Chemistry Regents Practice Test

Which compound becomes less soluble in water as the temperature of the solution is increased?

1. NaCl

2. KCl

3. HCl

4. AgCl

The correct answer is: HCl

The compound that becomes less soluble in water as the temperature of the solution is increased is AgCl (silver chloride). Unlike many salts which tend to be more soluble at higher temperatures, AgCl is classified as a sparingly soluble salt. The solubility of AgCl in water decreases as the temperature rises due to the exothermic nature of its dissolution process. When a solute dissolves in a solvent, energy is required to break apart the ionic lattice of the solid, and as the temperature increases, the equilibrium of the solubility reaction can shift. This often leads to a decrease in the solubility of some compounds like AgCl rather than an increase. In contrast, NaCl and KCl are both examples of salts that typically become more soluble in water as the temperature increases. HCl, when dissolved in water, behaves as a strong acid and is highly soluble, with its solubility being less dependent on temperature changes compared to AgCl. Therefore, while other compounds might show increased solubility with rising temperature, AgCl uniquely demonstrates the opposite behavior, making it the correct choice in this context.