Chemistry 9701/31 October/November 2021: question paper and mark scheme

Question

You will investigate a compound of a Group 1 element to determine which element is present. Group 1 carbonates decompose to give carbon dioxide when heated to high temperatures. X2CO3(s) → X2O(s) + CO2(g) FA 1 is the carbonate of the element, X2CO3. (a) Method ● Weigh a crucible with its lid and record the mass. ● Add 1.40–1.60 g of FA 1 to the crucible. ● Weigh the crucible and its lid with FA 1 and record the mass. ● Place the crucible on the pipe-clay triangle. Heat the crucible, with its lid on, gently for approximately 1 minute. Then heat strongly for another minute. ● Carefully remove the lid. Heat the crucible strongly for 4 minutes. ● Replace the lid and leave the crucible and residue to cool for at least 5 minutes. While the crucible is cooling you may wish to begin work on Question 2. ● Reweigh the crucible and contents with its lid. Record the mass. ● Remove the lid. Heat the crucible and contents strongly for a further 2 minutes. ● Replace the lid and leave the crucible and residue to cool for at least 5 minutes. Reweigh the crucible and residue with its lid. Record the mass. ● Calculate and record the mass of FA 1 added to the crucible. Calculate the mass of residue obtained. Results I II III IV V [5] (b) Calculations (i) Calculate the mass of carbon dioxide produced when the sample of X2CO3 was heated. mass of CO2 produced = …… g [1] (ii) Calculate the number of moles of X2CO3 needed to produce the mass of carbon dioxide calculated in (b)(i). moles of X2CO3 needed = …… mol [1] (iii) Use your answer to (b)(ii) and the information on page 2 to calculate the relative formula mass, Mr, of X2CO3. Mr of X2CO3 = …… [1] (iv) Use your answer to (b)(iii) to calculate the relative atomic mass, Ar, of X. Hence identify X. Explain how you reached your conclusion. X is …… . . …… . …… [2] (c) In this experiment you heated the sample of X2CO3 for approximately 8 minutes. Explain, using evidence from your results in (a), whether your sample of X2CO3 had decomposed completely. . …… . …… [1] [Total: 11]

Question

In this experiment you will titrate a solution of the hydroxide of a Group 1 element, Z, with sulfuric acid. The equation for the reaction is shown. Z may or may not be the same as X. 2ZOH(aq) + H2SO4(aq) → Z2SO4(aq) + 2H2O(l) FA 2 is 26.3 g dm–3 aqueous hydroxide of metal Z, ZOH. FA 3 is 0.0500 mol dm–3 sulfuric acid, H2SO4. bromophenol blue indicator (a) Method ● Pipette 25.0 cm3 of FA 2 into the 250 cm3 volumetric flask. ● Add distilled water to the flask to make 250 cm3 of solution. Shake the flask thoroughly to ensure complete mixing. Label this solution FA 4. ● Rinse the pipette with a little distilled water and then a little FA 4. ● Fill the burette with FA 3. ● Pipette 25.0 cm3 of FA 4 into a conical flask. ● Add a few drops of bromophenol blue indicator. ● Carry out 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 your recorded results show the accuracy of your practical work. ● Record in a suitable form in the space below all of your burette readings and the volume of FA 3 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 this value. 25.0 cm3 of FA 4 required …… cm3 of FA 3. [1] (c) Calculations (i) Give your answers to (c)(ii), (c)(iii) and (c)(iv) to the appropriate number of significant figures. [1] (ii) Calculate the number of moles of sulfuric acid present in the volume of FA 3 you calculated in (b). moles of H2SO4 = …… mol [1] (iii) Use your answer to (c)(ii) and the information on page 4 to calculate the concentration, in mol dm–3, of ZOH present in FA 4. concentration of FA 4 = …… mol dm–3 [1] (iv) Calculate the concentration, in mol dm–3, of ZOH in FA 2. concentration of FA 2 = …… mol dm–3 [1] (v) Use your answer to (c)(iv) and the information on page 4 to calculate the relative atomic mass, Ar, of Z. Hence identify Z. Show your working. Z is …… . [2] (d) Using the value for the relative atomic mass of Z that you calculated in (c)(v), calculate the percentage difference of your value from that shown in the Periodic Table. (If you did not obtain a value for the Ar of Z, assume it is 32.0. Note, this is not the correct value.) percentage difference = …… % [1] [Total: 15] Qualitative analysis Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. At each stage of any test you are to record details of the following: ● colour changes seen ● the formation of any precipitate and its solubility in an excess of the reagent added ● the formation of any gas and its identification by a suitable test. You should indicate clearly at what stage in a test a change occurs. If any solution is warmed, a boiling tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests for ions present should be attempted.

Question

Half-fill the 250 cm3 beaker with water and place it on a tripod and gauze above a heatproof mat. Heat the water until boiling and then turn off the Bunsen burner. You will use this as a hot water‑bath in 3(b)(i). (a) FA 5, FA 6 and FA 7 are solutions. Each solution contains one cation and one anion. Carbonate, CO32–, is not present in any of the solutions. (i) Carry out the following tests and record your observations. Use a 1 cm depth of solution in a test-tube for each test. observations test FA 5 FA 6 FA 7 Test 1 Add an equal depth of dilute sulfuric acid. Test 2 Add an equal depth of aqueous sodium carbonate. Test 3 Add an equal depth of aqueous magnesium chloride. [5] (ii) Use your observations in (a)(i) to suggest a possible formula for each of the following: The cation in FA 5 is …… . The cation in FA 6 is …… . The anion in FA 7 is …… . [3] (iii) Apart from using an indicator, suggest a further test that would confirm the identity of the anion in FA 7. Carry out this test and record the result. . …… . …… . …… [1] (iv) Did the result of your test in (a)(iii) confirm the identity of the anion in FA 7? Explain your answer. . …… . …… . …… [1] (b) FA 8 is an aqueous solution. (i) Carry out the following tests and record your observations. test observations Test 1 To a 1 cm depth of FA 8 in a test‑tube, add a few drops of acidified potassium manganate(VII). Place the tube in the hot water-bath. Test 2 To a 1 cm depth of FA 8 in a test‑tube, add a 1 cm length of magnesium ribbon. [2] (ii) For each observation, state what you can conclude about the chemical properties of FA 8. Test 1 …… Test 2 …… [2] [Total: 14] Qualitative Analysis Notes 1 Reactions of aqueous cations reaction with ion NaOH(aq) NH3(aq) aluminium, white ppt. white ppt. Al 3+(aq) soluble in excess insoluble in excess ammonium, no ppt. – NH4+(aq) ammonia produced on heating barium, faint white ppt. is nearly always no ppt. Ba2+(aq) observed unless reagents are pure calcium, white ppt. with high [Ca2+(aq)] no ppt. Ca2+(aq) chromium(III), grey-green ppt. grey-green ppt. Cr3+(aq) soluble in excess insoluble in excess copper(II), pale blue ppt. pale blue ppt. soluble in excess Cu2+(aq) insoluble in excess giving dark blue solution green ppt. turning brown on contact green ppt. turning brown on contact iron(II), with air with air Fe2+(aq) insoluble in excess insoluble in excess iron(III), red-brown ppt. red-brown ppt. Fe3+(aq) insoluble in excess insoluble in excess magnesium, white ppt. white ppt. Mg2+(aq) insoluble in excess insoluble in excess off-white ppt. rapidly turning brown off-white ppt. rapidly turning brown manganese(II), on contact with air on contact with air Mn2+(aq) insoluble in excess insoluble in excess zinc, white ppt. white ppt. Zn2+(aq) soluble in excess soluble in excess 2 Reactions of anions ion reaction carbonate, CO2 liberated by dilute acids CO3 2– chloride, gives white ppt. with Ag+(aq) (soluble in NH3(aq)) Cl –(aq) bromide, gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)) Br (aq) – iodide, gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq)) I –(aq) nitrate, NH3 liberated on heating with OH–(aq) and Al foil NO3–(aq) nitrite, NH3 liberated on heating with OH–(aq) and Al foil NO2–(aq) sulfate, gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids) SO42–(aq) sulfite, gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids) SO3 (aq)2– 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 (ppt. dissolves with excess CO2) chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint 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 89–103 104 105 106 107 108 109 110 111 112 114 116 actinoids Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Fl Lv francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium flerovium livermorium – – – – – – – – – – – – – 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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