Significant Figures

Significant Figures - CHEM 130 Fall 2007 - A. Bazell...

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CHEM 130 Fall 2007 - A. Bazell 1 Significant Figures all of the numbers in a measurement (the ones we are certain about, plus the first uncertain number) Rules for counting SF: 1) Some numbers have infinite number of SF • counted numbers 89 students • definitions 1000 m = 1 km • “exact numbers” 2.54 cm = 1 in 2) Nonzero integers are always significant: 1,256 = 4 SF’s 3) Zeros: a) Captured zeros (between other digits) are always significant: 1006 = 4 SF’s b) Leading zeros (preceding other digits) are never significant: 0.039 = 2 SF’s c) Trailing zeros (to the right of other digits) can be ambiguous. Trailing zeroes are significant only if the value includes a decimal point, or a dotted line separating significant from nonsignificant digits: 1,420 = 3 SF's 1,420 M = 4 SF's 1,410.0 = 5 SF's 10,000 = 1 SF's 10 M 000 = 2 SF's 10,0 M 00 = 3 SF's 10,00 M 0 = 4 SF's 10,000 M = 5 SF's 10,000.0 = 6 SF's Rules for calculating with SF: Rule 1) Addition, subtraction, averages: Look at the decimal place. 251.322 + 3.1 254.4 M 22 = 254.4 Rule 2) Multiplying or dividing: Count the number of SF (2.5631)(1.12) = 2.870672 = 2.87 Rules for rounding off numbers: 1) If the digit to be dropped is less than 5, simply drop the digit. 8.92
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Significant Figures - CHEM 130 Fall 2007 - A. Bazell...

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