# 2.7 Accuracy And Precision

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| By Harry Brielmann
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Harry Brielmann
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Although rarely used properly in everyday conversation, accuracy and precision are not the same things. Learn the difference here.

For scientists, accuracy and precision are very different and can be very confusing. Accuracy is the correctness of your answer meaning the closeness of your data to the accepted value by chemists, usually accessible online somewhere. When you're thinking accuracy, think percent error.
Precision regards the consistency of your results. This is the reason we always do Read moremore than one trial of an experiment, to determine precision. When thinking precision, compare it to the average of your results. If all of your numeric results are pretty close to the average, then you were precise in your experiment, meaning you conducted it the same way for each trial. When thinking precision, also consider significant figures. Try to record data to the most significant figures to ensure precision. More decimal places is more precise, which is why, when looking for precise results, you should measure with a graduated cylinder instead of a beaker because it gives you more decimal places.

• 1.

### My watch says it is 9:00 exactly and my iPod says 12:52.  The atomic clock says it is 3:33 exactly.  Are these two times accurate, precise, or neither?

• A.

Accurate

• B.

Precise

• C.

Neither

C. Neither
Explanation
They are not accurate because they are not reasonably close to the actual time. They are not precise because they are not consistent.

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• 2.

### My watch and an atomic clock which is never wrong both say 3:34.  My friend's watch says 3:34 also.  In relation to the atomic clock, are my friend and my watches

• A.

Accurate?

• B.

Precise?

• C.

Both?

• D.

Neither?

C. Both?
Explanation
The watches are accurate because they agree with a trustworthy source, the atomic clock. They are precise because they are consistent, and they read similar times.

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• 3.

### I want to measure exactly 24.53 mL of hydrochloric acid.  Which of the following would give me the best precision in my measurement?

• A.

Using a beaker that is labeled every 25 mL

• B.

Using a graduated cylinder that measures to the nearest tenth of a mL

• C.

Using a cracked old bottle and spilling some in the process

B. Using a graduated cylinder that measures to the nearest tenth of a mL
Explanation
The graduated cylinder with 0.1 mL markings is the most precise because the volume would be exact give or take .01mL. A beaker with 25 mL markings would be less precise because the volume would be variable by a greater amount. The fewer decimal places measured, the less precision.

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• 4.

### If you want a result to be accurate, then you are looking for it to be reasonably close to __________.

• A.

Results from other trials that you conducted

• B.

The value accepted by professional chemists

• C.

100

B. The value accepted by professional chemists
Explanation
You want the value accepted by professionals to be accurate. Results similar to your other trials would make the results precise.

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• 5.

### To a scientist, the words accuracy and precision are interchangeable.

• A.

True

• B.

False

B. False
Explanation
If you got this one wrong, rewatch the video and reread.

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• Current Version
• Mar 21, 2023
Quiz Edited by
ProProfs Editorial Team
• Apr 02, 2014
Quiz Created by
Harry Brielmann