A student performs a crystallizationon an impure sample of biphenyl. The sample
ID: 890639 • Letter: A
Question
A student performs a crystallizationon an impure sample of biphenyl. The sample weighs 0.5 g and contains about 5% impurity. Based on his knowledge of solubility, the student decides to use benzene as the solvent. After crystallization, the crystals are driedan d the final weight is found to be 0.02 g. Assume that all steps in the crystallization were performed correctly, there were no spills, and the student lost very little solid on any glassware or in any of the transfers. Why is the recovery so low?
Explanation / Answer
Solution :-
The recovery is low may be because all of the sample is not recrystallized this means some of the sample remain dissolved in the benzene which get washed out during the filtration process.
If the solution is not kept to cool to the room temperature or not kept in the ice bath for the recrystalllization. Then some of the sample remain dissolved in the solvent which get loss in the filtration process therefore the amount of the sample recrystallized is less than the expected amount.
Therefore it is very important to keep the solution for some time to initiate and complete crystallization of the sample from the solvent.
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