IGCSE Chemistry 0620/13 May/June 2025 Past Paper with Answers

Question 1

Liquid iron is cooled until it forms solid iron. Which statement about the particles in the iron is correct as it changes from a liquid to a solid?

1. the positions of the particles become fixed
2. the particles move further apart
3. the particles move faster
4. the attractions between the particles become weaker

Question 2

Particle diagrams use circles to represent atoms, with different shades for different kinds of atom. An element contains only one kind of atom, a compound contains different atoms chemically joined together, and a mixture contains different substances that are not chemically joined. Which diagram represents a mixture of an element and a compound?

1. a box containing some molecules each made of two identical atoms (an element) jumbled together with some molecules each made of two different atoms joined together (a compound)
2. a box containing only molecules that are each made of two identical atoms joined together, representing a single element with no compound present anywhere in the box
3. a box containing only single separate atoms that are all exactly the same kind, representing a single element with no joined molecules present in the box
4. a box containing only molecules that are each made of two different atoms joined together, representing a single compound with no separate element present in the box

Question 3

Which statement about an element and the arrangement of electrons in its atoms is correct?

1. sulfur is in the third period of the Periodic Table and has six outer shell electrons
2. aluminium is in the second period of the Periodic Table and has two occupied electron shells
3. helium is in Group VIII of the Periodic Table and has eight outer shell electrons
4. lithium is in Group I of the Periodic Table and has one occupied electron shell

Question 4 · Answer A

Step 1: The proton number is 68, so there are 68 protons, and a neutral atom has equal protons and electrons, giving 68 electrons. Step 2: The number of neutrons is the nucleon number minus the proton number, $167 - 68 = 99$. Step 3: So the atom has 68 protons, 99 neutrons and 68 electrons.

Question 5 · Answer A

Step 1: Rubidium is in Group I, so it has one outer electron and loses it to gain a full outer shell. Step 2: Losing one negative electron leaves a 1+ charge, so the ion is $\text{Rb}^+$. Step 3: So rubidium loses one electron and forms $\text{Rb}^+$.

Question 6 · Answer A

Step 1: A nitrogen atom has five outer electrons and each hydrogen has one. Step 2: Nitrogen forms one shared pair (single covalent bond) with each of the three hydrogen atoms, using three of its outer electrons. Step 3: The remaining two nitrogen electrons stay as one non-bonding lone pair, so the correct diagram has three bonds and one lone pair.

Question 7 · Answer A

Step 1: In graphite each carbon is bonded to only three other carbons, so statement 1 is wrong. Step 2: Graphite conducts because it has free (delocalised) electrons, not free ions, so statement 2 is wrong. Step 3: Graphite has layers that slide over each other, which is why it is used as a lubricant, so only statement 3 is correct.

Question 8 · Answer A

Step 1: The salt is magnesium chloride, which has the formula $\text{MgCl}_2$ because magnesium forms a 2+ ion. Step 2: Dilute hydrochloric acid is aqueous, so it is written HCl(aq), and the soluble salt is MgCl₂(aq). Step 3: Balancing gives $\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}$.

Question 9 · Answer A

Step 1: Each formula unit of $\text{CaCO}_3$ has a relative formula mass of 100 and contains one carbon atom of mass 12. Step 2: So carbon makes up $\frac{12}{100}$ of the mass of calcium carbonate. Step 3: In 100 g of calcium carbonate the mass of carbon is $\frac{12}{100} \times 100 = 12$ g.

Question 10 · Answer A

Step 1: Relative atomic mass takes into account that an element is a mixture of isotopes, so it is an average. Step 2: This average is compared with 1/12 of the mass of a carbon-12 atom, the standard reference. Step 3: So relative atomic mass is the average mass of the isotopes compared with 1/12 of a carbon-12 atom.

Question 11 · Answer A

Step 1: In molten potassium bromide the only ions present are potassium ions ($\text{K}^+$) and bromide ions ($\text{Br}^-$). Step 2: At the negative cathode the positive potassium ions gain electrons to form potassium metal. Step 3: At the positive anode the bromide ions lose electrons to form bromine, so bromine forms at the anode and potassium at the cathode.

Question 12 · Answer A

Step 1: A hydrogen-oxygen fuel cell reacts hydrogen with oxygen, the reverse of electrolysis of water. Step 2: The only product of this reaction is water. Step 3: So water is produced in the fuel cell.

Question 13 · Answer A

Step 1: The ammonium nitrate can be recovered unchanged, so it has only dissolved, not reacted to form a new substance. Step 2: The temperature decreases, which means energy is taken in from the surroundings, so the process is endothermic. Step 3: So the ammonium nitrate dissolves and the process is endothermic.

Question 14 · Answer A

Step 1: The rate is fastest when the volume of gas increases most quickly, that is the largest change in volume over a time period. Step 2: From 0 to 30 s the volume rises by 32 cm³, from 30 to 60 s by 27 cm³, from 60 to 90 s by 9 cm³, and from 90 to 120 s by 6 cm³. Step 3: The biggest increase is in the first 0 to 30 s period, so the rate is fastest then.

Question 15 · Answer A

Step 1: Transition elements form coloured compounds, and copper(II) compounds are typically blue. Step 2: Copper(II) sulfate dissolves in water to give a blue solution. Step 3: So copper(II) sulfate is the substance that forms a blue solution.

Question 16 · Answer A

Step 1: Reduction is the loss of oxygen and oxidation is the gain of oxygen. Step 2: The water ($\text{H}_2\text{O}$) loses its oxygen to become hydrogen, so it is reduced, while the carbon gains oxygen to become carbon monoxide, so it is oxidised. Step 3: So the substance that is reduced is water.

Question 17 · Answer A

Step 1: Warming an ammonium compound with aqueous sodium hydroxide releases ammonia gas, which is the test for the ammonium ion. Step 2: Ammonium chloride and ammonium nitrate both contain the ammonium ion, so both produce ammonia. Step 3: Aluminium nitrate has no ammonium ion, so only compounds 2 and 3 produce ammonia.

Question 18 · Answer A

Step 1: Hydrogen ions come from an acid and hydroxide ions come from an alkali, and they combine to form water. Step 2: An acid reacting with an alkali to form water is the definition of neutralisation. Step 3: So the reaction is a neutralisation reaction.

Question 19 · Answer A

Step 1: Acidic oxides are oxides of non-metals. Step 2: Carbon is a non-metal, so carbon dioxide is an acidic oxide. Step 3: Barium, copper and magnesium are metals, so their oxides are basic, leaving carbon dioxide as the acidic oxide.

Question 20 · Answer A

Step 1: A hydrated salt contains water of crystallisation, which is water chemically combined within the solid crystals. Step 2: This is different from a salt dissolved in water or a dry anhydrous salt. Step 3: So a hydrated salt is a solid salt that is chemically combined with water.

Question 21 · Answer A

Step 1: Metals are found on the left of the Periodic Table and non-metals on the right. Step 2: So moving left to right across a period the elements change from metals to non-metals. Step 3: This means the metallic character decreases from left to right across a period.

Question 22 · Answer A

Step 1: Group I metals react with water to give hydrogen and a hydroxide, so statement 1 is correct. Step 2: Going down Group I the melting point decreases (so statement 2 is wrong) and the density generally increases (so statement 3 is wrong). Step 3: The reactivity increases down the group, so statement 4 is correct, giving 1 and 4.

Question 23 · Answer A

Step 1: No reaction when X meets Y's ions means X is less reactive than Y, and no reaction when Y meets Z's ions means Y is less reactive than Z. Step 2: So the reactivity order is Z (most reactive) then Y then X (least reactive), which makes Z chlorine, Y bromine and X iodine. Step 3: Bromine (Y) is a red-brown liquid at room temperature and pressure, so that statement is correct.

Question 24 · Answer A

Step 1: Transition elements have high melting points and high densities, so a very low melting point or a low density rules an element out. Step 2: They also form coloured compounds, so a coloured oxide is expected rather than a white one. Step 3: Only the row with a high melting point of 1085 °C, a high density and a coloured (red solid) oxide fits a transition element.

Question 25 · Answer A

Step 1: The noble gases are monatomic gases, so statement 3 is correct. Step 2: Helium has only two outer electrons, so not all of them have eight, making statement 1 wrong. Step 3: The noble gases are unreactive and do not react with sodium, so statement 2 is wrong, leaving only statement 3.

Question 26 · Answer A

Step 1: Metals conduct heat well, so potassium has the higher thermal conductivity. Step 2: Metals are malleable while non-metals are brittle, so sulfur has the lower malleability. Step 3: So potassium has the higher thermal conductivity and sulfur has the lower malleability.

Question 27 · Answer A

Step 1: Overhead power cables need to be as light as possible, so the lower density of aluminium is a reason to choose it, making statement 1 a valid explanation. Step 2: Copper having the higher conductivity is a reason to choose copper, not aluminium, so statement 2 does not explain using aluminium. Step 3: Aluminium being more reactive is not a reason to use it for cables, so only statement 1 explains the choice.

Question 28 · Answer A

Step 1: A metal that reacts with cold water is the most reactive, so L is the most reactive. Step 2: A metal that reacts with steam (but not cold water) is more reactive than one that only reacts with acid, so J comes above K. Step 3: A metal that does not react with acid is the least reactive, so M is last, giving the order L, J, K, M.

Question 29 · Answer A

The chemical name for rust, the substance formed when iron corrodes in air and water, is hydrated iron(III) oxide.

Question 30 · Answer A

Step 1: Dissolved oxygen is needed by aquatic animals to breathe, so it is helpful, not harmful. Step 2: Nitrates and phosphates from fertilisers can cause excess plant growth that removes oxygen from the water, harming aquatic life. Step 3: So only the nitrates and phosphates (2 and 3) are harmful.

Question 31 · Answer A

Step 1: Clean, dry air is about 78% nitrogen and about 21% oxygen, with small amounts of argon and carbon dioxide. Step 2: Only nitrogen, at about 78%, is over 30% of the air. Step 3: So the gas that is over 30% of clean, dry air is nitrogen.

Question 32 · Answer A

Step 1: Fertilisers supply the main nutrients that plants need and that crops remove from the soil. Step 2: These nutrients are nitrogen, phosphorus and potassium, often labelled NPK. Step 3: So the elements replaced by fertilisers are nitrogen, potassium and phosphorus.

Question 33 · Answer A

Step 1: The reaction uses carbon dioxide and water, with chlorophyll and sunlight, to make glucose and oxygen. Step 2: This is the reaction carried out by green plants, which removes carbon dioxide from the air. Step 3: So the process is photosynthesis.

Question 34 · Answer A

Step 1: A homologous series is a family of compounds with the same general formula and the same functional group. Step 2: They have similar chemical properties because of this shared functional group, but their physical properties such as boiling point change down the series. Step 3: So the members are compounds with the same functional group.

Question 35 · Answer A

Step 1: Carboxylic acids fit the general formula $\text{C}_n\text{H}_{2n}\text{O}_2$, and Y ($\text{C}_4\text{H}_8\text{O}_2$) matches this, while the others do not have two oxygens. Step 2: Z ($\text{C}_6\text{H}_{14}$) has no oxygen, so it cannot be an alcohol, and W contains oxygen, so it is not a hydrocarbon. Step 3: X is $\text{C}_3\text{H}_6$ (propene), not ethene, so only the statement about Y is correct.

Question 36 · Answer A

Step 1: Fractions collected lower down the column have longer molecules, higher boiling points and higher viscosity. Step 2: Fuel oil has longer molecules than diesel oil, so it is more viscous, making that statement correct. Step 3: The other statements reverse the trends for volatility, chain length or boiling point, so they are wrong.

Question 37 · Answer A

Step 1: Alkanes are saturated, so they are generally unreactive apart from combustion and substitution with chlorine, making statement 1 correct, and they have the general formula $\text{C}_n\text{H}_{2n+2}$, making statement 2 correct. Step 2: Alkanes have only single carbon-carbon bonds, so statement 3 is wrong, and they do not decolourise bromine because they are saturated, so statement 4 is wrong. Step 3: So only statements 1 and 2 are correct.

Question 38 · Answer A

Step 1: Cracking must conserve atoms, so the products together must contain 6 carbon and 14 hydrogen atoms. Step 2: $\text{C}_4\text{H}_{10}$ and $\text{C}_2\text{H}_4$ add up to $\text{C}_6\text{H}_{14}$, which balances, and cracking typically gives a smaller alkane plus an alkene. Step 3: So the products are $\text{C}_4\text{H}_{10}$ and $\text{C}_2\text{H}_4$.

Question 39 · Answer A

Step 1: In chromatography, a substance always travels the same distance up the paper in the same conditions, so spots at the same height could be the same substance. Step 2: P's single spot and one of Q's spots reach the same height, so P and Q could share a coloured substance. Step 3: The line where the spots start is the baseline (not the solvent front), several spots show a mixture (not a pure substance), and the solvent rises above the baseline, so only the first statement is correct.

Question 40 · Answer A

Step 1: A yellow flame in a flame test shows that the sodium ion is present, so the metal is sodium. Step 2: Effervescence with dilute acid shows a carbonate, because carbonates react with acids to give carbon dioxide gas. Step 3: So T contains sodium ions and carbonate ions, making it sodium carbonate.