Cambridge A Level Chemistry 9701 — 2006 Oct/Nov Paper 5 · Variant 1

This document consists of 7 printed pages and 1 blank page. SP (SLM) T20656/2 © UCLES 2006 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level CHEMISTRY 9701/05 Paper 5 Practical Test October/November 2006 1 hour 30 minutes Candidates answer on the Question Paper. Additional materials: As listed in Instructions to Supervisors READ THESE INSTRUCTIONS FIRST Write your name, Centre number and candidate number, including practical session and laboratory where appropriate, in the spaces provided. 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. Answer all questions. You are advised to show all working in calculations. 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. Centre Number Candidate Number Name For Examiner’s Use 1 2 Total Session Laboratory

2 9701/05/O/N/06 For Examiner’s Use © UCLES 2006 1 FB 1 is a solution of sulphuric acid. FB 2 is 2.00 mol dm–3 sodium hydroxide, NaOH. Determining the concentration of sulphuric acid by thermometric titration. Record the temperature of each solution, taking care to wash and dry the thermometer before measuring the temperature of the second solution. Read the temperature to the nearest 0.5 °C, and record the temperature of each solution in Table 1.1. Calculate the average temperature of the two solutions. Table 1.1 / °C temperature of solution FB 1 temperature of solution FB 2 average temperature [2] Support the plastic cup in a 250 cm3 beaker. Use one of the measuring cylinders to transfer 40 cm3 of FB 2, sodium hydroxide solution, into the plastic cup. Replace the stopper or cover over FB 2 to prevent any reaction of carbon dioxide in the air with the sodium hydroxide. Using the second measuring cylinder transfer 10 cm3 of FB 1, sulphuric acid, into the sodium hydroxide in the plastic cup. Stir the mixture with the thermometer and note the highest temperature obtained. This temperature should be recorded in Table 1.2 for experiment 1. Empty, rinse and dry the plastic cup. Repeat the experiment with the other mixtures shown in Table 1.2 and record the highest temperature reached in each mixture. Table 1.2 experiment 1 2 3 4 5 6 volume of FB 2 / cm3 40 35 30 25 20 15 volume of FB 1 / cm3 10 15 20 25 30 35 maximum temperature / °C For each experiment use the average initial temperature from Table 1.1 to calculate and record the temperature rise after mixing the solutions. experiment 1 2 3 4 5 6 moles of sodium hydroxide 0.08 0.07 0.06 0.05 0.04 0.03 temperature rise / °C [4]

3 9701/05/O/N/06 [Turn over For Examiner’s Use © UCLES 2006 (a) Plot the temperature rise against moles of sodium hydroxide on the grid below. [2] (b) Draw two appropriate straight lines through your plotted points to show an end-point for the neutralisation. [1] (c) Deduce from your graph, the number of moles of sodium hydroxide that reacted at the end-point. …mol [1]

4 9701/05/O/N/06 For Examiner’s Use © UCLES 2006 (d) Use your answer to (c) and data from the lines in Table 1.2 marked with asterisks ( ) to calculate the volume of sulphuric acid, FB 1, reacting at the end-point. [1] (e) Calculate how many moles of sulphuric acid reacted with the sodium hydroxide at the end-point. 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) [1] (f) Calculate, in mol dm–3, the concentration of the sulphuric acid in FB 1. [1] Determining the enthalpy change for the reaction H+(aq) + NaOH(s) → H2O(l) + Na+(aq) Empty, rinse and dry the plastic cup used in the first part of the question. Using a measuring cylinder transfer 50 cm3 of FB 1 into the cup. When the temperature is steady, record its value in Table 1.3. Weigh the tube labelled FB 3 which contains solid sodium hydroxide. Record the mass in Table 1.3. Tip the contents of the tube into the plastic cup, stir, and record the highest temperature achieved in Table 1.3. Weigh the empty tube and record its mass in Table 1.3. Table 1.3 initial temperature of FB 1 / °C maximum temperature after mixing FB 1 and FB 3 / °C mass of tube + FB 3 / g mass of empty tube / g Complete the table by calculating the temperature rise and mass of FB 3 added. temperature rise / °C mass of FB 3 added / g [4]

5 9701/05/O/N/06 [Turn over For Examiner’s Use © UCLES 2006 (g) Calculate the heat energy released during the reaction of FB 1 and FB 3 in the cup. [Assume that 4.3 J are required to raise the temperature of 1 cm3 of solution by 1 °C.] energy released … … [1] (h) Use data from Table 1.3 and your answer to (f) to calculate which of sodium hydroxide or sulphuric acid is in excess. If you are unable to obtain a value in (f) use 1.50 mol dm–3 as the concentration of the sulphuric acid. 2NaOH(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) [Ar: Na, 23.0; O, 16.0; H, 1.0] … is in excess. [1] (i) Calculate the enthalpy change, ΔH, for the following reaction. H+(aq) + NaOH(s) → H2O(l) + Na+(aq) ΔH = …kJ mol–1 [1] [Total: 20]

6 9701/05/O/N/06 For Examiner’s Use © UCLES 2006 2 ASSESSMENT OF PLANNING SKILLS A sample of a mineral is found, on analysis, to contain the four elements, carbon, copper, hydrogen and oxygen. The mineral is believed to be either azurite, 2CuCO3.Cu(OH)2 or malachite, CuCO3.Cu(OH)2 Both of these minerals decompose on heating to form copper(II) oxide (CuO), carbon dioxide and water vapour. (a) Complete the equation, including state symbols, for the thermal decomposition of each mineral. azurite 2CuCO3.Cu(OH)2(s) → malachite CuCO3.Cu(OH)2(s) → [2] (b) Using only a chemical balance, a boiling-tube and a Bunsen burner, outline all the steps, in the correct order, that you would take to determine if the sample was azurite or malachite. DO NOT CARRY OUT YOUR PLAN … … … … … … … … … … … … …[5] a b c d e

7 9701/05/O/N/06 For Examiner’s Use © UCLES 2006 (c) Using the equations you have written in (a), explain by calculation, how you would process your experimental results to show if the sample of mineral was azurite or malachite. [Ar: C, 12.0; Cu, 63.5; H, 1.0; O, 16.0] … … … … … … … … … … … … … …[2] (d) If additional apparatus was available, what further measurement could be made during the thermal decomposition to confirm the identity of the mineral? … … … … …[1] [Total: 10] f g

8 9701/05/O/N/06 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 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 2006 question paper 9701 CHEMISTRY 9701/05 Paper 5 (Practical Test), maximum raw mark 30 This mark scheme is published as an aid to teachers and students, 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. The grade thresholds for various grades are published in the report on the examination for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the October/November 2006 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 - OCT/NOV 2006 9701 05 © UCLES 2006 1 Give one mark if the temperature of solutions FB 1 and FB 2 and all maximum temperatures are recorded to one decimal place. Withhold this mark if temperatures are recorded to 2 decimal places. Give one mark if the average temperature, correct to 1 decimal place, has been calculated for FB 1 and FB 2 (do not penalise decimal places twice) and the temperature rise for 0.07 mole (or 0.04 mole if appropriate) has been correctly calculated. [2] Accuracy Record the Supervisor’s standard, ringed, below the temperature rise box for experiment 2 (or experiment 5 if more appropriate). Compare the candidate’s temperature rise (corrected if necessary) for experiment 2 (or experiment 5 if more appropriate) with that obtained by the Supervisor. Award marks as follows: difference in ∆T / °C mark 0 to 0.5 4 0.5+ to 1.0 3 1.0+ to 2.0 2 2.0+ to 3.0 1 Greater than 3.0 0 [4]

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9701 05 © UCLES 2006 (a) Check the plotting of points for 0.08, 0.07, 0.04 and 0.03 mole of sodium hydroxide. Give two marks if all four points have been correctly plotted. Deduct one mark (no negative marks) for each point that has been incorrectly plotted. Also deduct from these two plotting marks (no negative marks) one mark for each of the following graphical errors: (i) moles of NaOH plotted on y-axis and ∆T plotted on the x-axis (ii) measured temperature (T) plotted instead of ∆T (iii) points are plotted in less than 4 large squares on either axis or an inappropriate scale has been selected. [2] (b) Give one mark if two straight lines have been drawn through the points and intersect. Accept two straight lines that meet (and stop) providing there is no free-hand drawing where the lines meet. Do not give this mark if curves have been drawn. If solutions have been carefully prepared there should be 3 points on each straight line with an end point between 0.05 and 0.06 mole of sodium hydroxide. [1] (c) Give one mark for correctly reading (correct to ½ small square) the moles of sodium hydroxide at the end-point from the graph. Accept a value from the intersection of any two straight lines or curves or the maximum of the graph if the two lines have been rounded. [1] Points that are on a vertical line of the grid (moles of NaOH) must be placed on the line – check the position of the centre of the cross or dot. (Penalise an error in the precision of placing an otherwise correct point only once) If uncertain about the position of the centre of a cross or dot check the other plotted points. Apply the penalty if there are two or more uncertainties points on the y-axis (∆T) should be plotted in the correct small square and within ½ small square of the position determined by the Examiner.

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9701 05 © UCLES 2006 (d) Give one mark for correctly calculating the volume of sulphuric acid at the end-point: Reacting Quantities moles of NaOH volume of H2SO4 / cm3 0.08 10 0.07 15 0.06 20 0.05 25 0.04 30 0.03 35 [1] Three ways of calculating the volume of H2SO4 (i) graph from NaOH moles x 0.08 40 - 50 = SO H of Volume 4 2 (ii) by inspection: moles NaOH 0.050 0.052 0.054 0.056 0.058 0.060 Volume H2SO4 /cm3 25.00 24.00 23.00 22.00 21.00 20.00 (iii) calculates the volume of sodium hydroxide graph from NaOH moles = 1000 volume x 2.0 , then calculates volume of H2SO4 volume of H2SO4 = 50 – volume of NaOH (e) Give one mark for 2 1 x (c) ans [1] (f) Give one mark for (d) ans 1000 x (e) ans [1]

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9701 05 © UCLES 2006 Enthalpy change check and correct if necessary the subtractions in Table 1.3 calculate 3 FB of mass e temperatur in rise correct to 1 decimal place record the candidate’s value alongside the Supervisor’s value. calculate, and record, the difference between the Supervisor and candidate. Award accuracy marks as follows: difference to Supervisor mark Up to 0.2 4 0.2+ to 0.4 3 0.4+ to 0.6 2 0.6+ to 1.0 1 Greater than 1.0 0 Deduct one mark from those awarded for accuracy (no negative marks) for each of the following: (i) in Table 1.3, any mass measurement has not been recorded to at least two decimal places. (This does not apply to a calculated mass of FB 3.) (ii) there is a subtraction error in Table 1.3 [4]

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9701 05 © UCLES 2006 (g) Give one mark for 50 x 4.3 x (candidate’s temperature rise from Table 1.3) or 50 x 4.3 x (candidate’s temperature rise from Table 1.3) x 1000 1 [1] (h) Give one mark for either of these expressions: (i) Moles of sodium hydroxide = 40 1.3 Table from mass (ii) Moles of sulphuric acid = (f) in calculated ion concentrat x 1000 50 OR Moles of sulphuric acid = 1.5 x 1000 50 Give one further mark for both expressions and correct statement of the reagent in excess. If (2 x moles of H2SO4) > moles of NaOH then H2SO4 is in excess. If (2 x moles of H2SO4) < moles of NaOH then NaOH is in excess. [2] (i) Give one mark for the following: If sulphuric acid is stated as in excess in (h), 1000 1 x (h) from NaOH of moles (g) ans If sodium hydroxide is in excess in (h), 2 1 x 1000 1 x (h) from SO H of moles (g) ans 4 2 Do not give this mark unless the numerical value is correctly in kJ. Give one mark if a negative (-ve) sign is shown. This is an independent mark. [2] There are 22 marking points in question 1. Record the marks awarded and cancel any marks in excess of 20, recording 20 Max. [Total for Question 1 20 marks]

Page 7 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9701 05 © UCLES 2006 2 ASSESSMENT OF PLANNING SKILLS. (a) Give one mark for correct stoichiometry and state symbols for malachite. CuCO3.Cu(OH)2 (s) → 2CuO(s) + CO2(g) + H2O(g) Give one mark for correct stoichiometry for azurite. 2CuCO3.Cu(OH)2 → 3CuO + 2CO2 + H2O [2] (b) Reward the following points (which are shown in the correct order): a Weigh the empty tube but not for taring the tube Do not give this mark if for example an evaporating basin has been weighed and used for heating the sample b Weigh the (tube) + mineral or Tared (tube) + mineral weighed or Known amount of mineral taken c Heat the mineral Do not allow heating using a water-bath d Cool and reweigh e (Continue heating and weighing) to constant mass (Reheating/reweighing twice can be accepted as heating to constant mass) Deduct one mark from these potential five marks (no negative marks) for any of the following: (i) the points are not awarded in a correct practical sequence or (ii) an unnecessary step (e.g. making a solution) has been introduced or (iii) apparatus has been used at this stage to collect/measure/test the gas(es) given off. [5] (c) (i) point (f) Give one mark if: the correct Mr for Malachite is seen = 221.0 and a calculation determines moles or masses of malachite and copper oxide or the correct Mr for Azurite is seen = 344.5 and a calculation determines moles or masses of azurite and copper oxide (ii) point (g) Give one mark if: the equivalent Mr and calculation is seen for the other mineral and the moles or masses compared and linked to the equations to show the identity of the mineral [2]

Page 8 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9701 05 © UCLES 2006 Both marks can be obtained from calculations that start with equal masses of malachite and azurite and show that azurite gives less CuO. Accept 221 mineral of mass etc where the candidate has “invented” exemplar masses even if the values calculated do not illustrate the ratios from the equation. Award point (g) if the correct process has been followed but an incorrect Mr has been used. Do NOT give credit for Mr of azurite = 422 Formula of azurite read as 2(CuCO3.Cu(OH)2) (d) Give one mark for any of the following: (i) measuring the volume of carbon dioxide evolved (ii) measuring mass of carbon dioxide and water vapour absorbed by soda-lime (iii) measuring mass of water absorbed by anhydrous calcium chloride, concentrated sulphuric acid or silica gel (iv) condensing water vapour and weighing the water collected [1] [Total for Question 2 10]