Chemistry 9701/34 May/June 2022: question paper and mark scheme

Question

Calcium carbonate reacts with hydrochloric acid to release carbon dioxide. CaCO3(s) + 2HCl (aq) → CaCl 2(aq) + CO2(g) + H2O(l) The concentration of the hydrochloric acid can be determined by reacting it with calcium carbonate and measuring the volume of carbon dioxide formed. FB 1 is hydrochloric acid, HCl. FB 2 is calcium carbonate, CaCO3. (a) Method ● Fill the tub with tap water to a depth of approximately 5 cm. ● Fill the 250 cm3 measuring cylinder completely with water. Hold a piece of paper towel firmly over the top, invert the measuring cylinder and place it in the water in the tub. ● Remove the paper towel and clamp the inverted measuring cylinder so the open end is in the water just above the base of the tub. ● Using the 50 cm3 measuring cylinder, transfer 50 cm3 of FB 1 into the flask. Check that the bung fits tightly into the neck of the flask, clamp the flask and place the end of the delivery tube into the inverted 250 cm3 measuring cylinder. ● Remove the bung from the neck of the flask. Tip all the FB 2, from the container, into the acid in the flask and replace the bung immediately. Remove the flask from the clamp and swirl it to mix the contents. ● Replace the flask in the clamp. Leave for several minutes, swirling the flask occasionally. You may wish to start Question 3 while the gas is being produced. ● When the reaction stops producing gas, record the final volume of gas in the measuring cylinder. Keep the flask and contents for use in 1(c)(i). volume of gas = …… cm3 [2] (b) Calculations (i) Calculate the amount, in mol, of carbon dioxide collected in the measuring cylinder. (Assume that 1 mol of gas occupies 24.0 dm3 under these conditions.) amount of CO2 = …… mol [1] (ii) Use your answer to (b)(i) and the equation on page 2 to calculate the concentration, in mol dm–3, of hydrochloric acid in FB 1. Show your working. concentration of HCl = …… mol dm–3 [2] (c) (i) A student thinks that the mass of FB 2 should be measured. Explain, by observing the contents of the flask, why this is not necessary. . …… . …… . …… [2] (ii) In this experiment some carbon dioxide is lost before the bung is replaced. Suggest a change that could be made to minimise the loss of gas. Explain how this change minimises the loss of gas. . …… . …… . …… [1] [Total: 8]

Question

In this experiment you will use a thermometric method to determine the concentration of a sample of alkali. You will mix varying volumes of acid with a fixed volume of the alkali and measure the temperature rises that occur. You will use your experimental data to calculate the enthalpy change for the neutralisation of the acid with alkali. FB 3 is aqueous sodium hydroxide, NaOH. FB 4 is 2.20 mol dm–3 hydrochloric acid, HCl. (a) Method ● Support the cup in the 250 cm3 beaker. ● Use the thermometer to measure the initial temperature of FB 3. initial temperature of FB 3 = …… °C ● Fill a burette with distilled water. ● Fill the other burette with FB 4. Label this burette FB 4. ● or Experiment 1, use the 10 cm3 pipette to transfer 10.0 cm3 of FB 3 into the cup. F ● dd 9.00 cm3 of distilled water from the burette into the same cup. A ● Add 1.00 cm3 of FB 4 from the other burette into the same cup. ● Stir the mixture and use the thermometer to measure the maximum temperature obtained. ● Record the maximum temperature in the table. ● Empty and shake dry the cup ready for use in Experiment 2. ● Repeat the method using 10.0 cm3 of FB 3 for each experiment and the volumes of water and FB 4 shown in the table. In each case, measure and record the maximum temperature. Table 2.1 volume water volume FB 4 maximum experiment / cm3 / cm3 temperature / °C 1 9.00 1.00 2 7.00 3.00 3 5.00 5.00 4 3.00 7.00 I 5 1.00 9.00 II III 6 IV 7 V Carry out two further experiments which will enable you to determine more precisely the volume of FB 4 that gives the highest maximum temperature. Record your measurements for these two experiments in the table. [5] (b) Plot a graph of the maximum temperature reached (y-axis) and the volume of FB 4 used (x-axis). The scale on the y-axis should include a temperature 2 °C above the highest maximum temperature reached. Circle any points you consider to be anomalous. I Draw two straight lines of best fit on your graph. One line should show where the maximum temperature recorded was increasing. The other line should be after the highest maximum II temperature. Extrapolate both lines so that they intersect. III Use your graph to determine the volume of FB 4 that reacts with 10.00 cm3 of FB 3. IV volume of FB 4 = …… cm3 [4] (c) (i) Give your answers to (c)(ii), (c)(iii), (c)(iv) and (c)(v) to an appropriate number of significant figures. [1] (ii) Calculate the amount, in mol, of hydrochloric acid in the volume of FB 4 in (b). If you were unable to determine an answer to (b) use 4.10 cm3 as the volume of FB 4. amount of HCl = …… mol [1] (iii) Use your answer to (c)(ii) and the information on page 4 to calculate the concentration, in mol dm–3, of sodium hydroxide in FB 3. concentration of NaOH = …… mol dm–3 [1] (iv) Calculate the energy released when the volume of FB 4 in (b) is neutralised by sodium hydroxide. Show your working. (Assume that 4.18 J of energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) energy released = …… J [2] (v) Use your answers to (c)(ii) and (c)(iv) to calculate the enthalpy change of neutralisation, in kJ mol–1, for 1.0 mol of hydrochloric acid. enthalpy change = …… …… kJ mol–1 sign value[1] (d) (i) The theoretical value of the enthalpy change of neutralisation is –57.6 kJ mol–1. Calculate the percentage error in your value of the enthalpy change from (c)(v). Show your working. (Assume that the conditions under which you carried out your experiment in (a) are identical to the conditions used to determine the theoretical value.) percentage error = …… % [1] (ii) Suggest one modification to the procedure used in (a) that would give a more accurate value for the enthalpy change of neutralisation. Do not suggest any modifications to apparatus in your answer. . …… . …… . …… . …… [1] [Total: 17] 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, heat until the water is nearly boiling and then turn off the Bunsen burner. This is your hot water bath for use in (a)(i). (a) You are provided with aqueous solutions FB 5, FB 6, FB 7 and FB 8. The solutions are known to be hydrochloric acid, hydrogen peroxide, methanoic acid and sulfuric acid. All the solutions have the same concentration. Note: the order of FB 5 to FB 8 does not correspond to the order of identities given above. (i) Carry out the following tests using a 2 cm depth of each reagent in a test-tube. Record your observations in Table 3.1. observations test FB 5 FB 6 FB 7 FB 8 Test 1 Add a piece of magnesium. 9 Table 3.1 Test 2 Add a few drops of acidified aqueous potassium manganate(VII). Place the test-tube in the hot water bath. [5] (ii) Use your observations to complete the sentences. Explain your answer. FB 7 is …… . FB 8 is …… . explanation …… . …… [2] (iii) Carry out one additional test that allows you to distinguish between FB 5 and FB 6. Record your test and the result you obtained. FB 5 is …… . FB 6 is …… . [2] (iv) Write an ionic equation for the reaction of magnesium with FB 5. Include state symbols. . …… [1] (v) Describe the observations that you would expect to see if the tests in (a)(i) were repeated using aqueous ethanoic acid. observation with magnesium …… . …… observation with acidified aqueous potassium manganate(VII) …… . …… [2] (b) FB 9 is an aqueous solution containing one cation from those listed in the Qualitative analysis notes. Carry out tests that would identify the cation present in FB 9. Record your tests, observations and the identity of the cation. The cation is …… . [3] [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 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. 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