Organic Chemistry Lab: If the approximate melting point of a sample is known, at

Question

Organic Chemistry Lab: If the approximate melting point of a sample is known, at what point compared to the anticipated melting point do you considerably slow down the rate of the heating? What is the rate you should heat the sample at after this point?

What I think: Generally, you need to give enough time for heat to be transferred equally from heating block to sample to the thermometer. If you go too fast, temperature at sample is very different than temperature at thermometer, and sample appears to have a wide range. However, I am not sure exactly WHAT POINT compared to the anticipated melting point too slow down the heating, and what rate you keep this at.

Explanation / Answer

A pure organic compound usually melts over a range of two degrees or less.Most errors come from heating the sample too fast. A heating rate of 1 to 2 degrees per minute ensures good results.Going faster than five degrees per minute means the result will definitely be poor. If a compound has a high melting point, it can take a long time to reach it at 1 or 2 degrees per minute. Unless you have prior knowledge of the expected melting point, it is advisable to have extra samples prepared ahead of time. Run the first sample at a high rate of heating to get an approximate melting point range. Then repeat the procedure but slow down the rate of heating as you approach the expected melting point.

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