CIE Mar 2016 v3 Paper 3 Q1

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You will determine the enthalpy change, H, of the reaction between magnesium and hydrochloric acid. To do this you will measure the change in temperature when a piece of magnesium ribbon reacts with an excess of hydrochloric acid. Mg(s) + 2HCl (aq)MgCl 2(aq) + H2(g) PMT FA 1 is hydrochloric acid, HCl. FA 2 is magnesium ribbon, Mg. (a) MethodWeigh the FA 2 and record the mass in the space below. Support the plastic cup in the 250 cm3 beaker. Coil the FA 2 so that it will fit into the bottom of the plastic cup then remove it. Use the measuring cylinder to transfer 25 cm3 of FA 1 into the plastic cup. Place the thermometer in the acid and tilt the cup if necessary so that the bulb of the thermometer is fully covered. Record the temperature at time = 0 in the table of results. Start timing and do not stop the clock until the whole experiment has been completed at time = 8 minutes. Record the temperature of the acid every half minute for 2 minutes. At time = 2 2 Record the temperature of the mixture at time = 3 minutes and complete the table by recording the temperature every half minute. Stir the mixture between thermometer readings. 1 minutes carefully drop the coil of FA 2 into the acid and stir the mixture. Results mass of FA 2 =g time / minutes temperature / C time / minutes 1 4 2 temperature / C 1 2 1 1 2 1 2 2 1 3 2 1 5 2 1 6 2 1 7 2 II III IV [4]UCLES 2016 9701/33/F/M/16<br /> PMT (b) Plot a graph of temperature on the y-axis against time on the x-axis on the grid below. The scale for the temperature axis should extend 10 C greater than the maximum temperature you recorded. You will use the graph to determine the theoretical maximum temperature rise at 2 2 1 minutes. II III IV Draw two lines of best fit through the points on your graph, the first for the temperature before adding FA 2 and the second for the cooling of the mixture once the reaction is complete. Extrapolate the two lines to 2 2 the theoretical rise in temperature at this time. 1 minutes, draw a vertical line between the two and determine theoretical rise in temperature at 2 2 1 minutes =C [4]UCLES 2016 9701/33/F/M/16 [Turn over<br /> PMT (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Use your answer to (b) to calculate the heat energy, in joules, given out when FA 2 is added to FA 1. (Assume 4.2 J of heat energy raises the temperature of 1.0 cm3 of the mixture by 1.0 C.) (ii) Use the Periodic Table on page 12 and your answer to (i) to calculate the enthalpy change, in kJ mol1, when 1 mole of magnesium, FA 2, reacts with hydrochloric acid, FA 1. heat energy evolved =J enthalpy change =kJ mol1 (sign) (value) [3] (d) A student carried out the same procedure using the same concentration of sulfuric acid, H2SO4, instead of hydrochloric acid. Before starting the experiment the student predicted that the enthalpy change would be twice that with hydrochloric acid. Was the student correct? Explain your answer.[1] (e) The enthalpy change determined in (c)(ii) is only an approximation of the actual value. Suggest and explain one improvement you would make to the method in (a) to increase the accuracy of the experiment.[1] [Total: 13]UCLES 2016 9701/33/F/M/16<br />

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