Cambridge IGCSE Chemistry 0620/42 is the May/June 2026 Paper 4 (Extended Theory), variant 2. It lasts 1 hour 15 minutes, is worth 80 marks and is sat by every Extended candidate. It had six compulsory questions, and one of them, on compounds of nitrogen, carried 21 marks. This guide goes through the paper question by question and shows what the official mark scheme gave marks for. The paper and its mark scheme are free on the Tutopiya Learning Portal.

For an overview of all six 0620 papers from this series, see IGCSE Chemistry 0620 May/June 2026 past papers: what came up and how it was marked.

0620/42 at a glance

Question	Topic	Marks	Main command word
1	Group I and Group VII elements from clues	6	Give
2	Bonding and structure: covalent, metallic and giant covalent	11	Complete, describe
3	Salts: zinc sulfate, solubility, lead(II) sulfate by precipitation	15	Name, describe
4	Transition elements, the chromate(VI)/dichromate(VI) equilibrium, alloys	13	Explain, state
5	Nitrogen compounds: Haber process, tests with ammonia, NF₃ energetics and bonding	21	State, calculate
6	Alcohols: names, formulas, combustion, oxidation, esters	14	Name, state
	Total	80

Question-by-question walkthrough

Question 1: Group I and Group VII elements (6 marks)

Every answer had to be the symbol of a Group I or Group VII element.

• From atomic clues (3 × 1 mark): 11 protons is Na, 35 electrons is Br, and molecules with Mr 254 are iodine, I (I₂ accepted). For bromine, “Br₂” and “Br⁻” were rejected, because the clue was about atoms.
• From uses and reactions (3 × 1 mark): bromine (Br) detects unsaturation, potassium (K) gives a lilac flame, and chlorine (Cl) displaces bromide ions. Fluorine was also accepted for the last one. Ions such as Br⁻ and Cl⁻ were rejected (K⁺ was accepted for the flame test), and a capital “CL” was ignored.

Question 2: bonding and structure (11 marks)

• The bonding table (7 marks): sodium chloride was done as an example. For bromine: covalent bonding, between Br and Br atoms. For magnesium: metallic bonding, between Mg²⁺ ions and electrons. For silicon(IV) oxide: Si and O atoms. Each of the seven blanks was a separate mark. “Intramolecular” was ignored for bromine’s bond type.
• What is overcome when bromine boils (1 mark): intermolecular forces (van der Waals or London forces also accepted). Hydrogen bonding was rejected, and so were “intermolecular forces between atoms”, because the forces are between molecules.
• Arrangement of ions in sodium chloride (2 marks): a regular arrangement of alternating ions, and those ions are positive and negative. “Regular” and “alternating” were both needed for the first mark. Any answer describing shared or delocalised electrons scored zero.
• Another giant covalent substance like SiO₂ (1 mark): diamond. Graphite and graphene were rejected and “carbon” on its own was ignored. Silicon and silicon carbide were also accepted.

Question 3: salts (15 marks)

Zinc sulfate was made by adding excess zinc carbonate to dilute sulfuric acid.

• Complete the equation (1 mark): the missing products were H₂O and CO₂.
• Another zinc compound that gives zinc sulfate (1 mark): zinc oxide or zinc hydroxide.
• One more sign the reaction is complete (1 mark): no more effervescence. “Effervescence” on its own was rejected, because the point is that it stops.
• The term for a solution holding the maximum solute (1 mark): saturated. “Super-saturated” was rejected.
• When crystals first appear (1 mark): solution A held 30 g in 200 cm³, and the maximum is 60 g in 100 cm³, so 30 g saturates 50 cm³.
• Mass from solution B (1 mark): at 20 cm³, only 12 g can stay dissolved, so 18 g crystallises. The mark scheme accepted 12 g or 18 g, because the question could be read either way.
• Reagents for lead(II) sulfate (2 marks): a soluble lead(II) salt such as lead(II) nitrate, and a soluble sulfate such as sodium sulfate. Sulfuric acid was rejected as the sulfate salt, and so were insoluble sulfates.
• The technique (1 mark): precipitation.
• Getting pure lead(II) sulfate (3 marks): filter, wash the residue with water, then dry it. The order matters: crystallising or evaporating before filtering scored zero, and filter-then-dry without washing scored 2.
• Ionic equation (2 marks): Pb²⁺(aq) + SO₄²⁻(aq) → PbSO₄(s), one mark for the equation and one for the state symbols. Writing charges on PbSO₄ was rejected.
• Another insoluble sulfate (1 mark): barium sulfate (calcium or silver sulfate also accepted).

Question 4: transition elements (13 marks)

• Two physical properties different from Group I (2 marks): transition elements have higher melting points and higher densities; strength or hardness was also accepted. Chemical properties, such as acting as catalysts or having variable oxidation states, were rejected, and conductivity was ignored.
• Formulas (2 marks): copper(I) oxide is Cu₂O and nickel(II) nitrate is Ni(NO₃)₂. Showing ionic charges in the formulas was rejected.
• Why the chromate/dichromate reaction is not redox (1 mark): there is no change in oxidation number. “No electron transfer” was ignored.
• Describing the equilibrium (2 marks): the forward and reverse rates are equal, and the concentrations are no longer changing. “The concentrations are equal” or “the same” was rejected.
• Why pressure has no effect (1 mark): no gases are involved. “Equal numbers of moles on each side” was rejected; this equilibrium has no gas moles at all.
• Why adding alkali moves the equilibrium to the left (2 marks): hydroxide ions react with (neutralise) the H⁺ ions, so the concentration of H⁺ falls. Comments about pH or rates were ignored.
• Alloys (3 marks): copper and zinc make brass; chromium and nickel with iron and a non-metal make stainless steel, and the non-metal is carbon. “Graphite” was ignored.

Question 5: compounds of nitrogen (21 marks)

• Sources of the raw materials (2 marks): hydrogen from methane (natural gas) or steam, and nitrogen from air. Combustion of methane was rejected as a source of hydrogen.
• Haber process equation (2 marks): N₂ + 3H₂ ⇌ 2NH₃, one mark for the species and one for the balanced equation.
• Typical pressure (1 mark): 20 000 kPa, with 15 000 to 25 000 kPa accepted. Watch the number of zeros: 200 000 is out of range.
• Ammonia with Cr³⁺ (2 marks): a green precipitate (grey-green accepted) of chromium(III) hydroxide.
• Zinc ions and ammonia added in a different order (2 marks): a few drops of ammonia form zinc hydroxide as a white precipitate; when the zinc ions are added to ammonia, the ammonia is in excess, so the precipitate dissolves (or never forms). Simply repeating “white precipitate forms” from the question earned nothing.
• How the equation shows exothermic and reversible (2 marks): ΔH is negative (−870 kJ/mol), and the equation uses the reversible arrow. “Because it’s negative” on its own, without saying what is negative, was ignored.
• Completing the reaction profile (3 marks): formulas of reactants and products on the right levels, an upward arrow labelled Ea from the reactants to the top of the hump, and a single downward arrow labelled ΔH from the reactant level to the product level. A diagonal line for ΔH was rejected.
• The H–F bond energy (4 marks): one mark per step, with error carried forward:
  • bonds broken: 3 × 390 + 3 × 150 = 1620 kJ
  • energy released forming bonds: 1620 + 870 = 2490 kJ
  • three H–F bonds: 2490 − (3 × 270) = 1680 kJ
  • one H–F bond: 1680 ÷ 3 = 560 kJ/mol (to at least 2 significant figures)
• Dot-and-cross diagram for NF₃ (3 marks): one shared pair in each N–F bond, a lone pair on nitrogen to complete its octet, and six non-bonding electrons on each fluorine. Using all dots or all crosses lost marks, because the electrons from each atom must be told apart.

Question 6: alcohols (14 marks)

A table gave methanol (A), ethanol (B) and two three-carbon alcohols, C (CH₃CH₂CH₂OH) and D (CH₃CH(OH)CH₃).

• Why alcohols have similar chemical properties (1 mark): they have the same functional group (–OH). “Hydroxide” and “similar functional group” were rejected.
• Electrons in a methanol molecule (1 mark): 18.
• Molecular formula of ethanol (1 mark): C₂H₆O.
• Names of C and D (2 × 1 mark): propan-1-ol and propan-2-ol, spelt correctly. Plain “propanol” was rejected for both.
• Why C₃H₇OH does not identify C (1 mark): it does not show which carbon the –OH is on; it could be propan-1-ol or propan-2-ol (they are structural isomers).
• Complete combustion of ethanol (2 marks): C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O, one mark for CO₂ and H₂O as the only products and one for balancing.
• Oxidation (3 × 1 mark): the acidified oxidising agent is potassium manganate(VII) (potassium dichromate(VI) also accepted); the organic product is ethanoic acid; and oxidation by bacteria makes vinegar. Getting the oxidation state wrong, or putting it in the wrong place, lost the oxidising agent mark.
• The ester from D and ethanoic acid (2 marks): one mark for a fully displayed ester link and one for the correct ester made from propan-2-ol, so the carbon joined to the ester oxygen carries two CH₃ groups. Every atom and bond in the ester link had to be shown.
• The other product (1 mark): water.

Where the marks are on 0620/42

• “Name” questions carried 15 of the 80 marks, from the bromine forces in 2(a)(ii) to the alloys and the alcohol names. Several needed exact spelling or an oxidation state.
• “State” carried 13 marks and “complete” carried 11, most of them in the 7-mark bonding table in 2(a)(i).
• “Write” carried 8 marks: formulas in 4(b) and equations in 3(e)(iv), 5(a)(ii) and 6(d).
• Calculations (determine, calculate, deduce) carried 7 marks, including the 4-mark bond-energy calculation in 5(c)(iii).
• “Explain” carried 7 marks and “describe” another 7. Most of these sat in Question 4(c) on equilibrium and 3(e)(iii) on the filter–wash–dry method.
• “Give” carried 7 marks (all of Question 1 plus 6(e)(ii)) and drawing carried 5 (the reaction profile and the ester).
• Question 5 alone is worth 21 marks, more than a quarter of the paper. Energetics, the Haber process and ion tests are worth securing first.

How to self-mark 0620/42 with the mark scheme

1. Learn the abbreviations first. A means accept, I means ignore, R means reject, M1, M2 and so on are the separate marking points, and ECF means error carried forward.
2. Mark calculations step by step. In 5(c)(iii), give yourself each of the four marks separately. A wrong early value still earns the later marks if you used it correctly.
3. Check the order of your method. In 3(e)(iii), filter, wash, dry. If your answer crystallises before filtering, it scores zero, however much else is right.
4. Check names and spellings. Propan-1-ol and propan-2-ol, potassium manganate(VII) with its oxidation state, chromium(III) hydroxide. Where a name is asked for, the name takes precedence over any formula you also wrote.
5. Watch equilibrium wording. In 4(c)(ii), “rates equal” scores; “concentrations equal” does not.
6. Apply the list rule. For “state two” in 4(a), mark only your first two answers. A wrong answer still uses up a place.
7. Log each lost mark as missing knowledge, a misread command word or a careless slip, and revise in that order.

Sit 0620/42 as a timed mock

The paper allows 75 minutes for 80 marks, a little under one minute per mark. A workable plan:

Block	Marks	Time
Question 1	6	5 minutes
Question 2	11	10 minutes
Question 3	15	14 minutes
Question 4	13	12 minutes
Question 5	21	19 minutes
Question 6	14	12 minutes
Check, especially equations, state symbols and the bond-energy working	–	3 minutes

Write every line of the bond-energy working on the answer lines given. Each line is a mark even if the final answer is wrong.

Other May/June 2026 0620 papers

• 0620 Paper 12 (Core Multiple Choice)
• 0620 Paper 22 (Extended Multiple Choice)
• 0620 Paper 32 (Core Theory)
• 0620 Paper 52 (Practical Test)
• 0620 Paper 62 (Alternative to Practical)

Practise and download

• Download 0620/42 and its mark scheme on the Learning Portal →
• All 0620 May/June 2026 papers: overview and marking patterns
• Try a free IGCSE Chemistry quiz

Need help with a 0620 topic? Book a free trial lesson with an IGCSE Chemistry tutor →

Frequently asked questions

What topics were on 0620 Paper 42 May/June 2026? +

Six questions: Group I and Group VII elements; bonding and structure; preparing zinc sulfate and lead(II) sulfate; transition elements and the chromate(VI)/dichromate(VI) equilibrium; compounds of nitrogen, including the Haber process and a bond-energy calculation; and alcohols.

How many marks is 0620/42 and how long is it? +

It is out of 80 marks and lasts 1 hour 15 minutes. Question 5, on compounds of nitrogen, is the biggest at 21 marks.

What was the H–F bond energy answer in 0620/42? +

560 kJ/mol. Bonds broken: 3 × 390 + 3 × 150 = 1620 kJ. Energy released forming bonds: 1620 + 870 = 2490 kJ. Take away three N–F bonds (3 × 270 = 810) to get 1680 kJ for three H–F bonds, then divide by 3. Each step earned one mark, with error carried forward.

What was the answer to the zinc sulfate solubility question in 0620/42? +

Crystals first appear when solution A has evaporated to 50 cm³, because 30 g of zinc sulfate saturates 50 cm³. For solution B, the mark scheme accepted 12 g or 18 g, because the question could be read as the mass still dissolved or the mass that crystallised.

Is 0620/42 the Core or Extended paper? +

Extended. Paper 4 is the Extended theory paper, sat alongside Paper 2 (Extended multiple choice) and either Paper 5 or Paper 6. Core candidates sit Paper 3 instead.

Where can I download 0620/42 May/June 2026 and its mark scheme? +

Both are free to download and print on the Tutopiya Learning Portal, on the Cambridge IGCSE Chemistry 0620 past papers page.

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