IGCSE Chemistry 0620 Paper 42, Oct/Nov 2024

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0620/42 · Oct/Nov 2024

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The formulae of the molecules A to I are shown in Table 1.1. Table 1.1

molecule	formula
A	$C_{2} H_{4}$
B	$C_{2} H_{5} O H$
C	$C O$
D	$C O_{2}$
E	$C l_{2}$
F	$N O_{2}$
G	$N_{2}$
H	$O_{2}$
I	$S O_{2}$

Answer the following questions about the molecules, A to I. Each letter may be used once, more than once or not at all. State which of the molecules A to I:

is an element with a triple bond

[1]

is a product of photosynthesis

[1]

is used as a fuel

[1]

turns limewater milky

[1]

undergoes a substitution reaction with alkanes

[1]

is a colourless liquid at r.t.p.

[1]

is unsaturated

[1]

is 21% of clean, dry air

[1]

is a reactant in the Haber process.

[1]

Aluminium is manufactured by the electrolysis of aluminium oxide.

State the name of the main ore of aluminium.

[1]

Name the substance mixed with aluminium oxide to reduce the operating temperature of the process.

[1]

Explain why the molten mixture in (b) conducts electricity.

[1]

d(i)

Table 2.1 contains some information about the processes which take place at the anode and the cathode. Table 2.1

anode	cathode
$2 O^{2 -} \to O_{2} + . . . . . . e^{-}$	$..........................................$

Complete Table 2.1: • Write the number of electrons needed to balance the ionic half-equation for the reaction at the anode. • Write the ionic half-equation for the reaction at the cathode.

[3]

d(ii)

State why the process at the anode is an oxidation.

[1]

d(iii)

Oxygen is formed at the anode. Explain why the main gas given off at the anode is carbon dioxide and not oxygen.

[2]

State why aluminium is used in food containers.

[1]

Aluminium reacts with fluorine to form the ionic compound aluminium fluoride. Complete the dot-and-cross diagram in Fig. 2.1 of the ions in aluminium fluoride. Give the charges on the ions.

[3]

Sulfur forms two chlorides, P and Q. Chloride P has the formula $S_{2} C l_{2}$ . Chloride Q has the formula $S C l_{2}$ .

Both chlorides are covalently bonded and have low melting points. Suggest, in terms of attraction between particles, why these chlorides have low melting points.

[2]

Chloride P, $S_{2} C l_{2}$ , forms when sulfur reacts with chlorine. Write the symbol equation for this reaction.

[1]

Complete the dot-and-cross diagram in Fig. 3.1 of a molecule of chloride Q, $S C l_{2}$ . Show outer electrons only.

[3]

Chloride P is converted to chloride Q by reaction with chlorine in a closed system. The reversible reaction reaches an equilibrium. $\underset{P}{S_{2} C l_{2} (g)} + C l_{2} (g) ⇌ \underset{Q}{2S C l_{2} (g)}$ The forward reaction is exothermic. Suggest two changes to the conditions which will result in a decrease in the concentration of chloride Q at equilibrium. 1 ................................................................................................................................................. 2 .................................................................................................................................................

[2]

e(i)

The rate of the forward reaction in (d) is determined by collision theory. The rate of reaction depends upon two factors: • the frequency of collisions between particles • the proportion of collisions which have energy greater than or equal to the activation energy. Define the term activation energy.

[1]

e(ii)

Give the symbol for activation energy.

[1]

e(iii)

Complete Table 3.1 to show the effect, if any, when the conditions are changed. Use only the words increases, decreases or no change. Table 3.1

change to conditions	effect on the frequency of collisions between particles	effect on the proportion of collisions which have energy greater than or equal to the activation energy
concentration of chlorine is increased
temperature is increased
a catalyst is added

[5]

The reaction of chloride P with chlorine is a redox reaction. $\underset{P}{S_{2} C l_{2} (g)} + C l_{2} (g) ⇌ \underset{Q}{2S C l_{2} (g)}$ The oxidation number of $C l$ in chloride P and chloride Q is –1. Use oxidation numbers to explain why: • sulfur is oxidised in the forward reaction • chlorine is oxidised in the reverse reaction.

[4]

Silver bromide, $A g B r$ , is made when aqueous silver ethanoate, $C H_{3} C O O A g$ , is added to aqueous sodium bromide, $N a B r$ . The equation for the reaction is shown in equation 1. equation 1 $C H_{3} C O O A g + N a B r \to C H_{3} C O O N a + A g B r$ The method includes the following steps. step 1 Add $200.0 c m^{3}$ of $0.0500 m o l / d m^{3}$ $C H_{3} C O O A g$ to a beaker. This volume contains $0.0100 m o l$ of ${A g}^{+}$ ions. step 2 Add $50.0 c m^{3}$ of aqueous $N a B r$ . This volume contains $0.0100 m o l$ of ${B r}^{-}$ ions. A precipitate forms. step 3 Filter the mixture. step 4 Dry the solid residue until all the water is removed. step 5 Record the mass of the dry residue.

Complete the ionic equation for the reaction by adding the missing state symbols. ${A g}^{+} (.......) + {B r}^{-} (.......) \to A g B r (.......)$

[1]

Name a different aqueous silver salt which could be used in step 1.

[1]

Use the information in step 2 to calculate the concentration of aqueous $N a B r$ .

[1]

State the colour of the precipitate which forms in step 2.

[1]

Use the information in step 1, step 2 and equation 1 to determine the number of moles of $A g B r$ formed. Use this value to calculate the mass of $A g B r$ formed.

[3]

Name the salt dissolved in the filtrate in step 3.

[1]

g(i)

The recorded mass of the dry residue in step 5 is greater than the mass calculated in (e) because a step is missing from the procedure. Suggest the missing step.

[1]

g(ii)

Name the substance responsible for the greater mass of the dry residue.

[1]

h(i)

Barium sulfate can be made by the same method but with different aqueous solutions. Suggest two aqueous solutions which can be added together to make barium sulfate.

[2]

h(ii)

Write the balanced symbol equation for this reaction.

[2]

Alkenes are manufactured by cracking larger alkane molecules.

State the source of the large alkane molecules used in cracking.

[1]

State two conditions needed for cracking large alkane molecules. 1 ................................................................................................................................................. 2 .................................................................................................................................................

[2]

c(i)

When one molecule of dodecane, $C_{12} H_{26}$ , is cracked, three molecules of but-1-ene and one other product are formed. Use molecular formulae to complete the symbol equation for this reaction. $C_{12} H_{26} \to ....................................... + .......................................$

[2]

c(ii)

Suggest the type of chemical reaction which happens during cracking.

[1]

d(i)

Propene will undergo polymerisation. Suggest the name of the polymer formed from propene.

[1]

d(ii)

Draw part of this polymer molecule to show three repeat units.

[3]

d(iii)

State the type of polymerisation propene undergoes.

[1]

Polyamides and polyesters are polymers. Polyamides can occur naturally or can be manufactured.

a(i)

Part of the structure of a polyamide is shown in Fig. 6.1. On Fig. 6.1, draw a circle around one amide linkage.

[1]

a(ii)

Complete Fig. 6.2 to show the structures of the two monomers needed to make the polymer in Fig. 6.1. Show all of the atoms and all of the bonds in the functional groups.

[2]

a(iii)

Name the other product formed in this polymerisation.

[1]

a(iv)

State the term given to natural polyamides.

[1]

a(v)

Name the type of monomers which are used to make natural polyamides.

[1]

a(vi)

One of the monomers which forms part of a natural polyamide has three carbon atoms. Complete Fig. 6.3 to show the displayed formula of this monomer.

[3]

b(i)

PET is a polyester. Name the two types of monomer molecules needed to make polyesters.

[2]

b(ii)

Draw part of the structure of PET which shows two repeat units. Show all of the atoms and all of the bonds in the linkages.

[3]

Mark scheme

0620/42 · Oct/Nov 2024

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1a · 1 mark

1 mark
G

1b · 1 mark

1 mark
H

1c · 1 mark

1 mark
B

1d · 1 mark

1 mark
D

1e · 1 mark

1 mark
E

1f · 1 mark

1 mark
B

1g · 1 mark

1 mark
A

1h · 1 mark

1 mark
H

1i · 1 mark

1 mark
G

2a · 1 mark

1 mark
bauxite

2b · 1 mark

1 mark
cryolite

2c · 1 mark

1 mark
(it has) mobile ions

2d(i) · 3 marks

M1
4
M2
Al3+ AND e-
M3
correct equation (Al3+ + 3e- → Al)

2d(ii) · 1 mark

1 mark
electrons are lost (from oxide ions)

2d(iii) · 2 marks

M1
anode / electrode made of carbon or graphite
M2
anode / electrode reacts with oxygen / burns / combusts (in oxygen)

2e · 1 mark

1 mark
aluminium is resistant to corrosion

2f · 3 marks

M1
eight crosses in second shell of Al
M2
seven dots and one cross in second shell of each F
M3
‘3+’ charge on Al ion on correct answer line AND ‘–‘ charge on each F ion on correct answer line

3a · 2 marks

M1
attraction between molecules
M2
attraction is weak

3b · 1 mark

1 mark
2S + Cl2 → S2Cl2

3c · 3 marks

M1
S with one dot-cross bonding pair with each Cl
M2
four non-bonding dots for S
M3
six non-bonding crosses for each Cl

3d · 2 marks

M1
decrease concentration of S2Cl2 / P and / or Cl2
M2
increase temperature

3e(i) · 1 mark

1 mark
the minimum energy that colliding particles must have to react

3e(ii) · 1 mark

1 mark
Ea

3e(iii) · 5 marks

M1
increases
M2
no change
M3
increases
M4
increases
M5
increases

3f · 4 marks

M1
oxidation number of S goes from +1
M2
oxidation number of S goes to +2
M3
oxidation number of Cl (goes from –1) to 0 (in Cl2)
M4
oxidation numbers of Cl AND S increase

4a · 1 mark

1 mark
Ag+(aq) + Br–(aq) → AgBr(s)

4b · 1 mark

1 mark
(silver) nitrate

4c · 1 mark

1 mark
0.01  1000 / 50 = 0.2(00) (mol/dm3)

4d · 1 mark

1 mark
cream

4e · 3 marks

M1
mol of AgBr = 0.01(00)
M2
Mr of AgBr = 188
M3
188 x 0.01 = 1.88 (g)

4f · 1 mark

1 mark
sodium ethanoate

4g(i) · 1 mark

1 mark
rinsing of residue

4g(ii) · 1 mark

1 mark
(crystals of) sodium ethanoate

4h(i) · 2 marks

M1
named soluble barium salt e.g. barium chloride / barium nitrate
M2
named soluble sulfate salt e.g. sodium sulfate / potassium sulfate / ammonium sulfate / sulfuric acid

4h(ii) · 2 marks

M1
any equation with BaSO4 as a product
M2
correct equation using soluble reactants

5a · 1 mark

1 mark
petroleum

5b · 2 marks

M1
high temperature
M2
catalyst

5c(i) · 2 marks

M1
C4H8
M2
correct equation (C12H26 → 3C4H8 + H2)

5c(ii) · 1 mark

1 mark
thermal decomposition

5d(i) · 1 mark

1 mark
poly(propene)

5d(ii) · 3 marks

M1
chain of six C atoms joined by single bonds in a chain
M2
three correctly placed CH3 groups
M3
correct structure AND continuation bonds

5d(iii) · 1 mark

1 mark
addition

6a(i) · 1 mark

1 mark
one amide linkage circled

6a(ii) · 2 marks

M1
two fully displayed carboxylic acid groups on the shaded box
M2
two fully displayed amino groups on the unshaded box

6a(iii) · 1 mark

1 mark
water

6a(iv) · 1 mark

1 mark
protein(s)

6a(v) · 1 mark

1 mark
amino acids

6a(vi) · 3 marks

M1
displayed NH2 or displayed COOH group present
M2
displayed NH2 and displayed COOH groups attached to same C atom
M3
correct displayed structure of 2-aminopropanoic acid

6b(i) · 2 marks

M1
dicarboxylic acids
M2
diols

6b(ii) · 3 marks

M1
any one correct fully displayed ester link between any two blocks
M2
three fully displayed inter-block ester links with correct orientation
M3
fully correct diagram showing two complete repeat units of polyester including continuation bonds

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