Cambridge A Level Chemistry 9701 — 2016 Oct/Nov Paper 3 · Variant 3

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 10 and 11. A copy of the Periodic Table is printed on page 12. 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 9701/33 Paper 3 Advanced Practical Skills 1 October/November 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 11 printed pages and 1 blank page. [Turn over IB16 11_9701_33/3RP © UCLES 2016 *7953822147* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/33/O/N/16 © UCLES 2016 1 Hydrogen peroxide, H2O2, can be oxidised to give oxygen, O2. This reaction happens rapidly in the presence of acidified potassium manganate(VII), KMnO4. 2MnO4 –(aq) + 5H2O2(aq) + 6H+(aq) → 2Mn2+(aq) + 5O2(g) + 8H2O(l) You will determine the concentration of a solution of hydrogen peroxide. You will first dilute the solution and then carry out a titration using acidified potassium manganate(VII), KMnO4. FA 1 is aqueous hydrogen peroxide, H2O2. FA 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 1.0 mol dm–3 sulfuric acid, H2SO4. (a) Method Dilution • Pipette 25.0 cm3 of FA 1 into the 250 cm3 volumetric flask. • Add distilled water to make 250 cm3 of solution and shake the flask thoroughly. • Label this diluted solution of hydrogen peroxide FA 4. Titration • Fill the burette with FA 2. • Rinse the pipette thoroughly with distilled water and then with a little FA 4. • Pipette 25.0 cm3 of FA 4 into a conical flask. • Use the measuring cylinder to add 25 cm3 of FA 3 to the conical flask. • 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 2 added in each accurate titration. Keep FA 3 and FA 4 for use in Question 2. [7] I II III IV V VI VII

3 9701/33/O/N/16 © UCLES 2016 [Turn over (b) From your accurate titration results, obtain a suitable value for the volume of FA 2 to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FA 4 required … cm3 of FA 2. [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 potassium manganate(VII) present in the volume of FA 2 calculated in (b). moles of KMnO4 = … mol (ii) Use your answer to (i) and the equation at the top of page 2 to calculate the number of moles of hydrogen peroxide present in 25.0 cm3 of FA 4. moles of H2O2 = … mol (iii) Calculate the concentration, in mol dm–3, of H2O2 in FA 4. concentration of H2O2 in FA 4 = … mol dm–3 (iv) Calculate the concentration, in mol dm–3, of H2O2 in FA 1. concentration of H2O2 in FA 1 = … mol dm–3 [4] [Total: 12]

4 9701/33/O/N/16 © UCLES 2016 2 In Question 1, hydrogen peroxide was oxidised to form oxygen. Hydrogen peroxide can also be reduced to form water. This occurs, for example, when hydrogen peroxide, H2O2, reacts with iodide ions, I–(aq), to form iodine, I2(aq). H2O2(aq) + 2H+(aq) + 2I–(aq) → I2(aq) + 2H2O(l) The rate of this reaction can be measured by adding acidified hydrogen peroxide, H2O2, to a mixture of iodide ions, I –, thiosulfate ions, S2O3 2–, and starch indicator. As the iodine is produced, it reacts immediately with the thiosulfate ions and is reduced back to iodide ions. I2(aq) + 2S2O3 2–(aq) → 2I–(aq) + S4O6 2–(aq) When all the thiosulfate has reacted, the iodine then turns the starch indicator blue-black. The rate of reaction may be determined by timing how long it takes the reaction mixture to turn blue-black. In this experiment you will measure two reaction times and use one of these to calculate the concentration of the thiosulfate ions in FA 6. FA 3 is 1.0 mol dm–3 sulfuric acid, H2SO4. FA 4 is the diluted hydrogen peroxide, H2O2, you prepared in 1(a). FA 5 is 1.0 mol dm–3 potassium iodide, KI. FA 6 is aqueous sodium thiosulfate, Na2S2O3. starch indicator Read through the instructions carefully before starting any practical work. (a) Method • Use the measuring cylinder to transfer 20 cm3 of FA 3 into the 100 cm3 beaker. • Use the measuring cylinder to add 10 cm3 of FA 4 into the 100 cm3 beaker. • Rinse the measuring cylinder with distilled water and drain. • Use the measuring cylinder to transfer 20 cm3 of FA 5 into the 250 cm3 beaker. • Use the measuring cylinder to transfer 20 cm3 of FA 6 into the 250 cm3 beaker. • Use the measuring cylinder to transfer 10 cm3 of starch indicator into the 250 cm3 beaker. • Add the contents of the 100 cm3 beaker to the 250 cm3 beaker and start timing immediately. • Stir the mixture once and place the beaker on a white tile. • Stop timing as soon as the solution turns blue-black. • Record this reaction time to the nearest second. • Rinse both beakers and drain. Keep all FA solutions and starch indicator for use in (c). reaction time = … s [2]

5 9701/33/O/N/16 © UCLES 2016 [Turn over (b) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) The expression for the rate of reaction is shown. rate = concentration of iodine at the reaction time reaction time The concentration of iodine at the reaction time is the concentration of iodine that would have been present at the time the blue-black colour appeared if no thiosulfate ions had been added. In this experiment, you should assume the rate = 2.61 × 10–5 mol dm–3 s–1. Use this value for the rate to calculate the concentration of iodine that would have been present at the reaction time if no thiosulfate ions had been added. concentration of I2 = … mol dm–3 (ii) Use your answer to (i) and the total reaction volume, to calculate the number of moles of iodine that would have been present at the reaction time if no thiosulfate ions had been added. (If you were unable to calculate an answer to (i), you should use the value of 1.32 × 10–3 mol dm–3. This may not be the correct value.) moles of I2 = … mol (iii) Calculate the number of moles of thiosulfate ions that reacted with the moles of I2, calculated in (ii). I2(aq) + 2S2O3 2–(aq) → 2I –(aq) + S4O6 2–(aq) moles of S2O3 2– = … mol (iv) Use your answer to (iii) to calculate the concentration of thiosulfate ions in FA 6. concentration of S2O3 2– in FA 6 = … mol dm–3 [4]

6 9701/33/O/N/16 © UCLES 2016 (c) Repeat the experiment in (a) using the following quantities of each reagent. • add to the 100 cm3 beaker 20 cm3 of FA 3 10 cm3 of FA 4 • add to the 250 cm3 beaker 20 cm3 of FA 5 10 cm3 of FA 6 10 cm3 of starch indicator 10 cm3 of distilled water • Add the contents of the 100 cm3 beaker to the 250 cm3 beaker and start timing immediately. • Stir the mixture once and place the beaker on a white tile. • Stop timing as soon as the solution turns blue-black. • Record this reaction time to the nearest second. reaction time = … s [1] (d) (i) Explain the relationship between the value of the reaction time in (a) and the value of the reaction time in (c). … … … (ii) A student states that the error in the total volume of the reaction mixture in (a) is the same as the error in the total volume of the reaction mixture in (c). State whether or not you agree with the student and explain your answer. … … … … [4] [Total: 11]

7 9701/33/O/N/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. 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. (a) FA 7, FA 8, FA 9 and FA 10 are solutions that each contain a metal cation from those listed in the Qualitative Analysis Notes on page 10. Carry out tests using reagents that will allow you to identify which metal ions are present. Draw a single table to record your observations. Complete the table below with your conclusions. solution FA 7 FA 8 FA 9 FA 10 metal ion present [11]

8 9701/33/O/N/16 © UCLES 2016 (b) Carry out the following test and record your observations. test observations To a 1 cm depth of FA 10 in a boiling tube add a 0.5 cm depth of 20 ‘vol’ hydrogen peroxide, then add one drop of aqueous sodium hydroxide. [2] (c) FA 11 is a solid that contains one anion from those listed in the Qualitative Analysis Notes on page 11. Place all of FA 11 into a boiling tube and add a 3 cm depth of distilled water. Stir until all the solid has dissolved. (i) Carry out the following test and record your observations. test observations To a 1 cm depth of the solution of FA 11 in a test-tube add dilute sulfuric acid. (ii) Use your observations from (i) to identify the anion in FA 11. The anion is … . (iii) Use the remaining solution of FA 11 in the boiling tube to carry out a further test to support your identification of the anion. Record details of this test. [4] [Total: 17]

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10 9701/33/O/N/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) 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 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

11 9701/33/O/N/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

12 9701/33/O/N/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 9 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 9701/33 Paper 3 Advanced Practical Skills 1 October/November 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 October/November 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 – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks 1(a) Initial and final readings and titre value for rough and initial and final reading for two (or more) accurate titrations 1 Appropriate headings and units and the volume of FA 2 added is recorded for each accurate titration. Headings must match readings Initial/start (burette) and reading/volume Final/end (burette) and reading/volume Titre or volume/vol/FA 2 and used/added (not “difference”, “total”, “V”) Units: /cm3 or (cm3) or in cm3 or cm3 for each volume. 1 All accurate burette readings (initial and final) 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) 1 Final uncorrected titre is within 0.10 cm3 of any previous uncorrected accurate titre. 1 Examiner rounds any accurate burette readings to the nearest 0.05 cm3, checks subtractions and then selects the ‘best’ accurate titres using the hierarchy: identical titres; titres within 0.05 cm3; titres within 0.1 cm3; etc., to calculate mean correct to 0.01 cm3. Examiner compares candidate’s titre value with that of the Supervisor. V, VI and VII Award V, VI and VII for δ ≤ 0.30 cm3 Award V and VI for 0.30 < δ ≤ 0.50 cm3 Award V only for 0.50 < δ ≤ 0.80 cm3 1 1 1 7

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks 1(b) Calculation of the mean Check mean titre is correctly calculated from clearly selected values (ticks or working) • Candidate must average two (or more) titres where the total spread is ≤ 0.20 cm3. • Working must be shown or ticks must be put next to the two (or more) accurate readings selected. • The mean should normally be quoted to 2 dp rounded to the nearest 0.01. [e.g. 26.667 must be rounded to 26.67.] Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 e.g. 26.325; allow mean to 1 dp if all accurate burette readings were given to 1 dp (ignoring initial given as 0) and the mean is exactly correct. [e.g. 26.0 and 26.2 = 26.1 is correct but 26.0 and 26.1 = 26.1 is incorrect.] Do not award this mark if: • the rough titre was used to calculate the mean; • the candidate carried out only 1 accurate titration; • burette readings were incorrectly subtracted to obtain any of the accurate titre values; • all burette readings (resulting in titre values used in the calculation of the mean) are integers. 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 1(c)(i) I Correctly calculates: ( ) 0.0200 1000 b × 1 1(c)(ii) and 1(c)(iii) II Correctly uses: (i) × 5/2 and (ii)/0.025 or (ii) × 1000/25 1 1(c)(iv) Correctly calculates: (iii) × 10 or (ii) × 1000/25 ×10 1

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks 3 or 4 significant figures in final answers to all parts (minimum 3 parts attempted) 1 4 Total: 12 Question Answer Marks 2(a) Examiner to calculate 10% and 20% of Supervisor’s time and round this to nearest second. Candidate’s time compared with supervisor’s time. Award 2 marks if time within 10% of supervisor Award 1 mark if time within 20% of supervisor 2 2(b)(i) Correctly calculates: 2.61 × 10–5 × reaction time from (a) 1

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks 2(b)(ii) Correctly uses: (i) × 0.080 or (i) × 80/1000 and no additional working 1 2(b)(iii) and 2(b)(iv) Correctly uses: 2 × ans (ii) and (iii)/0.020 or (iii) × 1000/20 1 Time recorded to nearest second in (a) and (c) and 2 – 4 sf in all answers in (b) (minimum 3 parts attempted) 1 4 2(c) Examiner calculates ratio of reaction time (a)/reaction time (b) Award if 1.80 ⩽ ratio ⩽ 2.80 1 1 2(d)(i) Time is less/shorter because the amount/volume/concentration of thiosulfate/FA 6 is less (ora) 1 Time is approximately half because (the amount/no. of moles/concentration of) the thiosulfate/FA 6 is half. 1

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks 2(d)(ii) (No because) the error is greater in (c) with some explanation e.g. because more readings taken/water added 1 The measuring cylinder is used more times in (c) or smaller volumes/10 cm3 instead of 20 cm3 are measured in (c) or 6 rather than 5 readings taken/more reagents used/water also added/added in addition or smaller volumes therefore greater percentage error 1 4 Total: 11

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks FA 7 is ZnSO4; FA 8 is (NH4)2Fe(SO4)2; FA 9 is CrK(SO4)2; FA 10 is MnSO4; FA 11 is NaNO2 3(a) Selects NaOH and NH3 1 Single table to show results with both NaOH and NH3. No repeat headings. At least two of the FAs tested 1 FA 7 FA 8 FA 9 FA 10 NaOH white ppt green ppt grey-green ppt off-white/ pale brown/ buff ppt excess soluble insoluble soluble insoluble NH3 white ppt green ppt grey-green ppt off-white/ pale brown/ buff ppt excess soluble insoluble insoluble insoluble 1 1 1 1 FA 8 ppt turning brown in air with either NaOH or NH3 FA 9 ppt dissolves to form (dark) green solution with excess NaOH FA 10 darkens/goes brown with either NaOH or NH3 1 1 1

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks FA 7 FA 8 FA 9 FA 10 Zn2+ Fe2+ Cr3+ Mn2+ Award 1 mark for 2 correct ions. Award 2 marks for all 4 correct. 1 1 11 3(b) (dark) brown ppt/solid/suspension/deposit and effervescence/bubbling/fizzing 1 positive test for oxygen – (gas/ O2) relights glowing splint 1 2 3(c)(i) blue solution and effervescence/bubbling/fizzing or brown fumes/gas 1 3(c)(ii) NO2 – or nitrite from either blue solution or brown gas 1

Page 9 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 33 © UCLES 2016 Question Answer Marks 3(c)(iii) selects NaOH and Al (for nitrite or nitrate) or selects (acidified) potassium manganate(VII)/ potassium permangate/ KMnO4 If carbonate in (ii) (from bubbling without brown gas in (i)) then allow use of limewater to test gas If halide from no reaction then allow use of AgNO3 and NH3 If sulfate/sulfite from no reaction then allow use of BaCl2/Ba(NO3)2 and HCl/HNO3 1 Warming (with NaOH and Al ) and gas/ammonia turns (damp red) litmus (paper) blue or Decolourises MnO4 – 1 4 Total: 17