{"id":1279,"date":"2018-04-11T22:51:03","date_gmt":"2018-04-12T02:51:03","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/chapter\/1-5-measurement-uncertainty-accuracy-and-precision\/"},"modified":"2019-06-20T14:02:08","modified_gmt":"2019-06-20T18:02:08","slug":"1-5-measurement-uncertainty-accuracy-and-precision","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/chapter\/1-5-measurement-uncertainty-accuracy-and-precision\/","title":{"raw":"2.3 Measurement Uncertainty, Accuracy, and Precision","rendered":"2.3 Measurement Uncertainty, Accuracy, and Precision"},"content":{"raw":"<div class=\"bcc-box bcc-highlight\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Define accuracy and precision<\/li>\r\n \t<li>Distinguish exact and uncertain numbers<\/li>\r\n \t<li>Correctly represent uncertainty in quantities using significant figures<\/li>\r\n \t<li>Apply proper rounding rules to computed quantities<\/li>\r\n<\/ul>\r\n<\/div>\r\nWhen recording a measurement, <em>how<\/em> you record it is just as important as <em>what<\/em> you record. You must consider the precision of the instrument you are using.\u00a0 <strong>Accuracy<\/strong> is the extent to which a measured value coincides with the true or accepted value.\u00a0 <strong>Precision<\/strong>\u00a0refers to the \u201cfineness\u201d (i.e. the number of digits) of the measurement as well as the reproducibility.\u00a0 <strong>Significant figures<\/strong> are those digits in an experimentally measured quantity that establish the precision with which the value is known.\u00a0 A precise measurement may not be accurate!!\r\n<p id=\"fs-idm288863760\">Counting is the only type of measurement that is free from uncertainty, provided the number of objects being counted does not change while the counting process is underway. The result of such a counting measurement is an example of an <strong>exact number<\/strong>. If we count eggs in a carton, we know <em>exactly<\/em> how many eggs the carton contains. The numbers of defined quantities are also exact. By definition, 1 foot is exactly 12 inches, 1 inch is exactly 2.54 centimeters, and 1 gram is exactly 0.001 kilogram. Quantities derived from measurements other than counting, however, are uncertain to varying extents due to practical limitations of the measurement process used.<\/p>\r\n\r\n<section id=\"fs-idm217277536\">\r\n<h2>Significant Figures in Measurement<\/h2>\r\n<p id=\"fs-idp11446448\">The numbers of measured quantities, unlike defined or directly counted quantities, are not exact. To measure the volume of liquid in a graduated cylinder, you should make a reading at the bottom of the meniscus, the lowest point on the curved surface of the liquid.<\/p>\r\n\r\n<figure id=\"fs-idm337865984\"><figcaption><\/figcaption>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1300\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_Measure-2.jpg\" alt=\"This diagram shows a 25 milliliter graduated cylinder filled with about 20.8 milliliters of fluid. The diagram zooms in on the meniscus, which is the curved surface of the water that is visible when the graduated cylinder is viewed from the side. You make the reading at the lowest point of the curve of the meniscus.\" width=\"1300\" height=\"743\" \/> <strong>Figure 1.<\/strong> To measure the volume of liquid in this graduated cylinder, you must mentally subdivide the distance between the 21 and 22 mL marks into tenths of a milliliter, and then make a reading (estimate) at the bottom of the meniscus.[\/caption]<\/figure>\r\n<p id=\"fs-idm176542448\">Refer to the illustration in <a href=\"#fs-idm337865984\" class=\"autogenerated-content\">Figure 1<\/a>. The bottom of the meniscus in this case clearly lies between the 21 and 22 markings, meaning the liquid volume is <em>certainly<\/em> greater than 21 mL but less than 22 mL. The meniscus appears to be a bit closer to the 22-mL mark than to the 21-mL mark, and so a reasonable estimate of the liquid\u2019s volume would be 21.6 mL. In the number 21.6, then, the digits 2 and 1 are certain, but the 6 is an estimate. Some people might estimate the meniscus position to be equally distant from each of the markings and estimate the tenth-place digit as 5, while others may think it to be even closer to the 22-mL mark and estimate this digit to be 7. Note that it would be pointless to attempt to estimate a digit for the hundredths place, given that the tenths-place digit is uncertain. In general, numerical scales such as the one on this graduated cylinder will permit measurements to one-tenth of the smallest scale division. The scale in this case has 1-mL divisions, and so volumes may be measured to the nearest 0.1 mL.<\/p>\r\n<p id=\"fs-idm254904560\">This concept holds true for all measurements, even if you do not actively make an estimate. If you place a quarter on a standard electronic balance, you may obtain a reading of 6.72 g. The digits 6 and 7 are certain, and the 2 indicates that the mass of the quarter is likely between 6.71 and 6.73 grams. The quarter weighs <em>about<\/em> 6.72 grams, with a nominal uncertainty in the measurement of \u00b1 0.01 gram. If we weigh the quarter on a more sensitive balance, we may find that its mass is 6.723 g. This means its mass lies between 6.722 and 6.724 grams, an uncertainty of 0.001 gram. Every measurement has some <strong>uncertainty<\/strong>, which depends on the device used (and the user\u2019s ability). All of the digits in a measurement, including the uncertain last digit, are called <strong>significant figures<\/strong> or <strong>significant digits<\/strong>. Note that zero may be a measured value; for example, if you stand on a scale that shows weight to the nearest pound and it shows \u201c120,\u201d then the 1 (hundreds), 2 (tens) and 0 (ones) are all significant (measured) values.<\/p>\r\n<p id=\"fs-idm264880544\">Whenever you make a measurement properly, all the digits in the result are significant. But what if you were analyzing a reported value and trying to determine what is significant and what is not? Well, for starters, all nonzero digits are significant, and it is only zeros that require some thought. We will use the terms \u201cleading,\u201d \u201ctrailing,\u201d and \u201ccaptive\u201d for the zeros and will consider how to deal with them.<\/p>\r\n<span id=\"fs-idm244068192\">\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits5_img-2.jpg\" alt=\"The left diagram uses the example of 3090. The zero in the hundreds place is labeled \u201ccaptive\u201d and the zero in the ones place is labeled trailing. The right diagram uses the example 0.008020. The three zeros in the ones, tenths, and hundredths places are labeled \u201cleading.\u201d The zero in the ten-thousandths place is labeled \u201ccaptive\u201d and the zero in the millionths place is labeled \u201ctrailing.\u201d\" width=\"650\" height=\"222\" class=\"aligncenter\" \/><\/span>\r\n<p id=\"fs-idp31100592\">Starting with the first nonzero digit on the left, count this digit and all remaining digits to the right. This is the number of significant figures in the measurement unless the last digit is a trailing zero lying to the left of the decimal point.<\/p>\r\n<span id=\"fs-idp40720144\">\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits1_img-2.jpg\" alt=\"The left diagram uses the example of 1267 meters. The number 1 is the first nonzero figure on the left. 1267 has 4 significant figures in total. The right diagram uses the example of 55.0 grams. The number 5 in the tens place is the first nonzero figure on the left. 55.0 has 3 significant figures. Note that the 0 is to the right of the decimal point and therefore is a significant figure.\" \/><\/span>\r\n<p id=\"fs-idm177076640\">Captive zeros result from measurement and are therefore always significant. Leading zeros, however, are never significant\u2014they merely tell us where the decimal point is located.<\/p>\r\n<span id=\"fs-idm113793344\">\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits2_img-2.jpg\" alt=\"The left diagram uses the example of 70.607 milliliters. The number 7 is the first nonzero figure on the left. 70.607 has 5 significant figures in total, as all figures are measured including the 2 zeros. The right diagram uses the example of 0.00832407 M L. The number 8 is the first nonzero figure on the left. 0.00832407 has 6 significant figures.\" \/><\/span>\r\n<p id=\"fs-idm262013360\">The leading zeros in this example are not significant. We could use exponential notation (as described in Appendix B) and express the number as 8.32407 \u00d7 10<sup>\u22123<\/sup>; then the number 8.32407 contains all of the significant figures, and 10<sup>\u22123<\/sup> locates the decimal point.<\/p>\r\n<p id=\"fs-idm210460000\">The number of significant figures is uncertain in a number that ends with a zero to the left of the decimal point location. The zeros in the measurement 1,300 grams could be significant or they could simply indicate where the decimal point is located. The ambiguity can be resolved with the use of exponential notation: 1.3 \u00d7 10<sup>3<\/sup> (two significant figures), 1.30 \u00d7 10<sup>3<\/sup> (three significant figures, if the tens place was measured), or 1.300 \u00d7 10<sup>3<\/sup> (four significant figures, if the ones place was also measured). In cases where only the normal notation is used (1300 g), all trailing zeros are not significant, therefore the measurement would have two significant figures.\u00a0 Though, if the measurement was express with an explicit decimal place (1300. g), then the trailing zeros would be significant, and\u00a0therefore the measurement would have four significant figures.<\/p>\r\n<span id=\"fs-idp29412624\">\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits3_img-2.jpg\" alt=\"This figure uses the example of 1300 grams. The one and the 3 are significant figures as they are clearly the result of measurement. The 2 zeros could be significant if they were measured or they could be placeholders.\" \/><\/span>\r\n\r\n&nbsp;\r\n\r\n[caption id=\"attachment_3163\" align=\"aligncenter\" width=\"535\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs-300x243.jpg\" alt=\"\" width=\"535\" height=\"433\" class=\" wp-image-3163\" \/> <strong>Figure 2:<\/strong> Summary: How to determine the number of significant figures in measurements.[\/caption]\r\n\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 1<\/h3>\r\nDetermine the correct measurement reading for the following volume:\r\n\r\n<a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1-300x295.jpg\" alt=\"\" width=\"100\" height=\"98\" class=\"alignnone wp-image-3170\" \/><\/a>\r\n\r\n&nbsp;\r\n\r\n<strong>Solution<\/strong>\r\n\r\nBecause the beaker has gradations of 100 mL, we know that it is at least 200 mL. It is the tens position that is uncertain. Thus we can only record to that position. The reading should be 220 mL. Better still\u2014clarify the significant figures by using scientific notation, which would be 2.2 x 10<sup>2<\/sup> mL.\r\n\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\r\nDetermine the correct reading for the following temperature:\r\n\r\n<a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1-300x59.jpg\" alt=\"\" width=\"300\" height=\"59\" class=\"alignnone wp-image-3171 size-medium\" \/><\/a>\r\n\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answer<\/em><\/strong><\/p>\r\n14.8<sup>o<\/sup>C\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 2<\/h3>\r\n<p id=\"ball-ch02_s03_p06\" class=\"para\">Use each diagram to report a measurement to the proper number of significant figures.<\/p>\r\n<a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM.png\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM.png\" alt=\"\" width=\"659\" height=\"242\" class=\"aligncenter wp-image-4640 size-full\" \/><\/a>\r\n\r\n&nbsp;\r\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\r\n<p class=\"simpara\">a) The arrow is between 4.0 and 5.0, so the measurement is at least 4.0. The arrow is between the third and fourth small tick marks, so it\u2019s at least 0.3. We will have to estimate the last place. It looks like about one-third of the way across the space, so let us estimate the hundredths place as 3. Combining the digits, we have a measurement of 4.33 psi (psi stands for \u201cpounds per square inch\u201d and is a unit of pressure, like air in a tire). We say that the measurement is reported to three significant figures.<\/p>\r\n<p class=\"simpara\">b)The rectangle is at least 1.0 cm wide but certainly not 2.0 cm wide, so the first significant digit is 1. The rectangle\u2019s width is past the second tick mark but not the third; if each tick mark represents 0.1, then the rectangle is at least 0.2 in the next significant digit. We have to estimate the next place because there are no markings to guide us. It appears to be about halfway between 0.2 and 0.3, so we will estimate the next place to be a 5. Thus, the measured width of the rectangle is 1.25 cm. Again, the measurement is reported to three significant figures.<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\r\n<p id=\"ball-ch02_s03_p07\" class=\"para\">What would be the reported width of this rectangle?<\/p>\r\n<p class=\"para\"><a href=\"http:\/\/opentextbc.ca\/introductorychemistry\/wp-content\/uploads\/sites\/17\/2014\/09\/Rectangle.png\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Rectangle-1.png\" alt=\"Rectangle\" class=\"alignnone wp-image-4615\" width=\"301\" height=\"192\" \/><\/a><\/p>\r\n\r\n<div class=\"informalfigure small\" id=\"ball-ch02_s03_f04\"><\/div>\r\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answer<\/em><\/strong><\/p>\r\n<p id=\"ball-ch02_s03_p08\" class=\"para\">0.63 cm<\/p>\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 3<\/h3>\r\n<p id=\"ball-ch02_s03_p12\" class=\"para\">Give the number of significant figures in each measurement.<\/p>\r\n<p class=\"para\">a) 36.7 m\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 0.006606 s\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 c) 2,002 kg\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 d) 306,490,000 people<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\r\n<p class=\"simpara\">a) By rule 1, all nonzero digits are significant, so this measurement has three significant figures.<\/p>\r\n<p class=\"simpara\">b) By rule 4, the first three zeros are not significant, but by rule 2 the zero between the sixes is; therefore, this number has four significant figures.<\/p>\r\n<p class=\"simpara\">c) By rule 2, the two zeros between the twos are significant, so this measurement has four significant figures.<\/p>\r\n<p class=\"simpara\">d) The four trailing zeros in the number are not significant, but the other five numbers are, so this number has five significant figures.<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\r\n<p id=\"ball-ch02_s03_p13\" class=\"para\">Give the number of significant figures in each measurement.<\/p>\r\n<p class=\"para\">a) 0.000601 m\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 65.080 kg<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answers<\/em><\/strong><\/p>\r\n<p class=\"simpara\">a) three significant figures\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) five significant figures<\/p>\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 4<\/h3>\r\nDetermine the number of significant figures in the following measurements\r\na) 0.002040 g\u00a0\u00a0\u00a0 b) 300 mL\u00a0\u00a0\u00a0 c) 3.021 x 10<sup>5<\/sup> g\u00a0\u00a0\u00a0 d) 31 pencils (counted exactly, not an estimate)\r\n\r\n&nbsp;\r\n\r\n<strong>Solution<\/strong>\r\n\r\na) 4 significant figures. The leading zeros do not count, but the trailing zero does (as there\u2019s a decimal point).\r\n\r\nb) By the above rules, 1 significant figure, because there\u2019s no decimal point showing; 300. mL would be 3 sig figs. (To emphasize 1 sig fig it would be better to write the measurement in scientific notation, as 3 x 10<sup>2<\/sup> mL, rather than just \u201c300\u00a0mL\u201d.)\r\n\r\nc) 4 significant figures. (No leading or trailing zeros.) Note that we only consider the digits in the numerical portion of the scientific notation, not the power of 10.\r\n\r\nd) Unlimited significant figures. This is an exact number, as it has been counted.\r\n\r\n&nbsp;\r\n\r\n<strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong>\r\n<p id=\"ball-ch02_s03_p17\" class=\"para\">Determine the number of significant figures in the following measurements.\r\na)\u00a0 0.00100 m\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 b)\u00a0 2.0900 x 10<sup>3<\/sup> mL\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 c) 100.0 <sup>o<\/sup>C<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answers<\/em><\/strong><\/p>\r\na) 3 significant figures\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 5\u00a0significant figures\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 c) 4\u00a0significant figures\r\n\r\n<\/div>\r\nWhen determining significant figures, be sure to pay attention to reported values and think about the measurement and significant figures in terms of what is reasonable or likely when evaluating whether the value makes sense. For example, the official January 2014 census reported the resident population of the US as 317,297,725. Do you think the US population was correctly determined to the reported nine significant figures, that is, to the exact number of people? People are constantly being born, dying, or moving into or out of the country, and assumptions are made to account for the large number of people who are not actually counted. Because of these uncertainties, it might be more reasonable to expect that we know the population to within perhaps a million or so, in which case the population should be reported as 3.17 \u00d7 10<sup>8<\/sup> people.\r\n\r\n<\/section><section id=\"fs-idm191691888\">\r\n<h2>Significant Figures in Calculations<\/h2>\r\n<p id=\"fs-idm277117616\">A second important principle of uncertainty is that results calculated from a measurement are at least as uncertain as the measurement itself. We must take the uncertainty in our measurements into account to avoid misrepresenting the uncertainty in calculated results. One way to do this is to report the result of a calculation with the correct number of significant figures, which is determined by the following three rules for <strong>rounding<\/strong> numbers:<\/p>\r\n\r\n<ol id=\"fs-idm65809616\">\r\n \t<li>When we add or subtract numbers, we should round the result to the same number of decimal places as the number with the least number of decimal places (the least precise value in terms of addition and subtraction).<\/li>\r\n \t<li>When we multiply or divide numbers, we should round the result to the same number of digits as the number with the least number of significant figures (the least precise value in terms of multiplication and division).<\/li>\r\n \t<li>If the digit to be dropped (the one immediately to the right of the digit to be retained) is less than 5, we \u201cround down\u201d and leave the retained digit unchanged; if it is more than 5, we \u201cround up\u201d and increase the retained digit by 1; if the dropped digit <em>is<\/em> 5, we round up or down, whichever yields an even value for the retained digit. (The last part of this rule may strike you as a bit odd, but it\u2019s based on reliable statistics and is aimed at avoiding any bias when dropping the digit \u201c5,\u201d since it is equally close to both possible values of the retained digit.)<\/li>\r\n<\/ol>\r\n<p id=\"fs-idm107335696\">The following examples illustrate the application of this rule in rounding a few different numbers to three significant figures:<\/p>\r\n\r\n<ul id=\"fs-idm192081680\">\r\n \t<li>0.028675 rounds \u201cup\u201d to 0.0287 (the dropped digit, 7, is greater than 5)<\/li>\r\n \t<li>18.3384 rounds \u201cdown\u201d to 18.3 (the dropped digit, 3, is less than 5)<\/li>\r\n \t<li>6.8752 rounds \u201cup\u201d to 6.88 (the dropped digit is 5, and the retained digit is even)<\/li>\r\n \t<li>92.85 rounds \u201cdown\u201d to 92.8 (the dropped digit is 5, and the retained digit is even)<\/li>\r\n<\/ul>\r\n<p id=\"fs-idm178562592\">Let\u2019s work through these rules with a few examples.<\/p>\r\n\r\n<div class=\"textbox shaded\" id=\"fs-idp40552528\">\r\n<h3>Example 5<\/h3>\r\n<p id=\"fs-idm303504976\">Round the following to the indicated number of significant figures:<\/p>\r\n<p id=\"fs-idm277227680\">a) 31.57 (to two significant figures)<\/p>\r\n<p id=\"fs-idm113120528\">b) 8.1649 (to three significant figures)<\/p>\r\n<p id=\"fs-idp33608880\">c) 0.051065 (to four significant figures)<\/p>\r\n<p id=\"fs-idm208861552\">d) 0.90275 (to four significant figures)<\/p>\r\n&nbsp;\r\n<p id=\"fs-idm125552432\"><strong>Solution<\/strong>\r\na) 31.57 rounds \u201cup\u201d to 32 (the dropped digit is 5, and the retained digit is even)<\/p>\r\n<p id=\"fs-idm180680048\">b) 8.1649 rounds \u201cdown\u201d to 8.16 (the dropped digit, 4, is less than 5)<\/p>\r\n<p id=\"fs-idm167789680\">c) 0.051065 rounds \u201cdown\u201d to 0.05106 (the dropped digit is 5, and the retained digit is even)<\/p>\r\n<p id=\"fs-idm174540832\">d) 0.90275 rounds \u201cup\u201d to 0.9028 (the dropped digit is 5, and the retained digit is even)<\/p>\r\n&nbsp;\r\n<p id=\"fs-idm185983232\"><strong><em>Test Yourself<\/em><\/strong>\r\nRound the following to the indicated number of significant figures:<\/p>\r\n<p id=\"fs-idm69923072\">a) 0.424 (to two significant figures)<\/p>\r\n<p id=\"fs-idm65589936\">b) 0.0038661 (to three significant figures)<\/p>\r\n<p id=\"fs-idm107300848\">c) 421.25 (to four significant figures)<\/p>\r\n<p id=\"fs-idm258155488\">d) 28,683.5 (to five significant figures)<\/p>\r\n&nbsp;\r\n\r\n<strong><em>Answers<\/em><\/strong>\r\n\r\na) 0.42 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 0.00387 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0c) 421.2 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0d) 28,684\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\" id=\"fs-idp61408240\">\r\n<h3>Example 6<\/h3>\r\n<p id=\"fs-idm327587104\">Rule: When we add or subtract numbers, we should round the result to the same number of decimal places as the number with the least number of decimal places (i.e., the least precise value in terms of addition and subtraction).<\/p>\r\nPerform the following calculations taking significant figures into account.\r\n<p id=\"fs-idm318611824\">a) Add 1.0023 g and 4.383 g.<\/p>\r\n<p id=\"fs-idm288438480\">b) Subtract 421.23 g from 486 g.<\/p>\r\n&nbsp;\r\n<p id=\"fs-idm277651872\"><strong>Solution<\/strong><\/p>\r\n<p id=\"fs-idm21393952\">a) $latex \\displaystyle \\begin{array}{r}1.0023 \\text{g} \\\\ +4.383 \\;\\;\\text{g} \\\\ \\hline 5.3853 \\text{g} \\end{array} $<\/p>\r\n<p id=\"fs-idm107330240\">Answer is 5.385 g (round to the thousandths place; three decimal places)<\/p>\r\n<p id=\"fs-idm257863024\">b) $latex \\displaystyle \\begin{array}{r}486 \\;\\;\\;\\;\\; \\text{g} \\\\ -421.23 \\text{g} \\\\ \\hline 64.77 \\text{g} \\end{array} $<\/p>\r\n<p id=\"fs-idp47889280\">Answer is 65 g (round to the ones place; no decimal places)<\/p>\r\n<span id=\"fs-idm330284704\">\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits4_img-2.jpg\" alt=\"Figure A shows 1.0023 being added to 4.383 to yield the answer 5.385. 1.0023 goes to the ten thousandths place, but 4.383 goes to the thousandths place, making it the less precise of the two numbers. Therefore the answer, 5.3853, should be rounded to the thousandths, to yield 5.385. Figure B shows 486 grams minus 421.23 grams, which yields the answer 64.77 grams. This answer should be round to the ones place, making the answer 65 grams.\" \/><\/span>\r\n\r\n&nbsp;\r\n<p id=\"fs-idm97432976\"><strong><i>Test Yourself<\/i><\/strong><\/p>\r\na) Add 2.334 mL and 0.31 mL.\r\n<p id=\"fs-idm113279504\">b) Subtract 55.8752 m from 56.533 m.<\/p>\r\n&nbsp;\r\n\r\n<strong><em>Answers<\/em><\/strong>\r\n\r\na) 2.64 mL \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b) 0.658 m\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 7<\/h3>\r\n<p id=\"ball-ch02_s03_p17\" class=\"para\">Express the final answer to the proper number of significant figures.<\/p>\r\n<p class=\"para\">a) 101.2 +\u00a018.702 = ?<\/p>\r\n<p class=\"para\">b) 202.88 \u2212 1.013 = ?<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\r\n<p class=\"simpara\">a) If we use a calculator to add these two numbers, we would get 119.902. However, most calculators do not understand significant figures, and we need to limit the final answer to the tenths place. Thus, we drop the 02 and report a final answer of 119.9 (rounding down).<\/p>\r\n<p class=\"simpara\">b) A calculator would answer 201.867. However, we have to limit our final answer to the hundredths place. Because the first number being dropped is 7, which is greater than 7, we round up and report a final answer of 201.87.<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\r\n<p id=\"ball-ch02_s03_p18\" class=\"para\">Express the answer for 3.445 +\u00a090.83 \u2212 72.4 to the proper number of significant figures.<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answer<\/em><\/strong><\/p>\r\n<p id=\"ball-ch02_s03_p19\" class=\"para\">21.9<\/p>\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\" id=\"fs-idp34148976\">\r\n<h3>Example 8<\/h3>\r\n<p id=\"fs-idm194335568\">Rule: When we multiply or divide numbers, we should round the result to the same number of digits as the number with the least number of significant figures (the least precise value in terms of multiplication and division).<\/p>\r\nPerform the following calculations taking significant figures into account.\r\n<p id=\"fs-idm176907440\">a) Multiply 0.6238 cm by 6.6 cm.<\/p>\r\n<p id=\"fs-idp40092848\">b) Divide 421.23 g by 486 mL.<\/p>\r\n&nbsp;\r\n<p id=\"fs-idm318303792\"><strong>Solution<\/strong><\/p>\r\n<p id=\"fs-idp11052048\">a) $latex 0.6238 \\text{ cm} \\times 6.6 \\text{ cm} = 4.11708 \\text{ cm}^2 \\rightarrow \\text{result is 4.1} \\text{cm}^2 \\text{(round to two significant figures)} \\\\[0.75em] \\text{four significant figures} \\times \\text{two significant figures} \\rightarrow \\text{two significant figures answer} $<\/p>\r\n<p id=\"fs-idm194468576\">b) $latex \\frac{421.23 \\text{g}}{486 \\text{mL}}=0.86728 \\dots \\text{g\/mL} \\rightarrow \\text{result is 0.867 g\/mL (round to three significant figures)} \\\\[0.75em] \\frac{\\text{five significant figures}}{\\text{three significant figures}} \\rightarrow \\text{three significant figures answer} $<\/p>\r\n&nbsp;\r\n<p id=\"fs-idp45405152\"><strong><i>Test Yourself<\/i><\/strong><\/p>\r\na) Multiply 2.334 cm and 0.320 cm.\r\n<p id=\"fs-idm155228848\">b) Divide 55.8752 m by 56.53 s.<\/p>\r\n&nbsp;\r\n\r\n<strong><em>Answers<\/em><\/strong>\r\n\r\na) 0.747 cm<sup>2<\/sup>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b) 0.9884 m\/s\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 9<\/h3>\r\n<p id=\"ball-ch02_s03_p22\" class=\"para\">Express the final answer to the proper number of significant figures.<\/p>\r\n<p class=\"para\">a) 76.4 \u00d7 180.4 = ?<\/p>\r\n<p class=\"para\">b) 934.9 \u00f7 0.00455 = ?<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\r\n<p class=\"simpara\">a) The first number has three significant figures, while the second number has four significant figures. Therefore, we limit our final answer to three significant figures: 76.4 \u00d7 180.4 = 13,782.56 = 13,800.<\/p>\r\n<p class=\"simpara\">b) The first number has four significant figures, while the second number has three significant figures. Therefore we limit our final answer to three significant figures: 934.9 \u00f7 0.00455 = 205,472.5275\u2026 = 205,000.<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\r\n<p id=\"ball-ch02_s03_p23\" class=\"para\">Express the final answer to the proper number of significant figures.<\/p>\r\n<p class=\"para\">a) 22.4 \u00d7 8.314 = ?<\/p>\r\n<p class=\"para\">b) 1.381 \u00f7 6.02 = ?<\/p>\r\n&nbsp;\r\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answers<\/em><\/strong><\/p>\r\n<p class=\"simpara\">a) 186 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b)\u00a00.229<\/p>\r\n\r\n<\/div>\r\n<p id=\"fs-idp31178224\">In the midst of all these technicalities, it is important to keep in mind the reason why we use significant figures and rounding rules\u2014to correctly represent the certainty of the values we report and to ensure that a calculated result is not represented as being more certain than the least certain value used in the calculation.<\/p>\r\n\r\n<\/section>\r\n<div id=\"fs-idp86805728\" class=\"textbox shaded\">\r\n\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Interactive_200DPI-1-2.png\" alt=\"\" width=\"138\" height=\"86\" class=\"alignleft\" \/>\r\n<p id=\"fs-idm169361696\">Need a refresher or more practice with significant figures? Visit this site (<a href=\"https:\/\/viuvideos.viu.ca\/media\/Significant+Figures\/0_t8xwe4s9\">https:\/\/viuvideos.viu.ca\/media\/Significant+Figures\/0_t8xwe4s9<\/a>)\u00a0to go over the basics of significant figures.<\/p>\r\nVideo source: Significant figures by keyj\r\n\r\n<\/div>\r\n<section id=\"fs-idm191691888\">\r\n<div class=\"textbox shaded\" id=\"fs-idp40680240\">\r\n<h3>Example 10<\/h3>\r\n<p id=\"fs-idm180409728\">One common bathtub is 13.44 dm long, 5.920 dm wide, and 2.54 dm deep. Assume that the tub is rectangular and calculate its approximate volume in liters.<\/p>\r\n&nbsp;\r\n<p id=\"fs-idm209075984\"><strong>Solution<\/strong><\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idm15365184\" style=\"text-align: center\">$latex \\begin{array}{r @{{}={}} l}V &amp; l \\times w\\times d \\\\ &amp; 13.44 \\text{ dm} \\times 5.920 \\text{ dm} \\times 2.54 \\text{ dm} \\\\ &amp; 202.09459\\dots \\text{ dm}^3 \\text{(value from calculator)} \\\\ &amp; 202 \\text{ dm}^3,\\;\\text{or}\\;202\\text{ L (answer rounded to three significant figures)} \\end{array}$<\/div>\r\n&nbsp;\r\n<p id=\"fs-idm219800928\"><strong><i>Test Yourself<\/i><\/strong><\/p>\r\nWhat is the density of a liquid with a mass of 31.1415 g and a volume of 30.13 cm<sup>3<\/sup>?\r\n\r\n&nbsp;\r\n\r\n<strong><em>Answer<\/em><\/strong>\r\n\r\n1.034 g\/mL\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\" id=\"fs-idm148976192\">\r\n<h3>Example 11<\/h3>\r\n<p id=\"fs-idp29940656\"><strong>Experimental Determination of Density Using Water Displacement<\/strong>\r\nA piece of rebar is weighed and then submerged in a graduated cylinder partially filled with water, with results as shown.<\/p>\r\n<span id=\"fs-idm332426528\">\r\n<a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_04_CylRebar-2.jpg\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_04_CylRebar-2.jpg\" alt=\"This diagram shows the initial volume of water in a graduated cylinder as 13.5 milliliters. A 69.658 gram piece of metal rebar is added to the graduated cylinder, causing the water to reach a final volume of 22.4 milliliters\" width=\"479\" height=\"364\" class=\"aligncenter\" \/><\/a><\/span>\r\n<p id=\"fs-idm245394240\">a) Use these values to determine the density of this piece of rebar.<\/p>\r\n<p id=\"fs-idm209220496\">b) Rebar is mostly iron. Does your result in (a) support this statement? How?<\/p>\r\n&nbsp;\r\n<p id=\"fs-idm325787440\"><strong>Solution\r\n<\/strong>The volume of the piece of rebar is equal to the volume of the water displaced:<\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idm180698816\" style=\"text-align: center\">$latex \\text{volume} = 22.4 \\text{mL} - 13.5 \\text{mL} = 8.9 \\text{mL} = 8.9 \\text{cm}^3 $<\/div>\r\n<p id=\"fs-idm181276752\">(rounded to the nearest 0.1 mL, per the rule for addition and subtraction)<\/p>\r\n<p id=\"fs-idp36085040\">The density is the mass-to-volume ratio:<\/p>\r\n\r\n<div class=\"equation\" id=\"fs-idp135143440\" style=\"text-align: center\">$latex \\text{density} = \\frac{\\text{mass}}{\\text{volume}} = \\frac{69.658 \\text{g}}{8.9 \\text{cm}^3} = 7.8 \\text{g\/cm}^3 $<\/div>\r\n<p id=\"fs-idm277303296\">(rounded to two significant figures, per the rule for multiplication and division)<\/p>\r\n<p id=\"fs-idm243666944\">From <a href=\"https:\/\/opentextbc.ca\/chemistry\/chapter\/measurements\/#fs-idm45639696\" class=\"autogenerated-content\">Table 3 in Chapter 2.2 Measurements<\/a>, the density of iron is 7.9 g\/cm<sup>3<\/sup>, very close to that of rebar, which lends some support to the fact that rebar is mostly iron.<\/p>\r\n&nbsp;\r\n<p id=\"fs-idm259990592\"><strong><em>Test Yourself<\/em><\/strong>\r\nAn irregularly shaped piece of a shiny yellowish material is weighed and then submerged in a graduated cylinder, with results as shown.<\/p>\r\n<span id=\"fs-idm283007920\">\r\n<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_04_CylGold-2.jpg\" alt=\"This diagram shows the initial volume of water in a graduated cylinder as 17.1 milliliters. A 51.842 gram gold colored rock is added to the graduated cylinder, causing the water to reach a final volume of 19.8 milliliters\" width=\"476\" height=\"363\" class=\"aligncenter\" \/><\/span>\r\n<p id=\"fs-idm272657872\">a) Use these values to determine the density of this material.<\/p>\r\n<p id=\"fs-idm166920160\">b) Do you have any reasonable guesses as to the identity of this material? Explain your reasoning.<\/p>\r\n&nbsp;\r\n\r\n<strong><em>Answers<\/em><\/strong>\r\n\r\na) 19 g\/cm<sup>3<\/sup>; (b) It is likely gold; the right appearance for gold and very close to the density given for gold in <a href=\"https:\/\/opentextbc.ca\/chemistry\/chapter\/measurements\/#fs-idm45639696\" class=\"autogenerated-content\">Table 3 in Chapter 2.2 Measurements<\/a>.\r\n\r\n<\/div>\r\n<\/section><section id=\"fs-idp33954960\">\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 12<\/h3>\r\nDetermine the answer and report to the appropriate number of significant figures.\r\n\r\na) What is the area of a card that measures 12.74 cm by 7.60 cm ?\r\n\r\nb) What is the total mass when three samples weighing 120.0 g, 24.318 g and 15 g are combined?\r\n\r\nc) (3.02 x 10<sup>3<\/sup>) + (4 x 10<sup>2<\/sup>) = ?\r\n\r\n&nbsp;\r\n\r\n<strong>Solution<\/strong>\r\n\r\na) The area is width x length. 12.74 cm x 7.60 cm = 96.824 according to a calculator. The 12.74 has 4 significant figures and 7.60 has three significant figures, thus the solution should be reported to 3 significant figures. Don\u2019t forget the units! cm x cm = cm<sup>2<\/sup>\r\n\r\nThe answer is 96.8 cm<sup>2<\/sup>\r\n\r\nb) When adding, be sure that all units are the same (all g in this case).\r\n0 g + 24.318 g + 15 g = 159.318 g according to a calculator. We must look at the decimal place (or place value). 120.0 is reported to the tenths position, 24.318 to the thousandths position, whereas 15 is reported to the ones position. The ones position is furthest to the left, thus the final answer must be rounded to that position.\r\n\r\nThe answer is 159 g\r\n\r\nc) Be careful! When adding and subtracting, the power of 10 must be the same. If we put them both to 103, we have (3.02 x 10<sup>3<\/sup>) + (0.4 x 10<sup>3<\/sup>). The answer can then be reported to the first decimal place (tenths) when using 10<sup>3<\/sup> (= 3.4 x 10<sup>3<\/sup>). We could also look at the non-scientific notation: 3.02 x 10<sup>3<\/sup> = <strong>302<\/strong>0, and 4 x 10<sup>2<\/sup> = <strong>4<\/strong>00 (sig. figs. in bold, for emphasis). Thus the first number is recorded to the tens position, whereas the second is to the hundreds position. final answer must be reported to the hundreds position.\r\n\r\nThe answer is 3.4 x 10<sup>3<\/sup>\r\n\r\n&nbsp;\r\n\r\n<strong><em>Test Yourself<\/em><\/strong>\r\n\r\nDetermine the answer and report to the appropriate number of significant figures.\r\na)\u00a0 17.1 + 0.24 \u2013 241\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 b)\u00a0 (1.32 x 10<sup>4<\/sup>) x (2 x 10<sup>2<\/sup>)\r\n\r\n&nbsp;\r\n\r\n<strong><em>Answers<\/em><\/strong>\r\n\r\na) -224\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 3 x 10<sup>6<\/sup>\r\n\r\n<\/div>\r\n<\/section>\r\n<div class=\"textbox shaded\">\r\n<h3 class=\"title\">Example 13<\/h3>\r\nIf a bagel has a mass of 28.3162 g when fresh and then a mass of 28.3094 g once dried out, what was the percent of moisture in the fresh bagel?\r\n\r\nWhere, % moisture = \u00a0 (mass of moisture\/original mass of object) \u00a0x 100% ,\r\n\r\ndetermine the solution and report to the appropriate number of significant figures.\r\n\r\n&nbsp;\r\n\r\n<strong>Solution<\/strong>\r\n\r\nTo determine the mass of moisture, we must subtract the dried mass from the original mass:\r\n28.3162 g \u2013 28.3094 g =\u00a0 0.0068 g. Note that if the question stopped here, the answer would be reported to the 4th decimal place, and has two significant figures.\r\n\r\nThe next step involves division:\u00a0\u00a0\u00a0<span style=\"text-decoration: underline\"> 0.0068 g<\/span> \u00a0\u00a0\u00a0x\u00a0 100%\u00a0 = 0.0240145\u2026%\r\n28.3162 g\r\n\r\nThe value 0.0068 g has 2 significant figures, 28.3162 g has 6 significant figures, and 100% as used here is an exact number, so the final answer can only be reported to 2 significant figures.\r\n\r\nThus the solution is rounded to 0.024% (or 2.4 x 10<sup>-2<\/sup>%, in scientific notation)\r\n\r\n&nbsp;\r\n\r\n<strong><em>Test Yourself<\/em><\/strong>\r\n\r\nIf a jogger runs for 2.0 hrs at 12.21 km\/hr, then again for another 2.0 hrs at 12.16 km\/hr, how far did she run in total?\r\n(Determine the solution and report to the appropriate number of significant figures.)\r\n\r\n&nbsp;\r\n\r\n<strong><em>Answer<\/em><\/strong>\r\n\r\n49 km\r\n\r\n<\/div>\r\n<section id=\"fs-idp33954960\">\r\n<h2>Accuracy and Precision<\/h2>\r\n<p id=\"fs-idp4474304\">Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to know both the <strong>precision<\/strong> and the <strong>accuracy<\/strong> of their results. Measurements are said to be precise if they yield very similar results when repeated in the same manner. A measurement is considered accurate if it yields a result that is very close to the true or accepted value. Precise values agree with each other; accurate values agree with a true value. These characterizations can be extended to other contexts, such as the results of an archery competition (<a href=\"#fs-idm1827280\" class=\"autogenerated-content\">Figure 3<\/a>).<\/p>\r\n\r\n<figure id=\"fs-idm1827280\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1300\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_Archery-2.jpg\" alt=\"Figures A through C each show targets with holes where the arrows hit. The archer in figure A was both accurate and precise as all 3 arrows are clustered in the center of the target. In figure B, the archer is precise but not accurate, as all 3 arrows are clustered together but to the upper right of the center of the target. In Figure C, the archer is neither accurate nor precise as the 3 holes are not close together and are located both to the upper right and right of the target.\" width=\"1300\" height=\"414\" \/> <strong>Figure 3.<\/strong> (a) These arrows are close to both the bull\u2019s eye and one another, so they are both accurate and precise. (b) These arrows are close to one another but not on target, so they are precise but not accurate. (c) These arrows are neither on target nor close to one another, so they are neither accurate nor precise.[\/caption]<\/figure>\r\n<p id=\"fs-idp174984224\">Suppose a quality control chemist at a pharmaceutical company is tasked with checking the accuracy and precision of three different machines that are meant to dispense 10 ounces (296 mL) of cough syrup into storage bottles. She proceeds to use each machine to fill five bottles and then carefully determines the actual volume dispensed, obtaining the results tabulated in <a href=\"#fs-idp31780400\" class=\"autogenerated-content\">Table 1<\/a>.<\/p>\r\n\r\n<table id=\"fs-idp31780400\" class=\"span-all\" summary=\"The volume, in milliliters, of cough medicine delivered by dispensers 1, 2 and 3 are shown in a table. The values for dispenser 1 are 283.3, 284.1, 283.9, 284.0, and 284.1. The values for dispenser 2 are 298.3, 294.2, 296.0, 297.8, and 293.9. The values for dispenser 3 are 296.1, 295.9, 296.1, 296.0, and 296.1.\">\r\n<thead>\r\n<tr valign=\"top\">\r\n<th>Dispenser #1<\/th>\r\n<th>Dispenser #2<\/th>\r\n<th>Dispenser #3<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td>283.3<\/td>\r\n<td>298.3<\/td>\r\n<td>296.1<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>284.1<\/td>\r\n<td>294.2<\/td>\r\n<td>295.9<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>283.9<\/td>\r\n<td>296.0<\/td>\r\n<td>296.1<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>284.0<\/td>\r\n<td>297.8<\/td>\r\n<td>296.0<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>284.1<\/td>\r\n<td>293.9<\/td>\r\n<td>296.1<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td colspan=\"3\"><strong>Table 1.<\/strong> Volume (mL) of Cough Medicine Delivered by 10-oz (296 mL) Dispensers<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<p id=\"fs-idp4939264\">Considering these results, she will report that dispenser #1 is precise (values all close to one another, within a few tenths of a milliliter) but not accurate (none of the values are close to the target value of 296 mL, each being more than 10 mL too low). Results for dispenser #2 represent improved accuracy (each volume is less than 3 mL away from 296 mL) but worse precision (volumes vary by more than 4 mL). Finally, she can report that dispenser #3 is working well, dispensing cough syrup both accurately (all volumes within 0.1 mL of the target volume) and precisely (volumes differing from each other by no more than 0.2 mL).<\/p>\r\n\r\n<\/section><section id=\"fs-idp223627024\" class=\"summary\">\r\n<h2>Key Concepts and Summary<\/h2>\r\n<p id=\"fs-idp108718096\">Quantities can be exact or measured. Measured quantities have an associated uncertainty that is represented by the number of significant figures in the measurement. The uncertainty of a calculated value depends on the uncertainties in the values used in the calculation and is reflected in how the value is rounded. Measured values can be accurate (close to the true value) and\/or precise (showing little variation when measured repeatedly).<\/p>\r\n\r\n<\/section>\r\n<div class=\"qandaset block\" id=\"ball-ch02_s03_qs01\">\r\n<div class=\"bcc-box bcc-info\">\r\n<h3>Exercises<\/h3>\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p1\" class=\"para\">1. Express each measurement to the correct number of significant figures.<\/p>\r\n<a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM.png\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM.png\" alt=\"\" width=\"617\" height=\"241\" class=\"aligncenter wp-image-4642 size-full\" \/><\/a>\r\n<p class=\"para\"><span style=\"font-size: 1em\">2. Express each measurement to the correct number of significant figures.<\/span><\/p>\r\n<a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM.png\"><img src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM.png\" alt=\"\" width=\"617\" height=\"235\" class=\"aligncenter size-full wp-image-4643\" \/><\/a>\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n<p class=\"para\"><span style=\"font-size: 1em\">3. How many significant figures do these numbers have?<\/span><\/p>\r\n\r\n<\/div>\r\na) \u00a023 \u00a0 \u00a0\u00a0b) \u00a023.0 \u00a0 \u00a0\u00a0c) \u00a00.00023 \u00a0 \u00a0\u00a0d) \u00a00.0002302\r\n\r\n4. \u00a0How many significant figures do these numbers have?\r\n\r\na) \u00a05.44 \u00d7 10<sup class=\"superscript\">8 \u00a0 \u00a0\u00a0<\/sup>b) \u00a01.008 \u00d7 10<sup class=\"superscript\">\u22125 \u00a0 \u00a0\u00a0<\/sup>c) \u00a043.09 \u00a0 \u00a0\u00a0d) \u00a00.0000001381\r\n\r\n5. \u00a0How many significant figures do these numbers have?\r\n\r\na) \u00a0765,890 \u00a0 \u00a0\u00a0b) \u00a0765,890.0 \u00a0 \u00a0\u00a0c) \u00a01.2000 \u00d7 10<sup class=\"superscript\">5 \u00a0 \u00a0\u00a0<\/sup>d) \u00a00.0005060\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p6\" class=\"para\">6) \u00a0How many significant figures do these numbers have?<\/p>\r\na) \u00a00.009 \u00a0 \u00a0\u00a0b) \u00a00.0000009 \u00a0 \u00a0\u00a0c) \u00a065,444 \u00a0 \u00a0\u00a0d) \u00a065,040\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p7\" class=\"para\">7. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\r\na) \u00a056.0 +\u00a03.44 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0b) \u00a00.00665 +\u00a01.004 = ?\r\n\r\nc) \u00a045.99 \u2212 32.8 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0d) \u00a045.99 \u2212 32.8 +\u00a075.02 = ?\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p8\" class=\"para\">8. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\r\na) \u00a01.005 +\u00a017.88 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b) \u00a056,700 \u2212 324 = ?\r\n\r\nc) \u00a0405,007 \u2212 123.3 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0d) \u00a055.5 +\u00a066.66 \u2212 77.777 = ?\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p9\" class=\"para\">9. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\r\na) \u00a056.7 \u00d7 66.99 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0b) \u00a01.000 \u00f7 77 = ?\r\n\r\nc) \u00a01.000 \u00f7 77.0 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0d) \u00a06.022 \u00d7 1.89 = ?\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p10\" class=\"para\">10. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\r\na) \u00a00.000440 \u00d7 17.22 = ? \u00a0 \u00a0 \u00a0 \u00a0 b) \u00a0203,000 \u00f7 0.044 = ?\r\n\r\nc) \u00a067 \u00d7 85.0 \u00d7 0.0028 = ? \u00a0 \u00a0 \u00a0\u00a0d) \u00a0999,999 \u00f7 3,310 = ?\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n\r\n11. \u00a0Write the number 87,449 in scientific notation with four significant figures.\r\n\r\n12. \u00a0Write the number 0.000066600 in scientific notation with five significant figures.\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n\r\n13. \u00a0Write the number 306,000,000 in scientific notation to the proper number of significant figures.\r\n\r\n14. \u00a0Write the number 0.0000558 in scientific notation with two significant figures.\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p13\" class=\"para\">15. \u00a0Perform each calculation and limit each answer to three significant figures.<\/p>\r\na) \u00a067,883 \u00d7 0.004321 = ?\r\n\r\nb) \u00a0(9.67 \u00d7 10<sup class=\"superscript\">3<\/sup>) \u00d7 0.0055087 = ?\r\n\r\n<\/div>\r\n<div class=\"question\">\r\n<p id=\"ball-ch02_s03_qs01_p14\" class=\"para\">16. \u00a0Perform each calculation and limit each answer to four significant figures.<\/p>\r\na) \u00a018,900 \u00d7 76.33 \u00f7 0.00336 = ?\r\n\r\nb) \u00a00.77604 \u00f7 76,003 \u00d7 8.888 = ?\r\n\r\n<span style=\"font-size: 1em\">17. \u00a0Express each of the following numbers in exponential notation with correct significant figures:<\/span>\r\n\r\n<\/div>\r\n<p id=\"fs-idp158645376\">a) 704 \u00a0 \u00a0\u00a0b) 0.03344 \u00a0 \u00a0\u00a0c) 547.9 \u00a0 \u00a0\u00a0d) 22086 \u00a0 \u00a0\u00a0e) 1000.00 \u00a0 \u00a0\u00a0f) 0.0000000651 \u00a0 \u00a0\u00a0g) 0.007157<\/p>\r\n18. \u00a0Indicate whether each of the following can be determined exactly or must be measured with some degree of uncertainty:\r\n<p id=\"fs-idp192668592\">a) the number of seconds in an hour<\/p>\r\n<p id=\"fs-idp131489888\">b) the number of pages in this book<\/p>\r\n<p id=\"fs-idp29050000\">c) the number of grams in your weight<\/p>\r\n<p id=\"fs-idp40603568\">d) the number of grams in 3 kilograms<\/p>\r\n<p id=\"fs-idp42867296\">e) the volume of water you drink in one day<\/p>\r\n<p id=\"fs-idp5273504\">f) the distance from San Francisco to Kansas City<\/p>\r\n19. \u00a0How many significant figures are contained in each of the following measurements?\r\n<p id=\"fs-idp191599120\">a) 53 cm \u00a0 \u00a0\u00a0b) 2.05 \u00d7 10<sup>8<\/sup> m \u00a0 \u00a0\u00a0c) 86,002 J \u00a0 \u00a0\u00a0d) 9.740 \u00d7 10<sup>4<\/sup> m\/s \u00a0 \u00a0\u00a0e) 10.0613 m<sup>3<\/sup><\/p>\r\n<p id=\"fs-idp115902336\">f) 0.17 g\/mL \u00a0 \u00a0\u00a0g) 0.88400 s<\/p>\r\n20. \u00a0Round off each of the following numbers to two significant figures:\r\n<p id=\"fs-idp367138576\">a) 0.436 \u00a0 \u00a0\u00a0b) 9.000 \u00a0 \u00a0\u00a0c) 27.2 \u00a0 \u00a0\u00a0d) 135 \u00a0 \u00a0\u00a0e) 1.497 \u00d7 10<sup>\u22123 \u00a0 \u00a0\u00a0<\/sup>f) 0.445<\/p>\r\n21. \u00a0Perform the following calculations and report each answer with the correct number of significant figures.\r\n<p id=\"fs-idp101772784\">a) 628 \u00d7 342 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0b) (5.63 \u00d7 10<sup>2<\/sup>) \u00d7 (7.4 \u00d7 10<sup>3<\/sup>)<\/p>\r\n<p id=\"fs-idp43333760\">c) $latex \\frac{28.0}{13.483} $ \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0d) 8119 \u00d7 0.000023<\/p>\r\n<p id=\"fs-idp2544704\">e) 14.98 + 27,340 + 84.7593 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0f) 42.7 + 0.259<\/p>\r\n22. \u00a0Consider the results of the archery contest shown in this figure.\r\n<p id=\"fs-idp29005776\">a) Which archer is most precise?<\/p>\r\n<p id=\"fs-idp32003568\">b) Which archer is most accurate?<\/p>\r\n<p id=\"fs-idp110085200\">c) Who is both least precise and least accurate?<\/p>\r\n<img id=\"fs-idp94481888\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_Archer2_img-2.jpg\" alt=\"4 targets are shown each with 4 holes indicating where the arrows hit the targets. Archer W put all 4 arrows closely around the center of the target. Archer X put all 4 arrows in a tight cluster but far to the lower right of the target. Archer Y put all 4 arrows at different corners of the target. All 4 arrows are very far from the center of the target. Archer Z put 2 arrows close to the target and 2 other arrows far outside of the target.\" width=\"1200\" height=\"463\" class=\"alignnone\" \/>\r\n\r\n&nbsp;\r\n\r\n<b>Answers<\/b>\r\n\r\n1. \u00a0a) \u00a0375 psi \u00a0 \u00a0\u00a0b) \u00a01.30 cm\r\n\r\n2. \u00a0a) 32.4 psi \u00a0 \u00a0 b) 0.90 cm\r\n\r\n3. \u00a0a) \u00a0two \u00a0 \u00a0\u00a0b) \u00a0three \u00a0 \u00a0\u00a0c) \u00a0two \u00a0 \u00a0\u00a0d) \u00a0four\r\n\r\n4. \u00a0a) \u00a0three \u00a0 b) \u00a0four \u00a0 \u00a0 \u00a0c) \u00a0four \u00a0 \u00a0 d) \u00a0four\r\n\r\n5. \u00a0a) \u00a0five \u00a0 \u00a0\u00a0b) \u00a0seven \u00a0 \u00a0\u00a0c) \u00a0five \u00a0 \u00a0\u00a0d) \u00a0four\r\n\r\n6. \u00a0a) \u00a0one \u00a0 \u00a0 b) \u00a0one \u00a0 \u00a0 \u00a0 \u00a0c) \u00a0five \u00a0 \u00a0 \u00a0d) four\r\n\r\n7.<strong> \u00a0<\/strong>a) \u00a059.4 \u00a0 \u00a0\u00a0b) \u00a01.011 \u00a0 \u00a0\u00a0c) \u00a013.2 \u00a0 \u00a0\u00a0d) \u00a088.2\r\n\r\n8. \u00a0a) \u00a018.88 \u00a0 b) \u00a056,400 \u00a0 \u00a0c) \u00a0404,884 \u00a0 d) \u00a044.4\r\n\r\n9. \u00a0a) \u00a03.80 \u00d7 10<sup class=\"superscript\">3 \u00a0 \u00a0\u00a0<\/sup>b) \u00a00.013 \u00a0 \u00a0\u00a0c) \u00a00.0130 \u00a0 \u00a0\u00a0d) \u00a011.4\r\n\r\n10. \u00a0a) \u00a00.00758 \u00a0 \u00a0 \u00a0b) \u00a04,600,000 \u00a0 \u00a0 c) \u00a016 \u00a0 \u00a0 d) \u00a0302\r\n\r\n11. \u00a08.745 \u00d7 10<sup class=\"superscript\">4 \u00a0 \u00a0<\/sup>\r\n\r\n12. \u00a06.6600 x 10<sup class=\"superscript\">\u22125<\/sup>\r\n\r\n13. \u00a03.06 x 10<sup>8<\/sup>\r\n\r\n14. \u00a05.6 x 10<sup>-5<\/sup>\r\n\r\n15. \u00a0a) \u00a0293 \u00a0 \u00a0\u00a0b) \u00a053.3\r\n<p id=\"fs-idp28073776\">16. \u00a0a) \u00a04.294 x 10<sup>8<\/sup> \u00a0 \u00a0 \u00a0b) \u00a09.060x10<sup>-5<\/sup><\/p>\r\n17. \u00a0a) 7.04 \u00d7 10<sup>2 \u00a0 \u00a0 \u00a0<\/sup>b) 3.344 \u00d7 10<sup>\u22122 \u00a0 \u00a0 \u00a0<\/sup>c) 5.479 \u00d7 10<sup>2 \u00a0 \u00a0 \u00a0<\/sup>d) 2.2086 \u00d7 10<sup>4 \u00a0 \u00a0 \u00a0<\/sup>e) 1.00000 \u00d7 10<sup>3 \u00a0 \u00a0 \u00a0<\/sup>f) 6.51 \u00d7 10<sup>\u22128<\/sup>\u00a0g) 7.157 \u00d7 10<sup>\u22123<\/sup>\r\n<p id=\"fs-idp120430064\">18. \u00a0a) exact \u00a0 \u00a0 \u00a0b) exact \u00a0 \u00a0 \u00a0c) uncertain \u00a0 \u00a0 \u00a0d) exact \u00a0 \u00a0 \u00a0e) uncertain \u00a0 \u00a0 \u00a0f) uncertain<\/p>\r\n<p id=\"fs-idm1331360\">19. \u00a0a) two \u00a0 \u00a0 \u00a0b) three \u00a0 \u00a0 \u00a0c) five \u00a0 \u00a0 \u00a0d) four \u00a0 \u00a0 \u00a0e) six \u00a0 \u00a0 \u00a0f) two \u00a0 \u00a0 \u00a0g) five<\/p>\r\n<p id=\"fs-idp133316128\">20. \u00a0a) 0.44 \u00a0 \u00a0 \u00a0b) 9.0 \u00a0 \u00a0 \u00a0c) 27 \u00a0 \u00a0 \u00a0d) 140 \u00a0 \u00a0 \u00a0e) 1.5 \u00d7 10<sup>\u22123 \u00a0 \u00a0 \u00a0<\/sup>f) 0.44<\/p>\r\n<p id=\"fs-idp42820064\">21. \u00a0a) 2.15 \u00d7 10<sup>5 \u00a0 \u00a0 \u00a0<\/sup>b) 4.2 \u00d7 10<sup>6 \u00a0 \u00a0 \u00a0<\/sup>c) 2.08 \u00a0 \u00a0 \u00a0d) 0.19 \u00a0 \u00a0 \u00a0e) 27,440 \u00a0 \u00a0 \u00a0f) 43.0<\/p>\r\n<p id=\"fs-idp27840096\">22. \u00a0a) Archer X \u00a0 \u00a0 \u00a0b) Archer W \u00a0 \u00a0 \u00a0c) Archer Y<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div>\r\n<h2>Glossary<\/h2>\r\n<strong>accuracy:\u00a0<\/strong>how closely a measurement aligns with a correct value\r\n\r\n<strong>exact number:\u00a0<\/strong>number derived by counting or by definition\r\n\r\n<strong>precision:\u00a0<\/strong>how closely a measurement matches the same measurement when repeated\r\n\r\n<strong>rounding:\u00a0<\/strong>procedure used to ensure that calculated results properly reflect the uncertainty in the measurements used in the calculation\r\n\r\n<strong>significant figures:\u00a0<\/strong>(also, significant digits) all of the measured digits in a determination, including the uncertain last digit\r\n\r\n<strong>uncertainty:\u00a0<\/strong>estimate of amount by which measurement differs from true value\r\n\r\n<\/div>","rendered":"<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Define accuracy and precision<\/li>\n<li>Distinguish exact and uncertain numbers<\/li>\n<li>Correctly represent uncertainty in quantities using significant figures<\/li>\n<li>Apply proper rounding rules to computed quantities<\/li>\n<\/ul>\n<\/div>\n<p>When recording a measurement, <em>how<\/em> you record it is just as important as <em>what<\/em> you record. You must consider the precision of the instrument you are using.\u00a0 <strong>Accuracy<\/strong> is the extent to which a measured value coincides with the true or accepted value.\u00a0 <strong>Precision<\/strong>\u00a0refers to the \u201cfineness\u201d (i.e. the number of digits) of the measurement as well as the reproducibility.\u00a0 <strong>Significant figures<\/strong> are those digits in an experimentally measured quantity that establish the precision with which the value is known.\u00a0 A precise measurement may not be accurate!!<\/p>\n<p id=\"fs-idm288863760\">Counting is the only type of measurement that is free from uncertainty, provided the number of objects being counted does not change while the counting process is underway. The result of such a counting measurement is an example of an <strong>exact number<\/strong>. If we count eggs in a carton, we know <em>exactly<\/em> how many eggs the carton contains. The numbers of defined quantities are also exact. By definition, 1 foot is exactly 12 inches, 1 inch is exactly 2.54 centimeters, and 1 gram is exactly 0.001 kilogram. Quantities derived from measurements other than counting, however, are uncertain to varying extents due to practical limitations of the measurement process used.<\/p>\n<section id=\"fs-idm217277536\">\n<h2>Significant Figures in Measurement<\/h2>\n<p id=\"fs-idp11446448\">The numbers of measured quantities, unlike defined or directly counted quantities, are not exact. To measure the volume of liquid in a graduated cylinder, you should make a reading at the bottom of the meniscus, the lowest point on the curved surface of the liquid.<\/p>\n<figure id=\"fs-idm337865984\"><figcaption><\/figcaption><figure style=\"width: 1300px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_Measure-2.jpg\" alt=\"This diagram shows a 25 milliliter graduated cylinder filled with about 20.8 milliliters of fluid. The diagram zooms in on the meniscus, which is the curved surface of the water that is visible when the graduated cylinder is viewed from the side. You make the reading at the lowest point of the curve of the meniscus.\" width=\"1300\" height=\"743\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 1.<\/strong> To measure the volume of liquid in this graduated cylinder, you must mentally subdivide the distance between the 21 and 22 mL marks into tenths of a milliliter, and then make a reading (estimate) at the bottom of the meniscus.<\/figcaption><\/figure>\n<\/figure>\n<p id=\"fs-idm176542448\">Refer to the illustration in <a href=\"#fs-idm337865984\" class=\"autogenerated-content\">Figure 1<\/a>. The bottom of the meniscus in this case clearly lies between the 21 and 22 markings, meaning the liquid volume is <em>certainly<\/em> greater than 21 mL but less than 22 mL. The meniscus appears to be a bit closer to the 22-mL mark than to the 21-mL mark, and so a reasonable estimate of the liquid\u2019s volume would be 21.6 mL. In the number 21.6, then, the digits 2 and 1 are certain, but the 6 is an estimate. Some people might estimate the meniscus position to be equally distant from each of the markings and estimate the tenth-place digit as 5, while others may think it to be even closer to the 22-mL mark and estimate this digit to be 7. Note that it would be pointless to attempt to estimate a digit for the hundredths place, given that the tenths-place digit is uncertain. In general, numerical scales such as the one on this graduated cylinder will permit measurements to one-tenth of the smallest scale division. The scale in this case has 1-mL divisions, and so volumes may be measured to the nearest 0.1 mL.<\/p>\n<p id=\"fs-idm254904560\">This concept holds true for all measurements, even if you do not actively make an estimate. If you place a quarter on a standard electronic balance, you may obtain a reading of 6.72 g. The digits 6 and 7 are certain, and the 2 indicates that the mass of the quarter is likely between 6.71 and 6.73 grams. The quarter weighs <em>about<\/em> 6.72 grams, with a nominal uncertainty in the measurement of \u00b1 0.01 gram. If we weigh the quarter on a more sensitive balance, we may find that its mass is 6.723 g. This means its mass lies between 6.722 and 6.724 grams, an uncertainty of 0.001 gram. Every measurement has some <strong>uncertainty<\/strong>, which depends on the device used (and the user\u2019s ability). All of the digits in a measurement, including the uncertain last digit, are called <strong>significant figures<\/strong> or <strong>significant digits<\/strong>. Note that zero may be a measured value; for example, if you stand on a scale that shows weight to the nearest pound and it shows \u201c120,\u201d then the 1 (hundreds), 2 (tens) and 0 (ones) are all significant (measured) values.<\/p>\n<p id=\"fs-idm264880544\">Whenever you make a measurement properly, all the digits in the result are significant. But what if you were analyzing a reported value and trying to determine what is significant and what is not? Well, for starters, all nonzero digits are significant, and it is only zeros that require some thought. We will use the terms \u201cleading,\u201d \u201ctrailing,\u201d and \u201ccaptive\u201d for the zeros and will consider how to deal with them.<\/p>\n<p><span id=\"fs-idm244068192\"><br \/>\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits5_img-2.jpg\" alt=\"The left diagram uses the example of 3090. The zero in the hundreds place is labeled \u201ccaptive\u201d and the zero in the ones place is labeled trailing. The right diagram uses the example 0.008020. The three zeros in the ones, tenths, and hundredths places are labeled \u201cleading.\u201d The zero in the ten-thousandths place is labeled \u201ccaptive\u201d and the zero in the millionths place is labeled \u201ctrailing.\u201d\" width=\"650\" height=\"222\" class=\"aligncenter\" \/><\/span><\/p>\n<p id=\"fs-idp31100592\">Starting with the first nonzero digit on the left, count this digit and all remaining digits to the right. This is the number of significant figures in the measurement unless the last digit is a trailing zero lying to the left of the decimal point.<\/p>\n<p><span id=\"fs-idp40720144\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits1_img-2.jpg\" alt=\"The left diagram uses the example of 1267 meters. The number 1 is the first nonzero figure on the left. 1267 has 4 significant figures in total. The right diagram uses the example of 55.0 grams. The number 5 in the tens place is the first nonzero figure on the left. 55.0 has 3 significant figures. Note that the 0 is to the right of the decimal point and therefore is a significant figure.\" \/><\/span><\/p>\n<p id=\"fs-idm177076640\">Captive zeros result from measurement and are therefore always significant. Leading zeros, however, are never significant\u2014they merely tell us where the decimal point is located.<\/p>\n<p><span id=\"fs-idm113793344\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits2_img-2.jpg\" alt=\"The left diagram uses the example of 70.607 milliliters. The number 7 is the first nonzero figure on the left. 70.607 has 5 significant figures in total, as all figures are measured including the 2 zeros. The right diagram uses the example of 0.00832407 M L. The number 8 is the first nonzero figure on the left. 0.00832407 has 6 significant figures.\" \/><\/span><\/p>\n<p id=\"fs-idm262013360\">The leading zeros in this example are not significant. We could use exponential notation (as described in Appendix B) and express the number as 8.32407 \u00d7 10<sup>\u22123<\/sup>; then the number 8.32407 contains all of the significant figures, and 10<sup>\u22123<\/sup> locates the decimal point.<\/p>\n<p id=\"fs-idm210460000\">The number of significant figures is uncertain in a number that ends with a zero to the left of the decimal point location. The zeros in the measurement 1,300 grams could be significant or they could simply indicate where the decimal point is located. The ambiguity can be resolved with the use of exponential notation: 1.3 \u00d7 10<sup>3<\/sup> (two significant figures), 1.30 \u00d7 10<sup>3<\/sup> (three significant figures, if the tens place was measured), or 1.300 \u00d7 10<sup>3<\/sup> (four significant figures, if the ones place was also measured). In cases where only the normal notation is used (1300 g), all trailing zeros are not significant, therefore the measurement would have two significant figures.\u00a0 Though, if the measurement was express with an explicit decimal place (1300. g), then the trailing zeros would be significant, and\u00a0therefore the measurement would have four significant figures.<\/p>\n<p><span id=\"fs-idp29412624\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits3_img-2.jpg\" alt=\"This figure uses the example of 1300 grams. The one and the 3 are significant figures as they are clearly the result of measurement. The 2 zeros could be significant if they were measured or they could be placeholders.\" \/><\/span><\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3163\" aria-describedby=\"caption-attachment-3163\" style=\"width: 535px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs-300x243.jpg\" alt=\"\" width=\"535\" height=\"433\" class=\"wp-image-3163\" srcset=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs-300x243.jpg 300w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs-768x622.jpg 768w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs-65x53.jpg 65w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs-225x182.jpg 225w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs-350x284.jpg 350w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/SigFigs.jpg 796w\" sizes=\"auto, (max-width: 535px) 100vw, 535px\" \/><figcaption id=\"caption-attachment-3163\" class=\"wp-caption-text\"><strong>Figure 2:<\/strong> Summary: How to determine the number of significant figures in measurements.<\/figcaption><\/figure>\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 1<\/h3>\n<p>Determine the correct measurement reading for the following volume:<\/p>\n<p><a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1-300x295.jpg\" alt=\"\" width=\"100\" height=\"98\" class=\"alignnone wp-image-3170\" srcset=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1-300x295.jpg 300w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1-768x754.jpg 768w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1-65x64.jpg 65w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1-225x221.jpg 225w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1-350x344.jpg 350w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Beaker1.jpg 824w\" sizes=\"auto, (max-width: 100px) 100vw, 100px\" \/><\/a><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Solution<\/strong><\/p>\n<p>Because the beaker has gradations of 100 mL, we know that it is at least 200 mL. It is the tens position that is uncertain. Thus we can only record to that position. The reading should be 220 mL. Better still\u2014clarify the significant figures by using scientific notation, which would be 2.2 x 10<sup>2<\/sup> mL.<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\n<p>Determine the correct reading for the following temperature:<\/p>\n<p><a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1-300x59.jpg\" alt=\"\" width=\"300\" height=\"59\" class=\"alignnone wp-image-3171 size-medium\" srcset=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1-300x59.jpg 300w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1-65x13.jpg 65w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1-225x44.jpg 225w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1-350x68.jpg 350w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Thermo1.jpg 604w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answer<\/em><\/strong><\/p>\n<p>14.8<sup>o<\/sup>C<\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 2<\/h3>\n<p id=\"ball-ch02_s03_p06\" class=\"para\">Use each diagram to report a measurement to the proper number of significant figures.<\/p>\n<p><a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM.png\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM.png\" alt=\"\" width=\"659\" height=\"242\" class=\"aligncenter wp-image-4640 size-full\" srcset=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM.png 659w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM-300x110.png 300w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM-65x24.png 65w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM-225x83.png 225w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.50.03-PM-350x129.png 350w\" sizes=\"auto, (max-width: 659px) 100vw, 659px\" \/><\/a><\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\n<p class=\"simpara\">a) The arrow is between 4.0 and 5.0, so the measurement is at least 4.0. The arrow is between the third and fourth small tick marks, so it\u2019s at least 0.3. We will have to estimate the last place. It looks like about one-third of the way across the space, so let us estimate the hundredths place as 3. Combining the digits, we have a measurement of 4.33 psi (psi stands for \u201cpounds per square inch\u201d and is a unit of pressure, like air in a tire). We say that the measurement is reported to three significant figures.<\/p>\n<p class=\"simpara\">b)The rectangle is at least 1.0 cm wide but certainly not 2.0 cm wide, so the first significant digit is 1. The rectangle\u2019s width is past the second tick mark but not the third; if each tick mark represents 0.1, then the rectangle is at least 0.2 in the next significant digit. We have to estimate the next place because there are no markings to guide us. It appears to be about halfway between 0.2 and 0.3, so we will estimate the next place to be a 5. Thus, the measured width of the rectangle is 1.25 cm. Again, the measurement is reported to three significant figures.<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\n<p id=\"ball-ch02_s03_p07\" class=\"para\">What would be the reported width of this rectangle?<\/p>\n<p class=\"para\"><a href=\"http:\/\/opentextbc.ca\/introductorychemistry\/wp-content\/uploads\/sites\/17\/2014\/09\/Rectangle.png\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Rectangle-1.png\" alt=\"Rectangle\" class=\"alignnone wp-image-4615\" width=\"301\" height=\"192\" \/><\/a><\/p>\n<div class=\"informalfigure small\" id=\"ball-ch02_s03_f04\"><\/div>\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answer<\/em><\/strong><\/p>\n<p id=\"ball-ch02_s03_p08\" class=\"para\">0.63 cm<\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 3<\/h3>\n<p id=\"ball-ch02_s03_p12\" class=\"para\">Give the number of significant figures in each measurement.<\/p>\n<p class=\"para\">a) 36.7 m\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 0.006606 s\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 c) 2,002 kg\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 d) 306,490,000 people<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\n<p class=\"simpara\">a) By rule 1, all nonzero digits are significant, so this measurement has three significant figures.<\/p>\n<p class=\"simpara\">b) By rule 4, the first three zeros are not significant, but by rule 2 the zero between the sixes is; therefore, this number has four significant figures.<\/p>\n<p class=\"simpara\">c) By rule 2, the two zeros between the twos are significant, so this measurement has four significant figures.<\/p>\n<p class=\"simpara\">d) The four trailing zeros in the number are not significant, but the other five numbers are, so this number has five significant figures.<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\n<p id=\"ball-ch02_s03_p13\" class=\"para\">Give the number of significant figures in each measurement.<\/p>\n<p class=\"para\">a) 0.000601 m\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 65.080 kg<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answers<\/em><\/strong><\/p>\n<p class=\"simpara\">a) three significant figures\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) five significant figures<\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 4<\/h3>\n<p>Determine the number of significant figures in the following measurements<br \/>\na) 0.002040 g\u00a0\u00a0\u00a0 b) 300 mL\u00a0\u00a0\u00a0 c) 3.021 x 10<sup>5<\/sup> g\u00a0\u00a0\u00a0 d) 31 pencils (counted exactly, not an estimate)<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Solution<\/strong><\/p>\n<p>a) 4 significant figures. The leading zeros do not count, but the trailing zero does (as there\u2019s a decimal point).<\/p>\n<p>b) By the above rules, 1 significant figure, because there\u2019s no decimal point showing; 300. mL would be 3 sig figs. (To emphasize 1 sig fig it would be better to write the measurement in scientific notation, as 3 x 10<sup>2<\/sup> mL, rather than just \u201c300\u00a0mL\u201d.)<\/p>\n<p>c) 4 significant figures. (No leading or trailing zeros.) Note that we only consider the digits in the numerical portion of the scientific notation, not the power of 10.<\/p>\n<p>d) Unlimited significant figures. This is an exact number, as it has been counted.<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\n<p id=\"ball-ch02_s03_p17\" class=\"para\">Determine the number of significant figures in the following measurements.<br \/>\na)\u00a0 0.00100 m\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 b)\u00a0 2.0900 x 10<sup>3<\/sup> mL\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 c) 100.0 <sup>o<\/sup>C<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answers<\/em><\/strong><\/p>\n<p>a) 3 significant figures\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 5\u00a0significant figures\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 c) 4\u00a0significant figures<\/p>\n<\/div>\n<p>When determining significant figures, be sure to pay attention to reported values and think about the measurement and significant figures in terms of what is reasonable or likely when evaluating whether the value makes sense. For example, the official January 2014 census reported the resident population of the US as 317,297,725. Do you think the US population was correctly determined to the reported nine significant figures, that is, to the exact number of people? People are constantly being born, dying, or moving into or out of the country, and assumptions are made to account for the large number of people who are not actually counted. Because of these uncertainties, it might be more reasonable to expect that we know the population to within perhaps a million or so, in which case the population should be reported as 3.17 \u00d7 10<sup>8<\/sup> people.<\/p>\n<\/section>\n<section id=\"fs-idm191691888\">\n<h2>Significant Figures in Calculations<\/h2>\n<p id=\"fs-idm277117616\">A second important principle of uncertainty is that results calculated from a measurement are at least as uncertain as the measurement itself. We must take the uncertainty in our measurements into account to avoid misrepresenting the uncertainty in calculated results. One way to do this is to report the result of a calculation with the correct number of significant figures, which is determined by the following three rules for <strong>rounding<\/strong> numbers:<\/p>\n<ol id=\"fs-idm65809616\">\n<li>When we add or subtract numbers, we should round the result to the same number of decimal places as the number with the least number of decimal places (the least precise value in terms of addition and subtraction).<\/li>\n<li>When we multiply or divide numbers, we should round the result to the same number of digits as the number with the least number of significant figures (the least precise value in terms of multiplication and division).<\/li>\n<li>If the digit to be dropped (the one immediately to the right of the digit to be retained) is less than 5, we \u201cround down\u201d and leave the retained digit unchanged; if it is more than 5, we \u201cround up\u201d and increase the retained digit by 1; if the dropped digit <em>is<\/em> 5, we round up or down, whichever yields an even value for the retained digit. (The last part of this rule may strike you as a bit odd, but it\u2019s based on reliable statistics and is aimed at avoiding any bias when dropping the digit \u201c5,\u201d since it is equally close to both possible values of the retained digit.)<\/li>\n<\/ol>\n<p id=\"fs-idm107335696\">The following examples illustrate the application of this rule in rounding a few different numbers to three significant figures:<\/p>\n<ul id=\"fs-idm192081680\">\n<li>0.028675 rounds \u201cup\u201d to 0.0287 (the dropped digit, 7, is greater than 5)<\/li>\n<li>18.3384 rounds \u201cdown\u201d to 18.3 (the dropped digit, 3, is less than 5)<\/li>\n<li>6.8752 rounds \u201cup\u201d to 6.88 (the dropped digit is 5, and the retained digit is even)<\/li>\n<li>92.85 rounds \u201cdown\u201d to 92.8 (the dropped digit is 5, and the retained digit is even)<\/li>\n<\/ul>\n<p id=\"fs-idm178562592\">Let\u2019s work through these rules with a few examples.<\/p>\n<div class=\"textbox shaded\" id=\"fs-idp40552528\">\n<h3>Example 5<\/h3>\n<p id=\"fs-idm303504976\">Round the following to the indicated number of significant figures:<\/p>\n<p id=\"fs-idm277227680\">a) 31.57 (to two significant figures)<\/p>\n<p id=\"fs-idm113120528\">b) 8.1649 (to three significant figures)<\/p>\n<p id=\"fs-idp33608880\">c) 0.051065 (to four significant figures)<\/p>\n<p id=\"fs-idm208861552\">d) 0.90275 (to four significant figures)<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm125552432\"><strong>Solution<\/strong><br \/>\na) 31.57 rounds \u201cup\u201d to 32 (the dropped digit is 5, and the retained digit is even)<\/p>\n<p id=\"fs-idm180680048\">b) 8.1649 rounds \u201cdown\u201d to 8.16 (the dropped digit, 4, is less than 5)<\/p>\n<p id=\"fs-idm167789680\">c) 0.051065 rounds \u201cdown\u201d to 0.05106 (the dropped digit is 5, and the retained digit is even)<\/p>\n<p id=\"fs-idm174540832\">d) 0.90275 rounds \u201cup\u201d to 0.9028 (the dropped digit is 5, and the retained digit is even)<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm185983232\"><strong><em>Test Yourself<\/em><\/strong><br \/>\nRound the following to the indicated number of significant figures:<\/p>\n<p id=\"fs-idm69923072\">a) 0.424 (to two significant figures)<\/p>\n<p id=\"fs-idm65589936\">b) 0.0038661 (to three significant figures)<\/p>\n<p id=\"fs-idm107300848\">c) 421.25 (to four significant figures)<\/p>\n<p id=\"fs-idm258155488\">d) 28,683.5 (to five significant figures)<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Answers<\/em><\/strong><\/p>\n<p>a) 0.42 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 0.00387 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0c) 421.2 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0d) 28,684<\/p>\n<\/div>\n<div class=\"textbox shaded\" id=\"fs-idp61408240\">\n<h3>Example 6<\/h3>\n<p id=\"fs-idm327587104\">Rule: When we add or subtract numbers, we should round the result to the same number of decimal places as the number with the least number of decimal places (i.e., the least precise value in terms of addition and subtraction).<\/p>\n<p>Perform the following calculations taking significant figures into account.<\/p>\n<p id=\"fs-idm318611824\">a) Add 1.0023 g and 4.383 g.<\/p>\n<p id=\"fs-idm288438480\">b) Subtract 421.23 g from 486 g.<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm277651872\"><strong>Solution<\/strong><\/p>\n<p id=\"fs-idm21393952\">a) [latex]\\displaystyle \\begin{array}{r}1.0023 \\text{g} \\\\ +4.383 \\;\\;\\text{g} \\\\ \\hline 5.3853 \\text{g} \\end{array}[\/latex]<\/p>\n<p id=\"fs-idm107330240\">Answer is 5.385 g (round to the thousandths place; three decimal places)<\/p>\n<p id=\"fs-idm257863024\">b) [latex]\\displaystyle \\begin{array}{r}486 \\;\\;\\;\\;\\; \\text{g} \\\\ -421.23 \\text{g} \\\\ \\hline 64.77 \\text{g} \\end{array}[\/latex]<\/p>\n<p id=\"fs-idp47889280\">Answer is 65 g (round to the ones place; no decimal places)<\/p>\n<p><span id=\"fs-idm330284704\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_SigDigits4_img-2.jpg\" alt=\"Figure A shows 1.0023 being added to 4.383 to yield the answer 5.385. 1.0023 goes to the ten thousandths place, but 4.383 goes to the thousandths place, making it the less precise of the two numbers. Therefore the answer, 5.3853, should be rounded to the thousandths, to yield 5.385. Figure B shows 486 grams minus 421.23 grams, which yields the answer 64.77 grams. This answer should be round to the ones place, making the answer 65 grams.\" \/><\/span><\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm97432976\"><strong><i>Test Yourself<\/i><\/strong><\/p>\n<p>a) Add 2.334 mL and 0.31 mL.<\/p>\n<p id=\"fs-idm113279504\">b) Subtract 55.8752 m from 56.533 m.<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Answers<\/em><\/strong><\/p>\n<p>a) 2.64 mL \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b) 0.658 m<\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 7<\/h3>\n<p id=\"ball-ch02_s03_p17\" class=\"para\">Express the final answer to the proper number of significant figures.<\/p>\n<p class=\"para\">a) 101.2 +\u00a018.702 = ?<\/p>\n<p class=\"para\">b) 202.88 \u2212 1.013 = ?<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\n<p class=\"simpara\">a) If we use a calculator to add these two numbers, we would get 119.902. However, most calculators do not understand significant figures, and we need to limit the final answer to the tenths place. Thus, we drop the 02 and report a final answer of 119.9 (rounding down).<\/p>\n<p class=\"simpara\">b) A calculator would answer 201.867. However, we have to limit our final answer to the hundredths place. Because the first number being dropped is 7, which is greater than 7, we round up and report a final answer of 201.87.<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\n<p id=\"ball-ch02_s03_p18\" class=\"para\">Express the answer for 3.445 +\u00a090.83 \u2212 72.4 to the proper number of significant figures.<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answer<\/em><\/strong><\/p>\n<p id=\"ball-ch02_s03_p19\" class=\"para\">21.9<\/p>\n<\/div>\n<div class=\"textbox shaded\" id=\"fs-idp34148976\">\n<h3>Example 8<\/h3>\n<p id=\"fs-idm194335568\">Rule: When we multiply or divide numbers, we should round the result to the same number of digits as the number with the least number of significant figures (the least precise value in terms of multiplication and division).<\/p>\n<p>Perform the following calculations taking significant figures into account.<\/p>\n<p id=\"fs-idm176907440\">a) Multiply 0.6238 cm by 6.6 cm.<\/p>\n<p id=\"fs-idp40092848\">b) Divide 421.23 g by 486 mL.<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm318303792\"><strong>Solution<\/strong><\/p>\n<p id=\"fs-idp11052048\">a) [latex]0.6238 \\text{ cm} \\times 6.6 \\text{ cm} = 4.11708 \\text{ cm}^2 \\rightarrow \\text{result is 4.1} \\text{cm}^2 \\text{(round to two significant figures)} \\\\[0.75em] \\text{four significant figures} \\times \\text{two significant figures} \\rightarrow \\text{two significant figures answer}[\/latex]<\/p>\n<p id=\"fs-idm194468576\">b) [latex]\\frac{421.23 \\text{g}}{486 \\text{mL}}=0.86728 \\dots \\text{g\/mL} \\rightarrow \\text{result is 0.867 g\/mL (round to three significant figures)} \\\\[0.75em] \\frac{\\text{five significant figures}}{\\text{three significant figures}} \\rightarrow \\text{three significant figures answer}[\/latex]<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idp45405152\"><strong><i>Test Yourself<\/i><\/strong><\/p>\n<p>a) Multiply 2.334 cm and 0.320 cm.<\/p>\n<p id=\"fs-idm155228848\">b) Divide 55.8752 m by 56.53 s.<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Answers<\/em><\/strong><\/p>\n<p>a) 0.747 cm<sup>2<\/sup>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b) 0.9884 m\/s<\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 9<\/h3>\n<p id=\"ball-ch02_s03_p22\" class=\"para\">Express the final answer to the proper number of significant figures.<\/p>\n<p class=\"para\">a) 76.4 \u00d7 180.4 = ?<\/p>\n<p class=\"para\">b) 934.9 \u00f7 0.00455 = ?<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong>Solution<\/strong><\/p>\n<p class=\"simpara\">a) The first number has three significant figures, while the second number has four significant figures. Therefore, we limit our final answer to three significant figures: 76.4 \u00d7 180.4 = 13,782.56 = 13,800.<\/p>\n<p class=\"simpara\">b) The first number has four significant figures, while the second number has three significant figures. Therefore we limit our final answer to three significant figures: 934.9 \u00f7 0.00455 = 205,472.5275\u2026 = 205,000.<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis bolditalic\">Test Yourself<\/em><\/strong><\/p>\n<p id=\"ball-ch02_s03_p23\" class=\"para\">Express the final answer to the proper number of significant figures.<\/p>\n<p class=\"para\">a) 22.4 \u00d7 8.314 = ?<\/p>\n<p class=\"para\">b) 1.381 \u00f7 6.02 = ?<\/p>\n<p>&nbsp;<\/p>\n<p class=\"simpara\"><strong><em class=\"emphasis\">Answers<\/em><\/strong><\/p>\n<p class=\"simpara\">a) 186 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b)\u00a00.229<\/p>\n<\/div>\n<p id=\"fs-idp31178224\">In the midst of all these technicalities, it is important to keep in mind the reason why we use significant figures and rounding rules\u2014to correctly represent the certainty of the values we report and to ensure that a calculated result is not represented as being more certain than the least certain value used in the calculation.<\/p>\n<\/section>\n<div id=\"fs-idp86805728\" class=\"textbox shaded\">\n<p><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Interactive_200DPI-1-2.png\" alt=\"\" width=\"138\" height=\"86\" class=\"alignleft\" \/><\/p>\n<p id=\"fs-idm169361696\">Need a refresher or more practice with significant figures? Visit this site (<a href=\"https:\/\/viuvideos.viu.ca\/media\/Significant+Figures\/0_t8xwe4s9\">https:\/\/viuvideos.viu.ca\/media\/Significant+Figures\/0_t8xwe4s9<\/a>)\u00a0to go over the basics of significant figures.<\/p>\n<p>Video source: Significant figures by keyj<\/p>\n<\/div>\n<section id=\"fs-idm191691888\">\n<div class=\"textbox shaded\" id=\"fs-idp40680240\">\n<h3>Example 10<\/h3>\n<p id=\"fs-idm180409728\">One common bathtub is 13.44 dm long, 5.920 dm wide, and 2.54 dm deep. Assume that the tub is rectangular and calculate its approximate volume in liters.<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm209075984\"><strong>Solution<\/strong><\/p>\n<div class=\"equation\" id=\"fs-idm15365184\" style=\"text-align: center\">[latex]\\begin{array}{r @{{}={}} l}V & l \\times w\\times d \\\\ & 13.44 \\text{ dm} \\times 5.920 \\text{ dm} \\times 2.54 \\text{ dm} \\\\ & 202.09459\\dots \\text{ dm}^3 \\text{(value from calculator)} \\\\ & 202 \\text{ dm}^3,\\;\\text{or}\\;202\\text{ L (answer rounded to three significant figures)} \\end{array}[\/latex]<\/div>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm219800928\"><strong><i>Test Yourself<\/i><\/strong><\/p>\n<p>What is the density of a liquid with a mass of 31.1415 g and a volume of 30.13 cm<sup>3<\/sup>?<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Answer<\/em><\/strong><\/p>\n<p>1.034 g\/mL<\/p>\n<\/div>\n<div class=\"textbox shaded\" id=\"fs-idm148976192\">\n<h3>Example 11<\/h3>\n<p id=\"fs-idp29940656\"><strong>Experimental Determination of Density Using Water Displacement<\/strong><br \/>\nA piece of rebar is weighed and then submerged in a graduated cylinder partially filled with water, with results as shown.<\/p>\n<p><span id=\"fs-idm332426528\"><br \/>\n<a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_04_CylRebar-2.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_04_CylRebar-2.jpg\" alt=\"This diagram shows the initial volume of water in a graduated cylinder as 13.5 milliliters. A 69.658 gram piece of metal rebar is added to the graduated cylinder, causing the water to reach a final volume of 22.4 milliliters\" width=\"479\" height=\"364\" class=\"aligncenter\" \/><\/a><\/span><\/p>\n<p id=\"fs-idm245394240\">a) Use these values to determine the density of this piece of rebar.<\/p>\n<p id=\"fs-idm209220496\">b) Rebar is mostly iron. Does your result in (a) support this statement? How?<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm325787440\"><strong>Solution<br \/>\n<\/strong>The volume of the piece of rebar is equal to the volume of the water displaced:<\/p>\n<div class=\"equation\" id=\"fs-idm180698816\" style=\"text-align: center\">[latex]\\text{volume} = 22.4 \\text{mL} - 13.5 \\text{mL} = 8.9 \\text{mL} = 8.9 \\text{cm}^3[\/latex]<\/div>\n<p id=\"fs-idm181276752\">(rounded to the nearest 0.1 mL, per the rule for addition and subtraction)<\/p>\n<p id=\"fs-idp36085040\">The density is the mass-to-volume ratio:<\/p>\n<div class=\"equation\" id=\"fs-idp135143440\" style=\"text-align: center\">[latex]\\text{density} = \\frac{\\text{mass}}{\\text{volume}} = \\frac{69.658 \\text{g}}{8.9 \\text{cm}^3} = 7.8 \\text{g\/cm}^3[\/latex]<\/div>\n<p id=\"fs-idm277303296\">(rounded to two significant figures, per the rule for multiplication and division)<\/p>\n<p id=\"fs-idm243666944\">From <a href=\"https:\/\/opentextbc.ca\/chemistry\/chapter\/measurements\/#fs-idm45639696\" class=\"autogenerated-content\">Table 3 in Chapter 2.2 Measurements<\/a>, the density of iron is 7.9 g\/cm<sup>3<\/sup>, very close to that of rebar, which lends some support to the fact that rebar is mostly iron.<\/p>\n<p>&nbsp;<\/p>\n<p id=\"fs-idm259990592\"><strong><em>Test Yourself<\/em><\/strong><br \/>\nAn irregularly shaped piece of a shiny yellowish material is weighed and then submerged in a graduated cylinder, with results as shown.<\/p>\n<p><span id=\"fs-idm283007920\"><br \/>\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_04_CylGold-2.jpg\" alt=\"This diagram shows the initial volume of water in a graduated cylinder as 17.1 milliliters. A 51.842 gram gold colored rock is added to the graduated cylinder, causing the water to reach a final volume of 19.8 milliliters\" width=\"476\" height=\"363\" class=\"aligncenter\" \/><\/span><\/p>\n<p id=\"fs-idm272657872\">a) Use these values to determine the density of this material.<\/p>\n<p id=\"fs-idm166920160\">b) Do you have any reasonable guesses as to the identity of this material? Explain your reasoning.<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Answers<\/em><\/strong><\/p>\n<p>a) 19 g\/cm<sup>3<\/sup>; (b) It is likely gold; the right appearance for gold and very close to the density given for gold in <a href=\"https:\/\/opentextbc.ca\/chemistry\/chapter\/measurements\/#fs-idm45639696\" class=\"autogenerated-content\">Table 3 in Chapter 2.2 Measurements<\/a>.<\/p>\n<\/div>\n<\/section>\n<section id=\"fs-idp33954960\">\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 12<\/h3>\n<p>Determine the answer and report to the appropriate number of significant figures.<\/p>\n<p>a) What is the area of a card that measures 12.74 cm by 7.60 cm ?<\/p>\n<p>b) What is the total mass when three samples weighing 120.0 g, 24.318 g and 15 g are combined?<\/p>\n<p>c) (3.02 x 10<sup>3<\/sup>) + (4 x 10<sup>2<\/sup>) = ?<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Solution<\/strong><\/p>\n<p>a) The area is width x length. 12.74 cm x 7.60 cm = 96.824 according to a calculator. The 12.74 has 4 significant figures and 7.60 has three significant figures, thus the solution should be reported to 3 significant figures. Don\u2019t forget the units! cm x cm = cm<sup>2<\/sup><\/p>\n<p>The answer is 96.8 cm<sup>2<\/sup><\/p>\n<p>b) When adding, be sure that all units are the same (all g in this case).<br \/>\n0 g + 24.318 g + 15 g = 159.318 g according to a calculator. We must look at the decimal place (or place value). 120.0 is reported to the tenths position, 24.318 to the thousandths position, whereas 15 is reported to the ones position. The ones position is furthest to the left, thus the final answer must be rounded to that position.<\/p>\n<p>The answer is 159 g<\/p>\n<p>c) Be careful! When adding and subtracting, the power of 10 must be the same. If we put them both to 103, we have (3.02 x 10<sup>3<\/sup>) + (0.4 x 10<sup>3<\/sup>). The answer can then be reported to the first decimal place (tenths) when using 10<sup>3<\/sup> (= 3.4 x 10<sup>3<\/sup>). We could also look at the non-scientific notation: 3.02 x 10<sup>3<\/sup> = <strong>302<\/strong>0, and 4 x 10<sup>2<\/sup> = <strong>4<\/strong>00 (sig. figs. in bold, for emphasis). Thus the first number is recorded to the tens position, whereas the second is to the hundreds position. final answer must be reported to the hundreds position.<\/p>\n<p>The answer is 3.4 x 10<sup>3<\/sup><\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Test Yourself<\/em><\/strong><\/p>\n<p>Determine the answer and report to the appropriate number of significant figures.<br \/>\na)\u00a0 17.1 + 0.24 \u2013 241\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 b)\u00a0 (1.32 x 10<sup>4<\/sup>) x (2 x 10<sup>2<\/sup>)<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Answers<\/em><\/strong><\/p>\n<p>a) -224\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 b) 3 x 10<sup>6<\/sup><\/p>\n<\/div>\n<\/section>\n<div class=\"textbox shaded\">\n<h3 class=\"title\">Example 13<\/h3>\n<p>If a bagel has a mass of 28.3162 g when fresh and then a mass of 28.3094 g once dried out, what was the percent of moisture in the fresh bagel?<\/p>\n<p>Where, % moisture = \u00a0 (mass of moisture\/original mass of object) \u00a0x 100% ,<\/p>\n<p>determine the solution and report to the appropriate number of significant figures.<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Solution<\/strong><\/p>\n<p>To determine the mass of moisture, we must subtract the dried mass from the original mass:<br \/>\n28.3162 g \u2013 28.3094 g =\u00a0 0.0068 g. Note that if the question stopped here, the answer would be reported to the 4th decimal place, and has two significant figures.<\/p>\n<p>The next step involves division:\u00a0\u00a0\u00a0<span style=\"text-decoration: underline\"> 0.0068 g<\/span> \u00a0\u00a0\u00a0x\u00a0 100%\u00a0 = 0.0240145\u2026%<br \/>\n28.3162 g<\/p>\n<p>The value 0.0068 g has 2 significant figures, 28.3162 g has 6 significant figures, and 100% as used here is an exact number, so the final answer can only be reported to 2 significant figures.<\/p>\n<p>Thus the solution is rounded to 0.024% (or 2.4 x 10<sup>-2<\/sup>%, in scientific notation)<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Test Yourself<\/em><\/strong><\/p>\n<p>If a jogger runs for 2.0 hrs at 12.21 km\/hr, then again for another 2.0 hrs at 12.16 km\/hr, how far did she run in total?<br \/>\n(Determine the solution and report to the appropriate number of significant figures.)<\/p>\n<p>&nbsp;<\/p>\n<p><strong><em>Answer<\/em><\/strong><\/p>\n<p>49 km<\/p>\n<\/div>\n<section id=\"fs-idp33954960\">\n<h2>Accuracy and Precision<\/h2>\n<p id=\"fs-idp4474304\">Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to know both the <strong>precision<\/strong> and the <strong>accuracy<\/strong> of their results. Measurements are said to be precise if they yield very similar results when repeated in the same manner. A measurement is considered accurate if it yields a result that is very close to the true or accepted value. Precise values agree with each other; accurate values agree with a true value. These characterizations can be extended to other contexts, such as the results of an archery competition (<a href=\"#fs-idm1827280\" class=\"autogenerated-content\">Figure 3<\/a>).<\/p>\n<figure id=\"fs-idm1827280\">\n<figure style=\"width: 1300px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_Archery-2.jpg\" alt=\"Figures A through C each show targets with holes where the arrows hit. The archer in figure A was both accurate and precise as all 3 arrows are clustered in the center of the target. In figure B, the archer is precise but not accurate, as all 3 arrows are clustered together but to the upper right of the center of the target. In Figure C, the archer is neither accurate nor precise as the 3 holes are not close together and are located both to the upper right and right of the target.\" width=\"1300\" height=\"414\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 3.<\/strong> (a) These arrows are close to both the bull\u2019s eye and one another, so they are both accurate and precise. (b) These arrows are close to one another but not on target, so they are precise but not accurate. (c) These arrows are neither on target nor close to one another, so they are neither accurate nor precise.<\/figcaption><\/figure>\n<\/figure>\n<p id=\"fs-idp174984224\">Suppose a quality control chemist at a pharmaceutical company is tasked with checking the accuracy and precision of three different machines that are meant to dispense 10 ounces (296 mL) of cough syrup into storage bottles. She proceeds to use each machine to fill five bottles and then carefully determines the actual volume dispensed, obtaining the results tabulated in <a href=\"#fs-idp31780400\" class=\"autogenerated-content\">Table 1<\/a>.<\/p>\n<table id=\"fs-idp31780400\" class=\"span-all\" summary=\"The volume, in milliliters, of cough medicine delivered by dispensers 1, 2 and 3 are shown in a table. The values for dispenser 1 are 283.3, 284.1, 283.9, 284.0, and 284.1. The values for dispenser 2 are 298.3, 294.2, 296.0, 297.8, and 293.9. The values for dispenser 3 are 296.1, 295.9, 296.1, 296.0, and 296.1.\">\n<thead>\n<tr valign=\"top\">\n<th>Dispenser #1<\/th>\n<th>Dispenser #2<\/th>\n<th>Dispenser #3<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td>283.3<\/td>\n<td>298.3<\/td>\n<td>296.1<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>284.1<\/td>\n<td>294.2<\/td>\n<td>295.9<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>283.9<\/td>\n<td>296.0<\/td>\n<td>296.1<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>284.0<\/td>\n<td>297.8<\/td>\n<td>296.0<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>284.1<\/td>\n<td>293.9<\/td>\n<td>296.1<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td colspan=\"3\"><strong>Table 1.<\/strong> Volume (mL) of Cough Medicine Delivered by 10-oz (296 mL) Dispensers<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p id=\"fs-idp4939264\">Considering these results, she will report that dispenser #1 is precise (values all close to one another, within a few tenths of a milliliter) but not accurate (none of the values are close to the target value of 296 mL, each being more than 10 mL too low). Results for dispenser #2 represent improved accuracy (each volume is less than 3 mL away from 296 mL) but worse precision (volumes vary by more than 4 mL). Finally, she can report that dispenser #3 is working well, dispensing cough syrup both accurately (all volumes within 0.1 mL of the target volume) and precisely (volumes differing from each other by no more than 0.2 mL).<\/p>\n<\/section>\n<section id=\"fs-idp223627024\" class=\"summary\">\n<h2>Key Concepts and Summary<\/h2>\n<p id=\"fs-idp108718096\">Quantities can be exact or measured. Measured quantities have an associated uncertainty that is represented by the number of significant figures in the measurement. The uncertainty of a calculated value depends on the uncertainties in the values used in the calculation and is reflected in how the value is rounded. Measured values can be accurate (close to the true value) and\/or precise (showing little variation when measured repeatedly).<\/p>\n<\/section>\n<div class=\"qandaset block\" id=\"ball-ch02_s03_qs01\">\n<div class=\"bcc-box bcc-info\">\n<h3>Exercises<\/h3>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p1\" class=\"para\">1. Express each measurement to the correct number of significant figures.<\/p>\n<p><a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM.png\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM.png\" alt=\"\" width=\"617\" height=\"241\" class=\"aligncenter wp-image-4642 size-full\" srcset=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM.png 617w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM-300x117.png 300w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM-65x25.png 65w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM-225x88.png 225w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.53.58-PM-350x137.png 350w\" sizes=\"auto, (max-width: 617px) 100vw, 617px\" \/><\/a><\/p>\n<p class=\"para\"><span style=\"font-size: 1em\">2. Express each measurement to the correct number of significant figures.<\/span><\/p>\n<p><a href=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM.png\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM.png\" alt=\"\" width=\"617\" height=\"235\" class=\"aligncenter size-full wp-image-4643\" srcset=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM.png 617w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM-300x114.png 300w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM-65x25.png 65w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM-225x86.png 225w, https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/Screen-Shot-2018-06-14-at-1.54.47-PM-350x133.png 350w\" sizes=\"auto, (max-width: 617px) 100vw, 617px\" \/><\/a><\/p>\n<\/div>\n<div class=\"question\">\n<p class=\"para\"><span style=\"font-size: 1em\">3. How many significant figures do these numbers have?<\/span><\/p>\n<\/div>\n<p>a) \u00a023 \u00a0 \u00a0\u00a0b) \u00a023.0 \u00a0 \u00a0\u00a0c) \u00a00.00023 \u00a0 \u00a0\u00a0d) \u00a00.0002302<\/p>\n<p>4. \u00a0How many significant figures do these numbers have?<\/p>\n<p>a) \u00a05.44 \u00d7 10<sup class=\"superscript\">8 \u00a0 \u00a0\u00a0<\/sup>b) \u00a01.008 \u00d7 10<sup class=\"superscript\">\u22125 \u00a0 \u00a0\u00a0<\/sup>c) \u00a043.09 \u00a0 \u00a0\u00a0d) \u00a00.0000001381<\/p>\n<p>5. \u00a0How many significant figures do these numbers have?<\/p>\n<p>a) \u00a0765,890 \u00a0 \u00a0\u00a0b) \u00a0765,890.0 \u00a0 \u00a0\u00a0c) \u00a01.2000 \u00d7 10<sup class=\"superscript\">5 \u00a0 \u00a0\u00a0<\/sup>d) \u00a00.0005060<\/p>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p6\" class=\"para\">6) \u00a0How many significant figures do these numbers have?<\/p>\n<p>a) \u00a00.009 \u00a0 \u00a0\u00a0b) \u00a00.0000009 \u00a0 \u00a0\u00a0c) \u00a065,444 \u00a0 \u00a0\u00a0d) \u00a065,040<\/p>\n<\/div>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p7\" class=\"para\">7. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\n<p>a) \u00a056.0 +\u00a03.44 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0b) \u00a00.00665 +\u00a01.004 = ?<\/p>\n<p>c) \u00a045.99 \u2212 32.8 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0d) \u00a045.99 \u2212 32.8 +\u00a075.02 = ?<\/p>\n<\/div>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p8\" class=\"para\">8. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\n<p>a) \u00a01.005 +\u00a017.88 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0b) \u00a056,700 \u2212 324 = ?<\/p>\n<p>c) \u00a0405,007 \u2212 123.3 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0d) \u00a055.5 +\u00a066.66 \u2212 77.777 = ?<\/p>\n<\/div>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p9\" class=\"para\">9. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\n<p>a) \u00a056.7 \u00d7 66.99 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0b) \u00a01.000 \u00f7 77 = ?<\/p>\n<p>c) \u00a01.000 \u00f7 77.0 = ? \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0d) \u00a06.022 \u00d7 1.89 = ?<\/p>\n<\/div>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p10\" class=\"para\">10. \u00a0Compute and express each answer with the proper number of significant figures, rounding as necessary.<\/p>\n<p>a) \u00a00.000440 \u00d7 17.22 = ? \u00a0 \u00a0 \u00a0 \u00a0 b) \u00a0203,000 \u00f7 0.044 = ?<\/p>\n<p>c) \u00a067 \u00d7 85.0 \u00d7 0.0028 = ? \u00a0 \u00a0 \u00a0\u00a0d) \u00a0999,999 \u00f7 3,310 = ?<\/p>\n<\/div>\n<div class=\"question\">\n<p>11. \u00a0Write the number 87,449 in scientific notation with four significant figures.<\/p>\n<p>12. \u00a0Write the number 0.000066600 in scientific notation with five significant figures.<\/p>\n<\/div>\n<div class=\"question\">\n<p>13. \u00a0Write the number 306,000,000 in scientific notation to the proper number of significant figures.<\/p>\n<p>14. \u00a0Write the number 0.0000558 in scientific notation with two significant figures.<\/p>\n<\/div>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p13\" class=\"para\">15. \u00a0Perform each calculation and limit each answer to three significant figures.<\/p>\n<p>a) \u00a067,883 \u00d7 0.004321 = ?<\/p>\n<p>b) \u00a0(9.67 \u00d7 10<sup class=\"superscript\">3<\/sup>) \u00d7 0.0055087 = ?<\/p>\n<\/div>\n<div class=\"question\">\n<p id=\"ball-ch02_s03_qs01_p14\" class=\"para\">16. \u00a0Perform each calculation and limit each answer to four significant figures.<\/p>\n<p>a) \u00a018,900 \u00d7 76.33 \u00f7 0.00336 = ?<\/p>\n<p>b) \u00a00.77604 \u00f7 76,003 \u00d7 8.888 = ?<\/p>\n<p><span style=\"font-size: 1em\">17. \u00a0Express each of the following numbers in exponential notation with correct significant figures:<\/span><\/p>\n<\/div>\n<p id=\"fs-idp158645376\">a) 704 \u00a0 \u00a0\u00a0b) 0.03344 \u00a0 \u00a0\u00a0c) 547.9 \u00a0 \u00a0\u00a0d) 22086 \u00a0 \u00a0\u00a0e) 1000.00 \u00a0 \u00a0\u00a0f) 0.0000000651 \u00a0 \u00a0\u00a0g) 0.007157<\/p>\n<p>18. \u00a0Indicate whether each of the following can be determined exactly or must be measured with some degree of uncertainty:<\/p>\n<p id=\"fs-idp192668592\">a) the number of seconds in an hour<\/p>\n<p id=\"fs-idp131489888\">b) the number of pages in this book<\/p>\n<p id=\"fs-idp29050000\">c) the number of grams in your weight<\/p>\n<p id=\"fs-idp40603568\">d) the number of grams in 3 kilograms<\/p>\n<p id=\"fs-idp42867296\">e) the volume of water you drink in one day<\/p>\n<p id=\"fs-idp5273504\">f) the distance from San Francisco to Kansas City<\/p>\n<p>19. \u00a0How many significant figures are contained in each of the following measurements?<\/p>\n<p id=\"fs-idp191599120\">a) 53 cm \u00a0 \u00a0\u00a0b) 2.05 \u00d7 10<sup>8<\/sup> m \u00a0 \u00a0\u00a0c) 86,002 J \u00a0 \u00a0\u00a0d) 9.740 \u00d7 10<sup>4<\/sup> m\/s \u00a0 \u00a0\u00a0e) 10.0613 m<sup>3<\/sup><\/p>\n<p id=\"fs-idp115902336\">f) 0.17 g\/mL \u00a0 \u00a0\u00a0g) 0.88400 s<\/p>\n<p>20. \u00a0Round off each of the following numbers to two significant figures:<\/p>\n<p id=\"fs-idp367138576\">a) 0.436 \u00a0 \u00a0\u00a0b) 9.000 \u00a0 \u00a0\u00a0c) 27.2 \u00a0 \u00a0\u00a0d) 135 \u00a0 \u00a0\u00a0e) 1.497 \u00d7 10<sup>\u22123 \u00a0 \u00a0\u00a0<\/sup>f) 0.445<\/p>\n<p>21. \u00a0Perform the following calculations and report each answer with the correct number of significant figures.<\/p>\n<p id=\"fs-idp101772784\">a) 628 \u00d7 342 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0b) (5.63 \u00d7 10<sup>2<\/sup>) \u00d7 (7.4 \u00d7 10<sup>3<\/sup>)<\/p>\n<p id=\"fs-idp43333760\">c) [latex]\\frac{28.0}{13.483}[\/latex] \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0d) 8119 \u00d7 0.000023<\/p>\n<p id=\"fs-idp2544704\">e) 14.98 + 27,340 + 84.7593 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0f) 42.7 + 0.259<\/p>\n<p>22. \u00a0Consider the results of the archery contest shown in this figure.<\/p>\n<p id=\"fs-idp29005776\">a) Which archer is most precise?<\/p>\n<p id=\"fs-idp32003568\">b) Which archer is most accurate?<\/p>\n<p id=\"fs-idp110085200\">c) Who is both least precise and least accurate?<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" id=\"fs-idp94481888\" src=\"https:\/\/pressbooks.bccampus.ca\/chem1114langaracollege\/wp-content\/uploads\/sites\/387\/2018\/04\/CNX_Chem_01_05_Archer2_img-2.jpg\" alt=\"4 targets are shown each with 4 holes indicating where the arrows hit the targets. Archer W put all 4 arrows closely around the center of the target. Archer X put all 4 arrows in a tight cluster but far to the lower right of the target. Archer Y put all 4 arrows at different corners of the target. All 4 arrows are very far from the center of the target. Archer Z put 2 arrows close to the target and 2 other arrows far outside of the target.\" width=\"1200\" height=\"463\" class=\"alignnone\" \/><\/p>\n<p>&nbsp;<\/p>\n<p><b>Answers<\/b><\/p>\n<p>1. \u00a0a) \u00a0375 psi \u00a0 \u00a0\u00a0b) \u00a01.30 cm<\/p>\n<p>2. \u00a0a) 32.4 psi \u00a0 \u00a0 b) 0.90 cm<\/p>\n<p>3. \u00a0a) \u00a0two \u00a0 \u00a0\u00a0b) \u00a0three \u00a0 \u00a0\u00a0c) \u00a0two \u00a0 \u00a0\u00a0d) \u00a0four<\/p>\n<p>4. \u00a0a) \u00a0three \u00a0 b) \u00a0four \u00a0 \u00a0 \u00a0c) \u00a0four \u00a0 \u00a0 d) \u00a0four<\/p>\n<p>5. \u00a0a) \u00a0five \u00a0 \u00a0\u00a0b) \u00a0seven \u00a0 \u00a0\u00a0c) \u00a0five \u00a0 \u00a0\u00a0d) \u00a0four<\/p>\n<p>6. \u00a0a) \u00a0one \u00a0 \u00a0 b) \u00a0one \u00a0 \u00a0 \u00a0 \u00a0c) \u00a0five \u00a0 \u00a0 \u00a0d) four<\/p>\n<p>7.<strong> \u00a0<\/strong>a) \u00a059.4 \u00a0 \u00a0\u00a0b) \u00a01.011 \u00a0 \u00a0\u00a0c) \u00a013.2 \u00a0 \u00a0\u00a0d) \u00a088.2<\/p>\n<p>8. \u00a0a) \u00a018.88 \u00a0 b) \u00a056,400 \u00a0 \u00a0c) \u00a0404,884 \u00a0 d) \u00a044.4<\/p>\n<p>9. \u00a0a) \u00a03.80 \u00d7 10<sup class=\"superscript\">3 \u00a0 \u00a0\u00a0<\/sup>b) \u00a00.013 \u00a0 \u00a0\u00a0c) \u00a00.0130 \u00a0 \u00a0\u00a0d) \u00a011.4<\/p>\n<p>10. \u00a0a) \u00a00.00758 \u00a0 \u00a0 \u00a0b) \u00a04,600,000 \u00a0 \u00a0 c) \u00a016 \u00a0 \u00a0 d) \u00a0302<\/p>\n<p>11. \u00a08.745 \u00d7 10<sup class=\"superscript\">4 \u00a0 \u00a0<\/sup><\/p>\n<p>12. \u00a06.6600 x 10<sup class=\"superscript\">\u22125<\/sup><\/p>\n<p>13. \u00a03.06 x 10<sup>8<\/sup><\/p>\n<p>14. \u00a05.6 x 10<sup>-5<\/sup><\/p>\n<p>15. \u00a0a) \u00a0293 \u00a0 \u00a0\u00a0b) \u00a053.3<\/p>\n<p id=\"fs-idp28073776\">16. \u00a0a) \u00a04.294 x 10<sup>8<\/sup> \u00a0 \u00a0 \u00a0b) \u00a09.060&#215;10<sup>-5<\/sup><\/p>\n<p>17. \u00a0a) 7.04 \u00d7 10<sup>2 \u00a0 \u00a0 \u00a0<\/sup>b) 3.344 \u00d7 10<sup>\u22122 \u00a0 \u00a0 \u00a0<\/sup>c) 5.479 \u00d7 10<sup>2 \u00a0 \u00a0 \u00a0<\/sup>d) 2.2086 \u00d7 10<sup>4 \u00a0 \u00a0 \u00a0<\/sup>e) 1.00000 \u00d7 10<sup>3 \u00a0 \u00a0 \u00a0<\/sup>f) 6.51 \u00d7 10<sup>\u22128<\/sup>\u00a0g) 7.157 \u00d7 10<sup>\u22123<\/sup><\/p>\n<p id=\"fs-idp120430064\">18. \u00a0a) exact \u00a0 \u00a0 \u00a0b) exact \u00a0 \u00a0 \u00a0c) uncertain \u00a0 \u00a0 \u00a0d) exact \u00a0 \u00a0 \u00a0e) uncertain \u00a0 \u00a0 \u00a0f) uncertain<\/p>\n<p id=\"fs-idm1331360\">19. \u00a0a) two \u00a0 \u00a0 \u00a0b) three \u00a0 \u00a0 \u00a0c) five \u00a0 \u00a0 \u00a0d) four \u00a0 \u00a0 \u00a0e) six \u00a0 \u00a0 \u00a0f) two \u00a0 \u00a0 \u00a0g) five<\/p>\n<p id=\"fs-idp133316128\">20. \u00a0a) 0.44 \u00a0 \u00a0 \u00a0b) 9.0 \u00a0 \u00a0 \u00a0c) 27 \u00a0 \u00a0 \u00a0d) 140 \u00a0 \u00a0 \u00a0e) 1.5 \u00d7 10<sup>\u22123 \u00a0 \u00a0 \u00a0<\/sup>f) 0.44<\/p>\n<p id=\"fs-idp42820064\">21. \u00a0a) 2.15 \u00d7 10<sup>5 \u00a0 \u00a0 \u00a0<\/sup>b) 4.2 \u00d7 10<sup>6 \u00a0 \u00a0 \u00a0<\/sup>c) 2.08 \u00a0 \u00a0 \u00a0d) 0.19 \u00a0 \u00a0 \u00a0e) 27,440 \u00a0 \u00a0 \u00a0f) 43.0<\/p>\n<p id=\"fs-idp27840096\">22. \u00a0a) Archer X \u00a0 \u00a0 \u00a0b) Archer W \u00a0 \u00a0 \u00a0c) Archer Y<\/p>\n<\/div>\n<\/div>\n<div>\n<h2>Glossary<\/h2>\n<p><strong>accuracy:\u00a0<\/strong>how closely a measurement aligns with a correct value<\/p>\n<p><strong>exact number:\u00a0<\/strong>number derived by counting or by definition<\/p>\n<p><strong>precision:\u00a0<\/strong>how closely a measurement matches the same measurement when repeated<\/p>\n<p><strong>rounding:\u00a0<\/strong>procedure used to ensure that calculated results properly reflect the uncertainty in the measurements used in the calculation<\/p>\n<p><strong>significant figures:\u00a0<\/strong>(also, significant digits) all of the measured digits in a determination, including the uncertain last digit<\/p>\n<p><strong>uncertainty:\u00a0<\/strong>estimate of amount by which measurement differs from true value<\/p>\n<\/div>\n","protected":false},"author":330,"menu_order":4,"template":"","meta":{"pb_show_title":"on","pb_short_title":"2.3 Measurement Uncertainty, Accuracy, and 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