1. Chemistry 3.1 Uncertainty in Measurements

2. I. Accuracy, Precision, & Error A. Accuracy – how close a measurement comes to the “true value”. 1. Ex: Throwing Darts true value = bull's-eye

3. B. Precision – how close a series of measurements are together. 1. Ex: Throwing Darts

4. C. Pg. 64 Explanation Poor Accuracy Good Precision Good Accuracy Good Precision Poor Accuracy Poor Precision

5. D. Error – the difference between the accepted value and the experimental value. 1. Formula – 2. Error = ex. value – accepted value | error | accepted value

6. E. Examples 1. In class you determine the melting point of salt is 755 deg C. The actual value is 805 deg C. What is your percent error?  [|755 - 805| / 805] x 100 =  6.2% error

7. II. Significant Figures A. Def – all digits known plus one estimated one. 1. Measurements must be recorded with significant figures.

8. 2. Rules (pg.66) -All other numbers are significant -zeros may or may not be significant -leading zeros are not significant  0.021 (sig fig) -captive zeros are significant  0.02033 (sig figs) -trailing zeros following the decimal point are significant  0.02030? (sig figs)  200 ? (sig figs)  200.0? (sig figs) 4 1 4

9. 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

10. 4. Scientific Notation + Sig figs A. All #’s in scientific notation are counted as significant figures. B. Ex: 3.0200 x 10 3 = sig figs 2.77 x 10 6 = sig figs 5 3

11. 5. Adding and subtracted A. The answer must not contain any sig figs beyond the place value common to all #’s B. Ex: 4.8 + 2.015 6.8 (not 6.815)

12. 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)

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