What is the value of K of this equilibrium?

Question

At equilibrium, an aqueous solution of formic acid (HCHO2) has these concentrations: [H+]=0.0061 M; [CHO−2]=0.0061 M; and [HCHO2]=0.207 M.

HCHO2(aq)↽−−⇀H+(aq)+CHO−2(aq)

What is the value of K of this equilibrium?

Answer 1

HCHO₂(aq) <==> H⁺(aq) + CHO₂^-

Kc = [H⁺][CHO₂^-] / [HCHO₂]

Kc = (0.0061)(0.0061) / (0.207)

Kc = 1.80x10^-4