Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

$\text{H}_2(g)$ and $\text{I}_2(g)$ undergo a reversible reaction to produce $\text{HI}(g)$, as shown in equation 1: $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$.
(a(i))[1]

Calculate the amount, in mol, of $\text{S}_2\text{O}_3^{2-}$ that is used up in the titration.

(a(ii))[2]

Use the result from (a)(i) to determine the amount, in mol, of $\text{I}_2$ in $1.00\,\text{dm}^3$ of solution A.

(b)[3]

In experiment 2, $0.100\,\text{mol}$ of $\text{H}_2(g)$, $0.200\,\text{mol}$ of $\text{I}_2(g)$ and $0.300\,\text{mol}$ of $\text{HI}(g)$ are mixed. At equilibrium, $0.154\,\text{mol}$ of $\text{I}_2$ remains. Calculate the amounts, in mol, of $\text{H}_2$ and $\text{HI}$ in the equilibrium mixture formed in experiment 2.

(c)[1]

In experiment 3, $0.0772\,\text{mol}$ of $\text{H}_2$ and $0.0986\,\text{mol}$ of $\text{I}_2$ are present in an equilibrium mixture at $298\,\text{K}$. Given $K_c = 7.94 \times 10^2$ for the reaction $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$, calculate the amount, in mol, of $\text{HI}$ present in the equilibrium mixture in experiment 3.

(d(i))[1]

Define a covalent bond.

(d(ii))[2]

Describe and explain the relative thermal stabilities of hydrogen halides $\text{HCl}$ and $\text{HI}$.

(d(iii))[1]

Use the data from (c) and (d) to suggest a value for the equilibrium constant for the dissociation of $\text{HBr}(g)$ at $298\,\text{K}$.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: $0.00658\,(0)\ \mathrm{mol}$

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