0620 Chemistry June 2025 Question Paper 42

1 Using numbers only, state the:

(a) percentage of nitrogen in clean, dry air [1]

(b) typical operating temperature of the Contact process in °C [1]

(c) number of metals in Period 3 of the Periodic Table [1]

(d) number of halogens which are gases at r.t.p [1]

(e) typical temperature for the fermentation of aqueous glucose in °C [1]

(f) number of unbranched structural isomers of C4H8 which decolourise aqueous bromine [1]

(g) number of covalent bonds in one molecule of ethanol [1]

(h) number of carbon atoms in one molecule of propyl butanoate [1]

[Total: 8]

2 This question is about covalent compounds.

(a) State what is meant by a covalent bond [2]

(b) Chlorine(I) oxide, Cl 2O, is a simple molecule with covalent bonds.

(i) State what is meant by (I) in the name chlorine(I) oxide [2]

(ii) Complete the dot-and-cross diagram in Fig. 2.1 of a molecule of chlorine(I) oxide.

Show outer electrons only. Cl Cl O Fig. 2.1

[3]

(iii) Explain, in terms of structure and bonding, why Cl 2O boils at a low temperature and does not thermally decompose into its constituent elements, Cl 2 and O2 [3]

(iv) Give two reasons why liquid Cl 2O is a poor conductor of electricity. 1 2 [2]

(c) Carbon and silicon(IV) oxide both exist as giant covalent structures.

(i) Name a giant covalent structure of carbon which conducts electricity [1]

(ii) Identify the particles responsible for the conduction of electricity in this covalent structure of carbon [1]

(iii) Silicon(IV) oxide contains silicon atoms, Si, and oxygen atoms, O.

Fig. 2.2 shows part of the giant covalent structure of silicon(IV) oxide.

Complete the diagram in Fig. 2.2 by adding the symbol for each of the 9 atoms shown. Fig. 2.2

[2]

[Total: 16]

3 This question is about electrolysis.

(a) Complete the definition of electrolysis by filling in the missing words.

The decomposition of compounds when or by the passage of an electric current.

[3]

(b) Electrolysis of aqueous copper(II) sulfate is carried out using the apparatus shown in Fig. 3.1. The electrodes are made of platinum. power supply + – Fig. 3.1

(i) State whether the mass of the cathode increases, decreases or remains the same when platinum electrodes are used [1]

(ii) Describe the change in appearance, if any, of the electrolyte when platinum electrodes are used [1]

(iii) Describe what is seen at the anode when platinum electrodes are used [1]

(iv) Write the ionic half-equation for the reaction at the anode [3]

(c) The electrolysis is repeated using copper electrodes.

(i) State whether the mass of the cathode increases, decreases or remains the same when copper electrodes are used [1]

(ii) Describe the change in appearance, if any, of the electrolyte when copper electrodes are used [1]

(d) Aluminium is extracted from its purified ore by electrolysis.

(i) Name this ore of aluminium [1]

(ii) Name the substance added to this process to reduce the operating temperature [1]

(iii) Explain why the anodes need to be continually replaced during this process [2]

[Total: 15]

4 Chromium is the element with atomic number 24 in the Periodic Table.

(a) The main ore of chromium is chromite. Chromite contains FeCr2O4.

FeCr2O4 reacts with carbon.

(i) Complete the equation for this reaction.

FeCr2O4 + 4C Fe + 2Cr + [1]

(ii) Suggest one disadvantage of extracting chromium by reacting chromite with carbon [1]

(b) Chromium can be mixed with nickel and other elements to form stainless steel.

Name the type of substance formed when a metal is mixed with other elements [1]

(c) (NH4)2Cr2O7 is a compound containing chromium.

The negative ion in (NH4)2Cr2O7 is Cr2O7 2–.

(i) State the sum of the oxidation numbers in the Cr2O7 2– ion [1]

(ii) The oxidation number of each O in Cr2O7 2– ions is –2.

Determine the oxidation number of each Cr in Cr2O7 2– ions. Show your working [2]

(iii) When (NH4)2Cr2O7 is heated the following reaction occurs. (NH4)2Cr2O7 Cr2O3 + 4H2O + N2

Calculate the volume of nitrogen gas produced at r.t.p., in cm3, when 1.26 g of (NH4)2Cr2O7 is heated using the following steps.

The Mr of (NH4)2Cr2O7 is 252. • Calculate the number of moles of (NH4)2Cr2O7 used mol • Determine the number of moles of N2 formed mol • Calculate the volume of N2 formed at r.t.p. in cm3 cm3

[3]

[Total: 9]

5 Alkali metals are reactive elements.

(a) State the group number of the alkali metals [1]

(b) Identify the alkali metal which:

(i) has the highest melting point [1]

(ii) has the highest density [1]

(iii) has the lowest reactivity [1]

(iv) burns with a lilac flame [1]

(v) is found in fertilisers to improve plant growth [1]

(c) Sodium sulfide, Na2S, is an ionic compound.

Complete Fig. 5.1 to show the electronic configurations of the ions in sodium sulfide.

Show the charges on the ions. Na S Na Fig. 5.1

[3]

(d) Rubidium has only two naturally occurring atoms, 85Rb and 87Rb.

(i) State the term given to these naturally occurring atoms of rubidium [1]

(ii) Complete Table 5.1 to show the number of protons, neutrons and electrons in the atom and ion of rubidium shown. Table 5.1 85Rb 87Rb+ protons neutrons electrons

[3]

(iii) The relative atomic mass of rubidium to one decimal place is 85.5.

Determine the relative abundance of 85Rb in rubidium. Express your answer as a percentage % [1]

[Total: 14]

6 Ethene, C2H4, is the first member of a family of similar compounds which contains the alkene functional group.

(a) State the term for a family of similar compounds which contain the same functional group [1]

(b) Determine the difference in relative molecular mass between C2H4 and the next member in this family of similar compounds [1]

(c) Write the symbol equation for the complete combustion of C2H4 [2]

(d) C2H4 reacts with steam to form ethanol.

C2H4(g) + H2O(g) C2H5OH(g) ΔH = – 45 kJ / mol

The process happens in a closed system and the reaction reaches an equilibrium.

The conditions for this process are 300 °C and 60 atm pressure. H3PO4 is used as a catalyst.

(i) Complete Table 6.1 to show the effect, if any, on the concentration of C2H4(g) when the following changes to the conditions are applied.

Only use the words increases, decreases or no change. Table 6.1 change to condition effect on the concentration of C2H4(g) at equilibrium temperature is decreased some C2H5OH(g) is removed pressure is increased a more effective catalyst is used

[4]

(ii) Explain, in terms of collision theory, why the rate of the forward reaction increases if the temperature increases [3]

(e) Compound B has the displayed formula shown in Fig. 6.1. C C C C O O H H C O O H H H H Fig. 6.1

(i) Deduce the molecular formula of compound B [1]

(ii) State why compound B is unsaturated [1]

(iii) Draw the structure of one repeat unit of the polymer formed when compound B undergoes addition polymerisation.

[2]

(iv) Explain why 1 mol of compound B reacts with 2 mol of sodium hydroxide, NaOH [1]

(v) Calculate the volume, in cm3, of 0.250 mol / dm3 NaOH that reacts with 0.100 mol of compound B.

volume = cm3 [2]

[Total: 18] 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 anthanoids 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 –