Chemistry 9701/34 May/June 2023: question paper and mark scheme

Question

You will investigate the enthalpy change of neutralisation, ∆Hneut, between aqueous sodium hydroxide of known concentration and a dilute organic acid. You will use your results to suggest the identity of the organic acid. The acid is a halogenocarboxylic acid containing one halogen atom, X, per molecule. NaOH(aq) + CH3CHXCOOH(aq) CH3CHXCOONa(aq) + H2O(l) FB 1 is 1.90 mol dm−3 sodium hydroxide, NaOH. FB 2 is a solution containing 312.5 g dm−3 of the organic acid CH3CHXCOOH. (a) Method ● Support the cup in the 250 cm3 beaker. ● Pipette 25.0 cm3 of FB 1 into the cup. ● Place the thermometer into FB 1. Record the temperature of FB 1 in Table 1.1. This is the temperature when the volume of FB 2 is 0.00 cm3. ● Fill the burette with FB 2. ● Run 5.00 cm3 of FB 2 into the cup containing FB 1. I ● Stir the mixture. Record the highest temperature observed. ● Run further 5.00 cm3 portions of FB 2 into the same cup. II ● On each addition of FB 2 stir the contents of the cup. Record the highest III temperature after each addition. Results Table 1.1 total volume of 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 FB 2 added / cm3 temperature / ºC [3] (b) (i) Plot a graph of temperature (y-axis) against volume of FB 2 added (x-axis) on the grid. Select a scale on the y-axis to include a temperature of 2 ºC above your maximum thermometer reading. Label any points you consider to be anomalous. Draw two lines of best fit, the first for the increase in temperature and the second for after the maximum temperature has been reached. Extrapolate the two lines so they intersect. This intersection corresponds to the volume of FB 2 required to form a neutral solution. I II III IV [4] (ii) Use your graph to determine the volume of FB 2 required to neutralise 25.0 cm3 of FB 1. 25.0 cm3 of FB 1 required …… cm3 of FB 2. [1] (c) Calculations (i) Calculate the energy change, in J, when the volume of FB 2 recorded in (b)(ii) neutralises 25.0 cm3 of FB 1. energy change = …… J [1] (ii) Calculate the amount, in mol, of sodium hydroxide, FB 1, pipetted into the cup. amount of NaOH = …… mol [1] (iii) Calculate the enthalpy change of neutralisation, ∆Hneut, in kJ mol−1, for 1.00 mol of sodium hydroxide reacting with FB 2. ∆Hneut = …… …… kJ mol−1 [1] sign value (iv) Use your answers to (b)(ii) and (c)(ii) and the information given on page 2 to calculate the relative formula mass, Mr, of the organic acid CH3CHXCOOH. Show your working. Mr of CH3CHXCOOH = …… [1] (v) The acid is known to be one of the following: CH3CHFCOOH, CH3CHCl COOH, CH3CHBrCOOH or CH3CHICOOH. Use your answer to (c)(iv) to identify the acid used to make solution FB 2. The acid in FB 2 is …… . [1] (vi) Calculate the percentage error in the relative formula mass, Mr, you calculated in (c)(iv). percentage error in Mr = …… % [1] [Total: 14]

Question

A gravimetric procedure can identify the metal in many metal carbonates. You will decompose a metal carbonate, MCO3, by heating to produce the metal oxide and carbon dioxide. You may assume this metal forms a stable metal oxide on heating. M is not a transition metal. MCO3(s) MO(s) + CO2(g) FB 3 is the metal carbonate MCO3. (a) Method ● Weigh the crucible with its lid. Record the mass. ● Add between 0.90 g and 1.10 g of FB 3 to the crucible. ● Weigh the crucible, lid and FB 3. Record the mass. ● Place the crucible on the pipe-clay triangle. ● Gently heat the crucible and contents for approximately 1 minute with the lid on. ● Remove the lid. Then heat the crucible and contents strongly for approximately 5 minutes. ● Replace the lid and leave the crucible to cool for at least 5 minutes. While the crucible is cooling, you may wish to begin work on Question 3. ● When the crucible is cool, weigh the crucible with its lid and contents. Record the mass. ● Calculate and record the mass of FB 3 added to the crucible, the mass of residue obtained and the mass loss. Keep the residue for use in 2(d). Results I II III IV V [5] (b) Calculations (i) Calculate the amount, in mol, of carbon dioxide lost on heating FB 3. amount of CO2 = …… mol [1] (ii) Use your answer to (b)(i) and your data from (a) to calculate the relative formula mass, Mr, of MCO3. Mr of MCO3 = …… [1] (iii) Use your answer to (b)(ii) to suggest the identity of metal M. Show your working. M is …… . [1] (c) A student carrying out the same experiment as in (a) spills a small quantity of solid just before carrying out the final weighing. State what effect this would have on the value of the Mr that is calculated for MCO3. Explain your answer. …… [1] (d) Normally, in this experiment, you would reheat and reweigh the crucible and contents until the mass is constant to ensure all the metal carbonate has decomposed. Suggest a chemical test to determine whether all the metal carbonate has decomposed. Record your test, observation and conclusion. test …… observation …… conclusion …… [2] [Total: 11] 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

Half fill the 250 cm3 beaker with water and place it on a gauze on the tripod. Heat the water until boiling then switch off your Bunsen burner. This will be your hot water bath. (a) FB 4, FB 5 and FB 6 are acids with the same concentration. Only one is an organic acid. (i) Carry out the following tests and record your observations in Table 3.1. Use a 1 cm depth of FB 4, FB 5 or FB 6 in a test-tube for each test. Table 3.1 observations test FB 4 FB 5 FB 6 Test 1 Add 1 or 2 drops of acidified aqueous potassium manganate(VII), then place the test-tube in the hot water bath. Test 2 Add a few copper turnings and place the test-tube in the hot water bath for a few minutes. Test 3 Add a 1 cm strip of magnesium ribbon, then leave the test-tube for 3 minutes and then shake the test-tube gently. At the end of the experiments rinse the test-tubes thoroughly. [7] (ii) Each of FB 4, FB 5 and FB 6 is one of the following acids: methanoic acid, nitric acid or sulfuric acid. Use your observations to suggest the identity of each acid. Explain your answers. FB 4 is …… . explanation …… FB 5 is …… . explanation …… FB 6 is …… . explanation …… [3] (b) The halogenocarboxylic acid in FB 2 was hydrolysed by heating with excess aqueous sodium hydroxide. The resulting solution is FB 7. (i) Carry out a test to check the identity of the halogen atom present in FB 2. Use a 1 cm depth of FB 7 in a test-tube for your test. State your reagents and record your observations at each stage of your test. From this test only, give the identity of the halogen present in FB 2. The halogen is …… . [3] (ii) Give the equation for the hydrolysis reaction of the halogenocarboxylic acid, FB 2, with excess hot aqueous sodium hydroxide. (If you were unable to identify the halogen in (b)(i), then use the formula CH3CHXCOOH.) …… [2] [Total: 15] 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 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. 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