Mengsel van zuren

In a mixture of strong and weak acid, the strong acid dissociates completely, significantly elevating H₃O⁺ ion concentration, while the weak acid only partially dissociates.

Le Châtelier's principle explains that the stronger acid suppresses the weaker acid's dissociation by shifting the equilibrium towards the reactants.

Consider a mixture of 0.15 M HCl and 0.30 M HCN. The strong acid yields a H₃O⁺ concentration of 0.15 M, making the H₃O⁺ concentration from the weak acid negligible.

So, the pH in a mixture of acids is predominantly dictated by the concentration of the strong acid.

Similarly, when a mixture of two weak acids of equal amounts is present, the relatively stronger acid is the primary pH determinant.

For example, in a mixture of HF and HCN, HF will be the major determinant of the mixture's pH, as it has a K_a of 3.5 × 10⁻⁴ which is almost a million times higher than the K_a of hydrocyanic acid.