2026 Cambridge IGCSE Chemistry (0620) Practice Paper with Answers

(a) Aluminium (\(\text{Al}\)) forms aluminium oxide (\(\text{Al}_2\text{O}_3\)), which is an amphoteric oxide that reacts with both acids and bases.

(b) Potassium (\(\text{K}\)) is an alkali metal in Group I that imparts a characteristic lilac colour to a non-luminous Bunsen flame.

(c) Bromine (\(\text{Br}\)) is a Group VII element (halogen) that is a red-brown liquid at room temperature and pressure.

(d) A neutral calcium atom has 20 electrons (configuration \(2,8,8,2\)). When it loses two outer-shell electrons to form \(\text{Ca}^{2+}\), it achieves the stable noble gas electronic configuration \(2,8,8\).

(e) Vanadium (\(\text{V}\)) is a transition element; vanadium(V) oxide (\(\text{V}_2\text{O}_5\)) is used as the catalyst to oxidise sulfur dioxide to sulfur trioxide in the Contact process.

(f) Helium (\(\text{He}\)) has proton number 2 and its atom contains only two electrons in a complete first shell.

(a) \(\text{Al}\) [1]
ALLOW aluminium / \(\text{Al}^{3+}\)

(b) \(\text{K}\) [1]
ALLOW potassium / \(\text{K}^+\)

(c) \(\text{Br}\) [1]
ALLOW bromine / \(\text{Br}_2\)

(d) \(\text{Ca}\) [1]
ALLOW calcium / \(\text{Ca}^{2+}\)

(e) \(\text{V}\) [1]
ALLOW vanadium

(f) \(\text{He}\) [1]
ALLOW helium

Note: If full names are given instead of symbols, credit is awarded provided the element is unambiguous. If more than one element is written per part, award 0 marks for that part unless an explicit correction is visible.

(a) (i) An ionic bond is the electrostatic attraction (M1) between oppositely charged ions (M2).

(ii) Magnesium (Group II) loses its 2 outer electrons to form a \(\text{Mg}^{2+}\) ion. Each fluorine atom (Group VII) gains 1 electron to form a fluoride ion, \(\text{F}^-\). In the diagram, the \(\text{Mg}^{2+}\) ion is shown with no outer shell electrons (or a full octet) and a \(2+\) charge. Two separate \(\text{F}^-\) ions (or a single \([\text{F}]^-\) preceded by the coefficient 2) are shown with 8 outer electrons (7 dots and 1 cross, or vice versa) and a \(-\) / \(1-\) charge.

(b) Silicon(IV) oxide has a giant covalent (macromolecular) structure, whereas carbon dioxide consists of simple molecules (M1).
Melting \(\text{SiO}_2\) requires breaking many strong covalent bonds, which requires a large amount of thermal energy (M2).
In \(\text{CO}_2\), only weak intermolecular forces (forces between molecules) need to be overcome, requiring very little energy (M3).

(c) In solid magnesium fluoride, the ions are held in fixed positions within the giant ionic lattice and cannot move (M1).
When molten, the ionic lattice breaks down so the ions are mobile / free to move to carry charge (M2).

(d) Each carbon atom in graphite forms three covalent bonds, leaving one delocalised electron per atom that is free to move throughout the layers (M1).

(a)(i)
M1: electrostatic attraction / forces [1]
M2: between oppositely charged ions / between positive and negative ions [1]
ALLOW: attraction between cations and anions
REJECT: attraction between atoms / molecules / nuclei and electrons (CON)

(a)(ii)
M1: \(\text{Mg}^{2+}\) ion drawn with 0 (or 8) outer electrons AND correct \(2+\) charge [1]
M2: \(\text{F}^-\) ion drawn with 8 outer electrons (7 of one symbol + 1 of the other) AND correct \(-\) / \(1-\) charge [1]
M3: correct 1:2 ratio shown (either two separate \(\text{F}^-\) ions drawn or a coefficient of 2 in front of \([\text{F}]^-\)) [1]

(b)
M1: \(\text{SiO}_2\) is giant covalent / macromolecular AND \(\text{CO}_2\) is simple molecular / simple covalent [1]
M2: (many) strong covalent bonds in \(\text{SiO}_2\) require a lot of energy to break [1]
M3: weak intermolecular forces / weak attractive forces between molecules in \(\text{CO}_2\) require little energy to overcome / break [1]
REJECT M3: breaking covalent bonds in \(\text{CO}_2\)

(c)
M1: (in solid) ions are fixed (in position / in lattice) / cannot move [1]
M2: (in molten) ions are mobile / free to move [1]
REJECT: electrons move (CON for ions)

(d)
M1: contains delocalised electrons (which are free to move) [1]
IGNORE: layers can slide

(a) (i) \(\text{ZnCO}_3\text{(s)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}\)
Correct balanced formulae: \(\text{ZnCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\text{O} + \text{CO}_2\)
State symbols: \(\text{(s)}\), \(\text{(aq)}\), \(\text{(aq)}\), \(\text{(l)}\), \(\text{(g)}\).

(ii) Steps:
1. Add zinc carbonate to dilute sulfuric acid (warmed) until zinc carbonate is in excess / no more dissolves / effervescence stops.
2. Filter the mixture to remove excess unreacted zinc carbonate (residue).
3. Heat the filtrate / solution to the point of crystallisation / until saturated (tested with a glass rod).
4. Allow the hot saturated solution to cool and form crystals.
5. Filter off the crystals and dry them between filter papers / in a warm desiccator / warm oven (below melting point).

(b) (i) \(\text{moles of } \text{H}_2\text{SO}_4 = \text{concentration} \times \text{volume in } \text{dm}^3 = 1.20 \times \frac{50.0}{1000} = 0.0600\text{ mol}\).

(ii) Mole ratio of \(\text{H}_2\text{SO}_4 : \text{ZnSO}_4 \cdot 7\text{H}_2\text{O} = 1 : 1\).
Theoretical moles of \(\text{ZnSO}_4 \cdot 7\text{H}_2\text{O} = 0.0600\text{ mol}\).
\(\text{Theoretical mass} = 0.0600 \times 287 = 17.22\text{ g}\) (or \(17.2\text{ g}\)).

(iii) \(\text{Percentage yield} = \frac{\text{actual mass}}{\text{theoretical mass}} \times 100 = \frac{12.9}{17.22} \times 100 = 74.9\%\).

(c) (i) Aqueous barium chloride / barium nitrate (or \(\text{BaCl}_2\text{(aq)}\) / \(\text{Ba(NO}_3\text{)}_2\text{(aq)}\)).

(ii) \(\text{Ba}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)}\).

(iii) Water molecules chemically bonded / trapped within the crystalline lattice / framework of a salt.

(a)(i)
- M1: Correct formulae of reactants and products: \(\text{ZnCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\text{O} + \text{CO}_2\) [1]
- M2: Correct state symbols throughout: \(\text{(s)}\), \(\text{(aq)}\), \(\text{(aq)}\), \(\text{(l)}\), \(\text{(g)}\) [1] (dependent on correct or near-miss formulae)

(a)(ii)
- M1: Add \(\text{ZnCO}_3\) to \(\text{H}_2\text{SO}_4\) until in excess / solid remains / no more dissolves / fizzing stops [1]
- M2: Filter to remove excess / unreacted \(\text{ZnCO}_3\) [1]
- M3: Heat / boil filtrate to crystallisation point / until saturated [1] (ALLOW evaporate some water / reduce volume by half; REJECT evaporate all water to dryness)
- M4: Leave / cool (to crystallise) [1]
- M5: Filter (crystals) AND dry with filter paper / in a desiccator / warm oven [1] (REJECT direct strong heating to dry crystals)

(b)(i)
- \(0.0600\text{ mol}\) or \(0.06\text{ mol}\) [1]

(b)(ii)
- M1: \(0.0600 \times 287\) [1]
- M2: \(17.22\text{ g}\) or \(17.2\text{ g}\) [1] (ALLOW ECF from (b)(i))

(b)(iii)
- \(\frac{12.9}{17.22} \times 100 = 74.9\%\) (or \(75.0\%\) if using \(17.2\)) [1] (ALLOW ECF from (b)(ii))

(c)(i)
- Barium chloride / barium nitrate / \(\text{BaCl}_2\) / \(\text{Ba(NO}_3\text{)}_2\) / barium hydroxide [1] (ALLOW aqueous barium salts; REJECT barium sulfate / barium carbonate)

(c)(ii)
- M1: Correct species: \(\text{Ba}^{2+} + \text{SO}_4^{2-} \rightarrow \text{BaSO}_4\) [1]
- M2: Correct state symbols: \(\text{(aq)} + \text{(aq)} \rightarrow \text{(s)}\) [1] (dependent on correct ions)

(c)(iii)
- Water (molecules) chemically combined / included within the crystalline structure / lattice [1]

(a) (i) Transition elements have higher densities, higher melting/boiling points, and greater hardness/tensile strength compared to Group I alkali metals.
(ii) Chloride ions have an oxidation state of \(-1\). For neutral \( \text{CoCl}_3 \), the oxidation number of cobalt is \(+3\).

(b) (i) Anhydrous cobalt(II) chloride is blue; addition of water turns it pink.
(ii) The forward reaction is endothermic (\( \Delta H > 0 \)). Increasing the temperature shifts the equilibrium in the endothermic direction to absorb heat, so the position of equilibrium shifts to the right.
(iii) The left-hand side contains 0 moles of gas, whereas the right-hand side contains 6 moles of gas. Decreasing the pressure favours the side with more moles of gas, shifting the equilibrium to the right.
(iv) A catalyst increases the rate of both forward and reverse reactions equally, so it has no effect on the equilibrium position or yield.

(c) (i) An alloy is a mixture of a metal with other elements.
(ii) In pure cobalt, the atoms are all the same size and arranged in regular layers which slide easily over one another when a force is applied. In the alloy, atoms of different sizes disrupt the regular arrangement of layers, making it harder for the layers to slide.

(a) (i) Any two from:
- Higher melting point / higher boiling point [1]
- Higher density [1]
- Harder / stronger / higher tensile strength [1]
IGNORE catalytic properties / coloured compounds (not physical differences from Group I)

(ii) +3 / +III / 3 [1]
REJECT -3

(b) (i) Blue to pink [1]
ALLOW turns pink

(ii) M1: Shifts to the right / shifts in the forward direction [1]
M2: Forward reaction is endothermic / absorbs heat / \( \Delta H \) is positive [1]

(iii) M1: Shifts to the right / shifts in the forward direction [1]
M2: (Right-hand side has) more moles / molecules of gas (ALLOW 6 moles of gas vs 0 moles of gas) [1]

(iv) No effect / no change [1]

(c) (i) Mixture of a metal with other elements / another metal / non-metal [1]
REJECT compound / chemically bonded together

(ii) M1: In pure cobalt, atoms / ions are in regular layers / rows (that can slide over each other) [1]
M2: In the alloy, atoms / particles of different sizes are present [1]
M3: Disrupts the regular structure / layers, preventing layers from sliding (over each other easily) [1]

(a)(i)
* Catalyst: Iron / Fe (ALLOW finely divided iron)
* Temperature: 450 °C (ALLOW 400–500 °C)
* Pressure: 200 atm / 20 000 kPa / 2 × 10⁷ Pa (ALLOW 150–250 atm / 15 000–25 000 kPa)

(a)(ii)
* The forward reaction is exothermic (\(\Delta H\) is negative).
* A lower temperature would increase the equilibrium yield of ammonia, but the rate of reaction would be too slow / particles have less kinetic energy and fewer successful collisions.
* A higher temperature would increase the rate of reaction, but would shift the equilibrium position to the left (decreasing the yield of ammonia).
* Thus, \(450\text{ }^{\circ}\text{C}\) is an optimum/compromise temperature that provides an acceptable yield at an economically viable rate.

(b)(i)
* Central nitrogen atom surrounded by three hydrogen atoms.
* Three shared pairs of electrons (one single covalent bond between N and each H atom).
* One lone pair of electrons on the nitrogen atom (no other unshared electrons on hydrogen).
* Complete octet (8 electrons) for N and duplet (2 electrons) for each H.

(b)(ii)
* Weak intermolecular forces / intermolecular attractions (REJECT: covalent bonds).

(c)(i)
* The minimum energy required by colliding particles to initiate a chemical reaction.

(c)(ii)
* Energy absorbed to break bonds (reactants):
\[1 \times (\text{N}\equiv\text{N}) + 3 \times (\text{H}-\text{H}) = 945 + 3(436) = 945 + 1308 = +2253\text{ kJ/mol}\]
* Energy released when bonds form (products):
\[2 \times 3 \times (\text{N}-\text{H}) = 6 \times 391 = 2346\text{ kJ/mol}\]
* Enthalpy change \(\Delta H\):
\[\Delta H = \text{Energy in} - \text{Energy out} = 2253 - 2346 = -93\text{ kJ/mol}\]

(c)(iii)
* Bond breaking is endothermic / takes in energy and bond making is exothermic / gives out energy.
* More energy is released during the formation of new bonds in \(\text{NH}_3\) than is absorbed to break the bonds in \(\text{N}_2\) and \(\text{H}_2\).

(d)(i)
* Energy of products level is lower than the energy of reactants level.
* Activation energy (\(E_\text{a}\)) is represented by a vertical arrow directed upwards from the reactants energy level to the peak of the curve.
* Enthalpy change (\(\Delta H\)) is represented by a vertical arrow directed downwards from the reactants energy level to the products energy level.

(d)(ii)
* Activation energy, \(E_\text{a}\): decreases / is lowered.
* Enthalpy change, \(\Delta H\): remains unchanged / no effect.
* Explanation: A catalyst provides an alternative pathway with a lower activation energy, but it does not change the energy levels of the reactants or products.

(a)(i) [3 marks]
* M1: iron / Fe [1]
* M2: \(450\text{ }^{\circ}\text{C}\) (ALLOW values in the range 400 to 500 °C) [1]
* M3: \(200\text{ atm}\) / \(20\,000\text{ kPa}\) / \(2 \times 10^7\text{ Pa}\) (ALLOW values in the range 150 to 250 atm) [1]

(a)(ii) [3 marks]
* M1: Forward reaction is exothermic / \(\Delta H\) is negative [1]
* M2: (At low temperatures) rate of reaction is too slow / few particles have energy \(\ge E_\text{a}\) [1]
* M3: (At high temperatures) position of equilibrium shifts to the left / lower yield of ammonia, so \(450\text{ }^{\circ}\text{C}\) provides a suitable compromise between rate and yield [1]

(b)(i) [2 marks]
* M1: Three shared pairs of electrons, each between N and one H [1]
* M2: One lone pair on N and no other electrons on H atoms [1]

(b)(ii) [1 mark]
* M1: Intermolecular forces / attractions between molecules [1]
(REJECT: covalent bonds / breaking bonds within molecules)

(c)(i) [1 mark]
* M1: Minimum energy that colliding particles must possess to react [1]
(ALLOW: minimum energy needed to start a reaction)

(c)(ii) [3 marks]
* M1: Energy absorbed to break bonds = \(945 + 3(436) = 2253\text{ (kJ)}\) [1]
* M2: Energy released in bond formation = \(2 \times 3 \times 391 = 2346\text{ (kJ)}\) [1]
* M3: Correct calculation of \(\Delta H = -93\text{ kJ/mol}\) with correct sign [1]
(ALLOW ECF for M3 if arithmetic error in M1 or M2)

(c)(iii) [2 marks]
* M1: Bond breaking absorbs energy / is endothermic AND bond making releases energy / is exothermic [1]
* M2: More energy is released forming bonds than is required/absorbed breaking bonds [1]

(d)(i) [3 marks]
* M1: Product level drawn below reactant level [1]
* M2: Activation energy (\(E_\text{a}\)) indicated by an upward arrow from reactant level to maximum/peak [1]
* M3: Overall energy change (\(\Delta H\)) indicated by a downward arrow from reactant level to product level [1]

(d)(ii) [3 marks]
* M1: (Activation energy) decreases / is lower [1]
* M2: (Enthalpy change) remains unchanged / no effect [1]
* M3: Catalyst provides an alternative reaction pathway with a lower activation energy [1]

(a)(i)
• Catalyst: concentrated phosphoric acid / \(\text{H}_3\text{PO}_4\)
• Temperature: \(300\,^\circ\text{C}\) (allow \(280\text{--}350\,^\circ\text{C}\))
• Pressure: \(6000\text{ kPa}\) / \(60\text{ atm}\) (allow \(5500\text{--}7000\text{ kPa}\) / \(55\text{--}70\text{ atm}\))

(a)(ii)
• Advantage: Uses renewable raw materials (e.g. sugar cane / glucose / plant material) or uses lower temperature/less energy intensive.
• Disadvantage: Slow process / batch process / produces impure ethanol that requires fractional distillation / low concentration of ethanol.

(b)(i)
• Oxidising agent: acidified potassium manganate(VII) / \(\text{KMnO}_4\)
• Colour change: purple to colourless

(b)(ii)
\(2\text{CH}_3\text{COOH} + \text{Mg} \rightarrow (\text{CH}_3\text{COO})_2\text{Mg} + \text{H}_2\)

(c)(i) Concentrated sulfuric acid / concentrated \(\text{H}_2\text{SO}_4\)
(c)(ii) Propyl ethanoate
(c)(iii) Displayed formula of propyl ethanoate showing every atom and bond:
H O H H H
| || | | |
H - C - C - O - C - C - C - H
| | | |
H H H H

(d)(i) Compounds with the same molecular formula but different structural formulae / structures.
(d)(ii) Propan-2-ol: \(\text{CH}_3\text{CH(OH)CH}_3\) or its fully displayed structure with the \(-\text{OH}\) group on carbon 2.

(a)(i)
• M1: (concentrated) phosphoric acid / \(\text{H}_3\text{PO}_4\) [1]
• M2: \(300\,^\circ\text{C}\) [ALLOW \(280\text{--}350\,^\circ\text{C}\)] [1]
• M3: \(60\text{ atm}\) / \(6000\text{ kPa}\) [ALLOW \(55\text{--}70\text{ atm}\) / \(5500\text{--}7000\text{ kPa}\)] [1]

(a)(ii)
• M1 Advantage: (raw material is) renewable / sustainable / sugar cane / plants / uses less energy [1] (IGNORE environmentally friendly unless qualified)
• M2 Disadvantage: batch process / slow reaction / produces dilute or impure ethanol / requires fractional distillation [1]

(b)(i)
• M1: acidified potassium manganate(VII) / \(\text{KMnO}_4\) [1] [ALLOW acidified potassium dichromate(VI)]
• M2: purple to colourless [1] [ALLOW orange to green if dichromate(VI) given in M1]

(b)(ii)
• M1: correct formulae of reactants and products: \(\text{CH}_3\text{COOH}\), \(\text{Mg}\), \((\text{CH}_3\text{COO})_2\text{Mg}\), \(\text{H}_2\) [1]
• M2: correct balancing: \(2, 1, 1, 1\) [1]

(c)(i)
• concentrated sulfuric acid / (conc.) \(\text{H}_2\text{SO}_4\) [1] [REJECT dilute sulfuric acid / hydrochloric acid]

(c)(ii)
• propyl ethanoate [1]

(c)(iii)
• correctly drawn displayed formula showing all \(\text{C}-\text{H}\), \(\text{C}-\text{C}\), \(\text{C}=\text{O}\), \(\text{C}-\text{O}\) bonds correctly [1]

(d)(i)
• compounds having the same molecular formula [1] but different structural formulae / different structures [1]

(d)(ii)
• propan-2-ol drawn correctly as \(\text{CH}_3\text{CH(OH)CH}_3\) or fully displayed [1]