Chemistry 0620/42 February/March 2025: question paper and mark scheme

Question

Using numbers only, state the: (a) percentage of oxygen in clean, dry air …… [1] (b) typical operating temperature, in °C, used in the Haber process …… [1] (c) number of atoms in a diatomic molecule …… [1] (d) maximum number of electrons in the second electron shell of an atom …… [1] (e) number of hydrogen atoms in an alkane with 7 carbon atoms …… [1] (f) number of particles in one mole, in standard form. …… [1] [Total: 6]

Question

This question is about ionic compounds. (a) State what is meant by the term ionic bond. …… [2] (b) Potassium sulfide, K2S, is an ionic compound. Complete the dot-and-cross diagram in Fig. 2.1 of the ions in potassium sulfide. Show the charges on the ions. K S K Fig. 2.1 [3] (c) Ionic compounds form giant ionic lattices. (i) Fig. 2.2 shows part of the giant ionic lattice structure of sodium chloride. Complete the diagram in Fig. 2.2 to show the ions present. Use ‘+’ for sodium ions and ‘–’ for chloride ions. One chloride ion has been completed for you. – Fig. 2.2 [2] (ii) State the name given to any positive ion. …… [1] (d) Ionic compounds can be decomposed by the passage of an electric current using inert electrodes. (i) State the name of this process. …… [1] (ii) Write the ionic half-equation for the reaction which takes place at the anode when molten potassium bromide, KBr, is decomposed by the passage of an electric current. …… [2] (iii) Name the products and state the observations at the negative and positive electrodes when dilute aqueous potassium bromide, KBr, is decomposed by the passage of an electric current. product at the negative electrode observations at the negative electrode products at the positive electrode …… and …… observations at the positive electrode [5] [Total: 16]

Question

The halogens are a group of elements in the Periodic Table. Chlorine is a member of this group. (a) State the group number of the halogens. …… [1] (b) State how many halogens there are in this group. …… [1] (c) Suggest the identity of the halogen which: (i) has the highest density …… [1] (ii) is the most reactive. …… [1] (d) State the name of the negative ions (anions) formed by halogens. …… [1] (e) State how many occupied electron shells there are in a bromine atom. …… [1] (f) Name the noble gas which has the same electronic configuration as a Br – ion. …… [1] (g) Aqueous chlorine, Cl 2, reacts with aqueous potassium iodide, KI. One of the products formed is iodine, I2. (i) Complete and balance the ionic equation for the reaction between Cl 2 and I – ions. State symbols are not required. Cl 2 + …… I – …… + I2 [2] (ii) Explain why this reaction is defined as a redox reaction. Give your answer in terms of electron transfer. …… [2] (h) Give the colour and state of iodine at room temperature and pressure. colour …… state …… [2] [Total: 13]

Question

Carbonyl chloride, COCl 2, is manufactured by reacting carbon monoxide with chlorine. CO(g) + Cl 2(g) COCl 2(g) ΔH = –105 kJ / mol The process takes place in a closed system, and an equilibrium is reached. The conditions for this process are 200 °C and 200 kPa. (a) Explain what is meant by the term closed system. …… [1] (b) State what the symbol ΔH represents. …… [1] (c) State how the value of ΔH shows that the forward reaction is exothermic. …… [1] (d) Deduce the value of ΔH for the reverse reaction. Include a sign in your answer. …… [1] (e) Complete Table 4.1 to show the effect, if any, on the concentration of COCl 2(g) at equilibrium when the following changes to the conditions are applied. Use only the words increases, decreases or no change. Table 4.1 effect on the concentration of change to conditions COCl 2(g) at equilibrium the temperature is increased some CO is added the pressure is increased a catalyst is added [4] (f) The equation for the reaction can be represented as shown in Fig. 4.1. Cl C O + Cl Cl C O ΔH = –105 kJ / mol Cl Fig. 4.1 Table 4.2 shows some bond energies. Table 4.2 bond C≡O Cl –Cl C–Cl bond energy in kJ / mol 1075 240 340 Use the bond energies in Table 4.2 and the value of ΔH for the reaction to calculate the bond energy, in kJ / mol, of the C=O bond. Use the following steps. • Calculate the energy needed to break the bonds in the reactants. …… kJ • Calculate the energy released when the bonds in carbonyl chloride form. …… kJ • Calculate the bond energy of the C=O bond. …… kJ / mol [3] (g) Complete the dot-and-cross diagram in Fig. 4.2 of a molecule of carbonyl chloride. Show outer shell electrons only. Cl C O Cl Fig. 4.2 [3] [Total: 14]

Question

Manganese is the element with atomic number 25 in the Periodic Table. Calcium is the element with atomic number 20 in the Periodic Table. (a) Complete Table 5.1 to show the number of protons, neutrons and electrons in the 55Mn atom and the 42Ca2+ ion. Table 5.1 55Mn 42Ca2+ protons neutrons electrons [3] (b) Manganese forms several oxides. The formulae of some of these oxides are shown. MnO Mn2O3 Mn3O4 MnO2 Mn2O7 (i) Suggest why manganese is expected to form coloured oxides. …… [1] (ii) State which other property of manganese is shown by the formation of several oxides. …… [1] (iii) State the formula of manganese(II) oxide. …… [1] (c) Mn3O4 is found in an ore of manganese. Manganese metal can be extracted from Mn3O4 using aluminium as the reducing agent. (i) Define the term reducing agent. …… [2] (ii) Complete the symbol equation by inserting the formula of the missing product and balancing the equation. …… Mn3O4 + …… Al …… + …… Mn [2] (d) MnO2 reacts with dilute hydrochloric acid as shown in the equation. MnO2 + 4HCl MnCl 2 + 2H2O + Cl 2 (i) Calculate the volume of chlorine gas formed, in cm3, at r.t.p. when excess MnO2 reacts with 50.0 cm3 of 0.200 mol / dm3 HCl . Use the following steps. • Calculate the number of moles of HCl used. …… mol • Determine the number of moles of Cl 2 formed. …… mol • Calculate the volume of Cl 2 formed. …… cm3 [3] (ii) Describe a test for chlorine gas. test …… observations …… [1] (iii) Explain, in terms of collision theory, why decreasing the temperature decreases the rate of this reaction. …… [3] [Total: 17]

Question

The structural formulae of two compounds, A and B, are shown. A B CH2=CHCH3 CH3CH=CHCH3 A and B are members of the same homologous series. (a) Give two reasons why the structural formulae of A and B show they are members of the same homologous series. 1 …… 2 …… [2] (b) Explain why A and B are both hydrocarbons. …… [1] (c) Write the symbol equation for the complete combustion of A. …… [2] (d) Deduce the empirical formula of A. …… [1] (e) Name compound B. …… [1] (f) A structural isomer of B is a member of the same homologous series. Draw the displayed formula of this structural isomer of B. [1] (g) Compound B reacts with aqueous bromine at room temperature to form product C. The equation is shown. B C CH3CH=CHCH3 + Br2 CH3CHBrCHBrCH3 (i) State why this is an addition reaction. …… [1] (ii) Describe the colour change in aqueous bromine during this reaction. from …… to …… [1] (iii) Name product C. …… [1] (h) Under certain conditions, one mole of B reacts with oxygen to form two moles of carboxylic acid D. Carboxylic acid D has two carbon atoms. (i) Draw the displayed formula of carboxylic acid D. [1] (ii) Name carboxylic acid D. …… [1] (iii) Complete the symbol equation for this reaction. CH3CH=CHCH3 + …… …… [1] [Total: 14] 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 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 12 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.).