If the ka of a monoprotic weak acid is 1.0 * 10-6, what is the ph of a 0.50 m solution of this acid?

Question

Chemistry

Kirsten Sexton

8 June, 03:16

If the ka of a monoprotic weak acid is 1.0 * 10-6, what is the ph of a 0.50 m solution of this acid?

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Blevins · Answer 1

Answer is: pH value of weak acid is 3.15.

Chemical reaction: HA (aq) ⇄ A⁻ (aq) + H⁺ (aq).

c (weak acid) = 0,5 M.

Ka (weak acid) = 1.0 ·10⁻⁶.

[A⁻] = [H⁺] = x.

[HA] = 0.5 M - x.

Ka = [A⁻]·[H⁺] / [HA].

1.0·10⁻⁶ = x² / (0,5 M - x).

Solve quadratic equation: x = [H⁺] = 0.0007 M.

pH = - log[H⁺].

pH = - log (0.0007 M).

pH = 3.15.