Edexcel Jan 2014 (IAL) Paper 6 Q3

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3 An ester is hydrolysed in the presence of an acid catalyst forming a carboxylic acid and an alcohol C. The alcohol contains four carbon atoms. In order to investigate the kinetics of this reaction, two solutions, X and Y, were made up. Solution X: 100 cm3 of a 0.20 mol dm3 solution of the ester Solution Y: 100 cm3 of a 0.20 mol dm3 solution of hydrochloric acid Flasks containing the two solutions were placed in a water bath at 50 oC and when both solutions had reached the temperature of the water bath, the solutions were mixed and a clock started. As soon as the clock was started, a 10 cm3 sample was taken from the reaction mixture, transferred to a cooled conical flask and titrated with 0.050 mol dm3 sodium hydroxide solution. Other samples were taken at two minute intervals and analysed in the same way. Results: Time/min Titre/cm3 V = (40titre)/cm3 20.0 20.0 23.4 16.6 26.2 13.8 28.5 11.5 30.5 9.5 10 32.1 7.9 12 33.4 6.6 14 34.5 5.5 16 35.5 4.5 V is directly proportional to the concentration of the ester remaining in the solution. (a) Why was each sample cooled before titration? (1)orange. (b) Two indicators are available for the titrations: phenolphthalein and methyl Which one should be used? Give a reason for your answer. (1) IndicatorReason(c) (i) Explain why the titre at time zero is 20.0 cm3 rather than 0.0 cm3. No calculation is required. (1)(ii) Explain why the titre increases as the reaction proceeds. (1)*P42975RA0616*<br /> (d) Plot a graph of V on the vertical axis against time on the horizontal axis. Use your graph to determine the order of the reaction by measuring two successive half-lives. (4) First half-lifeSecond half-lifeOrder*P42975RA0716* Turn over<br /> (e) The alcohol C is oxidized using potassium dichromate(VI) and dilute sulfuric acid. State the colour change observed. FromTo(f) The oxidation results in the formation of either a carboxylic acid or a ketone. (i) Suggest a chemical test that could be used to show that the purified product is a carboxylic acid. Give the observation that you would make when this test is carried out. (1) (2) ReagentObservation(ii) Suggest a chemical test that could be used to show that the purified product is a ketone. Give the observation that you would make when this test is carried out. (2) ReagentObservation(g) Tests show that C is oxidized to a carboxylic acid. What type of alcohol is C? (1)*P42975RA0816*<br /> (h) A simplified nmr spectrum for alcohol C is shown below: Chemical shift (cid:303) / ppm (i) What can you conclude from the fact that there are four sets of peaks? (1)(ii) Using your answers to (g) and (h)(i), and the fact that alcohol C contains four carbon atoms, draw the displayed formula of alcohol C. (iii) On the displayed formula you have drawn in (h)(ii), circle the atom or group of atoms responsible for the peak labelled Q. (1) (1) (Total for Question 3 = 17 marks) *P42975RA0916* Turn over<br />

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