What is the pH of a 0.029 M solution of potassium benzoate? The K_a value for benzoic acid is 6.46 $\times$ 10^-5.

Question

Quizplus · Accepted Answer

Potassium benzoate is a salt of benzoic acid and potassium hydroxide. In aqueous solution, it will dissociate to form benzoate ions and potassium ions. Since benzoate is a weak base, it will react with water to form hydroxide ions and benzoic acid.

Benzoic acid is a weak acid with a pKa value of 6.46. Therefore, we can use the Henderson-Hasselbalch equation to calculate the pH of the solution.

pH = pKa + log([base]/[acid])

pH = 6.46 + log([K+][C7H5O2-]/[C7H5O2H])

At equilibrium, the concentration of benzoic acid is equal to the concentration of benzoate ions produced by the dissociation of potassium benzoate. Therefore, we can substitute 0.029 M for both [K+][C7H5O2-] and [C7H5O2H].

pH = 6.46 + log(0.029/0.029) = 6.46

Therefore, the pH of the solution is 6.46, which is closest to choice C, 8.33.

What Is the PH of a 0 ×\times× 10-5

What Is the PH of a 0 $\times$ 10^-5