Significant Figures, Precision, and Accuracy!

Precision vs. Accuracy

• Accuracy-Refers to how

closely a measured value agrees with the correct value

• Precision-Refers to how

closely individual measurements agree with each other

Describe the following in terms of precision and/or accuracy…

• Scenario #1: A chemistry student uses a graduated cylinder to measure the volume of a liquid and found the measurement to be 20.1 mL. The actual measurement was 27.3 mL.

• Scenario #2: A man practices his dart throws in attempt to hit the bulls-eye! Here are his results:

Determining the number of sig. figs. in a number

• Picture a map of the U.S….

• If a decimal point is present in a number, count from the Pacific side.• Start counting with the first nonzero digit.• All digits from here to the end, including zeros, are significant.

Examples:

0.00682 Answer: 3

1.0 Answer: 2

60. Answer: 2

1.0 x 102 Answer: 2

• If the decimal point is absent, start counting from the Atlantic side.

• Start with the first nonzero digit.• All digits from here to the end,

including zeros, are significant.

Examples:Answer: 1

603 Answer: 3

6030 Answer: 3

60

Sig Fig Assignment:

• On a piece of notebook paper, copy the following numbers down, then indicate how many significant figures each number has:

a. 32 f. 310 002b. 32.0 g. 0.0048c. 45.1 h. 24.90d. 0.000045 i. 5.01e. 290 000 j. 34.00