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Question
Benzoic acid is a organic compound. Its crude sample can be purified by crystallisation from hot water. What characteristic differences in the properties of benzoic acid and the impurity make this process of purification suitable?
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Solution
Benzoic acid can be purified from hot water because of the following characteristics.
(i) Benzoic acid is more soluble in hot water and less soluble in cold water.
(ii) Impurities associated with benzoic acid is cooled, the impurities remain in the solution in water to such an extent that when a hot saturated solution of benzoic acid is cooled, the impurities remain in the solution.
Since, impure benzoic acid satisfies both these conditions, therefore benzoic acid can be purified by crystallization.
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