Chemistry 9701 · AS & A Level · Halogen compounds

Halogen compounds — practice question

Trihalomethanes are organic compounds in which three hydrogen atoms in methane have been substituted by halogen atoms, for example $\mathrm{CHCl}_3$.
(a(i))[2]

$\mathrm{CHCl}_3$ is a colourless liquid with a high vapour pressure. Explain what is meant by high vapour pressure.

(a(ii))[3]

One significant reaction of $\mathrm{CHCl}_3(g)$ is the production of $\mathrm{CHClF}_2(g)$, using the reversible equation below. $\mathrm{CHCl}_3(g) + 2\mathrm{HF}(g) \rightleftharpoons \mathrm{CHClF}_2(g) + 2\mathrm{HCl}(g)$ Use the data to calculate the enthalpy change of reaction, $\Delta H_r$, for the formation of $\mathrm{CHClF}_2(g)$ as shown in the equation.

(a(iii))[3]

The reaction in (ii) is carried out using a heterogeneous catalyst. Explain fully the meaning of the terms heterogeneous and catalyst.

(b(i))[1]

Give the meaning of the term enhanced greenhouse effect.

(b(ii))[2]

Explain how $\mathrm{CHClF}_2(g)$ may contribute to this effect.

(b(iii))[1]

Suggest another environmental problem associated with the use of $\mathrm{CHClF}_2$.

(c(i))[1]

State the type of polymerisation that occurs during the production of PTFE.

(c(ii))[1]

Draw the repeat unit of PTFE.

(c(iii))[1]

Suggest why PTFE is used as a coating for cooking pans.

(c(iv))[2]

Waste disposal can cause litter problems. State two other difficulties associated with the disposal of PTFE.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Gas/vapour is in equilibrium with liquid or solid” …

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