Question

If the ka of a monoprotic weak acid is 1.2 × 10-6, what is the ph of a 0.23 m solution of this acid?

Answer 1

Answer is: pH of monoprotic weak acid is 3.28.
Chemical reaction: HA(aq) ⇄ A⁻(aq) + H⁺(aq).
c(monoprotic acid) = 0.23 M.
Ka = 1.2·10⁻⁶.
[A⁻] = [H⁺] = x.
[HA] = 0.23 M - x.
Ka = [A⁻]·[H⁺] / [HA]. 
1.2·10⁻⁶ = x² / (0.23 M - x).
Solve quadratic equation: [H⁺] = 0.000524 M.
pH = -log[H⁺].
pH = -log(0.000524 M).
pH = 3.28.