Question

Prachi makes a saturated solution of potassium chloride in water at 353K and leaves the solution to cool at the room temperature. What would she observe as the solution cools? Explain.

Answer 1

Hint: In order to know what happens when the saturated solution cools, we must first know what a saturated solution is. Saturated solution is that solution in which the maximum amount of the solute particles can be dissolved in the solvent.

Complete Solution :
Let us first understand what a saturated solution is. A solution in which the maximum number of solute particles can be dissolved in a solvent is called the saturated solution. The point of saturation will be attained by the solution in which no more solute particles can be added.
Saturation can be classified into three types, they are:
- Saturated solution
- Unsaturated solution
- Supersaturated solution
- Saturated solution is the solution which is in equilibrium with respect to the dissolved solute particles. Example of a saturated solution is carbonated water.
- unsaturated solution is the solution is the solution which is not in equilibrium with respect to the dissolved solute particles. It says that further more solute particles can be dissolved. Example of Unsaturated solution is NaCl in water.
- Supersaturated solution is the solution which contains more solute particles dissolved in it, than the saturated solution. Example of supersaturated solution is dissolving sugar in saturated solution by heating.
Let us now come to the given question, it is given that Prachi is making a saturated solution of potassium chloride in water at a temperature of 353K. When she leaves the solution to cool in the room temperature the solubility of KCl in water will decrease. Due to this, the soluble potassium chloride will separate out in the form of crystals.

Note: We must always remember that saturated solution is different from the supersaturated solution. We should not confuse between the two. Supersaturated solution will have more solute particles dissolved in the solvent compared to saturated solution.