2.7 Accuracy And Precision

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?

Accurate

Precise

Neither

They are not accurate because they are not reasonably close to the actual time. They are not precise because they are not consistent.

Explanation

They are not accurate because they are not reasonably close to the actual time. They are not precise because they are not consistent.

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.... see moreAccuracy 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 more 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. see less

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

True

False

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

Explanation

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

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?

Using a beaker that is labeled every 25 mL

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

Using a cracked old bottle and spilling some in the process

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.

Explanation

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

Results from other trials that you conducted

The value accepted by professional chemists

100

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

Explanation

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

5. 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

Accurate?

Precise?

Both?

Neither?

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.

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.