Chemistry 0620/43 October/November 2025: question paper and mark scheme

Question

Atoms and ions are made from particles called electrons, neutrons and protons. (a) Complete Table 1.1. Table 1.1 particle relative charge relative mass 1 electron –1 1840 neutron proton [2] (b) Table 1.2 shows information about some atoms or ions. Complete Table 1.2. Table 1.2 atom or number of number of number of ion electrons neutrons protons 40Ca2+ 20 20 20 19F 9 9 9 10 9 8 [5] (c) (i) The relative atomic mass, Ar, of an element is the average mass of its isotopes compared to one atom of isotope X. Identify isotope X. …… [1] (ii) A sample of magnesium consists of two isotopes with mass numbers 24 and 26. [Ar: Mg, 24.3] Calculate the percentage abundance of the isotope of magnesium with mass number 24. percentage abundance = …… [1] [Total: 9] * 0000800000003 * DFD 3

Question

Table 2.1 shows the melting points, boiling points and electrical conductivities of seven substances, A, B, C, D, E, F and G. Table 2.1 melting point boiling point electrical conductivity electrical conductivity substance / °C / °C when solid when molten A 1600 2230 poor poor B –219 –183 poor poor C 770 1420 poor good D –39 357 good good E –7 58 poor poor F 44 280 poor poor G 1085 2562 good good (a) Identify which substance, A, B, C, D, E, F or G, is: (i) a gas at 25 °C …… [1] (ii) a solid consisting of simple molecules at 25 °C …… [1] (iii) a metal which is liquid at 25 °C. …… [1] (b) (i) Identify which substance, A, B, C, D, E, F or G, has a giant covalent structure. Use the information in Table 2.1 to give two reasons for your choice. substance …… reason 1 …… reason 2 …… [3] (ii) Identify which substance, A, B, C, D, E, F or G, is an ionic compound. Use the information in Table 2.1 to give one reason for your choice. substance …… reason …… [2] [Total: 8] * 0000800000004 * DFD 4

Question

This question is about aluminium and other metallic elements. (a) Aluminium is extracted from purified bauxite by electrolysis. Fig. 3.1 shows a diagram of the electrolytic cell used. waste gases positive electrodes negative electrode electrolyte aluminium Fig. 3.1 (i) State the name of the aluminium compound present in bauxite. …… [1] (ii) Name the substance that purified bauxite is dissolved in before electrolysis is carried out. …… [1] (iii) Name the substance that is used for the positive electrodes. …… [1] (iv) Write the ionic half-equation for the production of aluminium at the negative electrode. …… [2] (b) Aluminium is above zinc in the reactivity series. (i) When a piece of aluminium foil is added to aqueous zinc sulfate, a reaction is not immediately observed even though aluminium is above zinc in the reactivity series. Explain why a reaction is not immediately observed. …… [1] (ii) After a few minutes, a displacement reaction occurs between aluminium and aqueous zinc ions. Complete the ionic equation for this reaction. ……Al + ……Zn2+ ……Al 3+ + ……Zn [1] * 0000800000005 * DFD 5 (iii) State the oxidation number of zinc in: Zn2+ …… Zn. …… [2] (iv) Define the term reduction in terms of oxidation number. …… [1] (c) Aluminium reacts with iron(III) oxide. The equation is shown. 2Al + Fe2O3 Al 2O3 + 2Fe ΔH = – 850 kJ / mol (i) State the meaning of the symbol ΔH. …… [1] (ii) State what can be deduced about the reaction from the negative sign in ΔH = – 850 kJ / mol. …… [1] (d) Gallium has many similarities to aluminium. Gallium(III) oxide is an amphoteric oxide. State what is meant by the term amphoteric. …… [1] (e) The reaction of gallium(III) oxide, Ga2O3, with aqueous sodium hydroxide forms a salt which contains the negative ion GaO2–. The only other product is water. Write a symbol equation for this reaction. …… [2] (f) Deduce the formula of: • gallium(III) bromide …… • gallium(III) sulfate. …… [2] [Total: 17] DFD 6 * 0000800000007 * DFD 7

Question

This question is about chlorine and compounds of chlorine. (a) Gaseous chlorine reacts with gaseous phosphorus(III) chloride to form gaseous phosphorus(V) chloride. The reaction is a reversible reaction. When the three gases are in a closed container the system reaches equilibrium. Cl 2(g) + PCl 3(g) PCl 5(g) (i) Describe a reversible reaction at equilibrium in terms of: • the rate of the forward reaction and the rate of the reverse reaction • the concentrations of reactants and products. [2] (ii) Complete Table 4.1 using only the words increases, decreases or no change. Table 4.1 effect on the effect on the change to condition rate of the forward reaction equilibrium concentration of PCl 5 the pressure is decreased a catalyst is added increases [3] (iii) When the temperature of the equilibrium mixture is increased, the equilibrium concentration of PCl 5 decreases. State what conclusion about the forward reaction can be made from this information. …… [1] * 0000800000008 * DFD 8 (b) Ethene, C2H4, reacts with chlorine, Cl 2, to form 1,2-dichloroethane, CH2Cl CH2Cl . The equation for this reaction can be represented as shown. H H H H C C + Cl Cl Cl C C Cl H H H H Table 4.2 shows some bond energies. Table 4.2 bond bond energy in kJ / mol C–C 350 C=C 610 C–H 410 Cl –Cl 240 C–Cl 340 Use the bond energies in Table 4.2 to calculate the enthalpy change, in kJ / mol, of the reaction. Use the following steps. • Calculate the total energy needed to break the bonds in C2H4 and Cl 2. …… kJ • Calculate the total energy released when the bonds form in CH2Cl CH2Cl . …… kJ * 0000800000009 * DFD 9 • Calculate the enthalpy change of the reaction. Your answer should include a sign. …… kJ / mol [3] (c) Chlorine reacts with nitrogen to form nitrogen trichloride, NCl 3. Complete the dot-and-cross diagram in Fig. 4.1 of a molecule of NCl 3. Show outer shell electrons only. Cl N Cl Cl Fig. 4.1 [3] * 0000800000010 * DFD 10 (d) When solid magnesium carbonate, MgCO3, is added to dilute hydrochloric acid, HCl , a chemical reaction occurs. The equation for the reaction is shown. MgCO3(s) + 2HCl (aq) MgCl 2(aq) + CO2(g) + H2O(l) (i) Give two observations when solid magnesium carbonate is added to dilute hydrochloric acid. 1 …… 2 …… [2] (ii) Calculate the volume, in cm3, of CO2(g) that is produced at room temperature and pressure (r.t.p.) when 50.0 cm3 of 0.100 mol / dm3 HCl reacts with excess MgCO3. The volume of 1 mol of any gas is 24 000 cm3 at r.t.p. Use the following steps. • Calculate the number of moles of HCl in 50.0 cm3 of 0.100 mol / dm3 HCl . …… mol • Deduce the number of moles of CO2(g) produced. …… mol • Calculate the volume, in cm3, of CO2(g) produced at r.t.p. …… cm3 [3] [Total: 17] * 0000800000011 * DFD 11

Question

This question is about metallic compounds. (a) Insoluble metal salts, such as lead(II) sulfate, are made by precipitation. When aqueous lead(II) ions react with aqueous sulfate ions, a precipitate of lead(II) sulfate forms. A sample of pure lead(II) sulfate can be obtained from the precipitate formed. (i) Write an ionic equation for this precipitation reaction. Include state symbols. …… [3] (ii) State the name of an aqueous solution containing lead(II) ions. …… [1] (iii) State the name of an aqueous solution containing sulfate ions. …… [1] (iv) The lead(II) sulfate precipitate is separated from the rest of the reaction mixture by filtration. The impure lead(II) sulfate remains on the filter paper. State the general term given to an insoluble substance that remains on the filter paper during filtration. …… [1] (v) Describe how the lead(II) sulfate is purified after filtration. …… [2] * 0000800000012 * DFD 12 (b) Copper is a transition element. A list of properties of copper is shown. • It has good electrical conductivity. • It has variable oxidation states. • It forms soluble salts. • It forms coloured compounds. • It forms basic oxides. • It acts as a catalyst. (i) Give two properties from the list that show how copper is similar to metals in Group I of the Periodic Table. 1 …… 2 …… [2] (ii) Give two properties from the list that show how copper is different from metals in Group I of the Periodic Table. 1 …… 2 …… [2] [Total: 12] * 0000800000013 * DFD 13

Question

This question is about organic compounds. (a) Organic compound Q has the following composition by mass. C, 50.00%; H, 5.56%; O, 44.44% Calculate the empirical formula of compound Q. empirical formula = …… [3] (b) Organic compound R has the empirical formula CHO and a relative molecular mass of 116. Determine the molecular formula of compound R. molecular formula = …… [1] (c) Carboxylic acids react with alcohols to form esters. (i) Name the other product that is formed when a carboxylic acid reacts with an alcohol. …… [1] (ii) Name the type of catalyst that is used when a carboxylic acid reacts with an alcohol. …… [1] (iii) Ester S has the structural formula CH3CH2COOCH2CH2CH2CH3. Name the carboxylic acid and the alcohol which react together to form ester S. carboxylic acid …… alcohol …… [2] * 0000800000014 * DFD 14 (d) Fig. 6.1 shows part of a polymer structure. CH3 CH3 CH3 CH3 CH3 CH3 C C C C C C H H H H H H Fig. 6.1 (i) Name the type of polymerisation that is used to produce this polymer. …… [1] (ii) Suggest why it is not possible to write the molecular formula of this polymer. …… [1] (iii) State the number of monomer units that are needed to make the part of the polymer structure shown in Fig. 6.1. …… [1] (iv) Draw the displayed formula of the monomer used to make this polymer. [2] * 0000800000015 * DFD 15 (e) Fig. 6.2 shows part of the general structure of an amino acid. R C H Fig. 6.2 (i) Complete Fig. 6.2 to show all the atoms and all the bonds in the two functional groups of the amino acid. [2] (ii) Part of a natural polyamide structure is shown in Fig. 6.3. H O H O N C N C N C H O Fig. 6.3 On Fig. 6.3, draw a circle around one amide linkage. [1] (iii) State the name given to natural polyamides made from amino acids. …… [1] [Total: 17] The Periodic Table of Elements Group I II III IV V VI VII VIII 1 2 H He hydrogen helium Key 1 4 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 7 9 relative atomic mass 11 12 14 16 19 20 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 24 27 28 31 32 35.5 40 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 DFD 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 40 45 48 51 52 55 56 59 59 64 65 70 73 75 79 80 84 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 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 16 85 88 89 91 93 96 – 101 103 106 108 112 115 119 122 128 127 131 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 133 137 178 181 184 186 190 192 195 197 201 204 207 209 – – – 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 139 140 141 144 – 150 152 157 159 163 165 167 169 173 175 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 – 232 231 238 – – – – – – – – – – – The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.).