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Meltating point and recrystallization experiment Why was it necessary to allow the oil bath to cool...

Meltating point and recrystallization experiment

Why was it necessary to allow the oil bath to cool by at least 20C before performing the second determination of the melting point of your recrystallized benzoic acid?

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Recrystallization is done in order to get the pure version of a compound and in this case to get the melting point of benzoic acid in it's pure form. Once the crystals of pure benzoic acid have been formed, the temperature of the oil bath in which they were made in is reduced by some amount(20o C in this case) because if we put back the newly formed crystals of benzoic acid in the hot bath, there is a good chance that the crystals may melt or turn into liquid state thereby defeating the purpose of recrystallization itself.

Supercooling of liquid in the bath helps in nucleation and growth of benzoic acid crystals by providing thermodynamic force for the phase change thereby facilitating crystal formation.

Also, a cooler solvent in the bath ensures that none of the benzoic acid crystals dissolve in the oil bath.

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