CIE Nov 2015 v1 Paper 5 Q2

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PMT In an experiment, various masses of solid barium hydroxide are added to 60.0 cm3 of a solution of hydrochloric acid contained in a polystyrene cup. In each experiment a fresh sample of the acid is taken and its initial temperature is measured. After the barium hydroxide has been added, the acid is stirred and the maximum temperature reached is noted. The results of each experiment are recorded in the table below. (a) Complete the table below to give the temperature rise obtained from each experiment to one decimal place and the amount of barium hydroxide used in mol to three signi cantgures in each case. The mass of 1 mol of barium hydroxide is 171 g. initial temperature of HCl / C mass of barium hydroxide added /g maximum temperature reached / C temperature rise / C barium hydroxide added / mol 21.0 20.6 21.2 21.8 20.5 21.4 21.2 21.0 20.8 0.500 1.00 1.50 2.00 3.00 4.00 5.00 6.00 8.00 22.2 23.0 24.9 26.5 27.8 31.1 31.6 31.4 31.2 (b) (i) Using the grid on page 7, plot a graph to show how the temperature rise varies with the [1] moles of barium hydroxide added. [2]UCLES 2015 9701/51/O/N/15<br /> PMT 12.0 11.0 10.0 C/ e s i r e r u a r e p m e 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0.000 0.010 0.020 0.030 0.040 0.050 barium hydroxide added / mol (ii) Draw two lines of bestt on your graph and state the value on the x-axis at the point of intersection of the two lines. value on the x-axis at the point of intersection is[2]UCLES 2015 9701/51/O/N/15 [Turn over<br /> (c) Use the value on the x-axis at the point of intersection to calculate the concentration of the hydrochloric acid in mol dm3. PMT [2] (d) Explain the variation in temperature that takes place when barium hydroxide is added to the hydrochloric acid.[2] (e) (i) When the experiment is done in the way described, the results are not very accurate. Apart from limitations due to the accuracy of the measuring equipment, suggest why: all the temperature rises measured are less than theoretically should be expected,the temperature rises are more inaccurate as they approach their maximum value.[2] (ii) What improvement would you make to achieve greater accuracy?[1]UCLES 2015 9701/51/O/N/15<br /> PMT (f) In another experiment, 60.0 cm3 of ethanoic acid is used instead of the 60.0 cm3 of hydrochloric acid. If the ethanoic acid has the same concentration as the hydrochloric acid, draw on your graph another pair of lines to show the results you would expect to obtain. Explain your answer.[3] [Total: 15]UCLES 2015 9701/51/O/N/15 [Turn over<br />

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