What is the pH of a 0.0100 M sodium benzoate solution? K_b (C₇H₅O₂) = 1.5 × 10⁻¹⁰

Question

Quizplus · Accepted Answer

Sodium benzoate is a salt of benzoic acid, which makes it a basic salt. When it is dissolved in water, it undergoes hydrolysis where it reacts with water to produce benzoic acid and hydroxide ions. This means that the solution will have a pH greater than 7, making choices A and B incorrect. The Kb for the reaction is given as 1.5 × 10^-10, which means the Ka for benzoic acid is 6.7 × 10^-5. Using the equation Ka = [H+][C6H5COO-]/[HC6H5O2], we can find the concentration of [H+], which is equal to the pH of the solution. Plugging in the values, we get:

6.7 × 10^-5 = [H+]^2 / 0.0100
[H+] = 8.19 × 10^-4 M

Taking the negative log of the concentration gives us a pH of 8.09, making choice C the correct answer. Choice D and E can be eliminated based on the fact that they are both highly basic and unlikely for a solution of a basic salt.

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