To determine which change would decrease the pH of a base in a solution at equilibrium, we need to understand how pH and the concentration of hydroxide ions (OH⁻) are related.
pH is inversely related to the concentration of hydrogen ions (H⁺), and for basic solutions, pH is related to the concentration of hydroxide ions (OH⁻) through the formula:
\[ \text{pH} + \text{pOH} = 14 \] \[ \text{pOH} = -\log[\text{OH}^-] \]
As the concentration of OH⁻ decreases, the pOH increases, leading to a decrease in pH (since there is a relationship between pOH and pH).
Let's analyze each option:
A. Decreasing the amount of water added to the solute - This would increase the concentration of the base and therefore increase the concentration of OH⁻, leading to an increase in pH, not a decrease.
B. Decreasing the concentration of OH⁻ ions - This would directly decrease the concentration of hydroxide ions. Since pH is inversely related to OH⁻ concentration, decreasing the OH⁻ concentration would result in a lower pH.
C. Increasing the strength of the base - This typically results in a higher concentration of OH⁻ ions in solution, which would increase the pH.
D. Increasing the initial concentration of solute - This would generally increase the concentration of OH⁻ ions (if the solute is a base), which would lead to an increase in pH, not a decrease.
From this analysis, the correct answer is:
B. decreasing the concentration of OH⁻ ions.
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