Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Benzene may be turned into cyclohexane.
(a(i))[2]

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

(a(ii))[2]

State the bond angles in benzene and cyclohexane, and explain your reasoning. Bond angle in benzene ................. Bond angle in cyclohexane .................

(b(i))[3]

Draw a mechanism for benzene reacting with $\text{SO}_3\text{H}^+$. Include every curly arrow and charge needed.

(b(ii))[1]

Write an equation to show the formation of the $H_2SO_4$ catalyst.

(c)[2]

Suggest suitable reagents and conditions, and name the mechanism, for converting benzenesulfonic acid to 3-dodecylbenzenesulfonic acid. Reagents and conditions. Mechanism.

(d(i))[1]

Give the expression for the acid dissociation constant $K_{a2}$ for the equilibrium $\text{HSO}_4^- \rightleftharpoons \text{H}^+ + \text{SO}_4^{2-}$.

(d(ii))[1]

$\text{H}_2\text{SO}_4$ is a strong acid whereas $\text{HSO}_4^-$ 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 $0.0250 \text{ mol dm}^{-3}$ solution of benzoic acid has pH $2.90$. Calculate $K_a$ for benzoic acid.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: hydrogenation / reduction

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