AQA AS Jun 2016 Paper 2 Q2

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2 Alcohols such as methanol (CH3OH), ethanol (CH3CH2OH) and propan-1-ol (CH3CH2CH2OH) are good fuels. 0 2 . 1 A student carried out an experiment to determine the enthalpy of combustion of methanol.Methanol was placed in a spirit burner and the mass of the spirit burner measured. The student placed 100 g of water in a copper calorimeter and clamped it above the spirit burner. The burner was lit and allowed to burn for a few minutes. The flame was then extinguished and the new mass of the spirit burner found. The measured temperature rise was 38.0 C. The specific heat capacity of water is 4.18 J K1 g1. Figure 1, a diagram of the apparatus, is shown alongside Table 1 which shows the measurements the student recorded. Figure 1 Table 1 Mass of burner containing methanol before experiment Mass of burner containing methanol after experiment 214.02 g 212.37 g Use the students data to calculate an experimental value for the enthalpy of combustion of methanol in kJ mol1. [4 marks] *04* M/JUN16/7404/2<br />
. 2 Suggest one reason, other than incomplete combustion or heat transfer to the atmosphere, why the students value for the enthalpy of combustion of methanol is different from that in a Data Book. [1 mark] . 3 The uncertainty in each of the temperature readings from the thermometer in this experiment was 0.25 C. This gave an overall uncertainty in the temperature rise of 0.5 C. Calculate the percentage uncertainty for the use of the thermometer in this experiment. [1 mark] . 4 The student said correctly that using a thermometer with an overall uncertainty for the rise in temperature of 0.5 C was adequate for this experiment. Explain why this thermometer was adequate for this experiment. [1 mark] . 5 The enthalpy of combustion of ethanol is 1371 kJ mol1. The density of ethanol is 0.789 g cm3. Calculate the heat energy released in kJ when 0.500 dm3 of ethanol is burned. Give your answer to an appropriate number of significant figures. [3 marks] 0 2 0 2 0 2 0 2 *05* Turn overM/JUN16/7404/2<br />

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