Final answer:
To purify compound C, use fractional crystallization which takes advantage of different solubilities at different temperatures. Dissolve compound C in a solvent at a high temperature, then lower the temperature to cause it to crystallize out of solution and separate it from the insoluble compound D.
Step-by-step explanation:
To purify compound C, you could use a technique called fractional crystallization. This process takes advantage of the fact that compounds have different solubilities at different temperatures.
Since compound D is completely insoluble in water, it will not dissolve during the fractional crystallization process. By carefully controlling the temperature, you can dissolve compound C in a solvent at a high temperature and then lower the temperature to cause compound C to crystallize out of solution. This will separate it from the insoluble compound D.
Once compound C has crystallized, it can be separated from the solvent and dried to obtain pure compound C. The insoluble compound D can be discarded.