Answer the following question given this paragraph: 

When compounds are synthesized, they often have contaminating materials mixed in with them. The process of recrystallization can be used to remove these impurities. The crystals are dissolved in a hot solvent, forming a solution. When the solvent is cooled the compound is no longer as soluble and will precipitate out of solution, leaving other materials still dissolved.


Q: Recrystallization is a process that can remove what, which result when compounds are synthesized?


A:
contaminants