Question

Consider a solution of two weak acids $W{A}_1$ and $W{A}_2$.
Which of the following statement(s) is/are correct?

• A. These two acids will dissociate less than in their individual solutions of the same concentration.
• B. Common ion effect is not observed in case of mixture of two weak acids.
• C. These two acids will dissociate more than in their individual solutions of the same concentration.
• D. Common ion effect is observed in case of a mixture of two weak acids.

Answer 1

Answer: (A), (D)

Common ion effect is observed in case of a mixture of two weak acids.

The dissociation of two weak acids $W{A}_1$ and $W{A}_2$ is less than in their individual solutions having same concentrations because of the common ion effect exerted by the H+ ions of one on the other.
When the two solutions are mixed, the concentration of $H^{+}$ ions increases, and hence the equilibrium shifts backwards.
Shifting of equilibrium backwards means that reaction goes towards reactant side. Hence the degree of dissociation decreases.