(a)[2]
Explain what the term buffer solution means.
(b(i))[1]
Write the formula for the acid dissociation constant, $K_a$, associated with ammonium ions, $\text{NH}_4^+(aq)$.
(b(ii))[2]
Write two equations showing how a solution containing ammonium ions, $\text{NH}_4^+(aq)$, and ammonia, $\text{NH}_3(aq)$, may behave as a buffer.
(b(iii))[3]
The value of $K_a$ for $\text{NH}_4^+(aq)$ is $5.6 \times 10^{-10}$ at $298\ \text{K}$. A buffer solution was made by adding $0.80\ \text{dm}^3$ of $0.25\ \text{mol dm}^{-3}$ ammonia, in excess, to $0.20\ \text{dm}^3$ of $0.20\ \text{mol dm}^{-3}$ hydrochloric acid. Calculate the pH of the buffer solution produced at $298\ \text{K}$.