Question

The acid-dissociation constant for benzoic acid (c6h5cooh) is 6.3×10−5. calculate the equilibrium concentration of c6h5cooh in the solution if the initial concentration of c6h5cooh is 6.3×10−2 m .

Answer 1

Answer is: the equilibrium concentration of benzoic acid is 0,06294 M.

Chemical reaction: C₆H₅COOH(aq) ⇄ H⁺(aq) + C₆H₅COO⁻(aq).

Ka(C₆H₅COOH) = 6,3·10⁻⁵.

c(C₆H₅COOH) = 6,3·10⁻² M.

[H⁺] = [C₆H₅COO⁻] = x; equilibrium concentration.
[C₆H₅COOH] = 0,063 M - x.
Ka = [H⁺] · [C₆H₅COO⁻] / [C₆H₅COOH].
0,000063 = x² / 0,063 M - x.
Solve quadratic equation: x = 0,00006 M.
[C₆H₅COOH] = 0,063 M - 0,00006 M.
[C₆H₅COOH] = 0,06294 M.