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# Precision vs. Accuracy for Physical Properties

APCHEM-WSLUX3

Two students are working on an AP Chemistry lab. Their assignment is to determine experimentally the density of a nonvolatile organic liquid, limonene. The accepted value for the density of limonene is 0.8422 g/mL. Each student conducts three separate density determinations and then calculates a mean (average) value for the density and the standard deviation for their three trials.

The results and calculations for each student are shown in the table below.

Student A Student B
Density #1 0.8421 g/mL 0.8408 g/mL
Density #2 0.8514 g/mL 0.8502 g/mL
Density #3 0.8355 g/mL 0.8332 g/mL
Mean Density 0.8430 g/mL O.8414 g/mL
Standard Deviation 0.0080 0.0085

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Of the four descriptions given below, which of the following BEST interprets the accuracy and precision of Student A and Student B?

A

Student A and Student B are equally accurate, but Student A has more precise results.

B

Student A and Student B are equally accurate, but Student B has more precise results.

C

Student A and Student B have equal accuracy and equal precision.

D

Student A has more accurate and more precise results than Student B.