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 steps in the crystallization are performed correctly there are no spills, and the student lost very little solid on any glassware or in any of the transfers. Why is the recovery so low?

Too much solvent (i.e., Benzene). You add the solvent drop wise and only enough until your compound dissolves.

The low recovery in this crystallization process can be attributed to several factors:

1. Solubility: The compound's solubility in the solvent plays a crucial role in the crystallization process. In this case, biphenyl has a higher solubility in benzene compared to the impurities. Therefore, during the crystallization process, when the biphenyl compound is dissolved in benzene, some impurities may remain dissolved and not precipitate along with the desired compound.

2. Purity of the Sample: The initial sample of biphenyl given by the student contained about 5% of impurities. Even though the student performed the crystallization correctly, there is always a possibility that some impurities were not completely removed during the process. This would result in a lower recovery of the pure biphenyl crystals.

3. Losses during Transfers: It is mentioned that the student did not lose much solid during the transfers, but it's difficult to avoid some loss during these operations. Some of the crystals might have been lost during filtration, decantation, or transfer from one container to another. Such losses can also contribute to the low recovery of the final product.

Overall, the combination of the solubility behavior, initial impurity content, and inevitable losses during transfers can lead to a low recovery of the pure biphenyl crystals in this crystallization process.