Homework Help: Chemistry

Posted by Nina on Wednesday, October 8, 2008 at 9:44pm.

A student performs a crystallization on 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 dried and the final weight is found to be 0.02 g. Assume that all the steps in the crystallization are performed correctly, there are no spills, and the student lost very littly solid on any glassware or in any of the transfers. Why is the recovery so low?

thanks so much in advance!

Chemistry - DrBob222, Wednesday, October 8, 2008 at 11:32pm
How soluble is biphenyl is benzene? Perhaps it is just too soluble, and/or there is not enough difference in solubility at low temp and high temp.
Chemistry - Joshua Creek, Friday, October 1, 2010 at 7:51pm
I had this same question in my last lab. The reason this occurs is due to the solubility of biphenyl and benzene. There is not much difference between room temp and boiling so not much is going to crystallize out. Benzene is too good of a solvent for biphenyl and shouldn't be used for re-crystallization.

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