Chemistry 9701/33 February/March 2024: question paper and mark scheme

Question

The ionic equation for the reaction between sodium thiosulfate and hydrochloric acid is: S2O32–(aq) + 2H+(aq) S(s) + SO2(aq) + H2O(l) The solid sulfur formed causes the reaction mixture to become cloudy and opaque. You will carry out experiments to investigate the relationship between the concentration of sodium thiosulfate and the rate of reaction. Small amounts of SO2 gas are released during this reaction. Take care to avoid inhaling this gas. It is important that, as soon as each experiment is complete, the contents of the beaker are emptied into the quenching bath and the beaker is rinsed thoroughly. FA 1 is 0.10 mol dm–3 sodium thiosulfate, Na2S2O3. FA 2 is 2.00 mol dm–3 hydrochloric acid, HCl . distilled water (a) Method Prepare a table for your results in the Results section on page 4. For each experiment the table should include: ● volume of FA 1 used ● volume of distilled water used ● reaction time ● relative rate. Relative rate can be calculated using the expression: 1000 relative rate = reaction time Experiment 1 ● Label a burette FA 1. Fill the burette with FA 1. ● Transfer 25.00 cm3 of FA 1 into a 100 cm3 beaker. ● Place the beaker on the printed insert. ● Use the 25 cm3 measuring cylinder to measure 10.0 cm3 of FA 2. ● Add the FA 2 to the FA 1 in the beaker and immediately start the stop-clock. Stir the mixture once. ● Look vertically down through the solution in the beaker at the print on the insert. ● Stop the stop-clock as soon as the print on the insert is no longer visible. ● Record the reaction time to the nearest second. ● Empty the contents of the beaker into the quenching bath. ● Rinse the beaker with water. Dry the beaker so that it is ready to be used in Experiment 2. Experiment 2 ● Transfer 12.50 cm3 of FA 1 into the 100 cm3 beaker. ● Label a second burette ‘water’. Fill this burette with distilled water. ● Transfer 12.50 cm3 of distilled water into the 100 cm3 beaker. ● Place the beaker on the printed insert. ● Use the 25 cm3 measuring cylinder to measure 10.0 cm3 of FA 2. ● Add the FA 2 to the solution in the beaker and immediately start the stop-clock. Stir the mixture once. ● Look vertically down through the solution in the beaker at the print on the insert. ● Stop the stop-clock as soon as the print on the insert is no longer visible. ● Record the reaction time to the nearest second. ● Empty the contents of the beaker into the quenching bath. ● Rinse the beaker with water. Dry the beaker so that it is ready to be used in the next experiment. Experiments 3–5 Carry out three further experiments to investigate how reaction times change with different volumes of FA 1. Do not use a volume of FA 1 less than 12.50 cm3. Results I II III IV V VI VII VIII [8] (b) Plot a graph, on the grid, of relative rate (y-axis) against volume of FA 1 (x-axis). The graph should not include the origin. Identify any anomalous point. Draw a line of best fit. I II III IV [4] (c) Use your graph to predict the reaction time if an experiment is carried out using 23.50 cm3 of FA 1 and distilled water. Show clearly on the grid how you determined the relative rate. reaction time = …… s [2] (d) The final instruction for each experiment is to rinse and dry the beaker. State the effect on the reaction time of not drying the beaker before carrying out each of Experiments 2–5. Explain your answer. …… [1] (e) A student repeats Experiment 1 but uses a 250 cm3 beaker in place of the 100 cm3 beaker. All other conditions remain the same. State whether each statement below is correct. Explain your answers. (i) The student records a longer time for this experiment because the 250 cm3 beaker is used. …… [1] (ii) A longer time is recorded because the rate of production of sulfur is slower. …… [1] [Total: 17]

Question

In this experiment you will determine the enthalpy change, ΔH, for the reaction between aqueous copper(II) sulfate and magnesium. CuSO4(aq) + Mg(s) Cu(s) + MgSO4(aq) FA 3 is 1.0 mol dm–3 copper(II) sulfate, CuSO4. FA 4 is magnesium powder, Mg. (a) Method ● Support the cup in the 250 cm3 beaker. ● Use the 50 cm3 measuring cylinder to transfer 50.0 cm3 of FA 3 into the cup. ● Weigh the stoppered container of FA 4. Record the mass. ● Measure the temperature of FA 3 in the cup. Record the temperature. ● Add the FA 4 to the FA 3 in the cup and stir the mixture constantly. ● Measure and record the maximum temperature reached. ● Reweigh the stoppered container and any residual FA 4. Record the mass. ● Calculate and record the mass of FA 4 used. ● Calculate and record the maximum temperature change that occurs during the reaction. [3] (b) Calculations (i) Calculate the heat energy produced in the reaction. heat energy produced = …… J [1] (ii) Determine which reactant, FA 3 or FA 4, is in excess for the reaction. Show your working. [1] (iii) Calculate the enthalpy change, ΔH, in kJ mol–1, for the reaction. ΔH = …… …… kJ mol–1 (sign) (value) [2] (c) A student suggests that the slow rate of the reaction using the method described in (a) means that heat energy is lost from the solution so the temperature change is inaccurate. Describe how you would change the method and processing of the results to improve the accuracy of the enthalpy change for this reaction. You should not change the quantities of FA 3 or FA 4 used. You may wish to illustrate your answer with a sketch graph. [3] [Total: 10] 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.

Question

(a) Each of the solutions FA 5, FA 6 and FA 7 has an anion containing sulfur. All the anions are listed in the Qualitative analysis notes. None of the anions is present in more than one compound. None of the solutions contain a cation listed in the Qualitative analysis notes. Use 1 cm depth of each solution in a test-tube for each test. Record your observations in Table 3.1. Table 3.1 observations test FA 5 FA 6 FA 7 Test 1 Add a few drops of aqueous acidified potassium manganate(VII) then leave it to stand for 2 minutes. Test 2 Add a piece of magnesium ribbon. Test 3 Add aqueous barium chloride or aqueous barium nitrate. [5] (b) (i) Use your observations from (a) to identify the formula of each of the anions present in FA 5, FA 6 and FA 7. FA 5 FA 6 FA 7 [2] (ii) Use your observations from (a), to suggest the identity of the cation present in FA 6. The cation in FA 6 is …… . Carry out a further test to check whether your suggestion is correct. Record your test and observations. State the identity of the cation in FA 6. The cation in FA 6 is …… . [2] (c) Write an ionic equation for one of the reactions in either Test 2 or Test 3 in (a). Include state symbols. …… [1] (d) FA 8 is a solid compound. (i) Gently warm (do not boil) a 4 cm depth of FA 6 in a boiling tube. Stop warming the FA 6, add all the FA 8 and shake the boiling tube. Filter the mixture into a second boiling tube. The filtrate will be used in (d)(ii). Describe the appearance of the residue and the filtrate. residue …… filtrate …… [1] (ii) To a 2 cm depth of the filtrate from (d)(i) in a test-tube, add an equal volume of aqueous potassium iodide. Record your observations. Filter the mixture into a test-tube for use in (d)(iii). …… [1] (iii) To a 1 cm depth of the filtrate from (d)(ii), add aqueous sodium hydroxide. Record your observations. …… [1] [Total: 13] 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 2 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+ 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 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 16 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