Question

Which of the following changes will likely increase the solubility of a solid solute but decrease the solubility of a gaseous solute?

A. Increasing the temperature

B. Increasing the molecular mass of the solute

C. Decreasing the atmospheric pressure

D. Decreasing the concentration

Answer 1

The solubility of solids in liquids is independent of pressure changes while the solubility of gases in liquids is highly pressure dependent. The first part rules out optin (C) as the correct answer.

Decreasing the concentration of both the solid solute and the gaseous solute decreases the amount available for solubilization and hence will reduce the solubility of both solids and gases in liquids. Therefore, we can rule out option (D).

Increasing the molecular mass of the solute increases the molar mass of both the solid and the gaseous solutes, but decreases the number of moles of the solute available for solubilization. Hence, both solid and gaseous solutes are rendered less soluble by an increase in molecular mass of the solute and hence, we can rule out option (B).

This leaves us with option (A) as the correct option. In general, the solubility of a solid solute increases with temperature. This is due to the fact that the kinetic energy of the solute molecules increases and the bonds in the solid break, thereby dissolving the solute molecules. Gaseous solutes also exhibit an increase in kinetic energy and breaking of bonds; therefore, the molecules can easily escape from the solution as vapor or gas. Thus, with increase in temperature, the actual amount of gaseous solute available for solubilization in the liquid is reduced and hence, the solubility of gaseous solutes decrease with increase in temperature.