OCR A Jun 2015 Paper 2 Q6

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6 A branched-chain alcohol J is a liquid and has the molecular formula C5H12O. 15 (a) A student does an experiment to measure the enthalpy change of combustion, Hc, of alcohol J. (i) The student burns alcohol J using the apparatus below. thermometer clamp wick beaker water spirit burner alcohol J The student found that combustion of 1.54 g of alcohol J changes the temperature of 180 g of water from 22.8 C to 75.3 C. The specific heat capacity of water is 4.18 J g1 K1.Calculate the amount, in mol, of alcohol J that burns.Calculate the enthalpy change of combustion, Hc, of alcohol J, in kJ mol1. Give your final answer to three significant figures. Hc =kJ mol1 [4]OCR 2015 Turn over<br />
 (ii) The calculated value of Hc from this experiment is different from the value obtained from data books. 16 Apart from heat loss, suggest two reasons for the difference. Assume that the calculation has been carried out correctly.[2] (b) The enthalpy change of combustion for alcohol J can also be determined indirectly from standard enthalpy changes of formation. (i) Write an equation, including state symbols, for the chemical change that represents the standard enthalpy change of formation of the liquid alcohol J, C5H12O.[1] (ii) The equation for the complete combustion of alcohol J is shown below. C5H12O(l) + 7O2(g) 5CO2(g) + 6H2O(l) Enthalpy changes of formation, Hf, are shown in the table. Substance Hf / kJ mol1 C5H12O(l) 366 CO2(g) 394 H2O(l) 286 Calculate the enthalpy change of combustion, Hc, of alcohol J from the information given above. Hc =kJ mol1 [3]OCR 2015<br />
 (c) The branched-chain alcohol J, C5H12O, was heated under reflux with excess H2SO4 / K2Cr2O7 to form an organic compound K with the infrared spectrum below. 17 100 e c n a t t i m s n a r t 50 0 4000 3000 2000 1500 wavenumber / cm1 1000 500Determine the structures for the branched-chain alcohol J and compound K. Your answer should explain all your reasoning using the evidence given.Write an equation for the reaction of J when heated under reflux with excess H2SO4 / K2Cr2O7 to form K. Use [O] to represent the oxidising agent. Your answer needs to be clear and well organised using the correct terminology.[6]OCR 2015 Turn over<br />
 18 (d) The alcohol J is soluble in water. Explain why alcohol J is soluble in water. Use a labelled diagram to support your answer. Include relevant dipoles and lone pairs.[1] [Total: 17]OCR 2015<br />
 19 BLANK PAGE Question 7 starts on page 20 PLEASE DO NOT WRITE ON THIS PAGEOCR 2015 Turn over<br />

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