CIE Jun 2016 v5 Paper 3 Q2

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PMT In this experiment you will determine the enthalpy change, H, for the decomposition of magnesium carbonate to magnesium oxide. MgCO3(s)MgO(s) + CO2(g) In order to do this, you will determine the enthalpy changes for the reactions of magnesium carbonate and magnesium oxide with sulfuric acid. Excess of the two magnesium compounds will be used in each experiment. Then you will use Hess Law to calculate the enthalpy change for the reaction above. FA 1 is sulfuric acid, H2SO4. FA 4 is magnesium carbonate, MgCO3. FA 5 is magnesium oxide, MgO. (a) Determination of the enthalpy change for the reaction of magnesium carbonate, FA 4, with sulfuric acid, FA 1 (i) MethodSupport the plastic cup inside the 250 cm3 beaker. Use a measuring cylinder to transfer 25 cm3 of FA 1 into the plastic cup. Measure and record the initial temperature of the FA 1 in the space below. Add all the FA 4 from the container to the FA 1 in the plastic cup. Stir constantly until the maximum temperature is reached. Measure and record the maximum temperature of the contents of the cup. Rinse out the plastic cup and shake to dry for use in (b). Calculate and record the temperature rise.UCLES 2016 9701/35/M/J/16<br /> PMT Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (ii) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 C.] energy produced =J (iii) Use your answer to 1(c)(v) to calculate the number of moles of sulfuric acid in 25 cm3 of FA 1. (If you were unable to calculate the concentration of sulfuric acid in FA 1, assume that it is 1.27 mol dm3. This is not the true value.) (iv) Calculate the enthalpy change, in kJ mol1, for the reaction below. MgCO3(s) + H2SO4(aq)MgSO4(aq) + CO2(g) + H2O(l) moles of H2SO4 =mol enthalpy change =kJ mol1 (sign) (value) [6]UCLES 2016 9701/35/M/J/16 [Turn over<br /> PMT (b) Determination of the enthalpy change for the reaction of magnesium oxide, FA 5, with sulfuric acid, FA 1 (i) MethodUse the measuring cylinder to transfer approximately 40 cm3 of FA 1 into the 100 cm3 beaker. Place the beaker on a tripod and gauze. Heat FA 1 in the beaker until the temperature is between 40 C and 50 C. Support the plastic cup in the 250 cm3 beaker. Use the measuring cylinder to transfer 25 cm3 of hot FA 1 into the plastic cup. CARE. Measure and record, in the space below, the initial temperature of FA 1 in the plastic cup. Immediately, add all the FA 5 from the container to the FA 1 in the plastic cup. Stir constantly until the maximum temperature is reached. Measure and record the maximum temperature. Calculate and record the temperature rise. Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (ii) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 C.] (iii) Use your answer to (a)(iii) to calculate the enthalpy change, in kJ mol1, for the reaction below. MgO(s) + H2SO4(aq)MgSO4(aq) + H2O(l) energy produced =J enthalpy change =kJ mol1 (sign) (value) [4]UCLES 2016 9701/35/M/J/16<br /> PMT (c) Use your values for the enthalpy changes calculated in (a)(iv) and (b)(iii) to calculate the enthalpy change for the reaction below. Show clearly how you obtained your answer by drawing a Hess Law energy cycle. (If you were unable to calculate the enthalpy changes, assume that the value of the enthalpy change in (a)(iv) is 58.7 kJ mol1 and the value in (b)(iii) is 140.3 kJ mol1. Note: these are not the correct values.) MgCO3(s)MgO(s) + CO2(g) enthalpy change =kJ mol1 (sign) (value) [2] (d) (i) Calculate the maximum percentage error in the temperature rise in (b)(i). percentage error =% (ii) The magnesium oxide, FA 5, was weighed with a balance measuring to one decimal place. A student suggested that the accuracy of the experiment in (b)(i) would be improved by weighing FA 5 using a balance measuring to two decimal places. State and explain whether or not the student is correct.[2]UCLES 2016 9701/35/M/J/16 [Total: 14] [Turn over<br />

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