Chemistry 9701/35 May/June 2025: question paper and mark scheme

Question

Group 1 metal carbonates react with dilute acids to form a salt, water and carbon dioxide. The identity of the metal, M, can be determined by measuring the volume of carbon dioxide produced when excess acid is added to a known mass of the carbonate, M2CO3. FA 1 is the metal carbonate, M2CO3. FA 2 is 0.250 mol dm−3 sulfuric acid, H2SO4. (a) Method • Weigh the container with FA 1. Record the mass in the space for results. • Fill the tub with water to a depth of approximately 5 cm. • Fill the 250 cm3 measuring cylinder completely with water. Holding 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. • Use the 50 cm3 measuring cylinder to transfer 50.0 cm3 of FA 2 into the flask labelled X. Check that the bung fits tightly into the neck of flask X, clamp flask X and place the delivery tube into the inverted 250 cm3 measuring cylinder. • Remove the bung from the neck of the flask. Add all of the FA 1 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 and leave until the fizzing stops. Swirl the flask occasionally. • Weigh the container with any residual FA 1. Record the mass. • Calculate and record the mass of FA 1 that is added to the acid. • When no more gas is collected, record the final volume of gas. You may wish to start Question 2 or Question 3 while the gas is being collected. Results I II III [3] (b) Calculations (i) Calculate the amount, in mol, of carbon dioxide collected in the measuring cylinder (at room conditions). amount of CO2 = …… mol [1] (ii) Write an equation for the reaction between sulfuric acid and the metal carbonate, M2CO3. Include state symbols. …… [1] (iii) Use your answers to (b)(i) and (b)(ii) to deduce the amount, in mol, of the metal carbonate in the mass of FA 1 you used in your experiment. amount of M2CO3 = …… mol Hence, calculate the relative formula mass, Mr, of the metal carbonate. Mr of M2CO3 = …… [1] (iv) Use your answer to (b)(iii) to calculate the relative atomic mass, Ar, of metal M. Hence, identify metal M in FA 1. Ar of M = …… M is …… . [2] (c) A student carries out a similar experiment on a powdered Group 2 carbonate. The student determines the relative atomic mass, Ar, to be 49.3 and concludes that the metal in the carbonate is calcium. Calculate the percentage error in the student’s result. Show your working. percentage error in Ar of Ca = …… % [1] (d) Suggest why the method you used in (a) would be unsuitable for use with small lumps of calcium carbonate. …… [1] [Total: 10]

Question

The identity of a Group 1 metal in a metal carbonate may also be determined by titration with acid. Z2CO3 is a Group 1 metal carbonate. The metal may or may not be the same as that in FA 1. You will determine which metal is present in Z2CO3. FA 3 is 7.26 g dm−3 Z2CO3. FA 4 is 0.0500 mol dm−3 sulfuric acid, H2SO4. FA 5 is bromophenol blue indicator. (a) Method • Fill the burette with FA 4. • Pipette 25.0 cm3 of FA 3 into a conical flask. • Add a few drops of FA 5 to the same 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 sure any recorded results show the precision of your practical work. • Record, in a suitable form in the space below, all your burette readings and the volume of FA 4 added in each accurate titration. Results 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 obtain the mean value. 25.0 cm3 of FA 3 required …… cm3 of FA 4. [1] (c) Calculations (i) Calculate the amount, in mol, of sulfuric acid present in the volume of FA 4 in (b). amount of H2SO4 = …… mol [1] (ii) Use your answer to (c)(i) to calculate the amount, in mol, of Z2CO3 in 1.0 dm3 of FA 3. amount of Z2CO3 = …… mol [1] (iii) Use your answer to (c)(ii) to determine the identity of metal Z. Metal Z is …… . [2] (d) Z2CO3 also exists as the hydrated salt. State whether your titre will increase or decrease if 7.26 g of hydrated Z2CO3 is dissolved to prepare 1 dm3 of FA 3. Explain your answer. …… [1] (e) A titration is a more accurate method of determining the relative atomic mass of the metal in a metal carbonate than gas collection. Give two reasons why titration is a more accurate method. 1 …… 2 …… [2] [Total: 15] 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. If any solid is heated, a hard‑glass test‑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 tripod and gauze. Heat the water until boiling then switch off your Bunsen burner. This is your hot water bath for use in (b). (a) FA 6 and FA 7 are aqueous solutions that each contain one cation and one anion. All the ions are listed in the Qualitative analysis notes. None of the ions contains nitrogen. (i) Carry out the following tests using a 1 cm depth of FA 6 or FA 7 in a test‑tube for each test. Record your observations in Table 3.1. Table 3.1 observations test FA 6 FA 7 Test 1 Add aqueous sodium hydroxide. Test 2 Add aqueous ammonia, then let the mixture stand for 5 minutes. Test 3 Add hydrogen peroxide, mix well, then add aqueous sodium hydroxide. [4] (ii) Carry out tests to identify the anions in FA 6 and FA 7. Record your tests and observations in a suitable form in the space below. [4] (iii) Use your observations from (a)(i) and (a)(ii) to deduce the formulae of FA 6 and FA 7. FA 6 is …… . FA 7 is …… . [2] Ensure your water bath is hot and the Bunsen burner is turned off before you start (b). (b) FA 8 is an organic liquid containing one functional group and only the elements C, H and O. You will carry out two tests to investigate FA 8. For each test you will record your observations and then conclude one of the following: • at least two types of compound that FA 8 could be or • one type of compound that FA 8 cannot be. (i) To a 1 cm depth of FA 8 in a test‑tube, add a few drops of acidified aqueous potassium manganate(VII), then place the test‑tube in the hot water bath. observation …… conclusion …… [2] (ii) To a 1 cm depth of FA 8 in a test‑tube, add a small spatula measure of sodium carbonate. observation …… conclusion …… [2] (iii) Suggest a further test you could carry out to identify one of the types of compound that you have concluded could be FA 8. State the reagent you would use. State what a positive result would indicate about the identity of FA 8. Do not carry out your test. reagent …… conclusion from a positive result …… [1] [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 = 6.02 × 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 138.9 140.1 140.9 144.2 – 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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