A KCl solution containing 42g of KCl per 100.0 g of water is cooled from 60 C to 0 C . What will happen during cooling?

Answer 1

Since the solubility of KCl is about 45 g at 60 ∘C, a KCl solution containing 42 g in 100 g of water at 60∘C is holding less solute than possible at that temperature and is unsaturated. The solubility of KCl is about 27 g at 0 ∘C, so a KCl solution containing 42 g in 100 g of water at 0 ∘C is holding as much solute as possible at that temperature and is saturated. Therefore, the excess solute will precipitate as the solution cools.

Answer 2

Answer Requested

The amount that precipitates should be the difference between the mass of KCl
present initially and the solubility value for KCl at 0 ∘C:

mass precipitate=(initial dissolved mass)−(solubility at 60∘C)=42g−27g=15gKCl precipitates