Question

When preparing for an important synthesis you attempt to recrystallize a starting
material from benzene. You start off by dissolving 4g of material in 100 mL of boiling
benzene. Thereafter filtering off some insoluble impurities, you allow the solution to cool to
room temperature. You then cover the flask, and put it in the freezer for a couple hours. When you return, you expect to find beautiful needle-like crystals, but instead you instead find a
clear solution with no precipitate. What are some things that could have gone wrong?
How could you try to fix the problem?

Answer 1

Usually, for recrystallization process, selection of the solvent is critical. You need to choose a solvent in which your solute is sparingly soluble at room temperature and is completely soluble at higher temperature. Thus, when you heat, your solvent dissolves solute and on cooling, it will crystalize.

From the explanation given above z it seems like benzene solvent can dissolve your solute completely in both cold and hot conditions. Try with different solvents like methanol or ethanol..