0620/42 Cambridge IGCSE - Mark Scheme March 2023
First Proof
Cambridge Assessment International Education
Cambridge International General Certificate of Secondary Education
CHEMISTRY 0620/42
Paper 4 Theory (Extended) February/March 2023
MARK SCHEME
Maximum Mark : 80
Page 1 of 7
0620/42 Cambridge IGCSE - Mark Scheme March 2023
First Proof
Question Answer Marks Guidance
1a M1 Carbon dioxide / CO2 1
1b 78 (%) 1
1c Calcium oxide A CaO
A CaCO3 / limestone? (CaCO3 slurry also used
1 in desulfurisation).
1d Catalytic converter 1
1ei CH4 1
1eii Lowest Mr 1 I ‘lightest gas’ Check latest MS (Mar 2021?)
1f Toxic 1 A ‘kills you’ etc
1g M1 Oxygen A sugar or carbohydrate?
M2 Glucose 2
1h M1 2 dot and cross double bonds
2 pairs of non-bonding e on O and 0 non-bonding e on C 2 A four individual non-bonding e
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Page 2 of 7
0620/42 Cambridge IGCSE - Mark Scheme March 2023
First Proof
Question Answer Marks Guidance
2a Metallic 1
2bi Lighted splint and (squeaky) pop 1 R Glowing splint
2bii 14 1 A range?
2biii Universal indicator / pH paper 1 R indicators such as litmus/thymolphthalein?
2biv 2Na(s) + H2O(l) 2NaOH(aq) + H2(g)
M1 NaOH as a product
M2 correct equation
M3 state symbols 3
2ci Isotopes 1
2cii
Li
6
Li+
7
protons 3 3
neutrons 3 4
electrons 3 2
Each row ✔ 3
2ciii M1 (10 x 6) + (90 x 7) = 690 M1 use of abundance x mass
M2 690/10 = 6.9 M2 mass of average atom to one dp
2 6.9
2civ M1 Both K with new octet of dots
M2 O with octet of 6 crosses and 2 dots
M3 Charges 3
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Page 3 of 7
0620/42 Cambridge IGCSE - Mark Scheme March 2023
First Proof
Question Answer Marks Guidance
3a Air
Methane 2 I steam A natural gas?
3bi Enthalpy change 1 I energy change
3bii ΔH is negative 1
3iii 450
20,000
Iron 3
3ciii
Decrease
decreases Decrease
none 4
3cv M1 E increases Check latest MS (June 2021)
M2 Frequency of collision increases
M3 Higher percentage of collisions above Ea 3
3ci H2SO4 1
3cii fertiliser 1
3ciii M1 Mr of (NH4)2SO4 = 132 I SF / rounding beyond whole numbers
M2 = 28/M1 = 100 x (28/132) = 21% 2
18
Question Answer Marks Guidance
4ai Zinc 1
Page 4 of 7
0620/42 Cambridge IGCSE - Mark Scheme March 2023
First Proof
Question Answer Marks Guidance
4aii Alloy 1
4bi Ductility/ductile 1
4bii electrons 1
4ci High mpt 1
4cii (Good) catalytic behaviour 1 A form complex ions
4di Waters of crystallisation 1
4dii blue 1
4diii CuSO4.5H2O 2
4ei basic 1
4eii The oxidation number of copper 1 A Ox state
4eiii M1 Mr Cu(NO3)2 = 188
M2 = 0.0200 x M1 = 0.0200 x 188 = 3.76g 2
4eiv M1 Moles of Gas formed = 0.0200 x 5/2 = 0.05(00)
M2 M1 x 24.0 = 1.2(0) 2
4ev 2Al + 3CuO Al2O3 + 3Cu
M1 Products M2 rest of equation 2
18
Same functional f
Question Answer Marks Guidance
5a Same functional group 1
5b Carboxylic acids 1
Page 5 of 7
0620/42 Cambridge IGCSE - Mark Scheme March 2023
First Proof
Question Answer Marks Guidance
5c CnH2n+1COOH 1 R CnH2n+1COOH
5d M1 Propan-2-ol
M2 Displayed formula of propan-2-ol 2
5ei C10H22 C3H8 + C3H6 + C4H8 A 2C2H4
M1 C3H8 + C3H6
M2 Rest of equation 2
5eii Cracking 1
5fi M1 6 C atoms in a chain with continuation bonds
M2 3 x CH3 at 2 C intervals 2 M2 A any possible arrangement (syntactic etc)
5fii Addition 1
5gi Sodium propanoate 1
5gii CH3CH2COO –
1
5hi phosphoric acid A any inorganic acid
1 formula must be correct in absence of a name
5hii ethyl propanaote 1
5hiii M1 Displayed formula of ester link
M2 rest of molecule 2 M2 A ECF from 5hii
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Page 6 of 7
0620/42 Cambridge IGCSE - Mark Scheme March 2023
First Proof
Question Answer Marks Guidance
6ai
6aii
6aiii
6b
6ci
6cii
6di
6dii
6ei
6eii
6eiii
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