Question

On increasing the temperature, the solubility of the solute in the solvent:

• A. Increase
• B. Decrease
• C. Change
• D. Does not change

Hint:

Temperature affects solubility; for most solids, higher temperatures increase solubility.

Answer 1

The Correct Option is A

On increasing the temperature, the solubility of the solute in the solvent: 

• Option 1: Increase - This is the correct answer. In most cases, increasing the temperature increases the solubility of solid solutes in a liquid. This is because higher temperatures provide more energy for the solute particles to dissolve.
• Option 2: Decrease - This is incorrect. For most solid solutes, solubility increases with temperature. However, for gases, solubility tends to decrease with an increase in temperature.
• Option 3: Change - This is too vague. The solubility of a solute typically either increases or decreases with temperature, depending on the nature of the solute and solvent.
• Option 4: Does not change - This is incorrect. Solubility does change with temperature for most substances, especially for solids in liquids.

Explanation:

For most solid solutes in liquids, increasing the temperature increases solubility. This happens because higher temperatures provide more kinetic energy to the solute particles, making it easier for them to dissolve. However, for gases, solubility decreases as temperature increases.

Answer 2

Whether solubility rises or falls with temperature depends on whether dissolving the solute is itself a heat-absorbing or heat-releasing step, and Le Chatelier's principle tells us how the system reacts to added heat. Dissolving most solid solutes in a liquid absorbs heat (it is endothermic), so let's apply the principle to each option.

1. Increase: If dissolving a solid absorbs heat, then adding heat by raising the temperature pushes the equilibrium further toward the dissolved state, exactly as Le Chatelier's principle predicts for a system reacting to added heat on the absorbing side. More solute goes into solution, so solubility increases.
2. Decrease: This would be the case if dissolving released heat, which is true for gases in a liquid but is not the general behaviour for solids. Since the question asks about the general case, this does not fit for most solid solutes.
3. Change: This does not say which way the change goes, so it does not answer what the question is actually asking for.
4. Does not change: If temperature had no effect at all, the equilibrium between solid solute and dissolved solute would not shift with heat, but in the real behaviour of most solids this is not the case, solubility does shift.

Since dissolving a solid solute usually absorbs heat, adding more heat by raising the temperature shifts the balance toward more of it dissolving.

So the correct answer is Increase.