IGCSE Chemistry 0620/11 October/November 2025 Past Paper with Answers

Question 1

Which process describes the movement of a substance very slowly from an area of high concentration to an area of low concentration?

1. a substance diffusing through a liquid
2. a substance diffusing through the air
3. a solid melting
4. a liquid being frozen

Question 2

A potassium atom has atomic number (proton number) 19 and nucleon (mass) number 39. The potassium ion $\text{K}^+$ is formed from this atom by losing one electron. How many protons, neutrons and electrons are in the potassium ion $\text{K}^+$?

1. 19 protons, 20 neutrons and 18 electrons
2. 19 protons, 20 neutrons and 19 electrons
3. 20 protons, 19 neutrons and 18 electrons
4. 20 protons, 20 neutrons and 19 electrons

Question 3

Magnesium is in Group II and Period 3 of the Periodic Table. A magnesium atom loses electrons to form its ion. Which row shows the charge on a magnesium ion and the electronic configuration of the magnesium ion?

1. charge +2 with electronic configuration 2,8
2. charge +2 with electronic configuration 2,8,2
3. charge −2 with electronic configuration 2,8
4. charge −2 with electronic configuration 2,8,2

Question 4 · Answer A

Step 1: Sodium is a metal with 1 outer electron, which it loses to form a positive ion. Step 2: Chlorine is a non-metal with 7 outer electrons, which gains 1 electron to form a negative ion. Step 3: So sodium loses electrons and chlorine gains electrons.

Question 5 · Answer A

Step 1: Ionic strontium nitrate conducts electricity when molten or dissolved because the ions become free to move, and it has a high melting point. Step 2: Simple covalent cyclohexane has weak forces between molecules, so it has a low boiling point and does not conduct electricity. Step 3: The matching pair is strontium nitrate conducting in aqueous solution and cyclohexane having a low boiling point.

Question 6 · Answer A

Step 1: Covalent bonds form between non-metal atoms that share electrons. Step 2: Nitrogen is a non-metal and shares electrons with hydrogen to form ammonia. Step 3: Magnesium and sodium are metals (they form ionic bonds) and neon is an unreactive noble gas, so nitrogen is correct.

Question 7 · Answer A

Step 1: Graphite and diamond are both forms of carbon with giant covalent structures, so both have high melting points. Step 2: Only graphite conducts electricity, because it has free electrons; diamond does not. Step 3: Both are covalent, so the correct statement is that both have giant structures.

Question 8 · Answer A

Step 1: Calcium hydroxide is $\text{Ca(OH)}_2$ and calcium carbonate is an insoluble solid, $\text{CaCO}_3(\text{s})$. Step 2: The balanced equation is $\text{CO}_2 + \text{Ca(OH)}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$. Step 3: The correct formula and the (s) state symbol for the precipitate make the first equation right.

Question 9 · Answer A

Step 1: Moles of magnesium = 9.6 ÷ 24 = 0.4 mol. Step 2: The equation shows 2 mol of Mg form 2 mol of MgO, a 1:1 ratio, so 0.4 mol of MgO forms. Step 3: Mass of MgO = 0.4 × 40 = 16.0 g.

Question 10 · Answer A

Step 1: In molten zinc chloride the only ions are zinc ions and chloride ions. Step 2: Positive chloride ions are not present; chloride ions are negative and move to the positive electrode, where chlorine forms. Step 3: Zinc ions are positive and move to the negative electrode, where zinc metal forms.

Question 11 · Answer A

Step 1: A fuel cell combines hydrogen and oxygen to release energy and form water. Step 2: Oxygen exists as $\text{O}_2$ molecules, not single O atoms. Step 3: The correctly balanced equation is $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$.

Question 12 · Answer A

Step 1: Burning a fuel is combustion, which is an exothermic reaction. Step 2: Exothermic reactions always release thermal (heat) energy. Step 3: Carbon dioxide, carbon monoxide and oxides of nitrogen depend on the fuel and conditions, so only thermal energy is always produced.

Question 13 · Answer A

Step 1: When the products are at a lower energy than the reactants, energy has been released. Step 2: Energy released to the surroundings means the reaction is exothermic. Step 3: So thermal energy is given out to the surroundings and the reaction is exothermic.

Question 14 · Answer A

Step 1: A reaction is fastest when the surface area and the temperature are both highest. Step 2: Powder has a larger surface area than ribbon, and 50 °C is hotter than 45 °C. Step 3: So powder at 50 °C reacts fastest and finishes in the shortest time.

Question 15 · Answer A

Step 1: Heating drives off the water to give white anhydrous copper(II) sulfate, and adding water reforms the blue hydrated form. Step 2: A reaction that can go both forwards and backwards is reversible. Step 3: So the reaction is reversible.

Question 16 · Answer A

Step 1: Roman numerals in a chemical name show the oxidation number of the metal. Step 2: In iron(III) chloride the iron has an oxidation number of +3. Step 3: So the (III) is the oxidation number of iron, not an energy, rate or atom count.

Question 17 · Answer A

The unit of the concentration of a solution measured in moles is $\text{mol} / \text{dm}^3$.

Question 18 · Answer A

Step 1: Both lead(II) nitrate and potassium chloride are soluble in water. Step 2: When mixed they form insoluble lead(II) chloride, which is a precipitate. Step 3: The other pairs either include an insoluble reactant or form only soluble products, so no precipitate appears.

Question 19 · Answer A

Step 1: Basic oxides are oxides of metals. Step 2: Lithium oxide (1) and sodium oxide (3) are metal oxides, so they are basic. Step 3: Phosphorus oxide (2) and sulfur dioxide (4) are non-metal oxides, which are acidic, so the basic oxides are 1 and 3.

Question 20 · Answer A

Step 1: Transition elements have high densities and high melting points, and form coloured compounds. Step 2: They are also often used as catalysts. Step 3: So the correct statement is that cobalt can act as a catalyst.

Question 21 · Answer A

Step 1: Noble gases have a full (stable) outer shell of electrons. Step 2: Diagram 1 (2) is a full first shell like helium, and diagram 3 (2,8,8) is a full outer shell like argon. Step 3: Diagram 2 (2,8,7) has 7 outer electrons, an incomplete shell, so the noble gases are 1 and 3.

Question 22 · Answer A

Step 1: An alloy is a mixture of a metal with one or more other elements, usually metals. Step 2: Brass is made from copper and zinc. Step 3: So brass is a mixture of the metals copper and zinc.

Question 23 · Answer A

Step 1: A metal that reacts with cold water is more reactive than one that reacts only with acid, which is more reactive than one that does not react at all. Step 2: W reacts strongly with both (most reactive); Z reacts with cold water and acid (next); Y reacts only with acid; X does not react (least reactive). Step 3: From least to most reactive the order is X, Y, Z, W.

Question 24 · Answer A

Step 1: A barrier method coats the iron to keep out air and water. Step 2: Greasing (2) and painting (3) both form a coating that acts as a barrier. Step 3: Alloying with chromium (1) changes the metal itself rather than coating it, so the barrier methods are 2 and 3.

Question 25 · Answer A

Step 1: Bauxite is the ore of aluminium. Step 2: Aluminium is too reactive to be extracted by reduction with carbon, so it is extracted by electrolysis. Step 3: So the metal extracted from bauxite by electrolysis is aluminium.

Question 26 · Answer A

Step 1: Dissolving a solute such as sodium chloride raises the boiling point of water above 100 °C. Step 2: Adding water to anhydrous cobalt(II) chloride turns it from blue to pink, not blue. Step 3: Not all dissolved metal ions are beneficial, and sedimentation removes insoluble (not soluble) impurities, so only the first statement is correct.

Question 27 · Answer A

Step 1: Ethanol is $\text{C}_2\text{H}_5\text{OH}$, an alcohol with two carbon atoms and one –OH group. Step 2: The two carbons are joined by a single bond, with the –OH on the end carbon, giving $\text{CH}_3\text{CH}_2\text{OH}$. Step 3: The structure with $\text{CH}_3$ and $\text{CH}_2\text{OH}$ on a single C–C bond is ethanol.

Question 28 · Answer A

Step 1: Alkanes are saturated hydrocarbons that contain only carbon and hydrogen joined by single covalent bonds. Step 2: In ultraviolet light they react with chlorine by substitution, where a chlorine atom replaces a hydrogen atom. Step 3: So the correct statement is that they react with chlorine in a substitution reaction.

Question 29 · Answer A

Step 1: Methane is a greenhouse gas that contributes to global warming. Step 2: Sulfur dioxide causes acid rain (not cancer), particulates cause breathing problems and smog (not acid rain), and carbon monoxide is toxic (it does not cause photochemical smog). Step 3: So the correct pairing is methane causing global warming.

Question 30 · Answer A

Step 1: A general formula gives the same hydrogen-to-carbon relationship for every member. Step 2: $\text{C}_2\text{H}_4$, $\text{C}_3\text{H}_6$ and $\text{C}_4\text{H}_8$ all fit $\text{C}_n\text{H}_{2n}$ (the alkenes). Step 3: The other groups mix different general formulae, so only this group shares one general formula.

Question 31 · Answer A

Step 1: Gasoline is used as a fuel for cars, not for waxes and polishes, so row 1 is wrong. Step 2: Bitumen is collected at the bottom of the column, below gasoline, not above it, so row 2 is wrong. Step 3: Kerosene as jet fuel collected below gasoline (row 3) and refinery gas for heating and cooking at the top (row 4) are both correct, so only rows 3 and 4 are right.

Question 32 · Answer A

Step 1: Cracking breaks long alkanes into smaller alkanes, alkenes and sometimes hydrogen. Step 2: Alkenes (3) and hydrogen (1) are produced, but alcohols (2) and carboxylic acids (4) are not. Step 3: So the substances produced are 1 and 3.

Question 33 · Answer A

Step 1: The catalytic addition of steam to ethene needs a high temperature and a high pressure. Step 2: The conditions used are about 300 °C and 6000 kPa, with a phosphoric acid catalyst. Step 3: So the correct row is 300 °C and 6000 kPa.

Question 34 · Answer A

Step 1: Ethanoic acid is a weak acid and shows typical acid reactions. Step 2: With reactive metals it forms a salt and hydrogen gas. Step 3: With carbonates it gives carbon dioxide (not hydrogen), with oxides it gives salt and water (not oxygen), and being acidic it does not turn red litmus blue, so the metal reaction is correct.

Question 35 · Answer A

Step 1: The monomer $\text{CH}_2{=}\text{CH}_2$ has a C=C double bond, so it is ethene, not ethane, making statement 1 wrong. Step 2: Joining unsaturated monomers into one long chain with no other product is addition polymerisation, so statement 2 is correct. Step 3: Poly(ethene) is unreactive and does not easily decompose, so statement 3 is correct, giving 2 and 3.

Question 36 · Answer A

Step 1: A pure substance melts or boils sharply at a fixed temperature. Step 2: The wax melts over a range (45–49 °C), which shows it is impure, while the liquid boils at a fixed 141 °C, which shows it is pure. Step 3: So the wax is impure and the liquid is pure.

Question 37 · Answer A

Step 1: A single spot means a pure substance, while two or more spots mean a mixture. Step 2: Dyes P, Q and R each give one spot, so they are pure, but dye S gives two spots, so it is a mixture. Step 3: One of S's spots is level with Q, so S contains dye Q plus one other substance.

Question 38 · Answer A

Step 1: Filtration separates an insoluble solid from a liquid. Step 2: Copper(II) hydroxide is an insoluble solid and aqueous calcium chloride is a solution, so the solid stays on the filter paper and the solution passes through. Step 3: The other mixtures are two solutions, two miscible liquids, or two solids, none of which can be separated by filtration.

Question 39 · Answer A

Step 1: A gas that turns damp red litmus paper blue is ammonia, so the gas from solid 1 is ammonia. Step 2: A gas that relights a glowing splint is oxygen, so the gas from solid 2 is oxygen. Step 3: So solid 1 gives ammonia and solid 2 gives oxygen.

Question 40 · Answer A

Step 1: Adding aqueous sodium hydroxide to metal ions forms metal hydroxide precipitates of characteristic colours. Step 2: Copper(II) ions give a blue precipitate of copper(II) hydroxide. Step 3: Calcium gives white, chromium(III) gives green, and iron(II) gives a green precipitate, so the blue precipitate is copper(II).