Question

Answer the following :

The dissociation of HCN is suppressed by the addition of HCl. Explain.

Answer 1

i. HCN and HCl both dissociate to produce H⁺ ions which are common to both.

ii. HCN is a weak electrolyte. It dissociates to a little extent.

\[\ce{HCN_{(aq)} ⇌ H^+_{ (aq)} + CN^-}\]

iii. HCl is a strong electrolyte. It undergoes complete dissociation.

\[\ce{HCl_{(aq)} -> H^+_{ (aq)} + Cl^-_{ (aq)}}\]

Both HCN and HCl provide H⁺ ions.

iv. The concentration of H⁺ ions in the solution increases due to the complete dissociation of HCl.

v. According to Le-Chatelier’s principle, the effect of the stress (the addition of H⁺ ions from HCl) applied to the ionization equilibrium of HCN is reduced by shifting the equilibrium in the backward direction.

vi. H⁺ ions combine with `"CN"^-` ions to produce unionized HCN. Thus, the dissociation of HCN is suppressed by the addition of HCl.