A technician prepared a solution by heating 100 milliliters of distilled water while adding KCl crystals until no more KCl would dissolve. She then capped the clear solution and set it aside on the lab bench. After several hours she noticed the solution had become cloudy and some solid had settled to the bottom of the flask. Which statement best describes what happened?

A. As the solution cooled, evaporation of water increased the KCl concentration beyond its solubility

B. Water molecules, trapped with the KCl crystals, were released after heating

C. At lower temperatures the solubility of the KCl decreased and recrystallization occurred

D. At increased temperatures the solubility of KCl increased and remained too high after cooling

At lower temperatures the solubility of the KCl decreased and recrystallization occurred

Explanation:

Solubility refers to the amount of solute that dissolves in one litre of water at a particular temperature. Solubility is a property referring to the ability for a given substance, the solute, to dissolve in a solvent. It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium. The resulting solution is called a saturated solution.

Solubility is dependent on temperature. This is the reason why we must state the particular temperature at which a given solubility data was collected. Above or below the quoted temperature, the solubility data may no longer be accurate.

Let's return to the question, at elevated temperatures, we can see that the KCl is very soluble in water as evidenced by the clear solution obtained at high temperature. However, as the temperature decreases, the solubility of KCl also decreases accordingly and recrystallization of the solute occurred hence the formation of a cloudy solution and the settling of some solid at the bottom of the flask.