Lactic acid, CH3CH(OH)COOH, and pyruvic acid, CH3COCOOH, both contain two functional groups. [Figure 4.1] (structures of lactic acid and pyruvic acid)

1. (a)(i)Explain why lactic acid exists as optical isomers.[1]
2. (a)(ii)Give the systematic name of lactic acid.[1]
3. (a)(iii)Lactic acid forms hydrogen bonds with water. Complete Fig. 4.2 to show the formation of a hydrogen bond between one molecule of lactic acid and one molecule of water. Label the hydrogen bond. Show any relevant dipoles and lone pairs of electrons. [Figure 4.2][3]
4. (b)(i)Two possible syntheses of pyruvic acid are shown in Fig. 4.3 and Fig. 4.4. Each synthesis has a total of three steps. [Figure 4.3] (synthesis from propene) [Figure 4.4] (synthesis from ethanal) Complete the diagram in Fig. 4.5 to show the mechanism for the reaction of propene with Br2. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. [Figure 4.5][3]
5. (b)(ii)Write an equation for the oxidation of lactic acid to pyruvic acid, the third step of Fig. 4.4. Use [O] to represent one atom of oxygen from an oxidising agent. CH3CH(OH)COOH +[1]
6. (b)(iii)Complete Table 4.1 to give details of the reagents and conditions used in each of the two syntheses shown in Fig. 4.3 and Fig. 4.4. [Table 4.1] synthesis from propene (shown in Fig. 4.3) | synthesis from ethanal (shown in Fig. 4.4) ---|--- first step | Br2 | reagents and conditions used | second step | | third step | |[4]

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