The contamination of a pure organic with an impurity affects the observed meltin

Question

The contamination of a pure organic with an impurity affects the observed melting point only if the impurity dissolves to some extent in the liquid phase of the organic compound. Therefore, small granules of sand or broken glass (sand and glass have similar compositions, melt only at very high temperatures, and are totally insoluble) will not reduce the melting point of a pure organic compound with which they might be mixed. In a sample containing small grains of sand, what would you observe in the Mel-Temp apparatus when you melt the sample that would indicate to you that your sample contained this type of impurity? (How would the melted sample look different than the melted sample of a sample without the added contaminant?)

Explanation / Answer

Understanding the Melt-Temp apparatus -

While the internal design of this apparatus may vary, but basically the operator of the apparatus records the temperature range starting with the initial phase-change temperature and ending with the completed phase-change temperature. let us say that the solid starts to melt at T1. The process of melting is completed at temperature of T2.then average of this temperature(say T0) can be taken as the average melting point of the compound.This understanding will help us to answer this question ahead.

Situation-

A solid oragnic compound ,contaminated with solid impurities like sand grain, is melted in Melt-Temp apparatus.

We have to explain the observation.

Observation - The average melting point of mixture rises despite the fact that there is no depression in melting point caused by solid impurities.

Explanation-

The fact that there is no effect of solid impurity on the melting point is correct. But here we have to note down the working of a Melt-Temp apparatus. T1 is the temperature when the solid organic compound will start to melt. There will be no change in this starting temperature of melting and will resemble to that of a pure compound. However T2 will be relatively very large as the Melt-Temp apparatus will wait for the melting of the solid grains of sand which have quite large melting points , around 1,650 °C (3,002 °F).

Thus the average melting point of the contaminated solid compound will increase drastically.

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