Cambridge A Level Chemistry 9701 — 2013 Oct/Nov Paper 5 · Variant 1

READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fl uid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. You may lose marks if you do not show your working or if you do not use appropriate units. Use of a Data Booklet is unnecessary. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. CHEMISTRY 9701/51 Paper 5 Planning, Analysis and Evaluation October/November 2013 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Level This document consists of 9 printed pages and 3 blank pages. [Turn over IB13 11_9701_51/4RP © UCLES 2013 *3046788947* For Examiner’s Use 1 2 Total

2 9701/51/O/N/13 © UCLES 2013 For Examiner’s Use 1 Ammonium nitrate, NH4NO3, is soluble in water (approximately 2.5 mol / 100 g at 25 °C). The molar enthalpy of solution of a solid is defi ned as the enthalpy change when one mole of the solid is dissolved in water. NH4NO3(s) NH4 +(aq) + NO3 –(aq) ∆Hsoln = +26.5 kJ mol–1 (a) (i) Predict how the temperature of water, initially at 25 °C, would change as ammonium nitrate is dissolved. Explain this prediction in terms of lattice energy and the enthalpy of hydration of ions. Prediction of the temperature change … … … Explanation … … … … (ii) In the space below, sketch a graph to show your prediction of temperature change with concentration. Use two labelled axes and include an origin. [4] (b) If you were to carry out an experiment to investigate how the temperature change of the solution varies as the concentration changes name, (i) the independent variable, … (ii) the dependent variable. … [1]

3 9701/51/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (c) You are to plan an experiment to determine as accurately as possible how the temperature change varies when different solutions are made, each with different concentrations of ammonium nitrate. You are reminded that the approximate solubility of ammonium nitrate is 2.5 mol / 100 g at 25 °C. The following information gives some of the hazards associated with ammonium nitrate. Ammonium nitrate NH4NO3. Contact with combustible material may cause fi re. Ex- plosive when mixed with combustible material. Do not allow the salt to become contaminated with organic matter and do not grind it. Solutions should be diluted to less than 0.5 mol dm–3 for disposal. You should use only standard apparatus found in a school or college laboratory. Draw a diagram of the apparatus and experimental set up you would use showing clearly the following: (i) the apparatus used, such as the reaction vessel, and how the thermometer will be positioned in order to measure the temperature of the solution as accurately as possible, (ii) how the apparatus will be insulated. Label each piece of apparatus used, indicating its size or capacity and both the temperature range and the precision of the thermometer. [3]

4 9701/51/O/N/13 © UCLES 2013 For Examiner’s Use (d) Using the apparatus shown in (c) design an experiment to test your prediction in (a)(ii) of how the temperature change of the solution varies with solutions of different concentration. In addition to the apparatus normally found in a laboratory you are provided with the following materials; a supply of solid ammonium nitrate, distilled (deionised) water. Give a step-by-step description of how you would carry out the experiment to include; (i) the number of experiments you would do, (ii) the temperature measurements you would take, (iii) the volume of water you would use, (iv) a calculation to show the maximum mass of ammonium nitrate you could use for your volume of water in (iii) and a range of masses for the other experiments. [Ar: H, 1.0; N, 14.0; O, 16.0] [4]

5 9701/51/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (e) State one hazard that must be considered when planning the experiment and describe a precaution that should be taken to keep risks from this hazard to a minimum. You may use the information in (c) if you wish. … … … … … … [1] (f) In order to test your prediction in (a)(ii), you would need to plot a graph. In the space below, draw a table with appropriate headings, in which you would record all your experimental data and calculated values necessary for the construction of the graph. The headings must include the appropriate units. [2] [Total: 15]

6 9701/51/O/N/13 © UCLES 2013 For Examiner’s Use 2 The solubility of hydrated sodium sulfate, Na2SO4.10H2O, in water increases with temperature. At a temperature between 25 °C and 70 °C there is a transition and the solubility becomes that of Na2SO4. The units of solubility are grams per one hundred grams of water, g / 100 g water. An experiment was carried out to investigate this solubility and determine the transition temperature between the two forms of sodium sulfate. ● An empty boiling tube was weighed and the mass recorded. ● Some distilled water was added to the boiling tube and the new mass recorded. ● A small sample of hydrated sodium sulfate was added and this new mass recorded. ● The boiling tube was carefully heated with stirring until all the solid had dissolved. ● The apparatus was cooled slowly while constantly stirring and the temperature recorded when the fi rst crystals appeared in the tube. (a) The results of several of these experiments are recorded below. Process the results in the table to calculate the solubility, in g / 100 g water, of the sodium sulfate for each of the temperatures listed. Record these values to two decimal places in the additional columns of the table. You may use some or all of the columns. Label the columns you use. For each column you use include units where appropriate and an expression to show how your values are calculated. Use the column headings A to H for these expressions (e.g. A–B). A B C D E F G H experiment number mass of boiling tube / g mass of boiling tube + water / g mass of boiling tube + water + solid / g crystallising temperature °C 1 10.20 35.20 36.45 0.0 2 10.35 30.35 31.60 10.0 3 10.10 35.10 40.10 20.0 4 9.80 29.20 36.96 30.0 5 9.95 32.95 44.06 40.0 6 9.90 34.90 46.65 50.0 7 9.70 30.70 40.32 60.0 8 10.45 30.45 39.55 70.0 9 10.05 35.05 46.30 80.0 10 10.10 40.10 53.45 90.0 [3]

7 9701/51/O/N/13 © UCLES 2013 [Turn over (b) Plot a graph to show the variation of solubility (y-axis) with temperature (x-axis). Draw two curves of best fi t and extrapolate to locate their intersection at the transition temperature. [4]

8 9701/51/O/N/13 © UCLES 2013 For Examiner’s Use (c) From your graph, state the transition temperature and the solubility at which it occurs. [2] (d) (i) In an attempt to repeat the 4th experiment using the same masses of water and solid, the temperature was mistakenly read and recorded before crystals appeared. Place a cross on your graph to represent the point that would have been obtained. (ii) If this was a valid point, what effect would this have on your transition temperature? Explain your answer. … … … [2] (e) It was found that all the mass recordings in columns C and D had been made with a balance that had been zeroed incorrectly and they should all have been 0.3 g smaller. The masses recorded in column B can be considered to be accurate. Using the corrected masses from experiment 6 calculate the new value of the solubility. By comparing this with the original solubility value for experiment 6 calculate the percentage error difference. [2]

9 9701/51/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (f) From the pattern of solubility demonstrated by your graph, predict and explain whether the dissolving of the two forms of sodium sulfate in water are exothermic or endothermic reactions. prediction for Na2SO4.10H2O … … explanation … … … … prediction for Na2SO4 … … explanation … … … … [2] [Total: 15]

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CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Level MARK SCHEME for the October/November 2013 series 9701 CHEMISTRY 9701/51 Paper 5 (Planning, Analysis, Evaluation), maximum raw mark 30 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 2013 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 51 © Cambridge International Examinations 2013 Question Expected Answer Mark 1 (a) (i) (The temperature would) decrease The lattice enthalpy is more negative/exothermic than the (sum of the) enthalpies/energies of hydration. 1 1 (ii) OR OR ecf from 1(a)(i) 2

Page 3 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 51 © Cambridge International Examinations 2013 (b) (i) concentration/concentration change (ii) temperature change/decrease in temperature (allow ecf on (a)(i)) 1 (c) Diagram shows a container labelled with its capacity (between 25 cm³ and 250 cm³) and with the thermometer in a solution. The apparatus is insulated and has a lid. Thermometer range must include 25 °C and with a precision of between 0.1°C and 0.5 °C. 1 1 1 (d) A minimum of 5 workable experiments using masses or concentrations. Measures initial and final temperatures. Measures a volume of water AND the volume of water will fit into container labelled in (c). States a mass which is the maximum for a volume of water stated. 1 1 1 1 (e) Ammonium nitrate may cause a fire/explosion so must not be ground up OR dilute to less than 0.5 mol dm–3 before disposal. 1 (f) Columns must include units: Mass of ammonium nitrate used / any mass unit Volume / mass of water used / any volume or mass units Initial temperature / °C Final temperature / °C Temperature fall / change in temperature / °C Concentration of ammonium nitrate / any concentration units Four columns correct Five or six columns correct 1 1 [Total: 15]

Page 4 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 51 © Cambridge International Examinations 2013 2 (a) F G H solubility D–C / g C–B / g [(F × 100)] / G / g/ 100 g 1.25 25.00 5.00 1.25 20.00 6.25 5.00 25.00 20.00 7.76 19.40 40.00 11.11 23.00 48.30 11.75 25.00 47.00 9.62 21.00 45.81 9.10 20.00 45.50 11.25 25.00 45.00 13.35 30.00 44.50 Heading for final column calculating the solubility is given correctly with units. All data is to 2 decimal places. Allow 1 error. Data in final column is correct. Allow 1 error in computation. 1 1 1 (b) The x-axis must start at zero and be labelled ‘temperature / °C’ OR T / °C and y-axis as ‘solubility (of sodium sulfate) g/100g’. Plotted points must cover at least half the grid in both directions. All 10 points plotted correctly. First (left-hand) curve is smooth passing through (or extremely close to) all the points and does not deviate to accommodate a mis-plot or incorrect point. Curve intersects with a second curve at or above the candidate’s solubility for experiment 5. Second curve (right hand) is smooth passing through (or extremely close to) all the points and does not deviate to accommodate a mis-plot or incorrect point. 1 1 1 1 (c) the temperature is read correctly the solubility is read correctly 1 1 (d) (i) Cross is on the 40 g / 100 g line and to the right of the point plotted at 30 °C. 1 (ii) Transition temperature would be higher as intersection of curves would be at a higher temperature. 1 (e) Solubility is 47.6 (g / 100g) 1.2% OR 1.21% OR 1.28% OR 1.3% 1 1

Page 5 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 51 © Cambridge International Examinations 2013 (f) Na2SO4.10H2O endothermic because solubility increases with increasing temperature (or reverse argument) Na2SO4 exothermic because solubility decreases with increasing temperature (or reverse argument) For endothermic and exothermic correctly assigned For providing the correct reasons 1 1 [Total: 15]