1: If you heat your melting point tube too quickly, what will your observed melt

Question

1: If you heat your melting point tube too quickly, what will your observed melting point be in comparison to the actual melting point?

2: How fast should you heat a sample?

3: You melt a sample of 3,5-dinitrobenzoic acid (m.p. 205 oC) and you observe a melting point of 185-195 oC. What does this tell you about your sample of 3,5-dinitrobenzoic acid?

4. An unknown compound X is one of the four compounds listed in the table below. A mixture of X with o-toluic acid melts at 95 °C, a mixture of X with benzoic acid melts at 115 °C, a mixture of X with phenyl succinate melts at 117 °C, and a mixture of X with m-aminophenol melts at 121 °C. Give the identity of X and explain your reasoning.

Compound                  m.p., oC

o-toluic acid                102

benzoic acid                121

phenyl succinate         121

m-aminophenol           122

Explanation / Answer

1)

In a melting point experiment, If we were to heat a sample very fast. A lot of heat is provided instantly which would melt the crystals in the tube very quickly, even before the temperature of the thermometer reaches to that level.

So the observes melting point would be much lower than the actual melting point when sample is heated slowly.

3)

3,5- di Nitro benzoic acid containes some Impurities. Which can form the Hydrogen bonds.

4)

X can form the Hydrogen bonds. Hence it lowers the melting point value.

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