IGCSE Chemistry 0620/13 October/November 2025 Past Paper with Answers

Question 1

Substances can exist as solids, liquids or gases. In which states of matter are the particles a similar distance apart from each other?

1. solid and liquid only
2. solid, liquid and gas
3. solid and gas only
4. liquid and gas only

Question 2

A rigid container with a fixed shape is filled with gas and then sealed. The sealed container is then heated. Three possible changes are listed. 1: the volume of the gas decreases. 2: the gas molecules move faster. 3: the pressure inside the container increases. Which changes take place?

1. 2 and 3
2. 1 and 2
3. 1 only
4. 3 only

Question 3

A crystal of sodium chloride is dropped into a beaker of still water. Over time the sodium chloride particles spread out and become evenly distributed throughout the water. Which process or processes occur in this experiment?

1. both dissolving and diffusion
2. dissolving only
3. diffusion only
4. neither dissolving nor diffusion

Question 4 · Answer A

Step 1: P is a metal and Q is a non-metal, so the compound is held together by ionic bonding (electrons transferred from metal to non-metal). Step 2: P has 2 outer electrons so it loses both to form P²⁺, and Q has 7 outer electrons so each Q gains 1 to form Q⁻. Step 3: Balancing the charges needs one P²⁺ to two Q⁻, giving the formula PQ₂ with ionic bonding.

Question 5 · Answer A

Step 1: A neutral sulfur atom has 16 electrons; gaining 2 to form S²⁻ gives 18 electrons, arranged 2,8,8. Step 2: A neutral calcium atom has 20 electrons; losing 2 to form Ca²⁺ gives 18 electrons, also arranged 2,8,8. Step 3: Both ions have 18 electrons in the configuration 2,8,8, so the ion could be either S²⁻ or Ca²⁺.

Question 6 · Answer A

Step 1: Work out the proton numbers: W = 35−18 = 17, X = 37−20 = 17, Y = 39−20 = 19, Z = 40−22 = 18. Step 2: W and X both have proton number 17, so they are atoms of the same element (isotopes), making the first statement correct. Step 3: Y (19) and Z (18) are different elements in different groups and periods, and Z (18) has a lower proton number than Y (19), so the other statements are wrong.

Question 7 · Answer A

Step 1: An ionic bond forms between oppositely charged ions, that is positive cations and negative anions. Step 2: The attraction between these oppositely charged ions is strong, not weak. Step 3: So an ionic bond is a strong electrostatic attraction between cations and anions.

Question 8 · Answer A

Step 1: Simple molecular compounds have weak forces between their molecules, so only a little energy is needed to separate them, giving a low melting point. Step 2: They have no free-moving charged particles, so they do not conduct electricity even when molten. Step 3: So a simple molecular compound has a low melting point and poor electrical conductivity when molten.

Question 9 · Answer A

Step 1: A structure like diamond is a giant covalent lattice with many strong covalent bonds holding every atom in place. Step 2: These strong bonds throughout the structure make it very hard. Step 3: Like diamond it has no free electrons or ions (so it does not conduct), is insoluble in water, and is not soft like graphite, so the likely property is that it is very hard.

Question 10 · Answer A

Step 1: A molecular formula tells you which elements are present and how many atoms of each there are, for example H₂O has two hydrogen atoms and one oxygen atom. Step 2: So it shows both the number and the type of the different atoms in a molecule. Step 3: It does not just give a total count, a count of elements, or the spatial arrangement, so the correct definition is the number and type of different atoms.

Question 11 · Answer A

Step 1: The formula $\text{Ca(OH)}_2$ has one calcium, two oxygen and two hydrogen atoms. Step 2: Add the masses: calcium 40, oxygen 2 × 16 = 32, hydrogen 2 × 1 = 2. Step 3: The total is 40 + 32 + 2 = 74, so the relative formula mass is 74.

Question 12 · Answer A

Step 1: Electroplating coats an object with an attractive metal layer, so it improves the appearance (statement 1 correct). Step 2: The coating can protect the metal underneath from reacting, making it more resistant to corrosion (statement 3 correct). Step 3: Electroplating does not insulate the object or make it softer, so statements 2 and 4 are wrong, giving 1 and 3.

Question 13 · Answer A

Step 1: A hydrogen-oxygen fuel cell reacts hydrogen with oxygen to form water, so the equation $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ is correct (statement 1). Step 2: The hydrogen is supplied as a fuel, not taken from the air, so statement 2 is wrong. Step 3: The only product is water, which is harmless and does not cause respiratory problems, so statement 3 is wrong, leaving statement 1 only.

Question 14 · Answer A

Step 1: In an endothermic reaction energy is taken in from the surroundings, so the products store more energy than the reactants. Step 2: On a reaction pathway diagram this is shown by the products line being higher than the reactants line. Step 3: So the endothermic diagram is the one where the products are at a higher energy than the reactants.

Question 15 · Answer A

Step 1: A physical change makes no new substance and can usually be reversed; condensing steam to water just changes state, and dissolving sugar can be reversed by evaporation, so both are physical. Step 2: Rusting forms a new substance (hydrated iron oxide) and cracking breaks molecules into new ones, so both are chemical changes. Step 3: So the physical changes are 2 and 3.

Question 16 · Answer A

Step 1: Heating blue hydrated copper(II) sulfate drives off its water of crystallisation, leaving white anhydrous copper(II) sulfate. Step 2: This is a reversible reaction: the white anhydrous solid takes water back from the moist air. Step 3: Absorbing water reverses the change and reforms the blue hydrated copper(II) sulfate, so water is absorbed from the air and the reaction reverses.

Question 17 · Answer A

Step 1: Reduction is the loss of oxygen and oxidation is the gain of oxygen. Step 2: The silver oxide loses its oxygen to become silver, so it is reduced, while the carbon gains oxygen to become carbon dioxide, so it is oxidised. Step 3: So the substance that is reduced is the silver oxide.

Question 18 · Answer A

Step 1: A base dissolving in water makes an alkaline solution, which contains hydroxide ions, OH⁻. Step 2: Thymolphthalein is colourless in acid and neutral solutions but turns blue in alkali. Step 3: So in the alkaline solution the thymolphthalein turns blue, and the ion responsible is the hydroxide ion.

Question 19 · Answer A

Step 1: Ammonium chloride contains the ammonium ion, and calcium hydroxide is a base. Step 2: Warming an ammonium compound with a base releases ammonia gas, which is the test for the ammonium ion. Step 3: So the gas produced is ammonia.

Question 20 · Answer A

Step 1: Chemical properties are decided by the number of electrons in the outer shell. Step 2: Elements in the same group have the same number of outer shell electrons. Step 3: So L and M have similar chemical properties because they have the same number of electrons in the outer shell.

Question 21 · Answer A

Step 1: For metals, reactivity increases down a group, so the lower metal Y is more reactive than the higher metal X. Step 2: For non-metals, reactivity decreases down a group, so the higher non-metal W is more reactive than the lower non-metal Z. Step 3: So Y is more reactive than X, and W is more reactive than Z.

Question 22 · Answer A

Step 1: Use the solubility rules: most sulfates are soluble except calcium, barium and lead; most hydroxides are insoluble except group I and ammonium; silver chloride is insoluble. Step 2: Calcium sulfate, magnesium hydroxide and silver chloride are all insoluble. Step 3: Each of the other sets contains at least one soluble compound (such as sodium sulfate, calcium chloride or calcium nitrate), so only the first set is all insoluble.

Question 23 · Answer A

Step 1: The two metals are mixed, not chemically combined, so 18 carat gold is a mixture (statement 1) and an alloy (statement 3), which is a mixture of a metal with other elements. Step 2: Because the metals are not chemically joined it is not a compound, so statement 2 is wrong. Step 3: Metals conduct electricity, so the alloy conducts (statement 4), giving 1, 3 and 4.

Question 24 · Answer A

Step 1: G reacts vigorously with cold water and its oxide is not reduced by carbon, so G is the most reactive. Step 2: E reacts with steam but not cold water, placing it below G; H does not react with water or steam but does react with dilute acid, placing it below E. Step 3: F does not react with water or acid and its oxide is reduced by carbon, so F is the least reactive, giving the order G, E, H, F.

Question 25 · Answer A

Step 1: Some metal compounds provide essential minerals, and dissolved oxygen is needed by aquatic animals to breathe, so 1 and 3 are beneficial. Step 2: Plastics are pollutants that harm aquatic life, so statement 2 is not beneficial. Step 3: Nitrates and phosphates cause too much plant growth and remove oxygen, harming aquatic life, so statement 4 is not beneficial, giving 1 and 3.

Question 26 · Answer A

Step 1: In water treatment, activated carbon absorbs substances that cause unpleasant tastes and odours. Step 2: Chlorine is added separately to kill bacteria, not to remove tastes and odours. Step 3: So the element used to remove tastes and odours is carbon.

Question 27 · Answer A

Step 1: NPK fertilisers must supply nitrogen, phosphorus or potassium. Step 2: Sodium nitrate contains the nitrate ion, which provides nitrogen for plant growth. Step 3: The other salts (aluminium sulfate, magnesium chloride and calcium ethanoate) supply none of N, P or K, so the correct choice is sodium nitrate.

Question 28 · Answer A

Step 1: Photosynthesis uses carbon dioxide and water as raw materials and needs light energy, so 1, 3 and 4 are essential. Step 2: Oxygen is a product of photosynthesis, not a requirement, so statement 2 is not needed. Step 3: So the essential things are carbon dioxide, light and water (1, 3 and 4).

Question 29 · Answer A

Step 1: In reaction M, calcium carbonate is broken down by heat alone into simpler substances, which is thermal decomposition. Step 2: In reaction N, methane reacts with oxygen and burns, which is combustion. Step 3: So M is thermal decomposition and N is combustion.

Question 30 · Answer A

Step 1: Test each formula against $\text{C}_n\text{H}_{2n+2}$. For $\text{C}_3\text{H}_8$, 2n+2 = 2(3)+2 = 8, which matches, so it is an alkane. Step 2: $\text{C}_2\text{H}_2$ needs 6 hydrogens to be an alkane, $\text{C}_4\text{H}_8$ needs 10, and $\text{C}_5\text{H}_{10}$ needs 12, so none of these match. Step 3: Only one compound ($\text{C}_3\text{H}_8$) fits the alkane formula.

Question 31 · Answer A

Step 1: Pentane is a saturated alkane with only single bonds. Step 2: Alkanes react with chlorine (in the presence of light) by swapping a hydrogen atom for a chlorine atom, which is a substitution reaction. Step 3: So the reaction of pentane with chlorine is substitution.

Question 32 · Answer A

Step 1: Natural gas is mostly methane, typically around 90% by composition. Step 2: The other alkanes and the non-hydrocarbons together make up only a small part. Step 3: So the correct bar chart has a very tall methane bar and only small bars for the other alkanes and the non-hydrocarbons.

Question 33 · Answer A

Step 1: Alcohols burn in oxygen (combustion) to give carbon dioxide and water, so water is a product of their combustion. Step 2: Alcohols have the -OH functional group, which is different from the -COOH group of carboxylic acids, so that statement is wrong. Step 3: Fermentation happens at about 30 °C, not 300 °C, and ethanol is made from ethene with steam, not with hydrogen, so the only correct statement is that water is produced from the combustion of alcohols.

Question 34 · Answer A

Step 1: Hydrogen gas is produced when an acid reacts with a reactive metal, so P must be the metal sodium (sodium oxide would give water, not hydrogen). Step 2: An acid reacting with a metal gives a salt, and the salt of ethanoic acid is sodium ethanoate, so Q is sodium ethanoate. Step 3: So P is sodium and Q is sodium ethanoate.

Question 35 · Answer A

Step 1: The repeat unit -CH₂-CH₂- comes from a small molecule with a carbon-carbon double bond that opened up to join the chain. Step 2: That monomer is ethene, CH₂=CH₂, and the polymer made from it is named poly(ethene). Step 3: So the polymer is poly(ethene) and the monomer is ethene.

Question 36 · Answer A

Step 1: A plastic is hard to break down in the environment if it is unreactive, so it stays for a long time. Step 2: Not reacting with water (statement 2) and being resistant to oxidation (statement 3) both mean it does not break down, so these explain why it is difficult to remove. Step 3: Being a poor conductor (1) and having a low density (4) do not affect how easily it breaks down, so the answer is 2 and 3.

Question 37 · Answer A

Step 1: The graph needs the volume of gas at different times, so an apparatus that measures gas volume is required. Step 2: A gas syringe collects the gas and reads its volume directly from a scale. Step 3: A beaker and test-tube do not measure gas volume accurately, and a pipette measures liquid volumes, so the correct apparatus is a gas syringe.

Question 38 · Answer A

Step 1: Dye X did not move from the baseline, which means it is insoluble in the ethanol solvent, so statement 2 is correct. Step 2: One of S's spots is level with W, so S contains the dye W, making statement 4 correct. Step 3: S shows three spots (not two, so statement 1 is wrong) and none is level with Z (so statement 3 is wrong), leaving 2 and 4 only.

Question 39 · Answer A

Step 1: A white precipitate with sodium hydroxide points to calcium, aluminium or zinc, because chromium gives a green precipitate. Step 2: The aluminium and zinc hydroxide precipitates dissolve in excess sodium hydroxide, but the calcium hydroxide precipitate does not. Step 3: Since the white precipitate is insoluble in excess sodium hydroxide, the cation is the calcium ion.

Question 40 · Answer A

Step 1: A gas that bleaches damp litmus paper, turning it white, is chlorine. Step 2: Ammonia would turn damp red litmus blue, and carbon dioxide and oxygen do not bleach litmus. Step 3: So the gas that bleaches the litmus paper white is chlorine.