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A chemist performs an experiment to determine the concentration of an unknown acid. They titrate the acid with a known concentration of base, using an indicator to detect the equivalence point. They repeat the titration three times and obtain the following volumes of base required: 25.15 mL, 25.20 mL, and 25.18 mL. Which of the following best describes the precision of these measurements?
- AHigh precision, as the values are very close to each other.
- BLow precision, as the values are not exactly the same.
- CModerate precision, due to the slight variation between trials.
- DInsufficient data to determine precision.
Show answer & explanationAnswer & explanation
Correct answer: A. High precision, as the values are very close to each other.
Precision refers to the closeness of two or more measurements to each other. The three measurements (25.15 mL, 25.20 mL, and 25.18 mL) are all very close, with a range of only 0.05 mL, indicating high precision.
Why the other options are wrong
- B. The values are very close, indicating high, not low, precision.
- C. The variation is minimal, suggesting high precision rather than moderate.
- D. Three data points are sufficient to assess the spread and thus the precision.
Measurement Precision
The degree to which repeated measurements under unchanged conditions show the same results; the reproducibility of measurements.
- Refers to the closeness of multiple measurements to each other.
- Does not guarantee accuracy (closeness to the true value).
- Often quantified by standard deviation or range of values.
Memory trick: Accuracy hits the bullseye, Precision hits the same spot.