What can be done to obtain a second crop of crystals after the initial crystals have been collected?

To obtain a second crop of crystals, evaporating the filtrate and washings is an effective strategy. After the initial crystallization, there often remains a solution that contains some dissolved solute. By allowing this solution to evaporate, the concentration of the solute will increase, and as more solvent evaporates, the solution may become supersaturated. This enhanced concentration can lead to the formation of additional crystals as the solute comes out of solution.

Additionally, the solute's ability to form crystals from a concentrated solution is a common occurrence in recrystallization processes. As the solvent volume decreases, the equilibrium shifts towards solid formation, leading to the potential for a second crop of crystals. This method exploits the fact that cooling a saturated solution or allowing evaporation can encourage the crystallization of the solute remaining in the solution.

The other methods presented may not effectively yield a second crop of crystals. Recrystallizing the original solution again would typically not result in additional crystals since that assumes a fresh solution. Changing to a different solvent may not be compatible with the solute present and could hinder any further crystal growth. Similarly, storing at a lower temperature, while sometimes beneficial, may not effectively lead to crystallization from a solution that is already not