Cambridge A Level Chemistry 9701 — 2005 May/June Paper 5 · Variant 1

This document consists of 10 printed pages and 2 blank pages. SP (SC/SLM) S85065/2 © UCLES 2005 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level CHEMISTRY 9701/05 Paper 5 Practical Test May/June 2005 1 hour 30 minutes Candidates answer on the Question Paper. Additional materials: As listed in the Instructions to Supervisors. READ THESE INSTRUCTIONS FIRST Write your details, including practical session and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen in the spaces provided on the Question Paper. 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. The number of marks is given in brackets [ ] at the end of each question or part question. You are advised to show all working in calculations. Use of a Data Booklet is unnecessary. Centre Number Candidate Number Name For Examiner’s Use If you have been given a label, look at the details. If any details are incorrect or missing, please fill in your correct details in the space given at the top of this page. Stick your personal label here, if provided. 1 2 3 TOTAL SESSION LABORATORY

2 9701/05/M/J/05 1 FB 1 is 2.00 mol dm–3 hydrochloric acid, HCl. FB 2 is a solid carbonate, X2CO3 in a stoppered tube. FB 2 reacts with hydrochloric acid as shown in the equation below. X2CO3(s) + 2HClaq) →2XCl(aq) + H2O(l) + CO2(g) You are to determine the mass of carbon dioxide evolved in the reaction of the carbonate FB2 with excess hydrochloric acid and to calculate from the results of the experiment the relative atomic mass, Ar, of X. (a) Use a measuring cylinder to place 100 cm3 of FB 1 into a 250 cm3 conical flask. Weigh the flask and acid. Record the mass in Table 1.2. Weigh the stoppered tube containing FB 2. Record the mass in Table 1.1. Add the weighed FB 2, a little at a time with swirling, to the acid in the conical flask. N.B. Take care to avoid excessive bubbling and loss of acid as ‘spray’. When all of the FB 2 has been added from the tube, reweigh the empty tube (with its stopper) and record the mass in Table 1.1. Leave the flask to stand for 2-3 minutes and then reweigh the flask and solution. Record the mass in Table 1.2. Table 1.1 Table 1.2 [3] (b) Calculate the mass of FB 2 used. ………………… g [1] (c) Calculate the mass of carbon dioxide evolved. ………………… g [1] For Examiner’s Use © UCLES 2005 mass of stoppered tube + FB 2 / g mass of empty tube + stopper / g mass of flask + acid / g mass of flask + solution after the reaction / g

3 9701/05/M/J/05 [Turn over (d) Use your answer to (c) and the equation for the reaction to calculate the number of moles of X2CO3 that reacted. [Ar: C, 12.0; O, 16.0.] ………………… moles [1] (e) Calculate the relative molecular mass, Mr, of X2CO3. Mr = ………………… [1] (f) Calculate the relative atomic mass, Ar, of X. [Ar: C, 12.0; O, 16.0.] Ar = ………………… [1] [Total : 8] For Examiner’s Use © UCLES 2005

4 9701/05/M/J/05 2 FB 3 is 1.50 mol dm–3 sodium hydroxide, NaOH. FB 4 is an aqueous solution containing hydrochloric acid. FB 4 has been prepared by dissolving 42.40 g of the carbonate FB 2 in an excess of 3.00 mol dm–3 hydrochloric acid and making the solution up to 1 dm3 in a graduated flask by adding more 3.00 mol dm-3 hydrochloric acid. You are to perform a thermometric titration to determine the end-point for the reaction of FB 3 and FB 4. In a thermometric titration the end-point is when the maximum temperature change occurs. (a) Fill the burette with FB 4. Support the plastic cup in a 250 cm3 beaker and pipette into the cup 50.0 cm3 of FB 3. Record the steady temperature of FB 3 in Table 2.1. Read through the following instructions before starting the experiment. Run 3.00 cm3 of FB 4 from the burette into the cup, stir the solution with the thermometer and record the new steady temperature. Without delay run a further 3.00 cm3 of FB 4 from the burette, stir and record the steady temperature as before. Continue the addition of FB 4 in 3.00 cm3 portions, taking and recording the steady temperature each time, until 48.00 cm3 of solution FB 4 have been run from the burette. Record all temperatures in Table 2.1. The thermometer provided has a range from ………….. oC to ………….. oC and has graduations at each …………… oC. Table 2.1 [5] For Examiner’s Use © UCLES 2005
t (temperature – volume of initial FB 4 added temperature temperature) /cm3 / °C / °C 0 0 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00
t (temperature – volume of initial FB 4 added temperature temperature) /cm3 / °C / °C 27.00 30.00 33.00 36.00 39.00 42.00 45.00 48.00

5 9701/05/M/J/05 [Turn over (b) Plot a graph of
t against the volume of FB 4 added. Draw two smooth curves through the plotted points to find the end-point for the titration. [3] For Examiner’s Use © UCLES 2005

6 9701/05/M/J/05 (c) Read from the graph the volume of hydrochloric acid, FB4, at the end-point of the titration. ……………………………….. cm3 [1] (d) Use your answer to (c) and the equation for the reaction to calculate the concentration of the hydrochloric acid in FB 4. NaOH(aq) + HCl(aq) →NaCl(aq) + H2O(l) .…………… [1] (e) The solution FB 4 was prepared by dissolving 42.40 g of X2CO3 in 1 dm3 of 3.0 mol dm-3 HCl. Use this information and your answer to (d) to calculate the number of moles of HCl that reacted with the dissolved X2CO3. .…………… [1] (f) Calculate the relative molecular mass, Mr, of X2CO3. Calculate the relative atomic mass, Ar, of X. . [Ar: C, 12.0; O, 16.0.] Ar = ………………… [1] [Total : 12] For Examiner’s Use © UCLES 2005

7 9701/05/M/J/05 [Turn over 3 ANALYSIS AND EVALUATION (a) Indicate the size of the error you would expect in making measurements with the thermometer in question 2. … … …[1] (b) Why is it not necessary to consider the errors in the measuring cylinder used in question 1? … … …[1] For Examiner’s Use © UCLES 2005

8 9701/05/M/J/05 ASSESSMENT OF PLANNING SKILLS The relative atomic mass of X can also be determined by an experiment in which carbon dioxide is evolved in the reaction between a weighed sample of the carbonate of X and excess hydrochloric acid. The sample is added to the acid and the bung quickly re-inserted in the flask. The gas displaced from the apparatus is collected and its volume measured using the apparatus below. The acid is placed in a 250 cm3 conical flask and the gas collected by displacing water from an inverted 100 cm3 measuring cylinder. (c) In both Question 1 and the experiment above, the accuracy of the measured mass or volume can be improved by dissolving a small quantity of sodium carbonate in the acid before the start of the experiment. Suggest the reason behind this. … … … … … …[2] For Examiner’s Use © UCLES 2005

9 9701/05/M/J/05 [Turn over (d) For the experiment shown in the photograph, suggest two other major sources of error (not including that mentioned in part (c)) in the spaces provided on page 10. For each source of error describe a method of reducing this error, explaining the reasoning for your method. The data below may be relevant. Data Solubility of carbon dioxide gas at different temperatures The general gas equation pV = nRT The specific heat capacity of water = 4.18 J g-1 K-1 Vapour pressure of water at different temperatures Technical data for X2CO3 Minimum assay 99% Substances insoluble in water 0.0025% Water 0.35% Arsenic 0.0001% Lead 0.003% Sulphate 0.02% Iron 0.001% For Examiner’s Use © UCLES 2005 temperature solubility / oC /g CO2 per 100 g of water 0 0.348 25 0.145 40 0.097 60 0.058 temperature Vapour pressure / oC /Pa 20 2388 25 3167 30 4243 35 5623 40 7376

10 9701/05/M/J/05 (i) first major source of error … method for reducing this error … … explanation … …[3] (ii) second major source of error … … method for reducing this error … … explanation … …[3] [Total : 10] For Examiner’s Use © UCLES 2005

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© UCLES 2005 12 9701/05/M/J/05 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 Level MARK SCHEME for the June 2005 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 initially instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. Any substantial changes to the mark scheme that arose from these discussions will be recorded in the published Report on the Examination. 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 discussion or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the June 2005 question papers for most IGCSE and GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Grade thresholds for Syllabus 9701 (Chemistry) in the June 2005 examination. minimum mark required for grade: maximum mark available A B E Component 5 30 21 19 12 The thresholds (minimum marks) for Grades C and D are normally set by dividing the mark range between the B and the E thresholds into three. For example, if the difference between the B and the E threshold is 24 marks, the C threshold is set 8 marks below the B threshold and the D threshold is set another 8 marks down. If dividing the interval by three results in a fraction of a mark, then the threshold is normally rounded down.

June 2005 GCE A LEVEL MARK SCHEME MAXIMUM MARK: 30 SYLLABUS/COMPONENT: 9701/05 CHEMISTRY Paper 5 (Practical Test)

Page 1 Mark Scheme Syllabus Paper A LEVEL - JUNE 2005 9701 5 © University of Cambridge International Examinations 2005 1 (b) Check, and correct if necessary, the mass of FB 2 used. Give one mark if the mass has been correctly calculated. [1] If either weighing in Table 1.1 is not recorded to 2 decimal places or better deduct one mark from the accuracy mark below. (c) Check, and correct if necessary, the mass of carbon dioxide evolved. (mass of flask + acid) + mass of FB 2 - (mass of flask + solution after reaction) Give one mark if the mass has been correctly calculated. [1] ACCURACY - CANDIDATE SCRIPTS Calculate the ratio dioxide carbon of mass 2 FB of mass correct to 2 decimal places. Record the candidate’s ratio and the Supervisor’s ratio, ringed, below Table 1.1. Calculate the difference between the Supervisor’s ratio and the candidate’s ratio. Award accuracy marks as follows: Mark Difference 3 Up to 0.10 2 0.10+ to 0.20 1 0.20+ to 0.50 0 Greater than 0.50 [3] The theoretical ratio is 2.41 but some CO2 dissolves in the acid so values between 2.65 and 2.70 are more likely to be recorded. If a very large mass of carbon dioxide is recorded, check the ‘hundreds’ digit in the masses recorded and correct any error to provide an accuracy mark. (d) Give one mark for 44 dioxide carbon of mass s candidate' [1] (e) Give one mark for (d) to answer 2 FB of mass s candidate' [1] (f) Give one mark for 2 60] - (e) to [answer [1] Do NOT give the mark in (f) if a unit has been given in the final answer to (e) or (f). Ignore reference to atomic mass units/amu. [Total: 8]

Page 2 Mark Scheme Syllabus Paper A LEVEL - JUNE 2005 9701 5 © University of Cambridge International Examinations 2005 2 (a) ACCURACY - CANDIDATE SCRIPTS (i) On the candidate’s script circle the volume in Table 2.1 that produced the highest temperature for the Supervisor and the highest temperature recorded by the candidate. Compare the volume of acid giving maximum temperature as recorded by the candidate and by the Supervisor. Award a maximum of 2 accuracy marks as follows: Mark 2 Max temp at same volume of FB 3 as Supervisor 1 Max temp at Supervisor’s volume of FB 3 ± 3 cm3 0 Max temp at Supervisor’s volume of FB 3 ± more than 3 cm3 Where a candidate has the same temperature for consecutive volumes, use the first value. The expected maximum 30 or 33 cm3 [2] (ii) On the candidate’s script check, and correct where necessary the ∆t value for the maximum temperature recorded. Record the Supervisor’s ∆t value, ringed, against the table and calculate the difference in the ∆t values between Supervisor and candidate. Award accuracy marks as follows: [3] Mark Difference in ∆t/oC 3 up to 0.50 2 0.50+ to 1.0 1 1.0 to 1.5 0 greater than 1.5 Reduce this accuracy mark by one mark if any thermometer reading lacks a decimal place. Record (actual accuracy mark -1) under Table 2.1 and the net accuracy mark in the mark column.

Page 3 Mark Scheme Syllabus Paper A LEVEL - JUNE 2005 9701 5 © University of Cambridge International Examinations 2005 In some Centres the Erratum slip was not received and the solutions prepared did not give a maximum temperature rise - the temperature continued to rise after each addition of acid. If the Supervisor and the majority of candidates in a Centre have no maximum temperature rise award the first Accuracy marks (2 marks) as follows: Calculate the difference in ∆t values for Supervisor and candidate after the addition of 24.00 cm3 of FB 4. Record the Supervisor’s value in a ring against the table in the usual way. Give: 2 marks for a difference up to 0.5 oC 1 mark for a difference of 0.5+ oC to 1.0 oC 0 marks for a difference > 1.0 oC Award the second Accuracy marks (3 marks) as before, comparing the ∆t values at maximum temperature rise for candidate and Supervisor. See later for changes to the mark scheme for the remainder of the question.

Page 4 Mark Scheme Syllabus Paper A LEVEL - JUNE 2005 9701 5 © University of Cambridge International Examinations 2005 Graph (b) Give one mark if ∆t is plotted on the y-axis, the volume of FB 4 on the x-axis; the axes have been labelled (including unit) and sensible linear scales have been selected. Give one mark if the candidate’s ∆t value at the maximum temperature recorded, and the ∆t value for the volumes immediately before and after it have been plotted correctly. If two of these values are identical check the plotting of the next value away from the maximum that gives three different values of ∆t. The centre of the plotted point should be within ½ small square on either axis. If any of the three points above have not been plotted, check the nearest appropriate point in its place. Give one mark if two distinct, appropriate smooth curves (lines) have been drawn, one showing the temperature rising and the other the temperature falling. The lines must intersect. Do not give this mark if lines join all plotted points or the curves are rounded to meet at a particular volume at the maximum ∆t value. [3] (c) Give one mark for reading the end-point from the graph (within ½ small square on either axis). This mark can be given from a rounded maximum or from the mid-point of a plateau. This mark is not available where the candidate has recorded and plotted stepwise ∆t values for each addition of acid. [1] (d) Give one mark for 1.5 x (c) from point - end s candidate' 50 or equivalent two stage calculation [1] (e) Give one mark for 3.0 - answer to (d) [1] (f) Give one mark for 2 x (e) to answer 42.40 or       2 (e) to answer 40 . 42 and 2 60] - above answer [ A r = Ignore units in this calculation [1]

Page 5 Mark Scheme Syllabus Paper A LEVEL - JUNE 2005 9701 5 © University of Cambridge International Examinations 2005 Where the Erratum slip had not been received and the Supervisor and majority of candidates at a Centre did not obtain a maximum temperature - the temperature continuing to rise after each addition of acid - mark the remainder of the question as below. Graph Give one mark if ∆t is plotted on the y-axis, the volume of FB 4 on the x-axis; the axes have been labelled (including unit) and sensible linear scales have been selected. Give one mark if the candidate’s value for ∆t at 12 cm3, 18 cm3 and 24 cm3 have been plotted correctly. The centre of the plotted point should be within ½ small square on each axis. Give one mark for a smooth curve showing a good fit to the plotted points. [3] (c) This mark is not available. [0] (d) Give one mark for 1.5 x (c) from point - end s candidate' 50 or equivalent two stage calculation. [1] (e) Give one mark for 3.0 - answer to (d) [1] (f) Give one mark for 2 x (e) to answer 42.40 or       2 (e) to answer 40 . 42 AND Give one additional mark for 2 60] - above answer [ A r = [2] [Total: 12] 3 ANALYSIS AND EVALUATION (a) Give one mark if errors of the appropriate size are indicated for the thermometer used. -10 oC to 110 oC by 1 degree Error (±) 0.5 oC 0 oC to 50 oC by 0.5 degree Error (±) 0.25 oC 0 oC to 50 oC by 0.2 degree Error (±) 0.1 oC Units are not required. The answer given must relate to the graduations given on page 4. [1]

Page 6 Mark Scheme Syllabus Paper A LEVEL - JUNE 2005 9701 5 © University of Cambridge International Examinations 2005 (b) Give one mark for an answer that indicates the acid is in excess (precise measurement of volume not necessary). [1] (c) Give one mark for need to saturate the acid with carbon dioxide before carrying out the experiment or similar argument. Give one mark for answers such as: to ensure that all the CO2 produced is collected/measured, or so that all the CO2 liberated will be from the X2CO3, or so that no more CO2 dissolves (in the acid) during the experiment or explaining that a reduction in the mass of carbon dioxide evolved or volume of carbon dioxide collected will lead to a higher inaccurate value of Mr or Ar. [2] (d) For each major error identified: Give one mark for stating the nature of the error (E mark). This mark is given for identifying any deficiency/variable that will have an influence on the calculated value of Mr. e.g. Solubility of CO2 in water/temperature changes alter the volume of gas collected. Give one mark for indicating a suitable method of eliminating the error (M mark). This mark is for a practical way of rectifying the deficiency/keeping the variable constant. e.g. Collect the gas in a gas syringe/use of a water bath to control temperature. Give one mark for explaining how the error will be eliminated/reduced by the method selected (P mark). This mark must be for an explanation based on the method selected. e.g. No water involved in collection to dissolve the gas/knowing the temperature pV=nRT can be used in calculating moles of gas. Some candidates may miss the idea of saturating the HCl with CO2 in test (c) but give an error in (c) that would score one or more marks from section (d). These marks may be awarded unless the same error has been repeated on page 10. If the idea of saturating the acid with CO2 is given on p10 rather than on p8 the marks can be awarded retrospectively. The three marks in each section may be found at any point in a candidate’s answer. The error will often be found within the explanation. Annotate each mark as shown in the table which lists some possible answers. Other acceptable answers that meet the criteria above may be seen.

Page 7 Mark Scheme Syllabus Paper A LEVEL - JUNE 2005 9701 5 © University of Cambridge International Examinations 2005 Error ✓E Method ✓M Explanation ✓P 1 Loss of gas at start of experiment Carbonate placed inside flask before mixing If dropping funnel used… Sealed system Needs to compensate for acid added 2 Poor measurement of volume using measuring cylinder Replace cylinder with burette or gas syringe Greater accuracy of scales Use gas syringe to collect the gas No water in collecting apparatus Raise temperature of the water in the trough Solubility of CO2 decreases at higher temperatures Use an alternative solvent CO2 insoluble in the solvent 3 Solubility of CO2 in (collecting) water Saturate (collecting) water with CO2 All of gas collected as no more can dissolve 4 Gas collected in measuring cylinder is not at atmospheric pressure Equalise water levels inside and outside of measuring cylinder Read volume at atmospheric pressure Dry gas (but must not then be collected over water) Suitable drying agent suggested (even if dried and collected over water) 5 Gas collected contains water vapour Use gas syringe to collect the gas No water in collecting apparatus Lower temperature 6 water contained in gas or vapour pressure of water varies with temperature Control temperature - appropriate method described Make adjustment for svp to pressure of gas for controlled temperature 7 Gas collected contains water vapour which contributes to the gas pressure Correct for pressure for svp or Use a solvent with low vapour pressure (Temperature and) pressure readings necessary and correction from table 8 Volume of gas varies with changes in pressure Need to measure temperature of water bath and atmospheric pressure Moles of gas calculated using pV=nRT 9 Volume of gas varies with changes in temperature or Temperature not known/measured Use a constant temperature water bath Apply pV=nRT 10 Solid is damp or Reference to 0.35% water from the assay Dehydrate/heat the solid Lower volume of CO2 or too great a mass if not dried 11 CO2 is a non-ideal gas Use modified gas equation 12 Solubility of carbon dioxide in water varies with temperature Maintain a constant temperature - appropriate method described Use data to obtain to correct for dissolved carbon dioxide at the constant temperature 13 Reference to the solid only being 99% pure. The purity must be quoted from the assay Explaining: that carbonate impurities would increase carbon dioxide or unreactive components reduce carbon dioxide 2 x [3] [Total: 10] [Total for Paper: 30]