Chemistry 9701/21 May/June 2025: question paper and mark scheme

Question

(a) Solid sodium conducts electricity. Sodium oxide conducts electricity when molten but not when solid. (i) Name the type of bonding present in sodium and in sodium oxide. bonding in sodium …… bonding in sodium oxide …… [1] (ii) Explain how solid sodium conducts electricity. …… [1] (iii) Explain why sodium oxide conducts electricity when molten. …… [1] (b) Separate samples of sodium and sodium oxide are each added to an excess of cold water. (i) Write an equation for the reaction of sodium with cold water. …… [1] (ii) Write an equation for the reaction of sodium oxide with cold water. …… [1] (iii) Complete Table 1.1. Do not refer to temperature changes when considering observations for these reactions. Table 1.1 sodium sodium oxide one similarity in observation on addition to cold water one difference in observation on addition to cold water [2] (c) State the oxidation number of the Period 3 elements bonded to Cl in NaCl and PCl 5. Explain the difference in the oxidation number. …… [2] (d) Table 1.2 shows melting points of some oxides. Table 1.2 oxide melting point / °C SO2 –73 H 2O 0 SO3 17 SiO2 1610 MgO 2852 Al 2O3 2072 A student suggests the following hypothesis. The higher the oxidation number of the element combined with oxygen, the higher the melting point of the oxide. Use Table 1.2 to deduce if this hypothesis is true or false or if there is not enough information to make a conclusion. Explain your answer. …… [2] [Total: 11]

Question

A sample of iron is analysed using a mass spectrometer. The mass spectrum shows three isotopes of iron are present in the sample. (a) Define isotopes. …… [1] (b) Fig. 2.1 shows the mass spectrum of the sample of iron. 100 91.9 80 60 abundance /% 40 20 5.9 2.2 0 54.0 55.0 56.0 57.0 m/e Fig. 2.1 (i) Use Fig. 2.1 to calculate the relative atomic mass, Ar, of iron to one decimal place. Show your working. Ar of iron = …… [2] (ii) Complete Table 2.1 to show the number of protons and nucleons in one atom of 56Fe. Table 2.1 particle number of particles in one atom of 56Fe protons nucleons [2] (c) Deduce the number of pairs of electrons in the shell with principal quantum number n = 3 in an Fe atom. number of pairs of electrons …… [1] (d) Write an equation to represent the first ionisation energy of iron. …… [1] (e) Suggest how the value for the first ionisation energy of 54Fe compares to the first ionisation energy of 56Fe. Explain your answer in terms of the factors that affect ionisation energy. …… [4] [Total: 11]

Question

(a) Hexene reacts with hydrogen gas to produce hexane. reaction 1 C6H12(l) + H2(g) C6H14(l) Fig. 3.1 shows the distribution of energies of H2(g) molecules at temperature T. number of molecules EA energy Fig. 3.1 (i) Sketch on Fig. 3.1 the shape of the curve for the same sample of H2(g) molecules when the temperature is increased. [2] (ii) Explain why increasing the temperature increases the rate of reaction 1. …… [2] (iii) State the role of nickel when it is added to reaction 1. …… [1] (iv) Annotate Fig. 3.2 to show the effect of adding nickel to reaction 1 at temperature T. number of molecules EA energy Fig. 3.2 [1] (b) Define Le Chatelier’s principle. …… [2] (c) Reaction 2 shows the equilibrium reaction between X(g) and Y(g) to produce Z(g) in a sealed container. reaction 2 aX(g) + bY(g) cZ(g) Fig. 3.3 shows the effect of changing pressure on the percentage yield of Z(g) at two different temperatures, 300 K and 350 K. 60 300 K 50 40 yield / % 30 350 K 20 10 0 100 200 300 pressure / atm Fig. 3.3 Deduce two conclusions about reaction 2 using Fig 3.3. …… [2] [Total: 10]

Question

The structure of vitamin C is shown in Fig. 4.1. vitamin C OH HO O O HO OH Fig. 4.1 (a) Deduce the empirical formula of vitamin C. …… [1] (b) The concentration of vitamin C is found by titration with I2(aq). vitamin C Q OH OH I2 + HO O O HO O O + 2I– + 2H+ HO OH O O Fig. 4.2 A vitamin C tablet is dissolved in water to produce 200.0 cm3 of vitamin C solution. 5.00 cm3 of this vitamin C solution is added to a flask with approximately 150 cm3 of water and an indicator. Exactly 28.40 cm3 of 5.00 × 10–4 mol dm–3 I2(aq) reacts with the sample of vitamin C solution in the flask. [Mr: vitamin C, 176] (i) Calculate the amount, in mol, of I2(aq) added to the flask in this titration. amount of I2(aq) = …… mol [1] (ii) Use your answer to (b)(i) to calculate the mass, in g, of vitamin C in the tablet. Show your working. (If you were unable to calculate a value for the amount of I2(aq) in (b)(i), use the value 2.64 × 10– 4 mol. This is not the correct value.) mass of vitamin C in tablet = …… g [2] (iii) Deduce the role of I2(aq) in the reaction in Fig. 4.2. …… [1] (iv) Suggest two reasons why hot concentrated acidified potassium manganate(VII) is not a suitable reagent for producing Q from vitamin C. 1 …… 2 …… [2] (c) Predict two absorptions that will be seen in the infrared spectra of both vitamin C and Q. Describe the relevant bond and the specific functional group that is responsible for each absorption identified. vitamin C Q OH OH HO O O HO O O HO OH O O Fig. 4.3 …… [2] [Total: 9] Table 4.1 bond functional groups containing characteristic infrared absorption range the bond (in wavenumbers) / cm–1 C−O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide 1640–1690 carbonyl, carboxyl 1670–1740 ester 1710–1750 C≡N nitrile 2200–2250 C−H alkane 2850–2950 N−H amine, amide 3300–3500 O−H carboxyl 2500–3000

Question

Compound A contains the elements carbon, hydrogen and oxygen only. When A is heated with H2SO4(aq), compounds B and C are produced, as shown in Fig. 5.1. H2SO4(aq) B C A + 2H2O HOOCCH2COOH + 2CH3CH2OH heat Fig. 5.1 (a) Draw the structure of A. [2] (b) Name the type of reaction that occurs when A is heated with H2SO4(aq). …… [1] (c) When aqueous Na2CO3 is added to separate samples of B and C, effervescence is observed with B only. (i) Complete the equation to describe the reaction between B and an excess of aqueous Na2CO3. ……HOOCCH2COOH + ……Na2CO3 …… [1] (ii) Suggest why C does not react with aqueous Na2CO3 in a similar type of reaction to B. …… [1] (d) A student suggests a two-step synthesis to produce B, as shown in Fig. 5.2. step 1 step 2 B Cl CH2CH2CH2Cl HOCH2CH2CH2OH HOOCCH2COOH Fig. 5.2 (i) Identify the reagents and conditions required in steps 1 and 2. step 1 …… step 2 …… [2] (ii) Identify the type of reaction that HOCH2CH2CH2OH undergoes in step 2. …… [1] (e) B reacts with an excess of reducing agent R to produce D. An excess of PCl 5 is added to D. • A vigorous reaction occurs. • Misty fumes are seen. • Organic compound E is produced. (i) Identify the formula of the reducing agent R. …… [1] (ii) Complete the equation to describe the reaction of B with an excess of R. Use [H] to represent one atom of hydrogen from R. ……HOOCCH2COOH + ……[H] …… [2] (iii) Name organic compound E. …… [1] [Total: 12]

Question

Three bottles of colourless liquids labelled F, G and H contain separate pure samples of the compounds ethanal, propanal or propanone but not necessarily in that order. (a) State the functional group in ethanal, propanal and propanone. …… [1] (b) State a reagent and the relevant observation that confirm that F, G and H have the same functional group. reagent …… observation …… [2] (c) Separate samples of F, G and H are each tested with Tollens’ reagent and with alkaline I2(aq). The observations are shown in Table 6.1. Table 6.1 Tollens’ reagent alkaline I2(aq) F no observable change pale yellow precipitate G silver mirror pale yellow precipitate H silver mirror no precipitate (i) Use Table 6.1 to name the organic compounds in bottles F, G and H. F = …… G = …… H = …… [2] (ii) Identify the yellow precipitate produced when alkaline I2(aq) is added to separate samples of F and G. …… [1] (iii) Compound J does not contain the same functional group as F, G and H. Compound J also reacts with alkaline I2(aq) to produce a pale yellow precipitate. Suggest the structure of compound J. [1] [Total: 7] 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 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 138.9 140.1 140.9 144.2 – 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. 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