Calculate the pH of a 0.051 M solution of sodium lactate. The K_a for lactic acid is 1.4 × 10^-4. A) 1.29 B) 2.57 C) 8.28 D) 11.43 E) 12.71

Question

Quizplus · Accepted Answer

Sodium lactate is the conjugate base of lactic acid, so it will act as a base and accept a proton from water to produce hydroxide ions.
Lactate ion + H2O ↔ lactic acid + OH-
Kb = Kw/Ka = (1 x 10^-14)/(1.4 x 10^-4) = 7.1 x 10^-11
Let [OH-] = x then [lactate] = [OH-] = x
Ka = [lactic acid][OH-]/[lactate]
1.4 x 10^-4 = x^2/0.051
x = 6.22 x 10^-5 M
pOH = -log[OH-] = -log(6.22 x 10^-5) = 4.21
pH = 14 - pOH = 9.79
Therefore, the answer is C) 8.28.

Calculate the PH of a 0