Question

What criteria should you use to determine whether recrystallization or sublimation will be a better method of purification?

Answer 1

Both sublimation and recrystallization is used by chemists as purification technique of a solid.

Now, purification by sublimation involves transfer of solid to gas phase leaving behind the impurity in the solid phase and then the pure solid can be obtained by cooling.

Whereas, during recrystallization, impure solid is dissolved in minimum amount of suitable solvent by applying mild heating which on cooling precipitated out of the solution leaving behind the impurities in the solution.

So, when we have to purify a compound wheather we have to recrystallize or sublime that will basically depend on the nature of the particular compound. Only a few compounds like naphthalene, iodine crystals etc. can sublime.

When we have to purify a known compound, we have to look into it's properties (like solubilty, whether it sublime or not ) and then we have to take the dececion.

But when itb is an unknown compound, it is more feasible to go for recrystallization by dissolving the solid in suitable solvent by doing solubility test.