Chemistry 9701/33 May/June 2022: question paper and mark scheme

Question

Acids donate protons, H+, in aqueous solution. The number of moles of H+ donated per mole of acid is the proticity of the acid. In this experiment, you will carry out a titration to determine the proticity of phosphoric acid, H3PO4, when it reacts with sodium hydroxide, NaOH. FA 1 is aqueous phosphoric acid, containing 6.86 g dm–3 H3PO4. FA 2 is 0.150 mol dm–3 sodium hydroxide, NaOH. FA 3 is thymolphthalein indicator. (a) Method ● Fill the burette with FA 2. ● Pipette 25.0 cm3 of FA 1 into a conical flask. ● Add a few drops of FA 3. ● 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 sure any recorded results show the precision of your practical work. ● Record in a suitable form below all your burette readings and the volume of FA 2 added in each accurate titration. I II III IV V VI VII [7] (b) From your accurate titration results, calculate a suitable mean value to use in your calculations. Show clearly how you obtained the mean value. 25.0 cm3 of FA 1 required …… cm3 of FA 2. [1] (c) Calculations (i) Calculate the amount, in mol, of sodium hydroxide present in the volume of FA 2 calculated in (b). amount of NaOH = …… mol [1] (ii) Use the information on page 2 to calculate the amount, in mol, of phosphoric acid present in 25.0 cm3 of FA 1. amount of H3PO4 = …… mol [1] (iii) Deduce whether phosphoric acid behaves as a monoprotic, diprotic or triprotic acid in this titration. Explain your reasoning. H3PO4 is a ……protic acid. explanation . …… . …… [1] (iv) Give the equation for this reaction of phosphoric acid, H3PO4, with sodium hydroxide. . …… [1] (d) (i) A student uses a pipette that is labelled 25.0 ± 0.06 cm3 to measure FA 1. Calculate the maximum percentage error in the volume of FA 1. Show your working. maximum percentage error = ……% [1] (ii) The student suggests it would be more accurate to measure the volume of FA 1 with a burette instead of the pipette. State whether you agree with the student. Explain your answer. . …… . …… [1] [Total: 14] 2 In this experiment you will identify the metal, M, in a metal carbonate, MCO3, by thermal decomposition. MCO3(s) → MO(s) + CO2(g) FA 4 is the metal carbonate, MCO3. (a) Method ● Weigh the empty crucible with its lid. Record the mass. ● Transfer all the FA 4 from the container into the crucible. ● Weigh the crucible, lid and FA 4. Record the mass. ● Calculate and record the mass of FA 4 used. ● Place the crucible and contents on a pipe-clay triangle. ● Heat the crucible gently, with the lid on, for approximately 1 minute. ● Heat strongly, with the lid off, for a further 4 minutes. ● Replace the lid and leave the crucible to cool for at least 5 minutes. During the cooling period, you may wish to begin work on Question 3. ● When the crucible has cooled, weigh the crucible with its lid and contents. Record the mass. ● Heat strongly, with the lid off, for a further 2 minutes. ● Replace the lid and leave the crucible to cool for at least 5 minutes. ● When the crucible has cooled, reweigh the crucible with its lid and contents. Record the mass. ● Calculate and record the total loss of mass and the mass of residue obtained. ● This residue is FA 5. Keep FA 5 for use in 2(d). Results I II III IV V [5] (b) Calculations (i) Calculate the amount, in mol, of carbon dioxide given off in your experiment. amount of CO2 = …… mol [1] (ii) Calculate the relative formula mass, Mr, of MCO3. Mr of MCO3 = …… [1] (iii) From your results, deduce the identity of M. Show your reasoning. M is = …… [1] (c) A student carries out the same procedure, using the same mass of solid. However, the student uses the basic carbonate, MCO3•M(OH)2, instead of the pure carbonate, MCO3. When the metal hydroxide part of the basic carbonate decomposes, metal oxide and steam are produced. The metal carbonate part decomposes in the usual way. State how the loss of mass from the student’s solid compares with the loss of mass you obtained when you carried out your experiment. Explain your reasoning. . …… . …… [2] (d) Use a spatula to transfer a small quantity of your cold residue, FA 5, into a test-tube. Add about a 1 cm depth of dilute hydrochloric acid to the FA 5 in the test-tube. Record what you observe. . …… . …… State whether or not the thermal decomposition of MCO3 is complete. Justify your answer based on your observations. . …… . …… . …… [2] [Total: 12] Qualitative analysis For each test you should record all your observations in the spaces provided. Examples of observations include: ● colour changes seen ● the formation of any precipitate and its solubility (where appropriate) in an excess of the reagent added ● the formation of any gas and its identification (where appropriate) by a suitable test. You should record clearly at what stage in a test an observation is made. Where no change is observed you should write ‘no change’. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. If any solution is warmed, a boiling tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests should be attempted. 3 (a) Solutions FA 6 and FA 7 each contain one cation and one anion. All the ions are listed in the Qualitative analysis notes. (i) Carry out the following tests, using a 1 cm depth of FA 6 or FA 7 in a test‑tube for each test. Complete the table below. Table 3.1 observations test FA 6 FA 7 Test 1 Add an equal volume of aqueous potassium iodide, then add excess aqueous sodium thiosulfate. Test 2 Add a small spatula measure of zinc powder. Leave the mixture to stand. Test 3 Add a few drops of aqueous silver nitrate. Test 4 Add aqueous sodium hydroxide. [5] (ii) Construct an ionic equation for one of the reactions taking place in Test 2. Include state symbols. . …… [1] (b) FA 8 contains one anion and one cation. One of these ions contains nitrogen. Both ions are listed in the Qualitative analysis notes. (i) Transfer a small spatula measure of FA 8 into a hard‑glass test‑tube. Heat the test-tube gently at the start, then strongly until no further change occurs. Leave the test-tube to cool. Record all your observations. . …… . …… . …… . …… [2] (ii) Carry out further tests to identify each ion in FA 8. Record, in a table in the space below, the reagents, conditions and observations for the tests that positively identify each ion. You may wish to use the following page for rough working. Deduce the chemical formula of FA 8. You must use a boiling tube if any liquid is heated. The formula of FA 8 is …… . [6] [Total: 14] Use this page for any rough working. Qualitative analysis notes 1 Reactions of cations cation 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 warming barium, Ba2+(aq) faint white ppt. is observed unless no ppt. [Ba2+(aq)] is very low calcium, Ca2+(aq) white ppt. unless [Ca2+(aq)] is very no ppt. low chromium(III), Cr3+(aq) grey-green ppt. soluble in excess grey-green ppt. insoluble in excess giving dark green solution copper(II), Cu2+(aq) pale blue ppt. insoluble in excess pale blue ppt. soluble in excess giving dark blue solution iron(II), Fe2+(aq) green ppt. turning brown on green ppt. turning brown on contact with air contact with air insoluble in excess 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 off-white ppt. rapidly turning brown on contact with air on contact with air insoluble in excess insoluble in excess zinc, Zn2+(aq) white ppt. soluble in excess white ppt. soluble in excess

Question

Reactions of anions anion reaction carbonate, CO32– CO2 liberated by dilute acids chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)) bromide, Br –(aq) gives cream / off-white ppt. with Ag+(aq) (partially soluble in NH3(aq)) iodide, I–(aq) gives pale 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; decolourises acidified aqueous KMnO4 sulfate, SO42–(aq) gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids); gives white ppt. with high [Ca2+(aq)] sulfite, SO32–(aq) gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids); decolourises acidified aqueous KMnO4 thiosulfate, S2O32–(aq) gives off-white / pale yellow ppt. slowly with H+

Question

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 hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint 4 Tests for elements element test and test result iodine, I2 gives blue-black colour on addition of starch solution Important values, constants and standards molar gas constant R = 8.31 J K–1 mol–1 Faraday constant F = 9.65 × 104 C mol–1 Avogadro constant L = 6.022 × 1023 mol–1 electronic charge e = –1.60 × 10–19 C molar volume of gas Vm = 22.4 dm3 mol–1 at s.t.p. (101 kPa and 273 K) Vm = 24.0 dm3 mol–1 at room conditions ionic product of water Kw = 1.00 × 10–14 mol2 dm–6 (at 298 K (25 °C)) specific heat capacity of water c = 4.18 kJ kg–1 K–1 (4.18 J g–1 K–1) The Periodic Table of Elements Group 1 2 13 14 15 16 17 18 1 2 H He hydrogen helium Key 1.0 4.0 3 4 atomic number 5 6 7 8 9 10 Li Be atomic symbol B C N O F Ne lithium beryllium name boron carbon nitrogen oxygen fluorine neon 6.9 9.0 relative atomic mass 10.8 12.0 14.0 16.0 19.0 20.2 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar sodium magnesium aluminium silicon phosphorus sulfur chlorine argon 23.0 24.3 3 4 5 6 7 8 9 10 11 12 27.0 28.1 31.0 32.1 35.5 39.9 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 at www.cambridgeinternational.org after the live examination series. K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton 39.1 40.1 45.0 47.9 50.9 52.0 54.9 55.8 58.9 58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 12 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon 85.5 87.6 88.9 91.2 92.9 95.9 – 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3 55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 lanthanoids Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon 132.9 137.3 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 – – – 87 88 89–103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 actinoids Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson – – – – – – – – – – – – – – – – – 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 lanthanoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium 138.9 140.1 140.9 144.4 – 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.1 175.0 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 actinoids Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium – 232.0 231.0 238.0 – – – – – – – – – – – Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge