Final answer:
Crystallization is preferred over evaporation for producing copper II sulfate because it yields a purer form of the compound and allows impurities to remain dissolved in the solvent.
Step-by-step explanation:
When copper II sulfate solution is formed, it is often crystallized rather than evaporated due to several advantages that crystallization provides. One of the main reasons is that crystallization produces a purer form of the compound compared to evaporation. During the process of recrystallization, the copper sulfate crystals are dissolved in a hot solvent. Upon cooling, copper sulfate becomes less soluble, and it precipitates out of the solution as crystalline solid, leaving behind most of the impurities dissolved in the solvent. This method of purification is particularly useful because the water of crystallization, which gives copper sulfate its blue color, is retained. The white anhydrous form of copper sulfate, obtained when the water is removed, indicates the loss of these water molecules from the crystal structure. Evaporation, on the other hand, does not offer this level of purity and can sometimes introduce contaminants.