Chemistry 9701 · AS & A Level · Equilibria

Equilibria — practice question

Silver sulfide, $\text{Ag}_2\text{S}$, has very low solubility in water.
(a(i))[1]

Write an expression for the solubility product, $K_{sp}$, of $\text{Ag}_2\text{S(s)}$.

(a(ii))[2]

At $298\,\text{K}$, the solubility of $\text{Ag}_2\text{S(s)}$ in water is $1.16 \times 10^{-17}\,\text{mol dm}^{-3}$. Calculate the numerical value of the solubility product, $K_{sp}$, of $\text{Ag}_2\text{S(s)}$ at $298\,\text{K}$.

(a(iii))[2]

Calculate the minimum volume of water required to dissolve $1.00\,\text{g}$ of $\text{Ag}_2\text{S(s)}$ under standard conditions.

(b(i))[2]

Bromic(I) acid, $\text{HOBr(aq)}$, behaves as a weak acid. Its $K_a$ is $2.0 \times 10^{-9}\,\text{mol dm}^{-3}$. Calculate the pH of $0.20\,\text{mol dm}^{-3}\,\text{HOBr(aq)}$.

(b(ii))[2]

$5.0\,\text{cm}^3$ of $0.20\,\text{mol dm}^{-3}$ potassium hydroxide, $\text{KOH}$, are mixed with $20.0\,\text{cm}^3$ of $0.20\,\text{mol dm}^{-3}\,\text{HOBr(aq)}$. Calculate the pH of the buffer solution formed.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: $K_{sp} = [\text{Ag}^+][\text{S}^{2-}]$

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