1. Chemistry 100 Significant Figures

2. Rules for Significant Figures  Zeros used to locate decimal points are NOT significant. e.g., 0.5 kg = 5. X 10 2 g  1 sig. fig.  What if the measurement was 500 g? 5 x 10 2 g1 sig. fig. 5.0 x 10 2 g2 sig. figs. 5.00 x 10 2 g3 sig. figs.

3.  Certain values are exact (e.g., from definitions) 1 kg = 1000.00000……… g exactly 1 s = 1000.0000 …………. ms exactly 1 cal = 4.18400000 ……… J exactly.

4. Addition and Subtraction Operations.  Results from +, - operations should be reported to the same number of decimal places as that of the least precise term. 12.37+ 10.7 = 23.07 (calculator) 12.37  2 places after the decimal. 10.7  1 place after the decimal. Final answer must have only 1 place after the decimal = 23.1

5. Multiplication and Division Operations  Results from x,  operations should be rounded off to the same number of significant figures possessed by the least precise term. 0.80 x 217.81 = 174.248 0.80  2 sig. figs. 217.81  5 sig. figs. Final answer can only possess 2 sig. figs. = 1.7 x 10 2

6. Carrying digits through a long calculation  Example: 129 / 13.76 + 10.1 = 9.375 + 10.1 = 19.475 = 19.5  Usually carry an extra digit through the calculations, then round off the final answer according to the significant figure rules.