1. Honors Chemistry 1.6 Working with Numbers

2. I. Significant Figures/Digits A. Def – all digits known plus one estimated one. 1. Measurements must have sig figs. 2. Be as accurate as you can.

3. 2. Rules (pg.25-26) #1 All other/non-zero numbers are significant a. ex: 1,4,7… #2 Zeros may or may not be significant… a. leading zeros are not significant  0.0021 (sig fig) b. captive zeros are significant  2033 (sig figs)

4. c. After any non-zero number, trailing zeros following the decimal point are significant.  0.02030? (sig figs)  2.000? (sig figs) d. Zeros that set the decimal point are not significant.  470,000? (sig figs)  12,345,000 ? (sig figs) e. Zeros that show accuracy are significant.  470,000.? (sig figs)  12,345,000. ? (sig figs)  4.00? (sig figs) 4 4 2 5 6 8 3

5. 3. Rounding with Sig Figs -Express the following #’s to 3 sig figs  421798.076 = 422,000  0.00099985 =.00100  1 = 1.00  8222 = 8,220  0.42 =.420

6. 4. Scientific Notation + Sig figs A. All #’s in the coefficient are counted as significant. B. Ex: 3.0200 x 10 3 = sig figs 5

7. 5. Adding and subtracting A. The answer should be rounded to the same number of decimal places as the measurement with the least number of decimal places. B. Ex: 14.816 + 2.3 17.1 (not 17.116)

8. 6. Multiplication and Division A. The answer must not contain more sig figs than the least # of sig figs. B. Ex:3.1 x 4.01 12 (not 12.431)

9. II. Percent Error Formula This number never counts towards sig figs

10. B. Examples 1. In class you determine the melting point of salt is 755 deg C. The actual value is 805.05 deg C. What is your percent error?  [|755 – 805.05| / 805.05] x 100 =  6.2% error

11. In Class Problems 1. How many sig figs? a. 123 metersb. 30.0 meters c. 40,506 kgd. 6.455 x 10 3 kg 2. a. 3.45 + 9.001 b. 4.22 - 9.0 3. a. 3.4 x 5.345 b. 10.7 / 12.75 4. 6.33 x 10 3 + 5.1 x 10 4

12. In Class Answers: 1. a) 3 b) 3 c) 5 d) 4 2. a) 12.45 b) -4.8 3. a) 18 b) 0.839 4. 57000