Edexcel Jun 2016 (IAL) Paper 6 Q

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3 Six students attempted to carry out a two-stage synthesis of nitrobenzoic acids starting from ethyl benzoate, C6H5COOCH2CH3. There are two parts to the synthesis. In the first part, ethyl benzoate is hydrolysed to form benzoic acid, C6H5COOH. In the second part, benzoic acid is nitrated. Part 1Hydrolysis of ethyl benzoate The students were provided with the method outlined in the steps below. Step 1 Mix in a flask 6.0 cm3 ethyl benzoate (density = 1.05 g cm3) with an excess of aqueous sodium hydroxide solution (made by dissolving 2 g of sodium hydroxide in 25 cm3 water). Heat the mixture under reflux for 30 minutes. Step 2 Pour the contents of the flask into a beaker and add 1 mol dm3 dilute hydrochloric acid until the solution is acidic to universal indicator paper. Crystals of benzoic acid will form. Step 3 Filter off the crystals under reduced pressure. Step 4 Dissolve the crystals in the minimum volume of boiling water and then filter. Step 5 Allow the solution to cool so that crystals of benzoic acid form. Filter off the crystals. A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46666A01124* 11 Turn over<br /> (a) Student A followed the method exactly and obtained 0.021 mol of benzoic acid crystals. Calculate the percentage yield of the benzoic acid obtained by Student A. [Molar mass of ethyl benzoate = 150 g mol1] (2) D O N O T W R I T E I N T H I S A R E A Percentage yield =% (b) Student B dissolved just 1 g of sodium hydroxide instead of 2 g. This student carried on with the experiment. Show, by calculation, that Student B did not have an excess of sodium hydroxide. (2) D O N O T W R I T E I(c) Student C dissolved 10 g of sodium hydroxide instead of 2 g. This student noticed the mistake and started the experiment again. Explain why Student C did not need to start again. (1)12 *P46666A01224* N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> (d) Student D decided to miss out Steps 4 and 5. This students mass of crystals was greater than the mass of crystals obtained by Student A. The benzoic acid obtained by Student A had fewer impurities than the benzoic acid obtained by Student D. Name the procedure described in step 4 and 5, and explain why the benzoic acid prepared by Student A was purer than that obtained by Student D. (1)(e) Student E decided not to carry out Steps 2, 3, 4 and 5. Instead, Student E evaporated off the water after Step 1 and found that 4.6 g of crystals had been formed, which was more than the mass obtained by Student A. One reason why Student E obtained a greater mass of crystals than Student A was that the product was not benzoic acid. Give the structural formula of the organic product that Student E obtained. (f) Student F ran out of time and filtered the solution in Step 5 before it had cooled properly. A low yield was obtained. Explain why Student Fs failure to cool fully the solution resulted in a low yield. (1) (1)A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46666A01324* 13 Turn over<br /> Part 2Nitration of benzoic acid The students nitrated the benzoic acid and used chromatography to separate the three organic products. The students suspected that the three products were isomers with the structures shown below, labelled P, Q and R. COOH NO2 COOH COOH NO2 NO2 (g) A student measured the melting temperature range of one of the separated products (Sample 1). The student then recrystallized the sample and took the melting temperature range of the recrystallized product (Sample 2). The students results are shown below. Sample 1 melting temperature range before recrystallization was 136C to 140C Sample 2 melting temperature range after recrystallization was 144C to 146C 14 The melting temperatures for the three structural isomers from a database are shown below.2-nitrobenzoic acid (P) 148C3-nitrobenzoic acid (Q) 142C4-nitrobenzoic acid (R) 241C *P46666A01424* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D (i) Why are the melting temperatures of Sample 1 and Sample 2 different? (1)(ii) Suggest which isomer is present in these samples. Justify your answer. (2)A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46666A01524* 15 Turn over<br /> (h) (i) Can the number of peaks in the low resolution proton nmr spectroscopy be used to distinguish between the three isomers P, Q and R? Justify your answer. (2)D O N O T W R I T E I N T H I S A R E A(ii) In a mass spectrum, which m/e value could be used to confirm that only mono-nitration occurred in this reaction? (1) m/e value =(Total for Question 3 = 14 marks) 16 *P46666A01624* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D BLANK PAGE A E R A S I H T N I E T I R W T O N O D *P46666A01724* 17 Turn over<br />

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