Part 19 of Chapter 1 in Chemistry

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"When you do calculations involving numbers that do not have the same number of significant figures in each, it is important to keep these two rules in mind. In multiplication and division, a simple rule that usually holds is that the number of significant figures in a product or a quotient obtained from manipulating figures of measured quantities is the same as the number of significant figures in the quantity having the smaller number of significant figures. Example 1 4.29 cm x 3.24 cm = Solution: Unrounded answer = 13.8996 cm to the 2 Answer rounded to the correct number of significant figures=13.9 cm to the 2 Both measured quantities have three significant figures. Therefore, the answer should be rounded to three significant figures. Example 2 4.29cm x 3.2cm= Solution: Unrounded answer = 13.728 cm to the 2 Answer rounded to the correct number of significant figures=14cm to the 2 One of the measured quantities has only two significant figures. Therefore, the answer should be rounded to two significant figures. Example 3 8.47 cm to the 2/4.26 cm = Solution: Unrounded answer = 1.9882629 cm. Answer rounded to the correct number of significant figures= 1.99 cm. Both measured quantities have three significant figures. Therefore, the answer should be rounded to three significant figures. In addition, and subtraction, the simple rule is that when adding or subtracting measured quantities, the sum or difference should be rounded to the same number of decimal places as in the quantity having the least number of decimal places. Example 1 3.56 cm + 2.6 cm + 6.12 cm = Solution: Unrounded answer = 12.28 cm. Answer rounded to the correct number of significant figures =12.3 cm. one of the quantities added has only one decimal place, Therefore, the answer should be rounded to only one decimal place. Example 2 3.514 cm -2.13 cm = Solution: Unrounded answer = 1.384 cm. Answer rounded to the correct number of significant figures = 1.38 cm. One of the quantities has only two decimal places so the answer should be rounded to two decimal places." Chapter Summary and Internet Resources will be the last lesson given before the Review Questions and Answers to be given next Friday of Chapter 1.