[Jstub]

Question 1 (summed up): a Gellenkamp melting point apparatus found a substance melts at 127.2-130.3 degrees Celsius. The substance is either compound A, which melts at 121.2-122.3, or compound B, which melts at 135.3-136.1. Which one is it?

For this one, I assume it is compound B, and it has some impurities in it. That’s my thought process so far.

Question 2) when the capillary tube was filled with 1mm of substance X, it melted at 150-151 degrees Celsius. So what would the melting point be if they used 25mm instead (assuming they both heated up at 2 degrees per minute)?
And what would the melting point be for the 1mm sample if the heating rate was 15 degrees per minute?

[Borek]

For 1 - yes, substance can melt below its mp if it is impure, it can't melt above.

Is melting point an intensive, or extensive property?

[Jstub]

Intensive. But why is that relevant?

[Borek]

In general, as an intensive property, can it depend on the amount of substance?

In practice it tends to be tricky, as when the heating is too fast there is no time for equilibration, so depending on the exact construction of the apparatus sample/thermometer can be at a bit different temperatures. But - as with every process that depends on the heat transfer - it is quite difficult to predict exact results. That's why it is best to heat very slowly.

If memory serves me well fast heating tends to produce lower melting points, as thermometer is typically large and its temperature lags behind the sample.

[Jstub]

Thank you very much, this has been a lot of help. But just so we’re clear, there is no formula  that I can use to find out exactly what the range would be when the sample is larger? I’m supposed to answer with a new range, and I’m thinking the only way I could produce an actual estimate would be to say “if it melted after one degree, that means it took 30 seconds. So if we had 25mm instead, it would take 12.5 minutes. And after 12.5 minute, the temperature would be at 175 degrees Celsius” I know that’s not at all scientific, but it’s the only method I could think of to use math to actually estimate the new range.

[Borek]

But just so we’re clear, there is no formula  that I can use to find out exactly what the range would be when the sample is larger?

Exactly, no such formula. All you can say is that you expect the temperature to be higher, but everything more elaborate will be just reading tea leaves.