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) in most of the cases, the solubility of a compound increases with temperature. Therefore at higher temperature more of a compound is soluble. For recrystallization purpose, the compound should not se soluble(or very less soluble) at low temperature but should have solubility at higher temperatures in the solvent. The impurity should be soluble at low temperature as well.

b) like dissolves like principle always work. If a compound is polar, it will be soluble in a polar solvent and if non-polar, then it will be soluble in non-polar. For recrystallization purpose , the polarity of compound and solvent should match but predominantly at higher temperatures so that the compound becomes more soluble at higher temperatures. At low temperature, the polarity of the two should be different enough to not make the solute completely soluble.