A Work-Study student was hired to check and test some new CHEM 2020 experiments. One task was to check the reproducibility of the polarimeter. She was asked to repeat the resolution experiment by exactly the same procedure three times in order to estimate the experimental uncertainty in the determination of optical activity with the polarimeter. She isolated optically active phenylethylamine with malic acid (instead of tartaric acid) and obtained optical rotation values of

Question

A Work-Study student was hired to check and test some new CHEM 2020 experiments. One task was to check the reproducibility of the polarimeter. She was asked to repeat the resolution experiment by exactly the same procedure three times in order to estimate the experimental uncertainty in the determination of optical activity with the polarimeter. She isolated optically active phenylethylamine with malic acid (instead of tartaric acid) and obtained optical rotation values of

–37.8°, –41.0° and –41.8° and reported the value as –40.2°± 2.4° because, as she explained, all three of her measurements were within 2.4° of the average value. Is this a correct estimate of the reproducibility? Why not? If not, what should she have reported instead?

Answer 1

There is no "correct" value of a probability but some estimates are better than others. The "standard deviation" is probably better than the average deviation as a measure of uncertainty.