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?

Question

Cameron Andrews · Accepted Answer

All things being equal the average value should be reported.

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. Standard analysis would hold that 2/3 of the spread of values is the error value; however, if you recrystallized it from a 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. Given that your values appear to be drawn from the same population of measurements, I would quote the average value.

Naomi Aronson · Answer

undefined As a result, the reported melting point should be $ 55.75°C $. The average melting point of the substance would be $ 56.0°C + 55.0°C + 57.5°C + 55.5°C = 223.0°C $. This would be divided by the number of trials to get the average: $ \frac{223.0°C}{4} = 55.75°C $.