sigfigs02 - CHM 235 - Dr. Skrabal Significant Figures...

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Significant Figures • Definition: Minimum # of digits needed to express a number in scientific notation without a loss of accuracy • Example: Partial pressure of CO 2 in atmosphere 0.000356 atm. This number has 3 sig. figs., but leading zeros are only place-keepers and can cause some confusion. So express in scientific notation: 3.56 x 10 -4 atm This is much less ambiguous, as the 3 sig. figs. are clearly shown. CHM 235 - Dr. Skrabal
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Avoiding ambiguity • Consider the quantity 1000 g . A little ambiguous—how many sig. figs. are intended to be in this number? 1.000 x 10 3 g (4 sf) 1.00 x 10 3 g (3 sf) 1.0 x 10 3 g (2 sf) 1 x 10 3 g (1 sf) • Using scientific notation takes away the ambiguity.
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Rules for using sig. figs. in calculations • Addition and Subtraction – Answer goes to the same decimal place as the individual number containing the fewest number of sig. figs. to the right of decimal point. Example of addition: Formula weight of PbS: 207.2 + 32.066 = 239.266 b round to 239.3 Example of subtraction: 4.5237 – 1.06 = 3.4637 b round to 3.46
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sigfigs02 - CHM 235 - Dr. Skrabal Significant Figures...

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