16   7 This question is about some reactions of carbonyl compounds. (a) Methyl methacrylate is the monomer used to make the polymer perspex. It can be synthesised from propanone using the reaction scheme shown. propanone O CN O O methyl methacrylate Dehydration Compound A Compound B Reaction type 4 Reagent 2 Reagent 4 + conc. H2SO4 Step 2 Step 4 Step 3 HCl(aq) OH Reaction type 3 HCN / KCN Step 1 (i) Draw the mechanism for the reaction in Step 1. Include curly arrows and any relevant lone pairs and dipoles. (4) Turn over 17   (ii) Complete the table to show the information missing from the reaction scheme. (6) Reagent 2 Structure of compound A Reaction type 3 Structure of compound B Reagent 4 Reaction type 4 (iii) Complete the equation for the formation of the polymer from methyl methacrylate. (2) ............... O O 18   (b) Propanone can be formed from the fermentation of polysaccharides such as starch. The propanone can be separated from the fermentation mixture by distillation. Draw the apparatus used in the laboratory for distillation of propanone from the reaction mixture. (3) Turn over 19   (c) Carbonyl compounds, such as propanone, react with 2,4‑dinitrophenylhydrazine in solution (Brady’s reagent) to form a precipitate which can be used to identify the compound. The precipitate can be purified by recrystallisation. Details of the recrystallisation process are shown. Step 1 Dissolve the precipitate in the minimum volume of hot ethanol. Step 2 Warm a filter paper and funnel in an oven for use in Step 3. Step 3 Filter the solution whilst still warm to remove any undissolved solids, using gravity filtration. Step 4 Allow the filtrate to cool and recrystallise. Step 5 Filter the crystals under reduced pressure. Step 6 Rinse the crystals with a small amount of ice‑cold ethanol. Step 7 Dry the crystals between filter papers and leave in a desiccator. (i) Explain why the filter paper and funnel are warmed in an oven before Step 3. 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(ii) Explain how Steps 4 and 5 remove impurities from the crystalline product. 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Detailed descriptions of practical procedures are not required. 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(Total for Question 7 = 21 marks) Turn over 21   8 This question is about acids and bases. (a) Devise an experiment to determine the acid dissociation constant, Ka , for a solution of ethanoic acid, CH3COOH, of unknown concentration. Assume you have access to a pH meter and a solution of sodium hydroxide of similar concentration to the acid. Include how to determine Ka from your results. 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.................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 22   (b) 500 cm3 of a buffer solution of pH = 4.70 is required. Calculate the volume of 0.800 mol dm–3 sodium ethanoate solution and of 0.800 mol dm–3 ethanoic acid needed to make this buffer. [Ka for ethanoic acid = 1.74 × 10–5 mol dm–3] (3). (3) Turn over 23   (c) Calculate the pH of the solution formed when 51.2 cm3 of 0.927 mol dm–3 NaOH(aq) is mixed with 40.4 cm3 of 0.370 mol dm–3 H2SO4(aq). [Ionic product of water Kw = 1.00 × 10–14 mol2 dm–6] (6) (Total for Question 8 = 14 marks)