Cambridge A Level Chemistry 9701 — 2016 May/June Paper 3 · Variant 1

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 an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. 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. Qualitative Analysis Notes are printed on pages 12 and 13. A copy of the Periodic Table is printed on page 16. 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 9701/31 Paper 3 Advanced Practical Skills 1 May/June 2016 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level This document consists of 13 printed pages and 3 blank pages. [Turn over IB16 06_9701_31/4RP © UCLES 2016 *6428722285* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/31/M/J/16 © UCLES 2016 1 In this experiment you will determine the identity of the Group 2 metal, X, in the carbonate, XCO3. To do this you will react a known mass of XCO3 with excess hydrochloric acid, HCl, and measure the mass of carbon dioxide that is given off. FA 1 is XCO3. FA 2 is hydrochloric acid, HCl. (a) Method • Weigh the stoppered tube containing FA 1 and record its mass. • Use the measuring cylinder to transfer 25 cm3 of FA 2 into the 250 cm3 beaker. • Weigh the beaker containing the acid and record the mass. • Carefully add all the sample of FA 1 to the acid in the beaker. • Stir the mixture until there is no further reaction. • Reweigh the beaker and its contents and record the mass. KEEP THE CONTENTS OF THE BEAKER FOR USE IN QUESTION 2. • Reweigh the stoppered tube containing any residual FA 1 and record its mass. • Calculate the mass of FA 1 added to the acid and record this value. • Calculate the mass of carbon dioxide given off and record this value. [7] (b) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the number of moles of carbon dioxide given off when XCO3 reacted with the acid. Use the data in the Periodic Table on page 16. moles of CO2 = … mol (ii) Write the equation for the reaction of FA 1, XCO3, with hydrochloric acid, HCl. Include state symbols. … I II III IV V VI VII

3 9701/31/M/J/16 © UCLES 2016 [Turn over (iii) Use your answers to (i) and (ii) to calculate the number of moles of XCO3 that were added to the acid. moles of XCO3 = … mol (iv) Use your answer to (iii) to calculate the relative atomic mass, Ar, of X. Identify X. Ar of X = … X is … . [5] (c) One of the sources of error in this experiment is that it is very difficult to reduce acid spraying out of the beaker when the metal carbonate is added to the acid. (i) Explain what effect this acid spray would have on the value you calculated for the relative atomic mass, Ar, of X. … … … (ii) Why is a small amount of acid spray not likely to cause an error in the identification of X? … … (iii) How could you minimise acid spraying out of the beaker? … … … [3] [Total: 15] I II III IV V

4 9701/31/M/J/16 © UCLES 2016 2 In this experiment you will determine the concentration of the hydrochloric acid, FA 2, used in Question 1. You will first dilute the reaction mixture that you prepared in Question 1 and then titrate this diluted solution against sodium hydroxide, NaOH. HCl (aq) + NaOH(aq) → NaCl (aq) + H2O(l) FA 3 is 0.0400 mol dm–3 sodium hydroxide, NaOH. methyl orange indicator (a) Method Dilution • Transfer all the reaction mixture that you prepared in 1(a) from the 250 cm3 beaker to the 250 cm3 volumetric flask. • Rinse the beaker with a little distilled water and add these washings to the volumetric flask. • Fill the volumetric flask to the line with distilled water. Stopper the flask and shake it to ensure thorough mixing. • Label this solution FA 4. Titration • Fill the burette with FA 4. • Use a pipette to transfer 25.0 cm3 of FA 3 into a conical flask. • Add a few drops of methyl orange. • Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3. • Carry out as many accurate titrations as you think necessary to obtain consistent results. • Make certain any recorded results show the precision of your practical work. • Record in a suitable form below all of your burette readings and the volume of FA 4 added in each accurate titration. [4] I II III IV

5 9701/31/M/J/16 © UCLES 2016 [Turn over (b) From your accurate titration results, obtain a suitable value for the volume of FA 4 to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FA 3 required … cm3 of FA 4. [1] (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the number of moles of sodium hydroxide, NaOH, present in 25.0 cm3 of FA 3. moles of NaOH = … mol (ii) Calculate the number of moles of hydrochloric acid, HCl, present in 250 cm3 of FA 4. moles of HCl in 250 cm3 of FA 4 = … mol (iii) Use your answers to 1(b)(i) and 1(b)(ii) to calculate the number of moles of HCl that reacted with FA 1 in the experiment you carried out in Question 1. moles of HCl that reacted with FA 1 = … mol (iv) Use your answers to 2(c)(ii) and 2(c)(iii) to calculate the concentration of FA 2. concentration of FA 2 = … mol dm–3 [5]

6 9701/31/M/J/16 © UCLES 2016 (d) (i) One of the sources of error in determining the concentration of FA 2 involves measuring volumes of solutions in both Questions 1 and 2. State which volume of solution that you have measured has the greatest percentage error. How could you have reduced this error? … … … (ii) A student suggested that a greater mass of XCO3 should be used so that the average titre calculated in 2(b) would be a greater volume. Explain whether you agree with the student that this would lead to a greater volume for the average titre. … … … [2] [Total: 12]

7 9701/31/M/J/16 © UCLES 2016 [Turn over 3 Qualitative Analysis At each stage of any test you are to record details of the following. ● colour changes seen ● the formation of any precipitate ● the solubility of such precipitates in an excess of the reagent added 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, a boiling tube MUST be used. Rinse and reuse test-tubes and boiling tubes where possible. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. FA 5 is a mixture of two different salts. Each of these salts contains one cation and one anion from those listed on pages 12 and 13. You will identify the cations and anions present. (a) (i) Carry out the following test and record your observations. test observations Place a small spatula measure of FA 5 in a hard-glass test-tube and heat strongly. Test any gases that are given off. (ii) Identify one of the cations in FA 5. One of the cations in FA 5 is … . [2]

8 9701/31/M/J/16 © UCLES 2016 (b) Place the remaining sample of FA 5 in the 100 cm3 beaker. Half fill the beaker with distilled water and stir until FA 5 has fully dissolved. This may take some time. You will use this solution in the remaining tests. (i) Select reagents to identify the other cation present in FA 5. Carry out tests using these reagents and record your results in the space below. Identify the cation. The other cation in FA 5 is … . (ii) Carry out the following tests and record your observations. Identify one of the anions in FA 5. test observations To a 1 cm depth of the solution of FA 5 in a test-tube add aqueous barium chloride or aqueous barium nitrate, then add dilute hydrochloric acid. One of the anions in FA 5 is … .

9 9701/31/M/J/16 © UCLES 2016 [Turn over (iii) The remaining ion is a halide. Select a pair of reagents which can be used to identify the halide present. Carry out a test using these reagents and record your observations below. Suggest the identity of the halide anion present in FA 5. Explain why this test is not conclusive in this particular case. The other anion in FA 5 is … . … … … … [8] (c) Suggest the formulae of the two salts that could have been mixed to make FA 5. … and … [1]

10 9701/31/M/J/16 © UCLES 2016 (d) FA 6 and FA 7 are different organic liquids. Their possible identities are listed below. • 2-methylpropan-2-ol • propanal • propanone Half fill the 250 cm3 beaker with water and heat to about 50 °C. You will use this as a hot water bath. Turn off the Bunsen burner. Carry out the following tests and record your observations. test observations To a 1 cm depth of FA 6 in a test-tube, add a few drops of acidified potassium manganate(VII). If no reaction is seen, warm the solution in the hot water bath. To a 1 cm depth of FA 7 in a test-tube, add a few drops of acidified potassium manganate(VII). If no reaction is seen, warm the solution in the hot water bath. Suggest the identity of FA 6 and FA 7 with an explanation. FA 6 … FA 7 … [2] [Total: 13]

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12 9701/31/M/J/16 © UCLES 2016 Qualitative Analysis Notes 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) faint white ppt. is nearly always observed unless 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 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

13 9701/31/M/J/16 © UCLES 2016 2 Reactions of anions ion reaction carbonate, CO3 2– CO2 liberated by dilute acids chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)) bromide, Br –(aq) gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)) iodide, I –(aq) gives yellow ppt. with Ag+(aq) (insoluble in NH3(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) (insoluble in excess dilute strong acids) sulfite, SO3 2–(aq) 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, Cl 2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint

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16 9701/31/M/J/16 © UCLES 2016 To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. Group The Periodic Table of Elements 1 H hydrogen 1.0 2 He helium 4.0 1 2 13 14 15 16 17 18 3 4 5 6 7 8 9 10 11 12 3 Li lithium 6.9 4 Be beryllium 9.0 atomic number atomic symbol Key name relative atomic mass 11 Na sodium 23.0 12 Mg magnesium 24.3 19 K potassium 39.1 20 Ca calcium 40.1 37 Rb rubidium 85.5 38 Sr strontium 87.6 55 Cs caesium 132.9 56 Ba barium 137.3 87 Fr francium – 88 Ra radium – 5 B boron 10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 81 Tl thallium 204.4 6 C carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sn tin 118.7 82 Pb lead 207.2 22 Ti titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium 178.5 104 Rf rutherfordium – 23 V vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium – 24 Cr chromium 52.0 42 Mo molybdenum 95.9 74 W tungsten 183.8 106 Sg seaborgium – 25 Mn manganese 54.9 43 Tc technetium – 75 Re rhenium 186.2 107 Bh bohrium – 26 Fe iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium – 27 Co cobalt 58.9 45 Rh rhodium 102.9 77 Ir iridium 192.2 109 Mt meitnerium – 28 Ni nickel 58.7 46 Pd palladium 106.4 78 Pt platinum 195.1 110 Ds darmstadtium – 29 Cu copper 63.5 47 Ag silver 107.9 79 Au gold 197.0 111 Rg roentgenium – 30 Zn zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200.6 112 Cn copernicium – 114 Fl flerovium – 116 Lv livermorium – 7 N nitrogen 14.0 15 P phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 83 Bi bismuth 209.0 8 O oxygen 16.0 16 S sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium – 9 F fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 53 I iodine 126.9 85 At astatine – 10 Ne neon 20.2 18 Ar argon 39.9 36 Kr krypton 83.8 54 Xe xenon 131.3 86 Rn radon – 21 Sc scandium 45.0 39 Y yttrium 88.9 57–71 lanthanoids 89–103 actinoids 57 La lanthanum 138.9 89 Ac lanthanoids actinoids actinium – 58 Ce cerium 140.1 90 Th thorium 232.0 59 Pr praseodymium 140.9 91 Pa protactinium 231.0 60 Nd neodymium 144.4 92 U uranium 238.0 61 Pm promethium – 93 Np neptunium – 62 Sm samarium 150.4 94 Pu plutonium – 63 Eu europium 152.0 95 Am americium – 64 Gd gadolinium 157.3 96 Cm curium – 65 Tb terbium 158.9 97 Bk berkelium – 66 Dy dysprosium 162.5 98 Cf californium – 67 Ho holmium 164.9 99 Es einsteinium – 68 Er erbium 167.3 100 Fm fermium – 69 Tm thulium 168.9 101 Md mendelevium – 70 Yb ytterbium 173.1 102 No nobelium – 71 Lu lutetium 175.0 103 Lr lawrencium –

® IGCSE is the registered trademark of Cambridge International Examinations. This document consists of 5 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 9701/31 Paper 3 Advanced Practical Skills 1 May/June 2016 MARK SCHEME Maximum Mark: 40 Published 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 May/June 2016 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9701 31 © Cambridge International Examinations 2016 Question Indicative material Mark Total 1 (a) I Six identifiable masses recorded 1 [7] II All recorded masses have unambiguous headings and unit: / g or (g) or g (for each heading) by each entry. 1 III Four measured masses all recorded to the same number of decimal places minimum 1 decimal place 1 IV Correctly calculates mass of FA1 added and mass of CO2 evolved. 1 V, VI and VII Examiner compares corrected mass of FA1 / corrected mass of CO2 with supervisor value. Accuracy marks are awarded as shown. Award V, VI and VII if δ ⩽ 0.10 Award V and VI if 0.10 < δ ⩽ 0.20 Award V if 0.20 < δ ⩽ 0.40 3 (b) (i) I Correctly calculates n(CO2) (mass CO2 / 44) 1 [5] (ii) II Correct equation and all state symbols XCO3(s) + 2HCl(aq) → XCl 2(aq) + H2O(I) + CO2(g) 1 (iii) (iv) III (iii) = (i) and Expression mass of FA1 / (iii) shown in (iv) 1 (iv) IV Correctly uses 60 and the Mr to calculate Ar of X (mass of FA1 / (iii) – 60) 1 V Identifies X as Group 2 metal or ion with nearest Ar value (must have some working for Ar used). Be 9.0, Mg 24.3, Ca 40.1, Sr 87.6, Ba 137.3 1 (c) (i) Apparently more moles of CO2 (lost) so Ar of X is smaller. or Apparently more moles of XCO3 (used) so Ar of X is smaller. 1 (ii) Any 2 from: • Small loss in mass • not much difference to Ar so does not cause confusion in identity / still closest to identity of X 1

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9701 31 © Cambridge International Examinations 2016 Question Indicative material Mark Total (iii) Any 1 from • Add slowly / add a little at a time • Use a taller beaker (accept larger beaker) / use a conical flask • Use less solid • Use less concentrated acid • Use lumps of solid • Use cotton wool plug • Use a lower temperature 1 [3] Question 1 [15] 2 (a) I Initial and final readings and titre value for rough titre and initial and final reading for two (or more) accurate titrations 1 [4] II Titre values recorded for accurate titrations and Appropriate headings for the accurate titration table and cm3 units. • initial / start burette reading / volume / value • final / end burette and reading / volume / value • titre or volume / FA4 and used / added • unit: / cm3 or (cm3) or in cm3 or cm3 (for each heading) 1 III All accurate burette readings are recorded to nearest 0.05 cm3 Do not award this mark if: • 50.(00) is used as an initial burette reading • more than one final burette reading is 50.(00); • any burette reading is greater than 50.(00) • there is only one accurate titration 1 IV There are two uncorrected, accurate titres within 0.10 cm3 • Do not award this mark if, having performed two titres within 0.1 cm3, a further titration is performed which is more than 0.10 cm3 from the closer of the two initial titres, unless a further titration, within 0.10 cm3 of any other, has also been carried out. • Do not award the mark if any “accurate” burette readings (apart from initial 0 cm3) are given to zero dp 1

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9701 31 © Cambridge International Examinations 2016 Question Indicative material Mark Total (b) Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm3. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should be quoted to 2 dp, rounded to the nearest 0.01. Two special cases where the mean may not be to 2 dp: • Allow mean expressed to 3 dp only for 0.025 or 0.075 (e.g. 26.325) • Allow mean if expressed to 1 dp if all accurate burette readings were given to 1 dp and the mean is exactly correct. (e.g. 26.0 and 26.2 = 26.1 is allowed) (e.g. 26.0 and 26.1 = 26.1 is incorrect – should be 26.05.) Note: the candidate’s mean will sometimes be marked as correct even if it is different from the mean calculated by the examiner for the purpose of assessing accuracy. 1 [1] (c) (i) I Correctly calculates n(NaOH) = 0.001 1 [5] (ii) II Shows use of ( )( ) ( ) c i b 250 1 (iii) III Correctly calculates 2 × 1(b)(i) 1 (iv) IV Shows use of 2(c)(ii) + 2(c)(iii) either as expression or correct calculation 1 V Shows use of / 0.025(0) or × 40 or × 1000 / 25 1 (d) (i) States that the measuring cylinder / volume of FA2 has the greatest error and should be replaced by burette or pipette 1 [2] (ii) Student is correct / greater volume HCl used and greater mass would react with more HCl / would leave less HCl unreacted 1 Question 2 [12]

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9701 31 © Cambridge International Examinations 2016 Question Indicative material Mark Total FA5 is MnSO4 and NH4Cl; FA6 is propanone; FA7 is propanal; 3 (a) (i) Red litmus turns blue (then red) 1 [2] Condensation or sublimation / white smoke / white fumes 1 (a) (ii) and (b) (i) NH4 + / ammonium in 3(a)(ii) and Mn2+ / manganese(II) in 3(b)(i). 1 (b) (i) Selects NaOH and NH3 1 Off-white / beige / light brown precipitate with both NaOH and NH3 1 Both precipitates turns brown / darkens 1 (ii) white precipitate and insoluble in acid 1 (iii) Selects AgNO3 / silver nitrate and NH3 / ammonia 1 White precipitate and insoluble / partially soluble in ammonia 1 Cannot see if precipitate dissolves in ammonia / Mn2+ causes (off-white) precipitate (so cannot be used to distinguish between halides). 1 [8] (c) MnCl 2 and (NH4)2SO4 or MnSO4 and NH4Cl 1 [1] (d) Both observations required FA6 no reaction / solution turns pink and FA7 turns colourless / decolourises the KMnO4 1 [2] FA6 is either 2-methylpropan-2-ol or propanone as they cannot be oxidised (only 1 needed) and FA7 is propanal as it can be oxidised. 1 Question 3 [13]