Chemistry 9701 · AS & A Level · Carboxylic acids and derivatives

Carboxylic acids and derivatives — practice question

Lactic acid, $\text{CH}_3\text{CH(OH)COOH}$, and pyruvic acid, $\text{CH}_3\text{COCOOH}$, each have two functional groups.
(a(i))[1]

Explain why lactic acid is found as optical isomers.

(a(ii))[1]

Give the systematic name for lactic acid.

(a(iii))[3]

Lactic acid forms hydrogen bonds with water. Complete Fig. 4.2 to show how a hydrogen bond forms between one molecule of lactic acid and one molecule of water. Label the hydrogen bond. Show any relevant dipoles and lone pairs of electrons.

(b)

Fig. 4.3 and Fig. 4.4 show two possible routes to pyruvic acid. Each route contains three steps in total.

(b(i))[3]

Complete the diagram in Fig. 4.5 to show the mechanism for the reaction of propene with $\text{Br}_2$. Include charges, dipoles, lone pairs of electrons and curly arrows where needed.

(b(ii))[1]

Write an equation for the oxidation of lactic acid to pyruvic acid, the third step of Fig. 4.4. Use $[\text{O}]$ to show one atom of oxygen from an oxidising agent: $\text{CH}_3\text{CH(OH)COOH} + \ldots$

(b(iii))[4]

Complete Table 4.1 with the reagents and conditions used in each of the two syntheses shown in Fig. 4.3 and Fig. 4.4.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: has a chiral carbon / centre OR is made up of non-superimposable mirror images

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