Question

Hydrogen cyanide, HCN(l), is a pale blue, highly volatile liquid. It exists as gas above 26oC. It reacts with water to form H3O+(aq) and CN–(aq).

Which of the following pairs are conjugate acid base pairs of the reaction of hydrogen cyanide, HCN(l) with water?


a. HCN(aq) and /H3O+(aq)
b. HCN(aq) and H2O()
c. HCN(aq) and CN–(aq)
d. CN–(aq) and H3O+(aq)
e. CN–(aq) and H2O()

Answer 1

Reaction: HCN(aq) + H2O(l) ⇌ H3O+(aq) + CN–(aq).

Conjugate acid-base pairs differ by one proton. From the reaction the pairs are:
- HCN (acid) and CN– (its conjugate base)
- H3O+ (conjugate acid) and H2O (base)

Thus the correct choice from the list is c only.