Cambridge A Level Chemistry 9701 — 2007 Oct/Nov Paper 5 · Variant 1

This document consists of 9 printed pages and 3 blank pages. SPA (NF/CGW) T30933/8 © UCLES 2007 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level 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 fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You are advised to show all working in calculations. Use of 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. * 6 3 6 4 0 2 8 0 6 9 * CHEMISTRY 9701/05 Paper 5 Planning, analysis and evaluation October/November 2007 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. For Examiner’s Use 1 2 Total

2 9701/05/O/N/07 For Examiner’s Use © UCLES 2007 1 The hydroxides of Group I metals (LiOH, NaOH, KOH, RbOH, CsOH) are highly corrosive white solids which rapidly absorb water vapour on exposure to the atmosphere. All of these solids dissolve exothermically in water. The enthalpy change of solution, ΔHsoln, is the energy change associated with the following reaction. M represents the Group I metal. MOH(s) + (aq) M+(aq) + OH–(aq) The following diagram represents theoretical stages in the formation of aqueous MOH. lattice energy hydration enthalpy of the ions
H hydration
H soln M OH(s) + (aq) M +(g) + OH-(g) + (aq) M +(aq) + OH-(aq) Lattice energy and hydration enthalpy are both more exothermic when ions carry a higher charge and/or ions have a smaller radius. When comparing Group I hydroxides, changes in ΔHhydration are more significant than changes in lattice energy. (a) By considering trends in the size and charge of the ions, predict the likely trend in ΔHsoln from LiOH to CsOH and sketch your prediction. … … … LiOH NaOH CsOH RbOH KOH
Hsoln [2]

3 9701/05/O/N/07 [Turn over For Examiner’s Use © UCLES 2007 (b) The enthalpy change of solution, ΔHsoln, for any Group I hydroxide can be measured experimentally in the laboratory. In experiments to compare ΔHsoln for LiOH, NaOH, KOH, RbOH, CsOH state the independent variable … , the dependent variable … , the other variable to be controlled … … . [3] (c) Draw a labelled diagram to show the apparatus you would use to obtain data from which ΔHsoln could be determined. From the information given on page 2 and the apparatus you plan to use, identify two possible sources of error in the experiment and state how you would minimise the effect of each. error 1 … … error 2 … … [3] (d) Identify a health and safety risk in the experiment and explain how you would minimise it when carrying out the experiment. … … … [2]

4 9701/05/O/N/07 For Examiner’s Use © UCLES 2007 (e) Describe the procedure you would carry out to find the enthalpy change of solution, ΔHsoln, for one of the Group I hydroxides. Your plan should give a step-by-step description of the method, including • how you would measure the independent variable, • how you would measure the dependent variable, • appropriate masses and volumes of reagents. The following data may be of use in planning the detail of your experiment. Ar: Li, 6.9; Na, 23.0; K, 39.1; Rb, 85.5; Cs, 133.0, O, 16.0; H, 1.0 4.3 J are required to raise the temperature of 1.0 cm3 of any solution by 1°C. … … … … … … … … … … … … … … … … … … … … … [4]

5 9701/05/O/N/07 [Turn over For Examiner’s Use © UCLES 2007 (f) The procedure is repeated for each of the Group I hydroxides. Show how you would tabulate the results for all the experiments. [1] (g) Show how you would use the results of one experiment to calculate the enthalpy change of solution, ΔHsoln, for the reaction. [1] [Total: 16]

6 9701/05/O/N/07 For Examiner’s Use © UCLES 2007 2 Students were asked to investigate how the rate of reaction between magnesium ribbon and hydrochloric acid varied with change in concentration of the acid. 2HCl(aq) + Mg(s) MgCl2(aq) + H2(g) Student 1, looking at the equation, suggested the following. rate of production of hydrogen gas = k[HCl]2 This student used the following apparatus to investigate the rate of production of hydrogen gas, H2. gas syringe magnesium ribbon dilute hydrochloric acid The student used a 500 cm3 measuring cylinder to measure 100 cm3 of dilute acid into a conical flask. A 1 cm length (0.01 g) of magnesium ribbon was dropped into the acid in the flask and the stopper quickly replaced in the flask. The stop-clock was started and the volume of gas collected was measured at 0.5 minute intervals. The results of the experiment were recorded as shown in the table below. time / min volume of H2 / cm3 time / min volume of H2 / cm3 0.5 15.5 5.5 80.0 1.0 25.0 6.0 82.5 1.5 34.0 6.5 85.0 2.0 43.0 7.0 87.0 2.5 51.0 7.5 87.5 3.0 59.0 8.0 91.0 3.5 65.0 8.5 92.5 4.0 69.5 9.0 93.5 4.5 74.0 9.5 94.5 5.0 75.0 10.0 95.0

7 9701/05/O/N/07 [Turn over For Examiner’s Use © UCLES 2007 (a) Plot a graph of volume of hydrogen produced against time. [2] (b) Identify clearly on your graph any anomalous readings and suggest a reason for these anomalous readings. … … [1] (c) On the graph you have plotted, construct a line from which you can calculate the initial rate of reaction. Calculate the initial rate of reaction and show your working. initial rate = … cm3 min–1 [2]

8 9701/05/O/N/07 For Examiner’s Use © UCLES 2007 (d) By considering the experimental method described, explain why the plotted line does not pass through 0,0. … … [1] (e) Identify a further source of error in the method described and suggest a change to the method to reduce this error. … … … [1] (f) Students 2-8 carried out similar experiments with different concentrations of acid. The initial rate of reaction was calculated for each of their experiments and is shown in the table below. Enter in the table the initial rate you have calculated for Student 1. student volume of acid used / cm3 volume of water used / cm3 mass of magnesium used / g initial rate / cm3 min–1 relative concentration of acid 1 100 0 0.01 1.0 2 45 55 0.01 8.0 3 90 10 0.01 16.4 4 60 40 0.01 11.5 5 100 100 0.01 9.3 6 35 65 0.01 6.8 7 80 20 0.01 15.2 8 60 240 0.01 3.3 Use the additional column of the table to record calculated values for the relative concentration of the hydrochloric acid. relative concentration of acid = volume of acid used total volume [1]

9 9701/05/O/N/07 For Examiner’s Use © UCLES 2007 (g) Plot the initial rate of reaction against the relative concentration of the acid. [3] (h) Is the prediction made by Student 1 consistent with your graph? Explain your answer. … … … … … [2] (i) Do any of the points you have plotted in (g) reduce your confidence in the conclusion that can be drawn? Justify your answer. … … … … … [1] [Total: 14]

12 9701/05/O/N/07 BLANK PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2007 question paper 9701 CHEMISTRY 9701/05 Paper 5 (Practical 2), 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. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes must be read in conjunction with the question papers and the report on the examination. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the October/November 2007 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 05 © UCLES 2007 MARK SCHEME Breakdown of marks Question 1 Question 2 Skill Total marks Marks Defining the problem 5 5 0 Planning 15 marks Methods 10 10 0 Dealing with data 8 0 8 Evaluation 4 1 3 Analysis, conclusions and evaluation 15 marks Conclusion 3 0 3 Question Sections Indicative material Mark 1 (a) PLAN Problem Use of ion size and ionic charge or charge density to predict decreasing ∆Hsoln for LiOH to CsOH (Do not give this mark if reference is to size of atom rather than ion) Correct sketch for candidate predicted trend. Accept any appropriate downward or upward trend. Points alone are sufficient. If no trend is predicted in the first part of (a) the second mark can be given for a downward trend. 1 1 1 (b) PLAN Problem Independent variable accept any of the following; 1. mass/weight/moles/amount of MOH (not metal), 2. ”which MOH used”, 3. Group I hydroxide. Dependent variable accept any of the following; 1. temperature rise/change, 2. heat produced/energy change, 3. ∆Hsoln. Controlled variable accept either of the following; 1. volume/weight of water, (not amount) 2. mass of hydroxide – only allowed if “which hydroxide” is given as the independent variable. 1 1 1

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 05 © UCLES 2007 Question Sections Indicative material Mark 1 (c) PLAN Methods ACE Evaluation PLAN Methods Apparatus diagram showing (insulated) container and thermometer. Non-insulated beaker is acceptable. (Do not give this mark if there is a Bunsen or a water bath) Give one mark for any two of the following; 1. solid absorbing water vapour, 2. heat loss from apparatus, (accept open cup/calorimeter) (conduction, convection and radiation are treated as separate errors) 3. loss of material – solution overflows or spray, 4. inaccurate temperature measurement, 5. small temperature rise. Do not give this mark for reference to laboratory temperature or draughts in the laboratory. Give one mark for any two of the following - if linked to the source of error above; 1. keep weighed solid in closed container or use as soon as weighed (not kept under oil or in a vacuum) 2. practical improvement to insulation, 3. larger container or smaller quantities used, (accept use of lid for minimising spray) 4. more accurately calibrated thermometer, 5. use larger mass of the hydroxide or smaller volume of water. (Give one of these two marks for one error and step to minimise the error) 1 1 1 1 (d) PLAN Methods Identify the corrosive nature of the solid/aqueous hydroxides. If corrosive is identified as the hazard give this mark for using gloves or If solution boils over or sprays out but is not described as corrosive give this mark for using two of gloves, lab coat, eye protection, (face) mask 1 1

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 05 © UCLES 2007 Question Sections Indicative material Mark 1 (e) PLAN Methods 1. weighs a stated mass of named hydroxide. mass to be between 0.05 mol and 0.25 mol (See appendix) and candidate describes the weighing of the solid (two possible methods) (i) empty bottle/empty (plastic) cup; and bottle + solid/(plastic) cup + solid (ii) bottle + solid and bottle + residual solid 2. measures between 50 cm3 and 200 cm3 of water and describes the measurement of the volume (measuring cylinder, burette, pipette) (apparatus for measuring the water and the volume used may be shown in the diagram) (A larger or smaller volume of water can be accepted if it is related to a specified capacity container. e.g. 400 cm3 water in 500 cm3 beaker 30 cm3 water in 50 cm3 beaker) 3. Initial and highest temperatures recorded 4. Step by step procedure described Minimum steps required: Weigh solid, specified/measured volume of water and measured temperature rise 1 1 1 1 1 (f) PLAN Methods Table showing metal hydroxides two weighings - unless tare specified, initial and final temperatures. Ignore units. Do not give this mark if candidate lists metals for the experiment rather than the metal hydroxides unless the column is headed “metal hydroxide” / “hydroxide” or metals have been penalised in (e). If weighings are missing in (e) the mark can be given in (f) if the mass of metal hydroxide is tabulated. If temperature readings are missing in (e) the mark can be given in (f) if ∆T is tabulated. 1

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 05 © UCLES 2007 Question Sections Indicative material Mark 1 (g) PLAN Methods Shows how enthalpy change of solution is calculated for one hydroxide using moles T mc∆ Be certain that m refers to liquid and not solid or liquid + solid To gain this mark there must be an expression for converting mass of metal hydroxide to moles, including the correct numerical value for the appropriate Mr. This calculation or numerical evidence for Mr may be found in earlier work – (e) or (f) 1 Question 1 Total 16 Question Sections Indicative material Mark 2 (a) ACE Data Appropriate labels, units and linear scales that will accommodate all points in the data table Acceptable form of units (from 9701 syllabus) volume time / cm3 / min (cm3) (min) accept mins volume in cubic centimetres time in minutes Do not accept volume cm3 time min Points plotted correctly Points should be within ½ small square, in either direction) of the correct position and within the correct half of the appropriate small square. To gain this mark there must be an attempt to draw a smooth curve 1 1

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 05 © UCLES 2007 Question Sections Indicative material Mark 2 (b) ACE Evaluation ACE Evaluation Data at either 5.0 or 7.5 minutes identified (Ignore any other point) and suggests one of the following 1. irregular movement of syringe (sticking), 2. H2 gas lifts Mg out of the acid solution, 3. reading taken before indicated time. 1 2 (c) ACE Data Constructs initial “tangent”. Accept either of the following; 1. an attempted tangent to the curve at (t = 0), 2. a straight line drawn through the plotted points at 0.5, 1.0, 1.5 and 2.0 minutes. Reads coordinates from any tangent correct to ½ small square in either direction from the tangent and uses the coordinates in a correct expression for the gradient. 1 1 2 (d) ACE Evaluation Award the mark for either of the following; 1. stopwatch started after magnesium ribbon dropped into flask, (flask sealed and gas collected), 2. gas pushed into the syringe when inserting the bung. 2 (e) ACE Conclusions Identifies as a further source of error one of the following – and gives an appropriate method of reducing the error; 1. gas collected before timing starts or gas pushed into syringe when bung inserted – if not already given in (d), 2. use of 500 cm3 measuring cylinder to measure 100 cm3 of acid, 3. 0.01 g of magnesium weighed on a balance weighing to 2 decimal places. 4. loss of gas before the bung is inserted 1 2 (f) ACE Data Calculates relative concentration of acid in each mixture. (See appendix) (1 or 2 sig fig acceptable) (N.B. not all of the experiments have a total volume of 100 cm3) 1

Page 7 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 05 © UCLES 2007 MARK SCHEME 9701/05 November 2007 Page 6 of 7 Coordination Question Sections Indicative material Mark 2 (g) ACE Data Plots initial rate v relative concentration with appropriate labels, units and scales. Scales – points must be plotted over ½ length of each available axis. Do not penalise “awkward” scales. Points for students 3 4 and 8 correctly plotted and no others obviously wrong Points plotted to ½ small square in either direction and within correct half square Straight line drawn through points for students 2 – 8. Does not have to pass through 0,0. The straight line should have points either side of the line. 1 1 1 2 (h) ACE Conclusions Concludes that prediction is wrong for a straight line (or right for a curve) and refers to the shape of the graph. Only give this mark if the candidate has drawn a straight line through the points in (g) Concludes one of the following: 1. the rate of reaction = k[HCl], 2. reaction is first order wrt HCl, 3. reaction is directly proportional to [HCl] (even if straight line does not pass through 0,0), 4. the graph/line for a 2nd order reaction would be a curve/parabola. 1 1 2 (i) ACE Evaluation Award this mark for any answer that is acceptable for the points plotted, line drawn by the candidates. If the data has been correctly processed there should be a good distribution of points for a best-fit straight line. Ignore student 1 – unless the candidate refers to this point. If the relative concentration has been calculated to only 1 significant figure there is lower confidence in the point plotted for Student 2. 1 Question 2 Total 14

Page 8 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 05 © UCLES 2007 Appendix Question 1 (e) mass of metal hydroxide / g metal hydroxide Mr 0.05 mol 0.10 mol 0.15 mol 0.20 mol 0.25 mol LiOH 23.9 1.195 2.39 3.585 4.78 5.975 NaOH 40.0 2.00 4.00 6.00 8.00 10.00 KOH 56.1 2.805 5.61 8.415 11.22 14.025 RbOH 102.5 5.125 10.25 15.375 20.50 25.625 CsOH 150.0 7.50 15.00 22.50 30.00 37.50 Question 2 (f) student volume of acid used / cm3 volume of water used / cm3 mass of magnesium / g initial rate / cm3 min-1 relative concentration of acid 1 100 0 0.01 1.0 1.0 2 45 55 0.01 8.0 0.45 0.5 3 90 10 0.01 16.4 0.90 0.9 4 60 40 0.01 11.5 0.60 0.6 5 100 100 0.01 9.3 0.50 0.5 6 35 75 0.01 6.8 0.35 0.4 7 80 20 0.01 15.2 0.80 0.8 8 60 240 0.01 3.3 0.20 0.2 2 sig fig 1 sig fig