Which of the following methods would increase the solubility of a gas in water?

• A. Increasing the temperature of the water
• B. Decreasing the pressure above the solution
• C. Decreasing the temperature of the water
• D. Adding a salt to the solution

Answer: (C)

Verified step by step guidance

1. Recall Henry's Law, which states that the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. Mathematically, this is expressed as \(C = k_H \times P\), where \(C\) is the concentration (solubility) of the gas, \(k_H\) is Henry's law constant, and \(P\) is the partial pressure of the gas.
2. Understand the effect of temperature on gas solubility: Generally, the solubility of gases in water decreases as temperature increases because gas molecules gain kinetic energy and escape more easily from the solution.
3. Analyze the effect of pressure changes: Increasing the pressure above the solution increases gas solubility, while decreasing the pressure reduces it, according to Henry's Law.
4. Consider the effect of adding salt (salting out effect): Adding salt to water usually decreases the solubility of gases because the salt ions compete with gas molecules for space in the solvent.
5. Conclude that to increase the solubility of a gas in water, you should decrease the temperature or increase the pressure above the solution, but not add salt.