To determine which change would decrease the pH of a base in a solution at equilibrium, let's analyze each option:
A. Increasing the strength of the base - This would increase the concentration of OH⁻ ions in the solution, leading to an increase in pH (higher pH).
B. Increasing the initial concentration of solute - This could potentially increase the concentration of OH⁻ ions if solute is a base, which would lead to an increase in pH. If the solute was an acid, it would decrease the pH. However, it doesn't necessarily mean a decrease in pH universally.
C. Decreasing the concentration of OH⁻ ions - This would directly decrease the pH because it reduces the basicity of the solution, making it less basic (or more acidic).
D. Decreasing the amount of water added to the solute - This would lead to a more concentrated solution of the base, which would typically increase the concentration of OH⁻ ions and therefore increase the pH.
Based on the analysis:
C. decreasing the concentration of OH⁻ ions is the correct answer. This action would lead to a decrease in pH.
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