Edexcel Jun 2014 Paper 4 Q12

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SECTION C Answer ALL the questions. Write your answers in the spaces provided. 12 This question is about an experiment to determine the equilibrium constant, Kc, for the reaction between ethanoic acid and ethanol to form ethyl ethanoate and water. Two sealed test tubes were prepared. The first test tube contained 0.0400 mol ethanoic acid, 0.0400 mol of ethanol and 0.20 cm3 of concentrated hydrochloric acid. The second test tube contained 0.0400 mol ethyl ethanoate, 0.0400 mol of water and 0.20 cm3 of concentrated hydrochloric acid. After standing at 25C for two weeks, to ensure equilibrium is reached, the contents of each test tube were separately titrated with 0.200 mol dm3 sodium hydroxide solution. 0.20 cm3 of concentrated hydrochloric acid was also titrated with the same sodium hydroxide solution. (a) (i) Using data from the Data Booklet, calculate the volume, in cm3, of 0.0400 mol of ethanoic acid. (ii) What would be the best piece of apparatus to measure out the volumes of the liquids for the sealed test tubes? (2) (1)(iii) Suggest a reason why the test tubes were sealed. (1)(iv) Suggest a suitable indicator for the titration of the equilibrium mixture in either test tube, with the expected colour change. Justify your suggestion. (3) IndicatorColour change fromto Justification*P42972A01924* 19 Turn over<br /> (b) In this experiment, the following titres were obtained. Titration Contents of first test tube Contents of second test tube 0.20 cm3 concentrated hydrochloric acid Volume of 0.200 mol dm3 sodium hydroxide solution/cm3 77.10 77.05 11.70 (i) Write the equation for the reaction between ethanoic acid and ethanol to form ethyl ethanoate and water, using structural formulae. State symbols are not required. (ii) Calculate the number of moles of ethanoic acid present at equilibrium in the first test tube. (iii) Deduce the number of moles of ethanol present at equilibrium in the first test tube. (iv) Calculate the number of moles of ethyl ethanoate formed at equilibrium in the first test tube. (v) Write an expression for the equilibrium constant, Kc, for the reaction. Assuming the number of moles of water and ethyl ethanoate present at equilibrium are the same, calculate the equilibrium constant, Kc. (1) (2) (1) (1) (2) 20 *P42972A02024*<br /> (vi) Explain why the equilibrium constant for this reaction has no units. (1)(vii) Why, in fact, is the number of moles of water present in the equilibrium mixture greater than the number of moles of ethyl ethanoate? (1)(c) (i) What is the type of reaction that took place in each test tube? (2) First test tubeSecond test tube*(ii) Comment on the value of the titre for the equilibrium mixture in the second test tube compared to the first test tube. What characteristic feature of equilibrium reactions is demonstrated by the values of these titres? (2)(iii) State the role of the concentrated hydrochloric acid in the equilibrium reaction. (1)(Total for Question 12 = 21 Marks) TOTAL FOR SECTION C = 21 MARKS TOTAL FOR PAPER = 90 MARKS *P42972A02124* 21<br />

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