Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Benzene can be transformed into cyclohexane.
(a(i))[2]

For this reaction, name the reaction type and identify the reagent and conditions required.

(a(ii))[2]

State the bond angles for benzene and cyclohexane. Explain your answers.

(b(i))[3]

Draw the mechanism for the reaction between benzene and $\text{SO}_3\text{H}^+$ ions. Include every required curly arrow and charge.

(b(ii))[1]

Write an equation to show how the $\text{H}_2\text{SO}_4$ catalyst is regenerated.

(c)[2]

3-dodecylbenzenesulfonic acid can be made from benzenesulfonic acid. Suggest the reagents and conditions and name the mechanism for this reaction.

(d(i))[1]

Concentrated sulfuric acid dissociates in two steps: stage 1: $\text{H}_2\text{SO}_4 \rightleftharpoons \text{H}^+ + \text{HSO}_4^-$; stage 2: $\text{HSO}_4^- \rightleftharpoons \text{H}^+ + \text{SO}_4^{2-}$ with $K_{a2} = 1.0 \times 10^{-2}\,\text{mol dm}^{-3}$. Write the expression for the acid dissociation constant $K_{a2}$.

(d(ii))[1]

$\mathrm{H_2SO_4}$ is a strong acid, whereas $\mathrm{HSO_4^-}$ is a weak acid. Suggest how the size of the acid dissociation constant for stage 1 compares with $K_{a2}$.

(e)[2]

Benzoic acid, $\text{C}_6\text{H}_5\text{CO}_2\text{H}$, is a weak acid. A solution of $0.0250\,\text{mol dm}^{-3}$ benzoic acid has a pH of 2.90. Calculate $K_a$ of benzoic acid.

Worked solution & mark scheme

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