What happens when a supersaturated solution cools down?
The correct answer and explanation is:
When a supersaturated solution cools down, it becomes unstable and the excess solute that was dissolved beyond its solubility limit starts to precipitate out of the solution. A supersaturated solution occurs when a solution contains more solute than it would under normal conditions at a given temperature. This happens by carefully dissolving an excess amount of solute into a solvent at an elevated temperature and then allowing it to cool slowly. The cooling process does not immediately allow the solute to crystallize, so the solution becomes supersaturated.
The reason why the excess solute remains dissolved at first is that the cooling process is so gradual that the solute has not yet had a chance to form crystals or solidify. However, as the temperature decreases, the solubility of the solute decreases as well, and the solution cannot hold the excess solute any longer. To regain stability, the solution forces the excess solute to come out of solution in the form of crystals. This process is called recrystallization.
The formation of crystals can be triggered in a variety of ways. Sometimes, even a small disturbance, such as shaking the solution or introducing a seed crystal, can initiate the crystallization process. The solute will begin to form solid crystals, which will slowly accumulate and settle out of the solution, returning the system to a stable, unsaturated state.
In summary, when a supersaturated solution cools down, it undergoes a rapid crystallization process as the excess solute is no longer able to stay dissolved. The rate at which the crystallization occurs can depend on factors such as temperature, concentration, and the presence of nucleation sites.