<\/em>) + 12H<sub>2<\/sub>O(<em>g<\/em>) + 3N<sub>2<\/sub>(<em>g<\/em>)<\/div>\n<div data-type=\"equation\"><\/div>\n<div id=\"fs-idp4633776\" class=\"chemistry link-to-learning\" data-type=\"note\">\n<p id=\"fs-idm5712736\">Watch a brief <a href=\"http:\/\/openstaxcollege.org\/l\/16hybridrocket\">video<\/a> showing the test firing of a small-scale, prototype, hybrid rocket engine planned for use in the new Space Launch System being developed by NASA. The first engines firing at<span data-type=\"newline\"><br \/>\n<\/span>3 s (green flame) use a liquid fuel\/oxidant mixture, and the second, more powerful engines firing at 4 s (yellow flame) use a solid mixture.<\/p>\n<\/div>\n<p id=\"fs-idm580304\"><strong>Single-displacement (replacement) reactions<\/strong> are redox reactions in which an ion in solution is displaced (or replaced) via the oxidation of a metallic element. One common example of this type of reaction is the acid oxidation of certain metals:<\/p>\n<div id=\"fs-idp4619296\" style=\"text-align: center\" data-type=\"equation\">Zn(<em>s<\/em>) + 2HCl(<em>aq<\/em>) \u27f6 ZnCl<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>(<em>g<\/em>)<\/div>\n<p id=\"fs-idm50858768\">Metallic elements may also be oxidized by solutions of other metal salts; for example:<\/p>\n<div id=\"fs-idm10324592\" style=\"text-align: center\" data-type=\"equation\">Cu(<em>s<\/em>) + 2AgNO<sub>3<\/sub>(<em>aq<\/em>) \u27f6 Cu(NO<sub>3<\/sub>)<sub>2<\/sub>(<em>aq<\/em>) + 2Ag(<em>s<\/em>)<\/div>\n<p id=\"fs-idm10678768\">This reaction may be observed by placing copper wire in a solution containing a dissolved silver salt. Silver ions in solution are reduced to elemental silver at the surface of the copper wire, and the resulting Cu<sup>2+<\/sup> ions dissolve in the solution to yield a characteristic blue color (<a class=\"autogenerated-content\" href=\"#CNX_Chem_04_02_CuAgNO3\">(Figure)<\/a>).<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_04_02_CuAgNO3\" class=\"scaled-down\">\n<div class=\"bc-figcaption figcaption\">(a) A copper wire is shown next to a solution containing silver(I) ions. (b) Displacement of dissolved silver ions by copper ions results in (c) accumulation of gray-colored silver metal on the wire and development of a blue color in the solution, due to dissolved copper ions. (credit: modification of work by Mark Ott)<\/div>\n<p><span id=\"fs-idm51046320\" data-type=\"media\" data-alt=\"This figure contains three photographs. In a, a coiled copper wire is shown beside a test tube filled with a clear, colorless liquid. In b, the wire has been inserted into the test tube with the clear, colorless liquid. In c, the test tube contains a light blue liquid and the coiled wire appears to have a fuzzy silver gray coating.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_04_04_CuAgNO3-1.jpg\" alt=\"This figure contains three photographs. In a, a coiled copper wire is shown beside a test tube filled with a clear, colorless liquid. In b, the wire has been inserted into the test tube with the clear, colorless liquid. In c, the test tube contains a light blue liquid and the coiled wire appears to have a fuzzy silver gray coating.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<div id=\"fs-idp180799104\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idm59303872\"><strong>Describing Redox Reactions:<\/strong><\/p>\n<p>Identify which equations represent redox reactions, providing a name for the reaction if appropriate. For those reactions identified as redox, name the oxidant and reductant.<\/p>\n<p id=\"fs-idm23437408\">(a) ZnCO<sub>3<\/sub>(<em>s<\/em>) \u27f6 ZnO(<em>s<\/em>) + CO<sub>2<\/sub>(<em>g<\/em>)<\/p>\n<p id=\"fs-idm32376704\">(b) 2Ga(<em>l<\/em>) + 3Br<sub>2<\/sub>(<em>l<\/em>) \u27f6 2GaBr<sub>3<\/sub>(<em>s<\/em>)<\/p>\n<p id=\"fs-idp65112704\">(c) 2H<sub>2<\/sub>O<sub>2<\/sub>(<em>aq<\/em>) \u27f6 2H<sub>2<\/sub>O(<em>l<\/em>) + O<sub>2<\/sub>(<em>g<\/em>)<\/p>\n<p id=\"fs-idp65830752\">(d) BaCl<sub>2<\/sub>(<em>aq<\/em>) + K<sub>2<\/sub>SO<sub>4<\/sub>(<em>aq<\/em>) \u27f6 BaSO<sub>4<\/sub>(<em>s<\/em>) + 2KCl(<em>aq<\/em>)<\/p>\n<p id=\"fs-idp64660848\">(e) C<sub>2<\/sub>H<sub>4<\/sub>(<em>g<\/em>) + 3O<sub>2<\/sub>(<em>g<\/em>) \u27f6 2CO<sub>2<\/sub>(<em>g<\/em>) + 2H<sub>2<\/sub>O(<em>l<\/em>)<\/p>\n<p id=\"fs-idp502896\"><strong>Solution:<\/strong><\/p>\n<p>Redox reactions are identified per definition if one or more elements undergo a change in oxidation number.<\/p>\n<p id=\"fs-idp31047840\">(a) This is not a redox reaction, since oxidation numbers remain unchanged for all elements.<\/p>\n<p id=\"fs-idp218627312\">(b) This is a redox reaction. Gallium is oxidized, its oxidation number increasing from 0 in Ga(<em data-effect=\"italics\">l<\/em>) to +3 in GaBr<sub>3<\/sub>(<em data-effect=\"italics\">s<\/em>). The reducing agent is Ga(<em data-effect=\"italics\">l<\/em>). Bromine is reduced, its oxidation number decreasing from 0 in Br<sub>2<\/sub>(<em data-effect=\"italics\">l<\/em>) to \u22121 in GaBr<sub>3<\/sub>(<em data-effect=\"italics\">s<\/em>). The oxidizing agent is Br<sub>2<\/sub>(<em data-effect=\"italics\">l<\/em>).<\/p>\n<p id=\"fs-idp223712368\">(c) This is a redox reaction. It is a particularly interesting process, as it involves the same element, oxygen, undergoing both oxidation and reduction (a so-called <em data-effect=\"italics\">disproportionation reaction)<\/em>. Oxygen is oxidized, its oxidation number increasing from \u22121 in H<sub>2<\/sub>O<sub>2<\/sub>(<em data-effect=\"italics\">aq<\/em>) to 0 in O<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>). Oxygen is also reduced, its oxidation number decreasing from \u22121 in H<sub>2<\/sub>O<sub>2<\/sub>(<em data-effect=\"italics\">aq<\/em>) to \u22122 in H<sub>2<\/sub>O(<em data-effect=\"italics\">l<\/em>). For disproportionation reactions, the same substance functions as an oxidant and a reductant.<\/p>\n<p id=\"fs-idm40215792\">(d) This is not a redox reaction, since oxidation numbers remain unchanged for all elements.<\/p>\n<p id=\"fs-idm55300832\">(e) This is a redox reaction (combustion). Carbon is oxidized, its oxidation number increasing from \u22122 in C<sub>2<\/sub>H<sub>4<\/sub>(<em data-effect=\"italics\">g<\/em>) to +4 in CO<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>). The reducing agent (fuel) is C<sub>2<\/sub>H<sub>4<\/sub>(<em data-effect=\"italics\">g<\/em>). Oxygen is reduced, its oxidation number decreasing from 0 in O<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>) to \u22122 in H<sub>2<\/sub>O(<em data-effect=\"italics\">l<\/em>). The oxidizing agent is O<sub>2<\/sub>(<em data-effect=\"italics\">g<\/em>).<\/p>\n<p id=\"fs-idm9371232\"><strong>Check Your Learning:<\/strong><\/p>\n<p>This equation describes the production of tin(II) chloride:<\/p>\n<div id=\"fs-idm73301872\" style=\"text-align: center\" data-type=\"equation\">Sn(<em>s<\/em>) + 2HCl(<em>g<\/em>) \u27f6 SnCl<sub>2<\/sub>(<em>s<\/em>) + H<sub>2<\/sub>(<em>g<\/em>)<\/div>\n<p id=\"fs-idp98112752\">Is this a redox reaction? If so, provide a more specific name for the reaction if appropriate, and identify the oxidant and reductant.<\/p>\n<div id=\"fs-idp105853680\" data-type=\"note\">\n<div data-type=\"title\"><\/div>\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\n<p id=\"fs-idm50940704\">Yes, a single-replacement reaction. Sn(<em data-effect=\"italics\">s<\/em>) is the reductant, HCl(<em data-effect=\"italics\">g<\/em>) is the oxidant.<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idp98840016\" class=\"bc-section section\" data-depth=\"2\">\n<h4 data-type=\"title\"><strong>Balancing Redox Reactions via the Half-Reaction Method<\/strong><\/h4>\n<p id=\"fs-idm141853312\">Redox reactions that take place in aqueous media often involve water, hydronium ions, and hydroxide ions as reactants or products. Although these species are not oxidized or reduced, they do participate in chemical change in other ways (e.g., by providing the elements required to form oxyanions). Equations representing these reactions are sometimes very difficult to balance by inspection, so systematic approaches have been developed to assist in the process. One very useful approach is to use the method of half-reactions, which involves the following steps:<\/p>\n<p id=\"fs-idm64885712\">1. Write the two half-reactions representing the redox process.<\/p>\n<p id=\"fs-idm219773632\">2. Balance all elements except oxygen and hydrogen.<\/p>\n<p id=\"fs-idm339557376\">3. Balance oxygen atoms by adding H<sub>2<\/sub>O molecules.<\/p>\n<p id=\"fs-idm161858496\">4. Balance hydrogen atoms by adding H<sup>+<\/sup> ions.<\/p>\n<p id=\"fs-idm218459968\">5. Balance charge by adding electrons.<\/p>\n<p id=\"fs-idm31626864\">6. If necessary, multiply each half-reaction\u2019s coefficients by the smallest possible integers to yield equal numbers of electrons in each.<\/p>\n<p id=\"fs-idm241499680\">7. Add the balanced half-reactions together and simplify by removing species that appear on both sides of the equation.<\/p>\n<p id=\"fs-idm228573904\">8. For reactions occurring in basic media (excess hydroxide ions), carry out these additional steps:<\/p>\n<ol id=\"fs-idp48488192\" type=\"a\" data-mark-prefix=\"(\" data-mark-suffix=\")\">\n<li>Add OH<sup>\u2212<\/sup> ions to both sides of the equation in numbers equal to the number of H<sup>+<\/sup> ions.<\/li>\n<li>On the side of the equation containing both H<sup>+<\/sup> and OH<sup>\u2212<\/sup> ions, combine these ions to yield water molecules.<\/li>\n<li>Simplify the equation by removing any redundant water molecules.<\/li>\n<\/ol>\n<p id=\"fs-idm268418480\">9. Finally, check to see that both the number of atoms and the total charges<sup data-type=\"footnote-number\"><a href=\"#footnote1\" data-type=\"footnote-link\">1<\/a><\/sup> are balanced.<\/p>\n<div id=\"fs-idm53644080\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idp164751888\"><strong>Balancing Redox Reactions in Acidic Solution:<\/strong><\/p>\n<p>Write a balanced equation for the reaction between dichromate ion and iron(II) to yield iron(III) and chromium(III) in acidic solution.<\/p>\n<div id=\"fs-idm59837744\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + Fe<sup>2+<\/sup> \u27f6 Cr<sup>3+<\/sup> + Fe<sup>3+<\/sup><\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idp3143536\"><strong>Solution<\/strong><\/p>\n<ol id=\"fs-idp34895184\" class=\"stepwise\" type=\"1\">\n<li>\n<p id=\"fs-idp218612096\"><em data-effect=\"italics\">Write the two half-reactions<\/em>.<\/p>\n<p id=\"fs-idm9107808\">Each half-reaction will contain one reactant and one product with one element in common.<\/p>\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> \u27f6 Cr<sup>3+<\/sup><\/div>\n<\/li>\n<li>\n<p id=\"fs-idm63161856\"><em data-effect=\"italics\">Balance all elements except oxygen and hydrogen<\/em>. The iron half-reaction is already balanced, but the chromium half-reaction shows two Cr atoms on the left and one Cr atom on the right. Changing the coefficient on the right side of the equation to 2 achieves balance with regard to Cr atoms.<\/p>\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> \u27f6 2Cr<sup>3+<\/sup><\/div>\n<\/li>\n<li>\n<p id=\"fs-idm39730544\"><em data-effect=\"italics\">Balance oxygen atoms by adding<\/em> H<sub>2<\/sub>O <em data-effect=\"italics\">molecules<\/em>. The iron half-reaction does not contain O atoms. The chromium half-reaction shows seven O atoms on the left and none on the right, so seven water molecules are added to the right side.<\/p>\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div>\n<\/li>\n<li><em data-effect=\"italics\">Balance hydrogen atoms by adding<\/em> H<sup>+<\/sup><em data-effect=\"italics\">ions<\/em>. The iron half-reaction does not contain H atoms. The chromium half-reaction shows 14 H atoms on the right and none on the left, so 14 hydrogen ions are added to the left side.\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup><\/div>\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div>\n<\/li>\n<li>\n<p id=\"fs-idp23619040\"><em data-effect=\"italics\">Balance charge by adding electrons<\/em>. The iron half-reaction shows a total charge of 2+ on the left side (1 Fe<sup>2+<\/sup> ion) and 3+ on the right side (1 Fe<sup>3+<\/sup> ion). Adding one electron to the right side brings that side\u2019s total charge to (3+) + (1\u2212) = 2+, and charge balance is achieved.<\/p>\n<p id=\"fs-idm52131936\">The chromium half-reaction shows a total charge of (1 \u00d7 2\u2212) + (14 \u00d7 1+) = 12+ on the left side (1 Cr<sub>2<\/sub>O<sub>7<\/sub>}<sup>2\u2212<\/sup> ion and 14 H<sup>+<\/sup> ions). The total charge on the right side is (2 \u00d7 3+) = 6 + (2 Cr<sup>3+<\/sup> ions). Adding six electrons to the left side will bring that side\u2019s total charge to (12+ + 6\u2212) = 6+, and charge balance is achieved.<\/p>\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">Fe<sup>2+<\/sup> \u27f6 Fe<sup>3+<\/sup> + e<sup>&#8211;<\/sup><\/div>\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> + 6e<sup>&#8211;<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div>\n<\/li>\n<li>\n<p id=\"fs-idp2921088\"><em data-effect=\"italics\">Multiply the two half-reactions so the number of electrons in one reaction equals the number of electrons in the other reaction<\/em>. To be consistent with mass conservation, and the idea that redox reactions involve the transfer (not creation or destruction) of electrons, the iron half-reaction\u2019s coefficient must be multiplied by 6.<\/p>\n<div id=\"fs-idm158485920\" style=\"text-align: center\" data-type=\"equation\">6Fe<sup>2+<\/sup> \u27f6 6Fe<sup>3+<\/sup> + 6e<sup>&#8211;<\/sup><\/div>\n<div id=\"fs-idm115501120\" style=\"text-align: center\" data-type=\"equation\">Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> + 6e<sup>&#8211;<\/sup> \u27f6 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div>\n<\/li>\n<li>\n<p style=\"text-align: center\"><em data-effect=\"italics\">Add the balanced half-reactions and cancel species that appear on both sides of the equation<\/em>.<\/p>\n<\/li>\n<\/ol>\n<p style=\"text-align: center\">6Fe<sup>2+<\/sup> + Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> + 6e<sup>&#8211;<\/sup> \u27f6 6Fe<sup>3+<\/sup> + 6e<sup>&#8211;<\/sup> + 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/p>\n<div id=\"fs-idm208390896\" data-type=\"equation\"><\/div>\n<p id=\"fs-idp66154720\">\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Only the six electrons are redundant species. Removing them from each side of the equation yields the simplified, balanced equation here:<\/p>\n<div style=\"text-align: center\" data-type=\"equation\">6Fe<sup>2+<\/sup> + Cr<sub>2<\/sub>O<sub>7<\/sub><sup>2-<\/sup> + 14H<sup>+<\/sup> \u27f6 6Fe<sup>3+<\/sup> + 2Cr<sup>3+<\/sup> + 7H<sub>2<\/sub>O<\/div>\n<p id=\"fs-idm59483360\">A final check of atom and charge balance confirms the equation is balanced.<\/p>\n<table id=\"fs-idp8525760\" class=\"medium unnumbered\" summary=\"This table has three columns and six rows. The first column is unlabeled but the second and third columns are labeled, \u201cReactants,\u201d and \u201cProducts.\u201d Under the first column are the following: \u201cF e,\u201d \u201cC r,\u201d \u201cO,\u201d \u201cH,\u201d and, \u201ccharge.\u201d Under the \u201cReactants\u201d column are the numbers: 6, 2, 7, 14, 24 plus sign. Under the \u201cProducts\u201d column are the numbers: 6, 2, 7, 14 and 24 plus sign.\" data-label=\"\">\n<tbody>\n<tr valign=\"top\">\n<td data-align=\"left\"><\/td>\n<td data-align=\"left\">Reactants<\/td>\n<td data-align=\"left\">Products<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">Fe<\/td>\n<td data-align=\"left\">6<\/td>\n<td data-align=\"left\">6<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">Cr<\/td>\n<td data-align=\"left\">2<\/td>\n<td data-align=\"left\">2<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">O<\/td>\n<td data-align=\"left\">7<\/td>\n<td data-align=\"left\">7<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">H<\/td>\n<td data-align=\"left\">14<\/td>\n<td data-align=\"left\">14<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"left\">charge<\/td>\n<td data-align=\"left\">24+<\/td>\n<td data-align=\"left\">24+<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p id=\"fs-idp193051584\"><strong>Check Your Learning:<\/strong><\/p>\n<p>In basic solution, molecular chlorine, Cl<sub>2<\/sub>, reacts with hydroxide ions, OH<sup>\u2212<\/sup>, to yield chloride ions, Cl<sup>\u2212<\/sup>. and chlorate ions, ClO<sub>4<\/sub><sup>\u2212<\/sup>. HINT: This is a <em data-effect=\"italics\">disproportionation reaction<\/em> in which the element chlorine is both oxidized and reduced. Write a balanced equation for this reaction.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idm39281984\" data-type=\"note\">\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\n<p style=\"text-align: center\">3Cl<sub>2<\/sub>(<em>aq<\/em>) + 6OH<sup>&#8211;<\/sup>(<em>aq<\/em>) \u27f6 5Cl<sup>&#8211;<\/sup>(<em>aq<\/em>) + ClO<sub>3<\/sub><sup>&#8211;<\/sup>(<em>aq<\/em>) + 3H<sub>2<\/sub>O(<em>l<\/em>)<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm51820592\" class=\"summary\" data-depth=\"1\">\n<h3 data-type=\"title\"><strong>Key Concepts and Summary<\/strong><\/h3>\n<p id=\"fs-idp62302320\">Chemical reactions are classified according to similar patterns of behavior. A large number of important reactions are included in three categories: precipitation, acid-base, and oxidation-reduction (redox). Precipitation reactions involve the formation of one or more insoluble products. Acid-base reactions involve the transfer of hydrogen ions between reactants. Redox reactions involve a change in oxidation number for one or more reactant elements. Writing balanced equations for some redox reactions that occur in aqueous solutions is simplified by using a systematic approach called the half-reaction method.<\/p>\n<\/div>\n<div data-type=\"footnote-refs\">\n<h3 data-type=\"footnote-refs-title\"><strong>Footnotes<\/strong><\/h3>\n<ul data-list-type=\"bulleted\" data-bullet-style=\"none\">\n<li data-type=\"footnote-ref\"><a href=\"#footnote-ref1\" data-type=\"footnote-ref-link\">1<\/a><span data-type=\"footnote-ref-content\">The requirement of \u201ccharge balance\u201d is just a specific type of \u201cmass balance\u201d in which the species in question are electrons. An equation must represent equal numbers of electrons on the reactant and product sides, and so both atoms and charges must be balanced.<\/span><\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox shaded\" data-type=\"glossary\">\n<h3 data-type=\"glossary-title\"><strong>Glossary<\/strong><\/h3>\n<dl id=\"fs-idm39846352\">\n<dt>acid<\/dt>\n<dd id=\"fs-idm39845712\">substance that produces H<sub>3<\/sub>O<sup>+<\/sup> when dissolved in water<\/dd>\n<\/dl>\n<dl id=\"fs-idm54009824\">\n<dt>acid-base reaction<\/dt>\n<dd id=\"fs-idm54009184\">reaction involving the transfer of a hydrogen ion between reactant species<\/dd>\n<\/dl>\n<dl id=\"fs-idm54008672\">\n<dt>base<\/dt>\n<dd id=\"fs-idm54008032\">substance that produces OH<sup>\u2212<\/sup> when dissolved in water<\/dd>\n<\/dl>\n<dl id=\"fs-idm54007136\">\n<dt>combustion reaction<\/dt>\n<dd id=\"fs-idm28946480\">vigorous redox reaction producing significant amounts of energy in the form of heat and, sometimes, light<\/dd>\n<\/dl>\n<dl id=\"fs-idm28945840\">\n<dt>half-reaction<\/dt>\n<dd id=\"fs-idm28945200\">an equation that shows whether each reactant loses or gains electrons in a reaction.<\/dd>\n<\/dl>\n<dl id=\"fs-idm28944688\">\n<dt>insoluble<\/dt>\n<dd id=\"fs-idm28944048\">of relatively low solubility; dissolving only to a slight extent<\/dd>\n<\/dl>\n<dl id=\"fs-idm73914400\">\n<dt>oxidation<\/dt>\n<dd id=\"fs-idm73913760\">process in which an element\u2019s oxidation number is increased by loss of electrons<\/dd>\n<\/dl>\n<dl id=\"fs-idm73913072\">\n<dt>oxidation-reduction reaction<\/dt>\n<dd id=\"fs-idm73912432\">(also, redox reaction) reaction involving a change in oxidation number for one or more reactant elements<\/dd>\n<\/dl>\n<dl id=\"fs-idp57129632\">\n<dt>oxidation number<\/dt>\n<dd id=\"fs-idp57130272\">(also, oxidation state) the charge each atom of an element would have in a compound if the compound were ionic<\/dd>\n<\/dl>\n<dl id=\"fs-idp57130912\">\n<dt>oxidizing agent<\/dt>\n<dd id=\"fs-idp57131552\">(also, oxidant) substance that brings about the oxidation of another substance, and in the process becomes reduced<\/dd>\n<\/dl>\n<dl id=\"fs-idp57132192\">\n<dt>precipitate<\/dt>\n<dd id=\"fs-idp57132832\">insoluble product that forms from reaction of soluble reactants<\/dd>\n<\/dl>\n<dl id=\"fs-idp55089136\">\n<dt>precipitation reaction<\/dt>\n<dd id=\"fs-idp55089776\">reaction that produces one or more insoluble products; when reactants are ionic compounds, sometimes called double-displacement or metathesis<\/dd>\n<\/dl>\n<dl id=\"fs-idp55090448\">\n<dt>reduction<\/dt>\n<dd id=\"fs-idp55091088\">process in which an element\u2019s oxidation number is decreased by gain of electrons<\/dd>\n<\/dl>\n<dl id=\"fs-idp55091776\">\n<dt>reducing agent<\/dt>\n<dd id=\"fs-idp55092416\">(also, reductant) substance that brings about the reduction of another substance, and in the process becomes oxidized<\/dd>\n<\/dl>\n<dl id=\"fs-idp64227344\">\n<dt>single-displacement reaction<\/dt>\n<dd id=\"fs-idp64227984\">(also, replacement) redox reaction involving the oxidation of an elemental substance by an ionic species<\/dd>\n<\/dl>\n<dl id=\"fs-idp64228624\">\n<dt>soluble<\/dt>\n<dd id=\"fs-idp67578576\">of relatively high solubility; dissolving to a relatively large extent<\/dd>\n<\/dl>\n<dl id=\"fs-idp67579088\">\n<dt>solubility<\/dt>\n<dd id=\"fs-idp67579728\">the extent to which a substance may be dissolved in water, or any solvent<\/dd>\n<\/dl>\n<dl id=\"fs-idp67580240\">\n<dt>strong acid<\/dt>\n<dd id=\"fs-idp67580880\">acid that reacts completely when dissolved in water to yield hydronium ions<\/dd>\n<\/dl>\n<dl id=\"fs-idp67581392\">\n<dt>strong base<\/dt>\n<dd id=\"fs-idm4239184\">base that reacts completely when dissolved in water to yield hydroxide ions<\/dd>\n<\/dl>\n<dl id=\"fs-idm4238672\">\n<dt>weak acid<\/dt>\n<dd id=\"fs-idm4238032\">acid that reacts only to a slight extent when dissolved in water to yield hydronium ions<\/dd>\n<\/dl>\n<dl id=\"fs-idm4237408\">\n<dt>weak base<\/dt>\n<dd id=\"fs-idm4236768\">base that reacts only to a slight extent when dissolved in water to yield hydroxide ions<\/dd>\n<\/dl>\n<\/div>\n","protected":false},"author":1392,"menu_order":3,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-190","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":177,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/190","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/users\/1392"}],"version-history":[{"count":12,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/190\/revisions"}],"predecessor-version":[{"id":2117,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/190\/revisions\/2117"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/parts\/177"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/190\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/media?parent=190"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapter-type?post=190"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/contributor?post=190"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/license?post=190"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}