Cambridge A Level Chemistry 9701 — 2010 May/June Paper 3 · Variant 4

This document consists of 11 printed pages and 1 blank page. DC (SJF5449/CGW) 11614/4 © UCLES 2010 [Turn over * 1 6 2 6 1 3 0 2 0 2 * 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. Give details of the practical session and laboratory where appropriate, in the boxes 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. DO NOT WRITE IN ANY BARCODES. Answer all questions. 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. Qualitative Analysis Notes are printed on pages 10 and 11. 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 9701/34 Paper 32 Advanced Practical Skills May/June 2010 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Instructions to Supervisors For Examiner’s Use 1 2 Total Session Laboratory

2 9701/34/M/J/10 © UCLES 2010 For Examiner’s Use 1 Read through question 1 before starting any practical work. You are provided with the following reagents. • weighing bottles/tubes labelled FB 1, FB 2 and FB 3; each containing a different mass of sodium hydrogencarbonate, NaHCO3 • additional solid sodium hydrogencarbonate (approximately 10 g) • FB 4, 3.0 mol dm–3 hydrochloric acid, HCl The reaction of sodium hydrogencarbonate with hydrochloric acid is endothermic. By measuring the maximum temperature decrease when the different masses of sodium hydrogencarbonate react with hydrochloric acid you are to determine the enthalpy change of neutralisation for 1 mol of NaHCO3 with HCl. (a) Method • Weigh the bottle/tube containing the sodium hydrogencarbonate labelled FB 1. • Support the plastic cup in the 250 cm3 beaker. • Use the measuring cylinder to transfer 30 cm3 of FB 4 into the plastic cup. • Place the thermometer in the acid in the plastic cup and record the steady temperature of the acid. • Add the contents of the weighed tube, FB 1, to the acid in the plastic cup, a little at a time with constant stirring. • You should add the solid as quickly as possible – taking care to minimise any acid spray from the plastic cup. Avoid breathing any fumes from the experiment. • Record the minimum temperature obtained in the reaction. • Reweigh the emptied tube, FB 1, containing any remaining solid that was not tipped from the tube. • Empty and rinse the plastic cup. Rinse the thermometer. Shake dry the plastic cup. • Repeat the experiment using tubes labelled FB 2 and FB 3. In each experiment use 30 cm3 of FB 4. Carry out two further experiments. Using the empty weighing bottles/tubes, labelled FB 5 and FB 6, weigh two further masses of sodium hydrogencarbonate. Choose masses to enable you to plot an appropriate graph of temperature change against mass of sodium hydrogencarbonate. Results Record your results in an appropriate form showing, for each experiment, the measurements of mass and temperature and the calculated temperature fall. [9] i ii iii iv v vi vii viii ix

3 9701/34/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (b) Use the grid below to plot a graph of decrease in temperature (y-axis) against the mass of sodium hydrogencarbonate added (x-axis). Draw a line of best fit through the plotted points. You should consider if the best-fit line passes through the origin (0,0) of the graph. [4] i ii iii iv

4 9701/34/M/J/10 © UCLES 2010 For Examiner’s Use (c) Explain why the mass of NaHCO3 is plotted on the x-axis rather than on the y-axis. … … [1] (d) Construct the balanced equation for the reaction of NaHCO3 with hydrochloric acid. … [1] (e) Calculate the gradient of your graph. Show all of your working clearly, both construction lines on the graph and working in the calculation. [3] (f) Although there is insufficient acid in 30 cm3 of FB 4 to neutralise 1 mol of NaHCO3 it is possible to calculate the theoretical fall in temperature for this reaction. Use your answer from (e) to calculate this value. [Ar: C, 12.0; H, 1.0; Na, 23.0; O, 16.0] The theoretical fall in temperature for 1 mol of NaHCO3 = ………………………. °C [1] (g) Calculate the theoretical enthalpy change for the neutralisation of 1 mol of NaHCO3 by hydrochloric acid. Give your answer in kJ mol–1 and include the correct sign for the reaction. [4.3 J are absorbed or released when the temperature of 1 cm3 of solution changes by 1 °C.] ΔH = ……………………… kJ mol–1 [2]

5 9701/34/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (h) Suggest two ways in which your apparatus could be modified to reduce transfer of heat from the surroundings to the solution in the apparatus. modification 1 … … modification 2 … … [1] (i) State and explain why the experiment would be more accurate if the volumes of FB 4 had been measured using a burette instead of a measuring cylinder. … … [1] (j) The mass of NaHCO3 used in a further experiment and its associated temperature change are shown in the tables below. • The mass was obtained on a balance reading to 1 decimal place. • The thermometer used was graduated at 1 °C. Complete the table to show the errors in these results. mass of NaHCO3 5.6 g temperature change –12.0 °C maximum error in a single balance reading ± ………… g maximum error in a single thermometer reading ± ………… °C % error in measured mass ………… % % error in temperature change ………… % [2] (k) Two students add 6.0 g of sodium carbonate to 50.00 cm3 of 2.0 mol dm–3 hydrochloric acid. Each student repeats the experiment a number of times. The thermometer readings and temperature changes obtained consistently by each student are shown below. initial temperature / °C final temperature / °C temperature rise / °C student 1 20.0 28.0 8.0 student 2 19.0 27.0 8.0 Suggest the type of error shown by these results. … [1] [Total: 26]

6 9701/34/M/J/10 © UCLES 2010 For Examiner’s Use 2 FB 7 and FB 8 are aqueous solutions of salts. One of these contains two cations and one anion. The other contains one cation and one anion. Both FB 7 and FB 8 have a common cation. You will carry out tests to deduce the following. • the cations present in each solution • whether a sulfate ion is present in either solution At each stage of any test you are to record details of the following. • colour changes seen • the formation of any precipitate and the colour of the precipitate Where gases are released they should be identified by a test, described in the appropriate place in your observations. You should indicate clearly at what stage in a test a change occurs. Marks are not given for chemical equations. No additional tests for ions present should be attempted. If any solution is warmed directly with a Bunsen burner a boiling-tube MUST be used. Rinse and reuse test-tubes where possible. (a) Use information from the Qualitative Analysis Notes on page 11 to select a pair of reagents that, used together, determine whether a sulfate ion is present in either solution. The reagents are ………………………………………… followed by ………………………………………… . [1] (b) Use your chosen reagents to carry out tests on FB 7 and FB 8. Record your results in an appropriate form in the space below. [2]

7 9701/34/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (c) From your observations in (b) show with a tick which of the following statements is true. FB 7 contains the sulfate ion FB 8 contains the sulfate ion neither solution contains the sulfate ion Explain the evidence that supports your conclusion. … … [1] (d) Carry out the following tests on the solutions FB 7 and FB 8. Record your observations below. test observations FB 7 FB 8 To 1 cm depth of solution in a boiling-tube, add 2 cm depth of aqueous sodium hydroxide; then warm the solution gently. Care is needed when heating aqueous sodium hydroxide. To 1 cm depth of solution in a test-tube, add 2 cm depth of aqueous ammonia. [3] (e) To 1 cm depth of FB 7 in a test-tube add 1 cm depth of sodium hydroxide. Leave to stand for a few minutes. observation … … [1]

8 9701/34/M/J/10 © UCLES 2010 For Examiner’s Use (f) From your observations in (d) and (e) you should be able to identify the common cation in the solutions and the second cation in one of the solutions. The common cation present in both solutions is ………………………. . The second cation contained in one of the solutions is ………………………. . Explain how your observations support your conclusions for (i) the common cation, … … (ii) the second cation. … … [1] Read through the remainder of question 2 before starting further practical work. Heat a half-full 250 cm3 beaker of water for use as a hot water-bath. (g) FB 9, FB 10, FB 11 and FB 12 are organic compounds. Each contains one of the following different functional groups. • primary alcohol • secondary alcohol • aldehyde • ketone You are to react each of these compounds with some of the following reagents. • acidified aqueous potassium dichromate(VI) • 2,4-dinitrophenylhydrazine (2,4-DNPH) reagent • ammoniacal silver nitrate (Tollens’ reagent) You are provided with the first two reagents. You must prepare the last of these reagents, Tollens’ reagent, immediately before use. Follow the instructions in the box below. To 2 cm depth of aqueous silver nitrate in a boiling-tube add ½ cm depth of aqueous sodium hydroxide. This will produce a brown precipitate of silver(I) oxide. Add aqueous ammonia a little at a time, with continuous shaking, until the brown precipitate just dissolves. Do not add an excess of aqueous ammonia.

9 9701/34/M/J/10 © UCLES 2010 For Examiner’s Use In each of the following tests add a few drops of the reagent to 1 cm depth of FB 9, FB 10, FB 11 and FB 12 in separate test-tubes. In the tests using acidified potassium dichromate(VI) and Tollens’ reagent, if no initial reaction is seen, warm that tube and its contents in your hot water-bath. There is no need to heat any tube to which you have added 2,4-DNPH reagent. Do not heat any tube with a naked flame. Record your results in the table below. Do not carry out tests for the shaded boxes. reagent observations FB 9 FB 10 FB 11 FB 12 acidified potassium dichromate(VI) 2,4-DNPH reagent Tollens’ reagent [3] (h) State which of the solutions contain alcohols. Explain the observations leading to your conclusion. FB …………… and FB …………… contain alcohols. explanation … … State which solution contains the ketone. Explain the observations leading to your conclusion. FB …………… contains the ketone. explanation … … [2] [Total: 14]

10 9701/34/M/J/10 © UCLES 2010 Key: [ ppt. = precipitate. ] 1 Reactions of aqueous cations ion reaction with NaOH(aq) NH3(aq) aluminium, Al 3+(aq) white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH4 +(aq) no ppt. ammonia produced on heating – barium, Ba2+(aq) no ppt. (if reagents are pure) no ppt. calcium, Ca2+(aq) white ppt. with high [Ca2+(aq)] no ppt. chromium(III), Cr3+(aq) grey-green ppt. soluble in excess giving dark green solution grey-green ppt. insoluble in excess copper(II), Cu2+(aq) pale blue ppt. insoluble in excess blue ppt. soluble in excess giving dark blue solution iron(II), Fe2+(aq) green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron(III), Fe3+(aq) red-brown ppt. insoluble in excess red-brown ppt. insoluble in excess lead(II), Pb2+(aq) white ppt. soluble in excess white ppt. insoluble in excess magnesium, Mg2+(aq) white ppt. insoluble in excess white ppt. insoluble in excess manganese(II), Mn2+(aq) off-white ppt. rapidly turning brown on contact with air insoluble in excess off-white ppt. rapidly turning brown on contact with air insoluble in excess zinc, Zn2+(aq) white ppt. soluble in excess white ppt. soluble in excess [Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.]

11 9701/34/M/J/10 © UCLES 2010 2 Reactions of anions ion reaction carbonate, CO3 2– CO2 liberated by dilute acids chromate(VI), CrO4 2– (aq) yellow solution turns orange with H+(aq); gives yellow ppt. with Ba2+(aq); gives bright yellow ppt. with Pb2+(aq) chloride, Cl– (aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)); gives white ppt. with Pb2+(aq) bromide, Br– (aq) gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)); gives white ppt. with Pb2+(aq) iodide, I– (aq) gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq)); gives yellow ppt. with Pb2+(aq) nitrate, NO3 – (aq) NH3 liberated on heating with OH-(aq) and Al foil nitrite, NO2 – (aq) NH3 liberated on heating with OH-(aq) and Al foil; NO liberated by dilute acids (colourless NO → (pale) brown NO2 in air) sulfate, SO4 2– (aq) gives white ppt. with Ba2+(aq) or with Pb2+(aq) (insoluble in excess dilute strong acids); sulfite, SO3 2– (aq) SO2 liberated with dilute acids; gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids) 3 Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 gives a white ppt. with limewater (ppt. dissolves with excess CO2) chlorine, Cl2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium dichromate(VI) from orange to green

12 9701/34/M/J/10 © UCLES 2010 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 May/June 2010 question paper for the guidance of teachers 9701 CHEMISTRY 9701/34 Paper 32 (Advanced Practical Skills), maximum raw mark 40 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 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 May/June 2010 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 34 © UCLES 2010 Question 1 Round all thermometer readings to the nearest 0.5°C. Question Sections Indicative material Mark 1 (a) PDO Recording MMO Collection MMO Decisions MMO Quality (i) Presents data in single table of results – to include masses of tube with solid and residue, (mass of solid), initial and final temperatures and temperature change. (ii) All columns correctly labelled with appropriate unit shown. Must use solidus, brackets or describe unit fully in words. There must be at least one mass and one temperature. If units not included in column headings every entry must have the correct unit shown. (iii) All balance readings recorded to 1 or more decimal places and showing same precision of measurement (iv) All thermometer readings recorded to 0.5°C (must be at least one at 0.5°C) (v) Two additional masses of NaHCO3 evenly spaced between the other readings or one or both extending the plot (Not two between same pair) (Not within 0.5 g of any other) (Not >3.0 g away from any other) (vi) and (vii) Check and correct ∆T where necessary. Compare temperature fall with that obtained by the Supervisor for FB 2 Award (vi) and (vii) for a temp fall difference of 0.0°, 0.5° or 1.0°C Award (vi) only for a difference of 1.5°C (viii) and (ix) Check and correct ∆T where necessary. Compare temperature fall with that obtained by the Supervisor for FB 3 Award (viii) and (ix) for a temp fall difference of 0.0°, 0.5° or 1.0°C Award (viii) only for a difference of 1.5°C 1 1 1 1 1 2 2 [9]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 34 © UCLES 2010 Question Sections Indicative material Mark (b) PDO Layout (i) Temperature (fall) plotted on y-axis against mass of sodium hydrogencarbonate on x-axis. Clearly labelled axes (ignore units unless T/δT/θ or m as labels) Award even if final temp plotted (ii) Uniform and sensible scales that allow points to be plotted in at least half of the squares on each axis. (6 × 4 big squares) (iii) check the “sweep” that points plotted for all experiments recorded. Check the plotting of points for FB 1, FB 2 and FB 3 (and any other “suspect” point). Points should be within ½ of a small square, in the correct half of the small square. Not awarded if final T is plotted Not awarded if only FB 1, FB 2 and FB 3 are recorded (iv) Straight line drawn, passing within ½ small square of the origin and close to the majority of the points 1 1 1 1 [4] (c) PDO Layout Explains that the mass of sodium hydrogencarbonate is the independent (controlled) variable or Temperature change is the dependent variable (or words to that effect) 1 [1] (d) ACE Conclusion Gives correct equation for the reaction NaHCO3 + HCl → NaCl + H2O + CO2 (Not H2CO3) (Ignore state symbols) 1 [1] (e) PDO Display ACE Interpretation Construction on graph for determining the gradient clearly shown (Must span at least 3 large squares in each direction) and working shown for calculation (could be found on graph page) Reads intercepts or selects two points on the line to within ½ small square in either direction. Evaluates ∆y/∆x from candidate’s intercept figures to find gradient correctly to sf shown 1 1 1 [3] (f) ACE Interpretation Multiplies answer to (e) by 84 1 [1] (g) ACE Interpretation PDO Display Some use of 30 × 4.3 × (answer to (f)) Answer, in kJ mol–1, correct to 2 or 3 significant figures and showing +ve sign Correct answer is given by 0.129 × answer to (f) (No ecf from first part) 1 1 [2]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 34 © UCLES 2010 Question Sections Indicative material Mark (h) ACE Improvements Suggests use of a lid and increased/thicker insulation round the sides. (Accept use of a vacuum flask for improved insulation.) 1 [1] (i) ACE Improvements Lower % error with burette or more accurately calibrated (must refer to or infer scale/graduations/markings/divisions) 1 [1] (j) ACE Interpretation Maximum error in reading a balance reading to 1 decimal place is 0.05 g and Maximum error in reading a 1°C graduated thermometer is given as ±0.5°C Expected % errors 0.89/0.9 or 1.79/1.8% (correct for sf shown) for the balance and 8.3% for the thermometer. (allow ecf from first part – error (× 2)/0.056 and error × 2/0.12) This section may be marked horizontally or vertically 1 1 [2] (k) ACE Interpretation Systematic error stated (or explained in other words) 1 [1] Total [26]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 34 © UCLES 2010 Question 2 Question Sections Indicative material Mark FB 7 is (NH4)2SO4.FeSO4(aq); FB 8 is NH4Cl(aq) 2 (a) MMO Decisions Chooses barium chloride (or nitrate)/ Ba2+(aq)/solution containing Ba2+ (ions) followed by a specified mineral acid other than sulfuric acid or vice versa. (Allow if acid name specified in (b)) Do not accept lead nitrate/lead ions 1 [1] (b) PDO Recording MMO Collection Results for two solutions and two reagents (ecf from (a)) recorded in a single table with distinct separation between reagents (no repetition of solutions or reagents) Give one mark for correct observations with FB 7 and FB 8 Expected results: FB 7 – white ppt with Ba2+, insoluble in acid (do not award if H2SO4 added) FB 8 – No reaction or no precipitate If Pb2+ used then white ppt with both or obs as for Ba2+ Do not award if any obs are dashes except for FB 8 adding acid after Ba2+ 1 1 [2] (c) ACE Conclusion Mark consequentially on observations in (b) Expected conclusion Identifies FB 7 as solution containing SO4 2- from “white ppt with Ba2+, insoluble in acid given in evidence ecf allowed here. Allow deduction if H2SO4 has been added after Ba2+ (not with Pb2+) 1 [1] (d) MMO Collection One mark for two correct observations with NaOH(aq) – before heating FB 7 – green/dirty green/muddy green ppt FB 8 – no ppt/no change/no reaction The mark from (e) may be awarded here if the green ppt with FB 7 is recorded as turning brown One mark for correct observations with NaOH(aq) – after heating gas evolved turns red litmus paper blue for both FB 7 and FB 8 One mark for correct observations with NH3(aq) FB 7 – green ppt (as above) FB 8 – no ppt/no change/no reaction 1 1 1 [3] (e) MMO Collection Records brown precipitate/residue provided green ppt in first box of (d) 1 [1]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 34 © UCLES 2010 Question Sections Indicative material Mark (f) ACE Conclusions Mark consequentially on observations in (d) and (e) Expected conclusions: (i) Common cation is ammonium/NH4 +, from evolution of ammonia or alkaline gas (minimum) or clear ref back to relevant obs (ii) Second cation is Fe2+ in FB 7 from green ppt with NaOH and NH3 or green ppt, turning brown, with either. If Cr3+ then grey-green ppt with both alkalis or grey-green ppt with NaOH soluble in excess giving (dark) green solution or grey-green ppt insol in excess NH3 (no con obs) 1 [1] FB 9 is a ketone; FB 10 is a primary alcohol; FB 11 is a secondary alcohol; FB 12 is an aldehyde (g) MMO Collection One mark for correct observations with FB 9 and FB 12 One mark for two correct observations with FB 10 One mark for two correct observations with FB 11 See table below for expected observations 1 1 1 [3] observations reagent FA 9 FA 10 FA 11 FA 12 acidified dichromate no reaction/no change/yellow or orange soln (not no ppt*) (colour change to) green/blue-green/ cyan/turquoise (solution not ppt*) (colour change to) green/blue-green/ cyan/turquoise (solution not ppt*) *penalise ppt error once in this row If FB9 colour wrong penalise 1st of additional ppts 2,4-DNPH yellow ppt no reaction/ no change yellow ppt Tollens’ reagent no reaction/ no change/no ppt no reaction/ no change/no ppt silver mirror or black/grey solution or ppt (h) ACE Conclusions Mark consequentially on observations in (g) FB 10 and FB 11 contain the alcohols from both oxidised by dichromate(VI) and give no ppt with Tollens’ FB 9 contains the ketone from No reaction with dichromate (Cr2O7 2– obs all correct) or no reaction with Cr2O7 2– and yellow ppt with 2,4-DNPH. (If FB 12 selected evidence must have yellow ppt with 2,4-DNPH and no reaction with Tollens’) 1 1 [2] Total [14]