Chemistry 0620/41 October/November 2025: question paper and mark scheme

Question

Protons, neutrons and electrons are particles found in atoms. (a) Complete Table 1.1 to show the relative mass and relative charge of a proton, a neutron and an electron. Table 1.1 particle relative mass relative charge proton +1 neutron electron 1 1840 [2] (b) Some elements have many isotopes. (i) Define the term isotopes. …… [2] (ii) Explain why all isotopes of the same element have the same chemical properties. …… [1] (c) Complete Table 1.2. Table 1.2 number of number of number of atom or ion protons neutrons electrons 40 18Ar 18 18 32 2– 16S 16 22 28 20 [5] * 0000800000003 * DFD 3 (d) The term mass number is defined as the total number of protons and neutrons in the nucleus of an atom. State the name of one other term which is defined as the total number of protons and neutrons in the nucleus of an atom. …… [1] (e) Calculate the number of atoms in 2.00 g of argon. Give your answer in standard form. number of atoms = …… [2] [Total: 13] * 0000800000004 * DFD 4

Question

Calcium is an element in Group II of the Periodic Table. (a) Identify the element in Group II which has only five occupied electron shells. …… [1] (b) Name and describe the type of bonding found in elements in Group II. name …… description …… [4] (c) When a piece of calcium is added to some cold water containing universal indicator a reaction takes place. (i) Give three observations when this reaction takes place. 1 …… 2 …… 3 …… [3] (ii) Name the two products of this reaction. …… and …… [2] (d) Calcium burns in oxygen. (i) State the colour of the flame. …… [1] (ii) Write the symbol equation for this reaction. …… [2] * 0000800000005 * DFD 5 (e) Crystals of hydrated calcium nitrate contain water molecules. The formula of hydrated calcium nitrate is Ca(NO3)2•xH2O. x is a whole number. (i) State the term given to the water molecules present in hydrated crystals. …… [1] (ii) When hydrated calcium nitrate is heated gently, the following reaction occurs. Ca(NO3)2•xH2O Ca(NO3)2 + xH2O A sample of hydrated calcium nitrate is heated gently. 3.28 g of Ca(NO3)2 forms and the mass of the crystals decreases by 1.44 g. [M r: Ca(NO3)2, 164; H2O, 18] Determine the value of x in Ca(NO3)2•xH2O using the following steps. • Calculate the number of moles of Ca(NO3)2 that remain. …… mol • Calculate the number of moles of H2O given off. …… mol • Determine the value of x. x = …… [3] [Total: 17] * 0000800000006 * DFD 6

Question

A student makes crystals of the salt sodium sulfate, Na2SO4 . The student reacts 0.200 mol / dm3 dilute sulfuric acid, H2SO4(aq), with aqueous sodium hydroxide, NaOH(aq). The student uses the following steps. step 1 The student places 40.0 cm3 of NaOH(aq) into a conical flask. This volume contains 0.0100 moles of NaOH. step 2 The student adds a few drops of methyl orange indicator to the NaOH(aq) in the conical flask. step 3 The student adds 0.200 mol / dm3 H2SO4(aq) to the flask until the end-point is reached. step 4 The student transfers the mixture from the conical flask to an evaporating basin and obtains dry crystals. (a) Complete the symbol equation for the reaction. Include state symbols. H2SO4(aq) + 2NaOH(aq) Na2SO4(……) + ……(……) [2] (b) State the type of exothermic reaction taking place. …… [1] (c) Calculate the concentration of NaOH(aq) used in step 1. concentration of NaOH(aq) = …… mol / dm3 [1] (d) Name the item of apparatus the student uses to add H2SO4(aq) in step 3. …… [1] volume of H2SO4(aq) = …… cm3 [2] (f) State the colour change observed in step 3. from …… to …… [2] * 0000800000007 * DFD 7 (g) The dry crystals formed in step 4 are coloured and not white. This is because the student should do an additional step between step 3 and step 4. Suggest what the student should do in this additional step to produce white crystals. …… [1] (h) In step 4, the student gently heats the solution in the evaporating basin until the solution is saturated. The student then stops heating and leaves the hot solution to cool. Crystals start to appear. (i) Explain the term saturated solution. …… [2] (ii) Explain why crystals start to appear as the hot solution cools. …… [1] (iii) Suggest the effect, if any, on the mass of crystals collected in step 4 if the solution in the evaporating basin is allowed to dry without gentle heating. …… [1] [Total: 14] * 0000800000008 * DFD 8

Question

Gaseous sulfur tetrafluoride, SF4 , reacts with steam in a reversible reaction. SF4(g) + 2H2O(g) SO2(g) + 4HF(g) ΔH = –54 kJ / mol (a) Complete the reaction pathway diagram in Fig. 4.1 for this reaction. Include in your diagram: • the position and the formulae of the products • an arrow, labelled Ea , to show the activation energy • an arrow, labelled ΔH, to show the enthalpy change of the reaction. SF4(g) + 2H2O(g) energy progress of reaction Fig. 4.1 [4] * 0000800000009 * DFD 9 (b) The equation for the reaction can be represented as shown in Fig. 4.2. F H F H O H H F ΔH = –54 kJ / mol F S F + O S O + H F H O H H F F Fig. 4.2 Table 4.1 shows some bond energies. Table 4.1 bond S–F O–H H–F bond energy in kJ / mol 330 460 570 Use the bond energies in Table 4.1 and the value of ΔH of the reaction to calculate the S=O bond energy in kJ / mol. Use the following steps. • Calculate the energy needed to break the bonds in the reactants. …… kJ • Calculate the energy released when the bonds in the products form. …… kJ • Calculate the S=O bond energy. …… kJ / mol [4] * 0000800000010 * DFD 10 (c) The equation for the reaction is shown. SF4(g) + 2H2O(g) SO2(g) + 4HF(g) ΔH = –54 kJ / mol State the effect, if any, on the position of equilibrium when the following changes are made. Give a reason for each of your answers. • The temperature is increased. • The pressure is increased. • A catalyst is added. [5] (d) Explain, in terms of collision theory, why reducing the temperature decreases the rate of the reverse reaction. …… [3] [Total: 16] * 0000800000011 * DFD 11 Question 5 starts on the next page. * 0000800000012 * DFD 12

Question

This question is about the homologous series of alcohols. (a) A homologous series is a family of organic compounds whose members have the same general formula. (i) State the general formula for alcohols. …… [1] (ii) Give one other characteristic that is the same for all members of a homologous series. …… [1] (b) Ethanol can be manufactured by two methods: • method 1 uses glucose as the starting material • method 2 uses ethene as the starting material. (i) Complete Table 5.1. Table 5.1 method 1 method 2 glucose as ethene as starting material starting material typical temperature used / °C 1 1 two other essential conditions 2 2 [6] (ii) Write the symbol equation for the reaction in method 1. …… [2] (iii) Write the symbol equation for the reaction in method 2. …… [2] (c) Butane-1,4-diol has the structural formula HO — CH2 — CH2 — CH2 — CH2 — OH. (i) Deduce the molecular formula of butane-1,4-diol. …… [1] (ii) Butane-1,4-diol reacts with ethanoic acid. Determine the number of moles of ethanoic acid which react fully with one mole of butane-1,4-diol. …… [1] * 0000800000013 * DFD 13 (d) Butanedioic acid has the structural formula HOOC — CH2 — CH2 — COOH. (i) Deduce the empirical formula of butanedioic acid. …… [1] (ii) Name the gas formed when butanedioic acid reacts with sodium. …… [1] (e) Butane-1,4-diol can be represented as shown. HO OH Butanedioic acid can be represented as shown. HOOC COOH Butane-1,4-diol reacts with butanedioic acid to form a polymer. (i) Draw two repeat units of the polymer formed from the reaction of butane-1,4-diol with butanedioic acid. Show all the atoms and all the bonds in the ester linkages. [3] (ii) State the type of polymerisation when butane-1,4-diol reacts with butanedioic acid. …… [1] [Total: 20] DFD 14 * 0000800000015 * DFD 15 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.).