What is the value of K in this equilibrium?

Question

At equilibrium, an aqueous solution of formic acid (HCHO₂) has these concentrations: [H⁺] =0.0067 M;

[CHO₂^-]= 0.0067 M; and [HCHO₂]=0.249

HCHO₂(aq) ⇌ H⁺ (aq) +CHO₂^- (aq)

What is the value of K in this equilibrium?

K=?

Answer 1

By definition, an equilibrium constant K, in this case K_a, is equal to:

[CHO₂^-] [H⁺] / [HCHO₂]

= 0.0067 M*0.0067 M/0.249 M = 1.80 x 10^-4

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