0620 Chemistry March 2025 Question paper 42

1 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] , ,

2 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 K S 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] , ,

3 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] , ,

4 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 change to conditions effect on the concentration of 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.

C O + Cl Cl

C O Cl Cl

ΔH = –105 kJ / mol 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 Cl C O Fig. 4.2

[3]

[Total: 14] , ,

5 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] , ,

6 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] , , Group The Periodic Table of Elements 1 H hydrogen 1 2 He helium 4 I II III IV V VI VII VIII 3 Li lithium 7 4 Be beryllium 9 atomic number atomic symbol Key name relative atomic mass 11 Na sodium 23 12 Mg magnesium 24 19 K potassium 39 20 Ca calcium 40 37 Rb rubidium 85 38 Sr strontium 88 55 Cs caesium 133 56 Ba barium 137 87 Fr francium – 88 Ra radium – 5 B boron 11 13 Al aluminium 27 31 Ga gallium 70 49 In indium 115 81 Tl thallium 204 113 Nh nihonium – 6 C carbon 12 14 Si silicon 28 32 Ge germanium 73 50 Sn tin 119 82 Pb lead 207 22 Ti titanium 48 40 Zr zirconium 91 72 Hf hafnium 178 104 Rf rutherfordium – 23 V vanadium 51 41 Nb niobium 93 73 Ta tantalum 181 105 Db dubnium – 24 Cr chromium 52 42 Mo molybdenum 96 74 W tungsten 184 106 Sg seaborgium – 25 Mn manganese 55 43 Tc technetium – 75 Re rhenium 186 107 Bh bohrium – 26 Fe iron 56 44 Ru ruthenium 101 76 Os osmium 190 108 Hs hassium – 27 Co cobalt 59 45 Rh rhodium 103 77 Ir iridium 192 109 Mt meitnerium – 28 Ni nickel 59 46 Pd palladium 106 78 Pt platinum 195 110 Ds darmstadtium – 29 Cu copper 64 47 Ag silver 108 79 Au gold 197 111 Rg roentgenium – 30 Zn zinc 65 48 Cd cadmium 112 80 Hg mercury 201 112 Cn copernicium – 114 Fl flerovium – 116 Lv livermorium – 7 N nitrogen 14 15 P phosphorus 31 33 As arsenic 75 51 Sb antimony 122 83 Bi bismuth 209 115 Mc moscovium – 8 O oxygen 16 16 S sulfur 32 34 Se selenium 79 52 Te tellurium 128 84 Po polonium – 9 F fluorine 19 17 Cl chlorine 35.5 35 Br bromine 80 53 I iodine 127 85 At astatine – 117 Ts tennessine – 10 Ne neon 20 18 Ar argon 40 36 Kr krypton 84 54 Xe xenon 131 86 Rn radon – 118 Og oganesson – 21 Sc scandium 45 39 Y yttrium 89 57–71 lanthanoids 89–103 actinoids 57 La lanthanum 139 89 Ac lanthanoids actinoids The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.). actinium – 58 Ce cerium 140 90 Th thorium 232 59 Pr praseodymium 141 91 Pa protactinium 231 60 Nd neodymium 144 92 U uranium 238 61 Pm promethium – 93 Np neptunium – 62 Sm samarium 150 94 Pu plutonium – 63 Eu europium 152 95 Am americium – 64 Gd gadolinium 157 96 Cm curium – 65 Tb terbium 159 97 Bk berkelium – 66 Dy dysprosium 163 98 Cf californium – 67 Ho holmium 165 99 Es einsteinium – 68 Er erbium 167 100 Fm fermium – 69 Tm thulium 169 101 Md mendelevium – 70 Yb ytterbium 173 102 No nobelium – 71 Lu lutetium 175 103 Lr lawrencium – , ,