Question

The melting point of a white solid substance was determined in four repeated trials to be 56.0°C, 55.0°C, 57.5°C, 55.5°C. What temperature should be reported as the melting point as a result of these trials?

Answer 1

All things being equal the average value should be reported.

Explanation:

You often see in the literature the phrase, `"recrystallized to constant melting point"`; i.e. a material is successively recrystallized until a consistent melting point is achieved. Often, after repeat recrystallizations, (and each recrystallization step is a purification step!), the measured melting point goes up because the impurities that depress melting point are successively eliminated.

Given that your values are apparently drawn from the same population of measurements, I would quote the average value. Standard analysis would hold that 2/3 of the spread of values is the error value. On the other hand, if you recrystallized it from carefully dried solvent under an inert atmosphere, and found that the melting point went UP a few degrees, clearly this is the more correct melting point.