Acid Base Chemistry (Answer Completely)

Question

Sodium butanoate, C₃H₇COONa, is the salt of a weak acid, butanoic acid, C₃H₇COOH.

A 0.10 M solution of sodium butanoate has a pH of 8.91.

a. Calculate the [OH^-] in the sodium butanoate solution described above.

b. Calculate the value for the equilibrium constant, Kb, for the reaction:

C₃H₇COO^- + H₂O <-> C₃H₇COOH + OH^-

Answer 1

For this, you must look at the hydrolysis of C₃H₇COO^- (the conjugate base of C₃H₇COOH.

C₃H₇COO^- + H₂O ==> C₃H₇COOH + OH^-

a) From the pH = 8.91, we can calculate the pOH

pOH = 14 - 8.91 = 5.09

From the pOH, we can find the [OH^-]

[OH^-] = 1x10^-5.09 = 8.12x10^-6 M. This is also the [C₃H₇COOH]

b) Keq = [C₃H₇COOH][OH^-] / [C₃H₇COO^-]

Keq = (8.12x10^-6)(8.12x10^-6) / 0.10

Keq = 6.60x10^-10