{"id":778,"date":"2021-07-23T09:20:41","date_gmt":"2021-07-23T13:20:41","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/aperrott\/chapter\/ph-and-poh\/"},"modified":"2022-06-23T09:20:34","modified_gmt":"2022-06-23T13:20:34","slug":"ph-and-poh","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/aperrott\/chapter\/ph-and-poh\/","title":{"raw":"14.2 pH and pOH","rendered":"14.2 pH and pOH"},"content":{"raw":"&nbsp;\r\n<div class=\"textbox textbox--learning-objectives\">\r\n<h3><strong>Learning Objectives<\/strong><\/h3>\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Explain the characterization of aqueous solutions as acidic, basic, or neutral<\/li>\r\n \t<li>Express hydronium and hydroxide ion concentrations on the pH and pOH scales<\/li>\r\n \t<li>Perform calculations relating pH and pOH<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idp11137424\">As discussed earlier, hydronium and hydroxide ions are present both in pure water and in all aqueous solutions, and their concentrations are inversely proportional as determined by the ion product of water (<em data-effect=\"italics\">K<\/em><sub>w<\/sub>). The concentrations of these ions in a solution are often critical determinants of the solution\u2019s properties and the chemical behaviors of its other solutes, and specific vocabulary has been developed to describe these concentrations in relative terms. A solution is <strong>neutral <\/strong>if it contains equal concentrations of hydronium and hydroxide ions; <strong>acidic <\/strong>if it contains a greater concentration of hydronium ions than hydroxide ions; and <strong>basic <\/strong>if it contains a lesser concentration of hydronium ions than hydroxide ions.<\/p>\r\n<p id=\"fs-idm21650320\">A common means of expressing quantities that may span many orders of magnitude is to use a logarithmic scale. One such scale that is very popular for chemical concentrations and equilibrium constants is based on the p-function, defined as shown where \u201cX\u201d is the quantity of interest and \u201clog\u201d is the base-10 logarithm:<\/p>\r\n\r\n<div id=\"fs-idp27819744\" style=\"padding-left: 40px\" data-type=\"equation\">pX = \u2212log X<\/div>\r\n<p id=\"fs-idm40569744\">The <strong>pH<\/strong> of a solution is therefore defined as shown here, where [H<sub>3<\/sub>O<sup>+<\/sup>] is the molar concentration of hydronium ion in the solution:<\/p>\r\n\r\n<div id=\"fs-idm104306928\" style=\"padding-left: 40px\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>]<\/div>\r\n<p id=\"fs-idm112635600\">Rearranging this equation to isolate the hydronium ion molarity yields the equivalent expression:<\/p>\r\n\r\n<div id=\"fs-idm34387328\" style=\"padding-left: 40px\" data-type=\"equation\">[H<sub>3<\/sub>O<sup>+<\/sup>] = 10<sup>\u2212pH<\/sup><\/div>\r\n<p id=\"fs-idp55544688\">Likewise, the hydroxide ion molarity may be expressed as a p-function, or <span data-type=\"term\">pOH<\/span>:<\/p>\r\n\r\n<div id=\"fs-idp66748048\" style=\"padding-left: 40px\" data-type=\"equation\">pOH = \u2212log[OH<sup>\u2212<\/sup>]<\/div>\r\n<p id=\"fs-idp67153952\">or<\/p>\r\n\r\n<div id=\"fs-idp102994080\" style=\"padding-left: 40px\" data-type=\"equation\">[OH<sup>\u2212<\/sup>] = 10<sup>\u2212pOH<\/sup><\/div>\r\n<p id=\"fs-idm97029664\">Finally, the relation between these two ion concentrations expressed as p-functions is easily derived from the <em data-effect=\"italics\">K<\/em><sub>w<\/sub> expression:<\/p>\r\n\r\n<div id=\"fs-idp158230176\" style=\"padding-left: 40px\" data-type=\"equation\">K<sub>w<\/sub> = [H<sub>3<\/sub>O<sup>+<\/sup>][OH<sup>\u2212<\/sup>]<\/div>\r\n<div id=\"fs-idp50288944\" style=\"padding-left: 40px\" data-type=\"equation\">\u2212logK<sub>w<\/sub> = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>][OH<sup>\u2212<\/sup>] = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>] + \u2212log[OH<sup>\u2212<\/sup>]<\/div>\r\n<div id=\"fs-idm65790448\" style=\"padding-left: 40px\" data-type=\"equation\">pK<sub>w<\/sub> = pH + pOH<\/div>\r\n<p id=\"fs-idp11266224\">At 25\u00b0C, the value of <em data-effect=\"italics\">K<\/em><sub>w<\/sub> is 1.0 \u00d7 10<sup>\u221214<\/sup>, and so:<\/p>\r\n\r\n<div id=\"fs-idm26101984\" style=\"padding-left: 40px\" data-type=\"equation\">14.00 = pH + pOH<\/div>\r\n<p id=\"fs-idm103103632\">The hydronium ion molarity in pure water (or any neutral solution) is 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> at 25\u00b0C. The pH and pOH of a neutral solution at this temperature are therefore:<\/p>\r\n\r\n<div id=\"fs-idp111835440\" style=\"padding-left: 40px\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>] = \u2212log(1.0 \u00d7 10<sup>-7<\/sup> M) = 7.00<\/div>\r\n<div id=\"fs-idm65159184\" style=\"padding-left: 40px\" data-type=\"equation\">pOH = \u2212log[OH<sup>\u2212<\/sup>] = \u2212log(1.0 \u00d7 10<sup>-7<\/sup> M) = 7.00<\/div>\r\n<p id=\"fs-idp108462720\">And so, <em data-effect=\"italics\">at this temperature<\/em>, acidic solutions are those with hydronium ion molarities greater than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> and hydroxide ion molarities less than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> (corresponding to pH values less than 7.00 and pOH values greater than 7.00). Basic solutions are those with hydronium ion molarities less than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> and hydroxide ion molarities greater than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> (corresponding to pH values greater than 7.00 and pOH values less than 7.00).<\/p>\r\n<p id=\"fs-idm84564368\">Since the autoionization constant <em data-effect=\"italics\">K<\/em><sub>w<\/sub> is temperature dependent, these correlations between pH values and the acidic\/neutral\/basic adjectives will be different at temperatures other than 25\u00b0C. Unless otherwise noted, references to pH values are presumed to be those at 25\u00b0C (<a class=\"autogenerated-content\" href=\"#fs-idp56820128\">(Figure)<\/a>).<\/p>\r\n\r\n<table id=\"fs-idp56820128\" class=\"top-titled\" summary=\"This table has three columns and four rows. The first row is a header row, and it labels each column: \u201cClassification,\u201d \u201cRelative ion concentrations,\u201d and \u201cp H at 25 degrees C.\u201d Under the \u201cClassification\u201d column are the following: \u201cacidic,\u201d \u201cneutral,\u201d and \u201cbasic.\u201d Under the \u201cRelative ion concentrations\u201d column are the following, \u201c[ H subscript 2 O superscript plus sign ] is greater than [ O H superscript negative sign],\u201d \u201c[ H subscript 2 O superscript plus sign ] equals [ O H superscript negative sign ],\u201d and, \u201c[ H subscript 2 O superscript plus sign ] is less than [ O H superscript negative sing ].\u201d Under the \u201cp H at 25 degrees C\u201d column are the following: \u201cp H is less than 7,\u201d \u201cp H equals 7,\u201d and \u201cp H is greater than 7.\u201d\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"3\" data-align=\"center\">Summary of Relations for Acidic, Basic and Neutral Solutions<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th data-align=\"center\">Classification<\/th>\r\n<th data-align=\"center\">Relative Ion Concentrations<\/th>\r\n<th data-align=\"center\">pH at 25 \u00b0C<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td data-align=\"center\">acidic<\/td>\r\n<td data-align=\"center\">[H<sub>3<\/sub>O<sup>+<\/sup>] &gt; [OH<sup>\u2212<\/sup>]<\/td>\r\n<td data-align=\"center\">pH &lt; 7<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"center\">neutral<\/td>\r\n<td data-align=\"center\">[H<sub>3<\/sub>O<sup>+<\/sup>] = [OH<sup>\u2212<\/sup>]<\/td>\r\n<td data-align=\"center\">pH = 7<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-align=\"center\">basic<\/td>\r\n<td data-align=\"center\">[H<sub>3<\/sub>O<sup>+<\/sup>] &lt; [OH<sup>\u2212<\/sup>]<\/td>\r\n<td data-align=\"center\">pH &gt; 7<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<p id=\"fs-idp96882128\"><a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_phscale\">(Figure)<\/a> shows the relationships between [H<sub>3<\/sub>O<sup>+<\/sup>], [OH<sup>\u2212<\/sup>], pH, and pOH for solutions classified as acidic, basic, and neutral.<\/p>\r\n\r\n<div id=\"CNX_Chem_14_02_phscale\" class=\"bc-figure figure\">\r\n<div class=\"bc-figcaption figcaption\">The pH and pOH scales represent concentrations of H<sub>3<\/sub>O<sup>+<\/sup> and OH<sup>\u2212<\/sup>, respectively. The pH and pOH values of some common substances at 25\u00b0C are shown in this chart.<\/div>\r\n<span id=\"fs-idm15160336\" data-type=\"media\" data-alt=\"A table is provided with 5 columns. The first column is labeled \u201cleft bracket H subscript 3 O superscript plus right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript 1, including 10 superscript 0 or 1, 10 superscript negative 1, decreasing by single powers of 10 to 10 superscript negative 15. The second column is labeled \u201cleft bracket O H superscript negative right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript negative 15, increasing by single powers of 10 to including 10 superscript 0 or 1, and 10 superscript 1. The third column is labeled \u201cp H.\u201d Values listed in this column are integers beginning at negative 1, increasing by ones up to 14. The fourth column is labeled \u201cp O H.\u201d Values in this column are integers beginning at 15, decreasing by ones up to negative 1. The fifth column is labeled \u201cSample Solution.\u201d A vertical line at the left of the column has tick marks corresponding to each p H level in the table. Substances are listed next to this line segment with line segments connecting them to the line to show approximate p H and p O H values. 1 M H C l is listed at a p H of 0. Gastric juices are listed at a p H of about 1.5. Lime juice is listed at a p H of about 2, followed by 1 M C H subscript 3 C O subscript 2 H, followed by stomach acid at a p H value of nearly 3. Wine is listed around 3.5. Coffee is listed just past 5. Pure water is listed at a p H of 7. Pure blood is just beyond 7. Milk of Magnesia is listed just past a p H of 10.5. Household ammonia is listed just before a pH of 12. 1 M N a O H is listed at a p H of 0. To the right of this labeled arrow is an arrow that points up and down through the height of the column. A beige strip passes through the table and to this double headed arrow at p H 7. To the left of the double headed arrow in this beige strip is the label \u201cneutral.\u201d A narrow beige strip runs through the arrow. Just above and below this region, the arrow is purple. It gradually turns to a bright red as it extends upward. At the top of the arrow, near the head of the arrow is the label \u201cacidic.\u201d Similarly, the lower region changes color from purple to blue moving to the bottom of the column. The head at this end of the arrow is labeled \u201cbasic.\u201d\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_phscale-1.jpg\" alt=\"A table is provided with 5 columns. The first column is labeled \u201cleft bracket H subscript 3 O superscript plus right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript 1, including 10 superscript 0 or 1, 10 superscript negative 1, decreasing by single powers of 10 to 10 superscript negative 15. The second column is labeled \u201cleft bracket O H superscript negative right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript negative 15, increasing by single powers of 10 to including 10 superscript 0 or 1, and 10 superscript 1. The third column is labeled \u201cp H.\u201d Values listed in this column are integers beginning at negative 1, increasing by ones up to 14. The fourth column is labeled \u201cp O H.\u201d Values in this column are integers beginning at 15, decreasing by ones up to negative 1. The fifth column is labeled \u201cSample Solution.\u201d A vertical line at the left of the column has tick marks corresponding to each p H level in the table. Substances are listed next to this line segment with line segments connecting them to the line to show approximate p H and p O H values. 1 M H C l is listed at a p H of 0. Gastric juices are listed at a p H of about 1.5. Lime juice is listed at a p H of about 2, followed by 1 M C H subscript 3 C O subscript 2 H, followed by stomach acid at a p H value of nearly 3. Wine is listed around 3.5. Coffee is listed just past 5. Pure water is listed at a p H of 7. Pure blood is just beyond 7. Milk of Magnesia is listed just past a p H of 10.5. Household ammonia is listed just before a pH of 12. 1 M N a O H is listed at a p H of 0. To the right of this labeled arrow is an arrow that points up and down through the height of the column. A beige strip passes through the table and to this double headed arrow at p H 7. To the left of the double headed arrow in this beige strip is the label \u201cneutral.\u201d A narrow beige strip runs through the arrow. Just above and below this region, the arrow is purple. It gradually turns to a bright red as it extends upward. At the top of the arrow, near the head of the arrow is the label \u201cacidic.\u201d Similarly, the lower region changes color from purple to blue moving to the bottom of the column. The head at this end of the arrow is labeled \u201cbasic.\u201d\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<div id=\"fs-idp62701056\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idp97421056\"><strong>Calculation of pH from [H<sub>3<\/sub>O<sup>+<\/sup>]<\/strong><\/p>\r\nWhat is the pH of stomach acid, a solution of HCl with a hydronium ion concentration of 1.2 \u00d7 10<sup>\u22123 <\/sup><em data-effect=\"italics\">M<\/em>?\r\n<p id=\"fs-idm103954896\"><strong>Solution:<\/strong><\/p>\r\n\r\n<div id=\"fs-idm98702480\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>]<\/div>\r\n<div id=\"fs-idm79624528\" data-type=\"equation\">= \u2212log(1.2 \u00d7 10<sup>-3<\/sup> M)<\/div>\r\n<div id=\"fs-idm7356256\" data-type=\"equation\">= 2.92<\/div>\r\n<span data-type=\"newline\">\r\n<\/span> (When taking the log of a value, keep as many decimal places in the result as there are significant figures in the value.)\r\n<p id=\"fs-idp57469360\"><strong>Check Your Learning:<\/strong><\/p>\r\nWater exposed to air contains carbonic acid, H<sub>2<\/sub>CO<sub>3<\/sub>, due to the reaction between carbon dioxide and water:\r\n<div id=\"fs-idm45568144\" style=\"padding-left: 40px\" data-type=\"equation\">CO<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc H<sub>2<\/sub>CO<sub>3<\/sub>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idm106049328\">Air-saturated water has a hydronium ion concentration caused by the dissolved CO<sub>2<\/sub> of 2.0 \u00d7 10<sup>\u22126 <\/sup><em data-effect=\"italics\">M<\/em>, about 20-times larger than that of pure water. Calculate the pH of the solution at 25\u00b0C.<\/p>\r\n&nbsp;\r\n<div id=\"fs-idm61631152\" data-type=\"note\">\r\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\r\n<p id=\"fs-idm99369680\">5.70<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp57695872\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idm102910496\"><strong>Calculation of Hydronium Ion Concentration from pH<\/strong><\/p>\r\nCalculate the hydronium ion concentration of blood, the pH of which is 7.3.\r\n<p id=\"fs-idp11945040\"><strong>Solution:<\/strong><\/p>\r\n\r\n<div id=\"fs-idm108531776\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>] = 7.3<\/div>\r\n<div id=\"fs-idm49363536\" data-type=\"equation\">log[H<sub>3<\/sub>O<sup>+<\/sup>] = -7.3<\/div>\r\n<div id=\"fs-idp46442128\" data-type=\"equation\">[H<sub>3<\/sub>O<sup>+<\/sup>] = 10<sup>-7.3<\/sup> or [H<sub>3<\/sub>O<sup>+<\/sup>] = log<sup>-1<\/sup>(\u22127.3)<\/div>\r\n<div id=\"fs-idm58086272\" data-type=\"equation\">[H<sub>3<\/sub>O<sup>+<\/sup>] = 5 \u00d7 10<sup>-8<\/sup> M<\/div>\r\n<span data-type=\"newline\">\r\n<\/span> (On a calculator, take the antilog, or the \u201cinverse\u201d log, of \u22127.3, or calculate 10<sup>\u22127.3<\/sup>.)\r\n<p id=\"fs-idp487584\"><strong>Check Your Learning:<\/strong><\/p>\r\nCalculate the hydronium ion concentration of a solution with a pH of \u22121.07.\r\n\r\n&nbsp;\r\n<div id=\"fs-idp89672320\" data-type=\"note\">\r\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\r\n<p id=\"fs-idm9452560\">12 <em data-effect=\"italics\">M<\/em><\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp48828576\" class=\"chemistry sciences-interconnect\" data-type=\"note\">\r\n<div data-type=\"title\"><strong>Environmental Science<\/strong><\/div>\r\n<p id=\"fs-idm116727232\">Normal rainwater has a pH between 5 and 6 due to the presence of dissolved CO<sub>2<\/sub> which forms carbonic acid:<\/p>\r\n\r\n<div id=\"fs-idp66992000\" style=\"padding-left: 40px\" data-type=\"equation\">CO<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192\u00a0H<sub>2<\/sub>CO<sub>3<\/sub>(<em>aq<\/em>)<\/div>\r\n<div id=\"fs-idm103550896\" style=\"padding-left: 40px\" data-type=\"equation\">H<sub>2<\/sub>CO<sub>3<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc \u00a0HCO<sub>3<\/sub><sup>\u2212<\/sup>(aq) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\r\n<p id=\"fs-idp13883280\">Acid rain is rainwater that has a pH of less than 5, due to a variety of nonmetal oxides, including CO<sub>2<\/sub>, SO<sub>2<\/sub>, SO<sub>3<\/sub>, NO, and NO<sub>2<\/sub> being dissolved in the water and reacting with it to form not only carbonic acid, but sulfuric acid and nitric acid. The formation and subsequent ionization of sulfuric acid are shown here:<\/p>\r\n\r\n<div id=\"fs-idp39536896\" data-type=\"equation\">\r\n<div id=\"fs-idp66992000\" style=\"padding-left: 40px\" data-type=\"equation\">SO<sub>3<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192\u00a0H<sub>2<\/sub>SO<sub>4<\/sub>(<em>aq<\/em>)<\/div>\r\n<div id=\"fs-idm103550896\" style=\"padding-left: 40px\" data-type=\"equation\">H<sub>2<\/sub>SO<sub>4<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192 \u00a0HSO<sub>4<\/sub><sup>\u2212<\/sup>(aq) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\r\n<\/div>\r\n<p id=\"fs-idp93018416\">Carbon dioxide is naturally present in the atmosphere because most organisms produce it as a waste product of metabolism. Carbon dioxide is also formed when fires release carbon stored in vegetation or fossil fuels. Sulfur trioxide in the atmosphere is naturally produced by volcanic activity, but it also originates from burning fossil fuels, which have traces of sulfur, and from the process of \u201croasting\u201d ores of metal sulfides in metal-refining processes. Oxides of nitrogen are formed in internal combustion engines where the high temperatures make it possible for the nitrogen and oxygen in air to chemically combine.<\/p>\r\n<p id=\"fs-idm22038432\">Acid rain is a particular problem in industrial areas where the products of combustion and smelting are released into the air without being stripped of sulfur and nitrogen oxides. In North America and Europe until the 1980s, it was responsible for the destruction of forests and freshwater lakes, when the acidity of the rain actually killed trees, damaged soil, and made lakes uninhabitable for all but the most acid-tolerant species. Acid rain also corrodes statuary and building facades that are made of marble and limestone (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_AcidRain\">(Figure)<\/a>). Regulations limiting the amount of sulfur and nitrogen oxides that can be released into the atmosphere by industry and automobiles have reduced the severity of acid damage to both natural and manmade environments in North America and Europe. It is now a growing problem in industrial areas of China and India.<\/p>\r\n<p id=\"fs-idm22123696\">For further information on acid rain, visit this <a href=\"http:\/\/openstaxcollege.org\/l\/16EPA\">website<\/a> hosted by the US Environmental Protection Agency.<\/p>\r\n\r\n<div id=\"CNX_Chem_14_02_AcidRain\" class=\"scaled-down\">\r\n<div class=\"bc-figcaption figcaption\">(a) Acid rain makes trees more susceptible to drought and insect infestation, and depletes nutrients in the soil. (b) It also is corrodes statues that are carved from marble or limestone. (credit a: modification of work by Chris M Morris; credit b: modification of work by \u201cEden, Janine and Jim\u201d\/Flickr)<\/div>\r\n<span id=\"fs-idp11790976\" data-type=\"media\" data-alt=\"Two photos are shown. Photograph a on the left shows the upper portion of trees against a bright blue sky. The tops of several trees at the center of the photograph have bare branches and appear to be dead. Image b shows a statue of a man that appears to from the revolutionary war era in either marble or limestone.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_AcidRain-1.jpg\" alt=\"Two photos are shown. Photograph a on the left shows the upper portion of trees against a bright blue sky. The tops of several trees at the center of the photograph have bare branches and appear to be dead. Image b shows a statue of a man that appears to from the revolutionary war era in either marble or limestone.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm90070400\" class=\"textbox textbox--examples\" data-type=\"example\">\r\n<p id=\"fs-idp57499040\"><strong>Calculation of pOH<\/strong><\/p>\r\nWhat are the pOH and the pH of a 0.0125-<em data-effect=\"italics\">M<\/em> solution of potassium hydroxide, KOH?\r\n<p id=\"fs-idm55606544\"><strong>Solution:<\/strong><\/p>\r\nPotassium hydroxide is a highly soluble ionic compound and completely dissociates when dissolved in dilute solution, yielding [OH<sup>\u2212<\/sup>] = 0.0125 <em data-effect=\"italics\">M<\/em>:\r\n\r\n&nbsp;\r\n<div id=\"fs-idp97197664\" style=\"padding-left: 40px\" data-type=\"equation\">pOH = \u2212log[OH<sup>\u2212<\/sup>] = \u2212log(0.0125 M) =1.903<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idm11584304\">The pH can be found from the pOH:<\/p>\r\n\r\n<div id=\"fs-idm77730624\" style=\"padding-left: 40px\" data-type=\"equation\">pH + pOH = 14.00<\/div>\r\n<div id=\"fs-idm71245120\" style=\"padding-left: 40px\" data-type=\"equation\">pH =14.00 - pOH = 14.00-1.903 = 12.10<\/div>\r\n<div data-type=\"equation\"><\/div>\r\n<p id=\"fs-idm147912592\"><strong>Check Your Learning:<\/strong><\/p>\r\nThe hydronium ion concentration of vinegar is approximately 4 \u00d7 10<sup>\u22123 <\/sup><em data-effect=\"italics\">M<\/em>. What are the corresponding values of pOH and pH?\r\n\r\n&nbsp;\r\n<div id=\"fs-idm58824960\" data-type=\"note\">\r\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\r\n<p id=\"fs-idm165995920\">pOH = 11.6, pH = 2.4<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<p id=\"fs-idm165634608\">The acidity of a solution is typically assessed experimentally by measurement of its pH. The pOH of a solution is not usually measured, as it is easily calculated from an experimentally determined pH value. The pH of a solution can be directly measured using a pH meter (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_pHMeter\">(Figure)<\/a>).<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_14_02_pHMeter\" class=\"bc-figure figure\">\r\n<div class=\"bc-figcaption figcaption\">(a) A research-grade pH meter used in a laboratory can have a resolution of 0.001 pH units, an accuracy of \u00b1 0.002 pH units, and may cost in excess of \ud83d\udcb21000. (b) A portable pH meter has lower resolution (0.01 pH units), lower accuracy (\u00b1 0.2 pH units), and a far lower price tag. (credit b: modification of work by Jacopo Werther)<\/div>\r\n<span id=\"fs-idp134372032\" data-type=\"media\" data-alt=\"This figure contains two images. The first, image a, is of an analytical digital p H meter on a laboratory counter. The second, image b, is of a portable hand held digital p H meter.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_pHMeter-1.jpg\" alt=\"This figure contains two images. The first, image a, is of an analytical digital p H meter on a laboratory counter. The second, image b, is of a portable hand held digital p H meter.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\r\n<\/div>\r\n<p id=\"fs-idp57700960\">The pH of a solution may also be visually estimated using colored indicators (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_indicator\">(Figure)<\/a>). The acid-base equilibria that enable use of these indicator dyes for pH measurements are described in a later section of this chapter.<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Chem_14_02_indicator\" class=\"bc-figure figure\">\r\n<div class=\"bc-figcaption figcaption\">(a) A solution containing a dye mixture, called universal indicator, takes on different colors depending upon its pH. (b) Convenient test strips, called pH paper, contain embedded indicator dyes that yield pH-dependent color changes on contact with aqueous solutions.(credit: modification of work by Sahar Atwa)<\/div>\r\n<span id=\"fs-idp11928656\" data-type=\"media\" data-alt=\"This figure contains two images. The first shows a variety of colors of solutions in labeled beakers. A red solution in a beaker is labeled \u201c0.10 M H C l.\u201d An orange solution is labeled \u201c0.10 M C H subscript 3 C O O H.\u201d A yellow-orange solution is labeled \u201c0.1 M N H subscript 4 C l.\u201d A yellow solution is labeled \u201cdeionized water.\u201d A second solution beaker is labeled \u201c0.10 M K C l.\u201d A green solution is labeled \u201c0.10 M aniline.\u201d A blue solution is labeled \u201c0.10 M N H subscript 4 C l (a q).\u201d A final beaker containing a dark blue solution is labeled \u201c0.10 M N a O H.\u201d Image b shows pHydrion paper that is used for measuring pH in the range of p H from 1 to 12. The color scale for identifying p H based on color is shown along with several of the test strips used to evaluate p H.\"><img src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_indicator-1.jpg\" alt=\"This figure contains two images. The first shows a variety of colors of solutions in labeled beakers. A red solution in a beaker is labeled \u201c0.10 M H C l.\u201d An orange solution is labeled \u201c0.10 M C H subscript 3 C O O H.\u201d A yellow-orange solution is labeled \u201c0.1 M N H subscript 4 C l.\u201d A yellow solution is labeled \u201cdeionized water.\u201d A second solution beaker is labeled \u201c0.10 M K C l.\u201d A green solution is labeled \u201c0.10 M aniline.\u201d A blue solution is labeled \u201c0.10 M N H subscript 4 C l (a q).\u201d A final beaker containing a dark blue solution is labeled \u201c0.10 M N a O H.\u201d Image b shows pHydrion paper that is used for measuring pH in the range of p H from 1 to 12. The color scale for identifying p H based on color is shown along with several of the test strips used to evaluate p H.\" data-media-type=\"image\/jpeg\" \/><\/span>\r\n\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-idp58752272\">Concentrations of hydronium and hydroxide ions in aqueous media are often represented as logarithmic pH and pOH values, respectively. At 25\u00b0C, the autoionization equilibrium for water requires the sum of pH and pOH to equal 14.00 for any aqueous solution. The relative concentrations of hydronium and hydroxide ion in a solution define its status as acidic ([H<sub>3<\/sub>O<sup>+<\/sup>] &gt; [OH<sup>\u2212<\/sup>]), basic ([H<sub>3<\/sub>O<sup>+<\/sup>] &lt; [OH<sup>\u2212<\/sup>]), or neutral ([H<sub>3<\/sub>O<sup>+<\/sup>] = [OH<sup>\u2212<\/sup>]). At 25\u00b0C, a pH &lt; 7.00 indicates an acidic solution, a pH &gt; 7.00 a basic solution, and a pH = 7.00 a neutral solution.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idp66998992\" class=\"key-equations\" data-depth=\"1\">\r\n<h3 data-type=\"title\"><strong>Key Equations<\/strong><\/h3>\r\n<ul id=\"fs-idp46607520\" data-bullet-style=\"bullet\">\r\n \t<li>pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>]<\/li>\r\n \t<li>pH + pOH = p<em data-effect=\"italics\">K<\/em><sub>w<\/sub> = 14.00 at 25 \u00b0C<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div id=\"fs-idm61137872\" class=\"exercises\" data-depth=\"1\">\r\n<div id=\"fs-idm209904880\" data-type=\"exercise\">\r\n<div id=\"fs-idm15687280\" data-type=\"solution\">\r\n<p id=\"fs-idm81860944\"><\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\" data-type=\"glossary\">\r\n<h3 data-type=\"glossary-title\">Glossary<\/h3>\r\n<dl id=\"fs-idm64563696\">\r\n \t<dt>acidic<\/dt>\r\n \t<dd id=\"fs-idm110209904\">a solution in which [H<sub>3<\/sub>O<sup>+<\/sup>] &gt; [OH<sup>\u2212<\/sup>]<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm111671584\">\r\n \t<dt>basic<\/dt>\r\n \t<dd id=\"fs-idp49209968\">a solution in which [H<sub>3<\/sub>O<sup>+<\/sup>] &lt; [OH<sup>\u2212<\/sup>]<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp143891408\">\r\n \t<dt>neutral<\/dt>\r\n \t<dd id=\"fs-idm153784960\">describes a solution in which [H<sub>3<\/sub>O<sup>+<\/sup>] = [OH<sup>\u2212<\/sup>]<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm103907536\">\r\n \t<dt>pH<\/dt>\r\n \t<dd id=\"fs-idm14698528\">logarithmic measure of the concentration of hydronium ions in a solution<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp46966768\">\r\n \t<dt>pOH<\/dt>\r\n \t<dd id=\"fs-idm67584528\">logarithmic measure of the concentration of hydroxide ions in a solution<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<p>&nbsp;<\/p>\n<div class=\"textbox textbox--learning-objectives\">\n<h3><strong>Learning Objectives<\/strong><\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Explain the characterization of aqueous solutions as acidic, basic, or neutral<\/li>\n<li>Express hydronium and hydroxide ion concentrations on the pH and pOH scales<\/li>\n<li>Perform calculations relating pH and pOH<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idp11137424\">As discussed earlier, hydronium and hydroxide ions are present both in pure water and in all aqueous solutions, and their concentrations are inversely proportional as determined by the ion product of water (<em data-effect=\"italics\">K<\/em><sub>w<\/sub>). The concentrations of these ions in a solution are often critical determinants of the solution\u2019s properties and the chemical behaviors of its other solutes, and specific vocabulary has been developed to describe these concentrations in relative terms. A solution is <strong>neutral <\/strong>if it contains equal concentrations of hydronium and hydroxide ions; <strong>acidic <\/strong>if it contains a greater concentration of hydronium ions than hydroxide ions; and <strong>basic <\/strong>if it contains a lesser concentration of hydronium ions than hydroxide ions.<\/p>\n<p id=\"fs-idm21650320\">A common means of expressing quantities that may span many orders of magnitude is to use a logarithmic scale. One such scale that is very popular for chemical concentrations and equilibrium constants is based on the p-function, defined as shown where \u201cX\u201d is the quantity of interest and \u201clog\u201d is the base-10 logarithm:<\/p>\n<div id=\"fs-idp27819744\" style=\"padding-left: 40px\" data-type=\"equation\">pX = \u2212log X<\/div>\n<p id=\"fs-idm40569744\">The <strong>pH<\/strong> of a solution is therefore defined as shown here, where [H<sub>3<\/sub>O<sup>+<\/sup>] is the molar concentration of hydronium ion in the solution:<\/p>\n<div id=\"fs-idm104306928\" style=\"padding-left: 40px\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>]<\/div>\n<p id=\"fs-idm112635600\">Rearranging this equation to isolate the hydronium ion molarity yields the equivalent expression:<\/p>\n<div id=\"fs-idm34387328\" style=\"padding-left: 40px\" data-type=\"equation\">[H<sub>3<\/sub>O<sup>+<\/sup>] = 10<sup>\u2212pH<\/sup><\/div>\n<p id=\"fs-idp55544688\">Likewise, the hydroxide ion molarity may be expressed as a p-function, or <span data-type=\"term\">pOH<\/span>:<\/p>\n<div id=\"fs-idp66748048\" style=\"padding-left: 40px\" data-type=\"equation\">pOH = \u2212log[OH<sup>\u2212<\/sup>]<\/div>\n<p id=\"fs-idp67153952\">or<\/p>\n<div id=\"fs-idp102994080\" style=\"padding-left: 40px\" data-type=\"equation\">[OH<sup>\u2212<\/sup>] = 10<sup>\u2212pOH<\/sup><\/div>\n<p id=\"fs-idm97029664\">Finally, the relation between these two ion concentrations expressed as p-functions is easily derived from the <em data-effect=\"italics\">K<\/em><sub>w<\/sub> expression:<\/p>\n<div id=\"fs-idp158230176\" style=\"padding-left: 40px\" data-type=\"equation\">K<sub>w<\/sub> = [H<sub>3<\/sub>O<sup>+<\/sup>][OH<sup>\u2212<\/sup>]<\/div>\n<div id=\"fs-idp50288944\" style=\"padding-left: 40px\" data-type=\"equation\">\u2212logK<sub>w<\/sub> = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>][OH<sup>\u2212<\/sup>] = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>] + \u2212log[OH<sup>\u2212<\/sup>]<\/div>\n<div id=\"fs-idm65790448\" style=\"padding-left: 40px\" data-type=\"equation\">pK<sub>w<\/sub> = pH + pOH<\/div>\n<p id=\"fs-idp11266224\">At 25\u00b0C, the value of <em data-effect=\"italics\">K<\/em><sub>w<\/sub> is 1.0 \u00d7 10<sup>\u221214<\/sup>, and so:<\/p>\n<div id=\"fs-idm26101984\" style=\"padding-left: 40px\" data-type=\"equation\">14.00 = pH + pOH<\/div>\n<p id=\"fs-idm103103632\">The hydronium ion molarity in pure water (or any neutral solution) is 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> at 25\u00b0C. The pH and pOH of a neutral solution at this temperature are therefore:<\/p>\n<div id=\"fs-idp111835440\" style=\"padding-left: 40px\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>] = \u2212log(1.0 \u00d7 10<sup>-7<\/sup> M) = 7.00<\/div>\n<div id=\"fs-idm65159184\" style=\"padding-left: 40px\" data-type=\"equation\">pOH = \u2212log[OH<sup>\u2212<\/sup>] = \u2212log(1.0 \u00d7 10<sup>-7<\/sup> M) = 7.00<\/div>\n<p id=\"fs-idp108462720\">And so, <em data-effect=\"italics\">at this temperature<\/em>, acidic solutions are those with hydronium ion molarities greater than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> and hydroxide ion molarities less than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> (corresponding to pH values less than 7.00 and pOH values greater than 7.00). Basic solutions are those with hydronium ion molarities less than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> and hydroxide ion molarities greater than 1.0 \u00d7 10<sup>\u22127 <\/sup><em data-effect=\"italics\">M<\/em> (corresponding to pH values greater than 7.00 and pOH values less than 7.00).<\/p>\n<p id=\"fs-idm84564368\">Since the autoionization constant <em data-effect=\"italics\">K<\/em><sub>w<\/sub> is temperature dependent, these correlations between pH values and the acidic\/neutral\/basic adjectives will be different at temperatures other than 25\u00b0C. Unless otherwise noted, references to pH values are presumed to be those at 25\u00b0C (<a class=\"autogenerated-content\" href=\"#fs-idp56820128\">(Figure)<\/a>).<\/p>\n<table id=\"fs-idp56820128\" class=\"top-titled\" summary=\"This table has three columns and four rows. The first row is a header row, and it labels each column: \u201cClassification,\u201d \u201cRelative ion concentrations,\u201d and \u201cp H at 25 degrees C.\u201d Under the \u201cClassification\u201d column are the following: \u201cacidic,\u201d \u201cneutral,\u201d and \u201cbasic.\u201d Under the \u201cRelative ion concentrations\u201d column are the following, \u201c[ H subscript 2 O superscript plus sign ] is greater than [ O H superscript negative sign],\u201d \u201c[ H subscript 2 O superscript plus sign ] equals [ O H superscript negative sign ],\u201d and, \u201c[ H subscript 2 O superscript plus sign ] is less than [ O H superscript negative sing ].\u201d Under the \u201cp H at 25 degrees C\u201d column are the following: \u201cp H is less than 7,\u201d \u201cp H equals 7,\u201d and \u201cp H is greater than 7.\u201d\">\n<thead>\n<tr>\n<th colspan=\"3\" data-align=\"center\">Summary of Relations for Acidic, Basic and Neutral Solutions<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th data-align=\"center\">Classification<\/th>\n<th data-align=\"center\">Relative Ion Concentrations<\/th>\n<th data-align=\"center\">pH at 25 \u00b0C<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td data-align=\"center\">acidic<\/td>\n<td data-align=\"center\">[H<sub>3<\/sub>O<sup>+<\/sup>] &gt; [OH<sup>\u2212<\/sup>]<\/td>\n<td data-align=\"center\">pH &lt; 7<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"center\">neutral<\/td>\n<td data-align=\"center\">[H<sub>3<\/sub>O<sup>+<\/sup>] = [OH<sup>\u2212<\/sup>]<\/td>\n<td data-align=\"center\">pH = 7<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-align=\"center\">basic<\/td>\n<td data-align=\"center\">[H<sub>3<\/sub>O<sup>+<\/sup>] &lt; [OH<sup>\u2212<\/sup>]<\/td>\n<td data-align=\"center\">pH &gt; 7<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p id=\"fs-idp96882128\"><a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_phscale\">(Figure)<\/a> shows the relationships between [H<sub>3<\/sub>O<sup>+<\/sup>], [OH<sup>\u2212<\/sup>], pH, and pOH for solutions classified as acidic, basic, and neutral.<\/p>\n<div id=\"CNX_Chem_14_02_phscale\" class=\"bc-figure figure\">\n<div class=\"bc-figcaption figcaption\">The pH and pOH scales represent concentrations of H<sub>3<\/sub>O<sup>+<\/sup> and OH<sup>\u2212<\/sup>, respectively. The pH and pOH values of some common substances at 25\u00b0C are shown in this chart.<\/div>\n<p><span id=\"fs-idm15160336\" data-type=\"media\" data-alt=\"A table is provided with 5 columns. The first column is labeled \u201cleft bracket H subscript 3 O superscript plus right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript 1, including 10 superscript 0 or 1, 10 superscript negative 1, decreasing by single powers of 10 to 10 superscript negative 15. The second column is labeled \u201cleft bracket O H superscript negative right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript negative 15, increasing by single powers of 10 to including 10 superscript 0 or 1, and 10 superscript 1. The third column is labeled \u201cp H.\u201d Values listed in this column are integers beginning at negative 1, increasing by ones up to 14. The fourth column is labeled \u201cp O H.\u201d Values in this column are integers beginning at 15, decreasing by ones up to negative 1. The fifth column is labeled \u201cSample Solution.\u201d A vertical line at the left of the column has tick marks corresponding to each p H level in the table. Substances are listed next to this line segment with line segments connecting them to the line to show approximate p H and p O H values. 1 M H C l is listed at a p H of 0. Gastric juices are listed at a p H of about 1.5. Lime juice is listed at a p H of about 2, followed by 1 M C H subscript 3 C O subscript 2 H, followed by stomach acid at a p H value of nearly 3. Wine is listed around 3.5. Coffee is listed just past 5. Pure water is listed at a p H of 7. Pure blood is just beyond 7. Milk of Magnesia is listed just past a p H of 10.5. Household ammonia is listed just before a pH of 12. 1 M N a O H is listed at a p H of 0. To the right of this labeled arrow is an arrow that points up and down through the height of the column. A beige strip passes through the table and to this double headed arrow at p H 7. To the left of the double headed arrow in this beige strip is the label \u201cneutral.\u201d A narrow beige strip runs through the arrow. Just above and below this region, the arrow is purple. It gradually turns to a bright red as it extends upward. At the top of the arrow, near the head of the arrow is the label \u201cacidic.\u201d Similarly, the lower region changes color from purple to blue moving to the bottom of the column. The head at this end of the arrow is labeled \u201cbasic.\u201d\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_phscale-1.jpg\" alt=\"A table is provided with 5 columns. The first column is labeled \u201cleft bracket H subscript 3 O superscript plus right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript 1, including 10 superscript 0 or 1, 10 superscript negative 1, decreasing by single powers of 10 to 10 superscript negative 15. The second column is labeled \u201cleft bracket O H superscript negative right bracket (M).\u201d Powers of ten are listed in the column beginning at 10 superscript negative 15, increasing by single powers of 10 to including 10 superscript 0 or 1, and 10 superscript 1. The third column is labeled \u201cp H.\u201d Values listed in this column are integers beginning at negative 1, increasing by ones up to 14. The fourth column is labeled \u201cp O H.\u201d Values in this column are integers beginning at 15, decreasing by ones up to negative 1. The fifth column is labeled \u201cSample Solution.\u201d A vertical line at the left of the column has tick marks corresponding to each p H level in the table. Substances are listed next to this line segment with line segments connecting them to the line to show approximate p H and p O H values. 1 M H C l is listed at a p H of 0. Gastric juices are listed at a p H of about 1.5. Lime juice is listed at a p H of about 2, followed by 1 M C H subscript 3 C O subscript 2 H, followed by stomach acid at a p H value of nearly 3. Wine is listed around 3.5. Coffee is listed just past 5. Pure water is listed at a p H of 7. Pure blood is just beyond 7. Milk of Magnesia is listed just past a p H of 10.5. Household ammonia is listed just before a pH of 12. 1 M N a O H is listed at a p H of 0. To the right of this labeled arrow is an arrow that points up and down through the height of the column. A beige strip passes through the table and to this double headed arrow at p H 7. To the left of the double headed arrow in this beige strip is the label \u201cneutral.\u201d A narrow beige strip runs through the arrow. Just above and below this region, the arrow is purple. It gradually turns to a bright red as it extends upward. At the top of the arrow, near the head of the arrow is the label \u201cacidic.\u201d Similarly, the lower region changes color from purple to blue moving to the bottom of the column. The head at this end of the arrow is labeled \u201cbasic.\u201d\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<div id=\"fs-idp62701056\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idp97421056\"><strong>Calculation of pH from [H<sub>3<\/sub>O<sup>+<\/sup>]<\/strong><\/p>\n<p>What is the pH of stomach acid, a solution of HCl with a hydronium ion concentration of 1.2 \u00d7 10<sup>\u22123 <\/sup><em data-effect=\"italics\">M<\/em>?<\/p>\n<p id=\"fs-idm103954896\"><strong>Solution:<\/strong><\/p>\n<div id=\"fs-idm98702480\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>]<\/div>\n<div id=\"fs-idm79624528\" data-type=\"equation\">= \u2212log(1.2 \u00d7 10<sup>-3<\/sup> M)<\/div>\n<div id=\"fs-idm7356256\" data-type=\"equation\">= 2.92<\/div>\n<p><span data-type=\"newline\"><br \/>\n<\/span> (When taking the log of a value, keep as many decimal places in the result as there are significant figures in the value.)<\/p>\n<p id=\"fs-idp57469360\"><strong>Check Your Learning:<\/strong><\/p>\n<p>Water exposed to air contains carbonic acid, H<sub>2<\/sub>CO<sub>3<\/sub>, due to the reaction between carbon dioxide and water:<\/p>\n<div id=\"fs-idm45568144\" style=\"padding-left: 40px\" data-type=\"equation\">CO<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc H<sub>2<\/sub>CO<sub>3<\/sub>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idm106049328\">Air-saturated water has a hydronium ion concentration caused by the dissolved CO<sub>2<\/sub> of 2.0 \u00d7 10<sup>\u22126 <\/sup><em data-effect=\"italics\">M<\/em>, about 20-times larger than that of pure water. Calculate the pH of the solution at 25\u00b0C.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idm61631152\" data-type=\"note\">\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\n<p id=\"fs-idm99369680\">5.70<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idp57695872\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idm102910496\"><strong>Calculation of Hydronium Ion Concentration from pH<\/strong><\/p>\n<p>Calculate the hydronium ion concentration of blood, the pH of which is 7.3.<\/p>\n<p id=\"fs-idp11945040\"><strong>Solution:<\/strong><\/p>\n<div id=\"fs-idm108531776\" data-type=\"equation\">pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>] = 7.3<\/div>\n<div id=\"fs-idm49363536\" data-type=\"equation\">log[H<sub>3<\/sub>O<sup>+<\/sup>] = -7.3<\/div>\n<div id=\"fs-idp46442128\" data-type=\"equation\">[H<sub>3<\/sub>O<sup>+<\/sup>] = 10<sup>-7.3<\/sup> or [H<sub>3<\/sub>O<sup>+<\/sup>] = log<sup>-1<\/sup>(\u22127.3)<\/div>\n<div id=\"fs-idm58086272\" data-type=\"equation\">[H<sub>3<\/sub>O<sup>+<\/sup>] = 5 \u00d7 10<sup>-8<\/sup> M<\/div>\n<p><span data-type=\"newline\"><br \/>\n<\/span> (On a calculator, take the antilog, or the \u201cinverse\u201d log, of \u22127.3, or calculate 10<sup>\u22127.3<\/sup>.)<\/p>\n<p id=\"fs-idp487584\"><strong>Check Your Learning:<\/strong><\/p>\n<p>Calculate the hydronium ion concentration of a solution with a pH of \u22121.07.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idp89672320\" data-type=\"note\">\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\n<p id=\"fs-idm9452560\">12 <em data-effect=\"italics\">M<\/em><\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idp48828576\" class=\"chemistry sciences-interconnect\" data-type=\"note\">\n<div data-type=\"title\"><strong>Environmental Science<\/strong><\/div>\n<p id=\"fs-idm116727232\">Normal rainwater has a pH between 5 and 6 due to the presence of dissolved CO<sub>2<\/sub> which forms carbonic acid:<\/p>\n<div id=\"fs-idp66992000\" style=\"padding-left: 40px\" data-type=\"equation\">CO<sub>2<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192\u00a0H<sub>2<\/sub>CO<sub>3<\/sub>(<em>aq<\/em>)<\/div>\n<div id=\"fs-idm103550896\" style=\"padding-left: 40px\" data-type=\"equation\">H<sub>2<\/sub>CO<sub>3<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u21cc \u00a0HCO<sub>3<\/sub><sup>\u2212<\/sup>(aq) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\n<p id=\"fs-idp13883280\">Acid rain is rainwater that has a pH of less than 5, due to a variety of nonmetal oxides, including CO<sub>2<\/sub>, SO<sub>2<\/sub>, SO<sub>3<\/sub>, NO, and NO<sub>2<\/sub> being dissolved in the water and reacting with it to form not only carbonic acid, but sulfuric acid and nitric acid. The formation and subsequent ionization of sulfuric acid are shown here:<\/p>\n<div id=\"fs-idp39536896\" data-type=\"equation\">\n<div id=\"fs-idp66992000\" style=\"padding-left: 40px\" data-type=\"equation\">SO<sub>3<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192\u00a0H<sub>2<\/sub>SO<sub>4<\/sub>(<em>aq<\/em>)<\/div>\n<div id=\"fs-idm103550896\" style=\"padding-left: 40px\" data-type=\"equation\">H<sub>2<\/sub>SO<sub>4<\/sub>(<em>aq<\/em>) + H<sub>2<\/sub>O(<em>l<\/em>) \u2192 \u00a0HSO<sub>4<\/sub><sup>\u2212<\/sup>(aq) + H<sub>3<\/sub>O<sup>+<\/sup>(<em>aq<\/em>)<\/div>\n<\/div>\n<p id=\"fs-idp93018416\">Carbon dioxide is naturally present in the atmosphere because most organisms produce it as a waste product of metabolism. Carbon dioxide is also formed when fires release carbon stored in vegetation or fossil fuels. Sulfur trioxide in the atmosphere is naturally produced by volcanic activity, but it also originates from burning fossil fuels, which have traces of sulfur, and from the process of \u201croasting\u201d ores of metal sulfides in metal-refining processes. Oxides of nitrogen are formed in internal combustion engines where the high temperatures make it possible for the nitrogen and oxygen in air to chemically combine.<\/p>\n<p id=\"fs-idm22038432\">Acid rain is a particular problem in industrial areas where the products of combustion and smelting are released into the air without being stripped of sulfur and nitrogen oxides. In North America and Europe until the 1980s, it was responsible for the destruction of forests and freshwater lakes, when the acidity of the rain actually killed trees, damaged soil, and made lakes uninhabitable for all but the most acid-tolerant species. Acid rain also corrodes statuary and building facades that are made of marble and limestone (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_AcidRain\">(Figure)<\/a>). Regulations limiting the amount of sulfur and nitrogen oxides that can be released into the atmosphere by industry and automobiles have reduced the severity of acid damage to both natural and manmade environments in North America and Europe. It is now a growing problem in industrial areas of China and India.<\/p>\n<p id=\"fs-idm22123696\">For further information on acid rain, visit this <a href=\"http:\/\/openstaxcollege.org\/l\/16EPA\">website<\/a> hosted by the US Environmental Protection Agency.<\/p>\n<div id=\"CNX_Chem_14_02_AcidRain\" class=\"scaled-down\">\n<div class=\"bc-figcaption figcaption\">(a) Acid rain makes trees more susceptible to drought and insect infestation, and depletes nutrients in the soil. (b) It also is corrodes statues that are carved from marble or limestone. (credit a: modification of work by Chris M Morris; credit b: modification of work by \u201cEden, Janine and Jim\u201d\/Flickr)<\/div>\n<p><span id=\"fs-idp11790976\" data-type=\"media\" data-alt=\"Two photos are shown. Photograph a on the left shows the upper portion of trees against a bright blue sky. The tops of several trees at the center of the photograph have bare branches and appear to be dead. Image b shows a statue of a man that appears to from the revolutionary war era in either marble or limestone.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_AcidRain-1.jpg\" alt=\"Two photos are shown. Photograph a on the left shows the upper portion of trees against a bright blue sky. The tops of several trees at the center of the photograph have bare branches and appear to be dead. Image b shows a statue of a man that appears to from the revolutionary war era in either marble or limestone.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idm90070400\" class=\"textbox textbox--examples\" data-type=\"example\">\n<p id=\"fs-idp57499040\"><strong>Calculation of pOH<\/strong><\/p>\n<p>What are the pOH and the pH of a 0.0125-<em data-effect=\"italics\">M<\/em> solution of potassium hydroxide, KOH?<\/p>\n<p id=\"fs-idm55606544\"><strong>Solution:<\/strong><\/p>\n<p>Potassium hydroxide is a highly soluble ionic compound and completely dissociates when dissolved in dilute solution, yielding [OH<sup>\u2212<\/sup>] = 0.0125 <em data-effect=\"italics\">M<\/em>:<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idp97197664\" style=\"padding-left: 40px\" data-type=\"equation\">pOH = \u2212log[OH<sup>\u2212<\/sup>] = \u2212log(0.0125 M) =1.903<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idm11584304\">The pH can be found from the pOH:<\/p>\n<div id=\"fs-idm77730624\" style=\"padding-left: 40px\" data-type=\"equation\">pH + pOH = 14.00<\/div>\n<div id=\"fs-idm71245120\" style=\"padding-left: 40px\" data-type=\"equation\">pH =14.00 &#8211; pOH = 14.00-1.903 = 12.10<\/div>\n<div data-type=\"equation\"><\/div>\n<p id=\"fs-idm147912592\"><strong>Check Your Learning:<\/strong><\/p>\n<p>The hydronium ion concentration of vinegar is approximately 4 \u00d7 10<sup>\u22123 <\/sup><em data-effect=\"italics\">M<\/em>. What are the corresponding values of pOH and pH?<\/p>\n<p>&nbsp;<\/p>\n<div id=\"fs-idm58824960\" data-type=\"note\">\n<div data-type=\"title\"><strong>Answer:<\/strong><\/div>\n<p id=\"fs-idm165995920\">pOH = 11.6, pH = 2.4<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idm165634608\">The acidity of a solution is typically assessed experimentally by measurement of its pH. The pOH of a solution is not usually measured, as it is easily calculated from an experimentally determined pH value. The pH of a solution can be directly measured using a pH meter (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_pHMeter\">(Figure)<\/a>).<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_14_02_pHMeter\" class=\"bc-figure figure\">\n<div class=\"bc-figcaption figcaption\">(a) A research-grade pH meter used in a laboratory can have a resolution of 0.001 pH units, an accuracy of \u00b1 0.002 pH units, and may cost in excess of \ud83d\udcb21000. (b) A portable pH meter has lower resolution (0.01 pH units), lower accuracy (\u00b1 0.2 pH units), and a far lower price tag. (credit b: modification of work by Jacopo Werther)<\/div>\n<p><span id=\"fs-idp134372032\" data-type=\"media\" data-alt=\"This figure contains two images. The first, image a, is of an analytical digital p H meter on a laboratory counter. The second, image b, is of a portable hand held digital p H meter.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_pHMeter-1.jpg\" alt=\"This figure contains two images. The first, image a, is of an analytical digital p H meter on a laboratory counter. The second, image b, is of a portable hand held digital p H meter.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\n<\/div>\n<p id=\"fs-idp57700960\">The pH of a solution may also be visually estimated using colored indicators (<a class=\"autogenerated-content\" href=\"#CNX_Chem_14_02_indicator\">(Figure)<\/a>). The acid-base equilibria that enable use of these indicator dyes for pH measurements are described in a later section of this chapter.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Chem_14_02_indicator\" class=\"bc-figure figure\">\n<div class=\"bc-figcaption figcaption\">(a) A solution containing a dye mixture, called universal indicator, takes on different colors depending upon its pH. (b) Convenient test strips, called pH paper, contain embedded indicator dyes that yield pH-dependent color changes on contact with aqueous solutions.(credit: modification of work by Sahar Atwa)<\/div>\n<p><span id=\"fs-idp11928656\" data-type=\"media\" data-alt=\"This figure contains two images. The first shows a variety of colors of solutions in labeled beakers. A red solution in a beaker is labeled \u201c0.10 M H C l.\u201d An orange solution is labeled \u201c0.10 M C H subscript 3 C O O H.\u201d A yellow-orange solution is labeled \u201c0.1 M N H subscript 4 C l.\u201d A yellow solution is labeled \u201cdeionized water.\u201d A second solution beaker is labeled \u201c0.10 M K C l.\u201d A green solution is labeled \u201c0.10 M aniline.\u201d A blue solution is labeled \u201c0.10 M N H subscript 4 C l (a q).\u201d A final beaker containing a dark blue solution is labeled \u201c0.10 M N a O H.\u201d Image b shows pHydrion paper that is used for measuring pH in the range of p H from 1 to 12. The color scale for identifying p H based on color is shown along with several of the test strips used to evaluate p H.\"><img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-content\/uploads\/sites\/1463\/2021\/07\/CNX_Chem_14_02_indicator-1.jpg\" alt=\"This figure contains two images. The first shows a variety of colors of solutions in labeled beakers. A red solution in a beaker is labeled \u201c0.10 M H C l.\u201d An orange solution is labeled \u201c0.10 M C H subscript 3 C O O H.\u201d A yellow-orange solution is labeled \u201c0.1 M N H subscript 4 C l.\u201d A yellow solution is labeled \u201cdeionized water.\u201d A second solution beaker is labeled \u201c0.10 M K C l.\u201d A green solution is labeled \u201c0.10 M aniline.\u201d A blue solution is labeled \u201c0.10 M N H subscript 4 C l (a q).\u201d A final beaker containing a dark blue solution is labeled \u201c0.10 M N a O H.\u201d Image b shows pHydrion paper that is used for measuring pH in the range of p H from 1 to 12. The color scale for identifying p H based on color is shown along with several of the test strips used to evaluate p H.\" data-media-type=\"image\/jpeg\" \/><\/span><\/p>\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-idp58752272\">Concentrations of hydronium and hydroxide ions in aqueous media are often represented as logarithmic pH and pOH values, respectively. At 25\u00b0C, the autoionization equilibrium for water requires the sum of pH and pOH to equal 14.00 for any aqueous solution. The relative concentrations of hydronium and hydroxide ion in a solution define its status as acidic ([H<sub>3<\/sub>O<sup>+<\/sup>] &gt; [OH<sup>\u2212<\/sup>]), basic ([H<sub>3<\/sub>O<sup>+<\/sup>] &lt; [OH<sup>\u2212<\/sup>]), or neutral ([H<sub>3<\/sub>O<sup>+<\/sup>] = [OH<sup>\u2212<\/sup>]). At 25\u00b0C, a pH &lt; 7.00 indicates an acidic solution, a pH &gt; 7.00 a basic solution, and a pH = 7.00 a neutral solution.<\/p>\n<\/div>\n<div id=\"fs-idp66998992\" class=\"key-equations\" data-depth=\"1\">\n<h3 data-type=\"title\"><strong>Key Equations<\/strong><\/h3>\n<ul id=\"fs-idp46607520\" data-bullet-style=\"bullet\">\n<li>pH = \u2212log[H<sub>3<\/sub>O<sup>+<\/sup>]<\/li>\n<li>pH + pOH = p<em data-effect=\"italics\">K<\/em><sub>w<\/sub> = 14.00 at 25 \u00b0C<\/li>\n<\/ul>\n<\/div>\n<div id=\"fs-idm61137872\" class=\"exercises\" data-depth=\"1\">\n<div id=\"fs-idm209904880\" data-type=\"exercise\">\n<div id=\"fs-idm15687280\" data-type=\"solution\">\n<p id=\"fs-idm81860944\">\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\" data-type=\"glossary\">\n<h3 data-type=\"glossary-title\">Glossary<\/h3>\n<dl id=\"fs-idm64563696\">\n<dt>acidic<\/dt>\n<dd id=\"fs-idm110209904\">a solution in which [H<sub>3<\/sub>O<sup>+<\/sup>] &gt; [OH<sup>\u2212<\/sup>]<\/dd>\n<\/dl>\n<dl id=\"fs-idm111671584\">\n<dt>basic<\/dt>\n<dd id=\"fs-idp49209968\">a solution in which [H<sub>3<\/sub>O<sup>+<\/sup>] &lt; [OH<sup>\u2212<\/sup>]<\/dd>\n<\/dl>\n<dl id=\"fs-idp143891408\">\n<dt>neutral<\/dt>\n<dd id=\"fs-idm153784960\">describes a solution in which [H<sub>3<\/sub>O<sup>+<\/sup>] = [OH<sup>\u2212<\/sup>]<\/dd>\n<\/dl>\n<dl id=\"fs-idm103907536\">\n<dt>pH<\/dt>\n<dd id=\"fs-idm14698528\">logarithmic measure of the concentration of hydronium ions in a solution<\/dd>\n<\/dl>\n<dl id=\"fs-idp46966768\">\n<dt>pOH<\/dt>\n<dd id=\"fs-idm67584528\">logarithmic measure of the concentration of hydroxide ions in a solution<\/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-778","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":766,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/778","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":6,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/778\/revisions"}],"predecessor-version":[{"id":2171,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/778\/revisions\/2171"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/parts\/766"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapters\/778\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/media?parent=778"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/pressbooks\/v2\/chapter-type?post=778"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/contributor?post=778"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/aperrott\/wp-json\/wp\/v2\/license?post=778"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}