Question

a. what role does temperature play in the solubility of a compound in a given solvent? what is the ideal situation for recrystallization regarding a chosen solvent and temperature?

b. when purifying a compound by recrystallization, you need to consider the polarity of the solvent. how should the polarity of your chosen solvent compare to the polarity of your product? explain.

Answer 1

a. The solubility of a solute depend on the temperature

i) Decrease the solubility with increase the temperature: If a reaction is exothermic, the increase the temperature will decrease the solubility of the solute because already excess heat is produced in the reaction.

ii) Increase the solubility with increase the temperature: If a reaction is endothermic, the increase the temperature will increase the solubility of the solute because more heat will help to break the bonds in the solid by providing the energy.

The ideal situation are given below:

i) Solvent should not dissolve the the substrate at room temperature but it dissolve the substrate at the solvent,s boiling point.

ii) Solvent should dissolve the soluble impurities at room temperature.

iii) Solvent must not react with the substrate.

b. "Like dissolve like". If the compound dissolves in the polar solvents (e.g methanol, water, DMF etc) then the compound is polar and if compound dissolves in non polar solvents (e.g hexane, toluene, benzene etc) then the compound is non polar.