IGCSE Chemistry 0620/22 May/June 2025 Past Paper with Answers

Question 1

An ice cube is left in a warm room and melts to form a pool of water. What happens to the molecules of water as the ice cube melts?

1. they gain energy
2. they evaporate
3. they dissolve
4. they lose energy

Question 2

A sample of liquid X is first heated until it is a gas above its boiling point, then cooled so that it condenses and then freezes. Which description matches the graph of the temperature of X against time as it is cooled?

1. the temperature falls, levels off at a higher plateau as the gas condenses to liquid, falls again, then levels off at a lower plateau as the liquid freezes to solid
2. the temperature rises steadily the whole time, sloping upwards with no level plateau sections shown at any point on the graph
3. the temperature falls overall but shows only one level plateau, missing the second change of state expected on the cooling curve
4. the temperature falls but the lower freezing plateau is drawn before the higher condensing plateau, so the changes of state are in the wrong order

Question 3

An atom of zinc has a proton number of 30 and a nucleon (mass) number of 65. How many protons, electrons and neutrons are in this neutral atom of zinc?

1. 30 protons, 30 electrons and 35 neutrons
2. 30 protons, 35 electrons and 35 neutrons
3. 35 protons, 30 electrons and 30 neutrons
4. 35 protons, 35 electrons and 30 neutrons

Question 4 · Answer A

Step 1: The configuration 2,8,8 contains 18 electrons in total. Step 2: An argon atom has 18 electrons, and a chloride ion is a chlorine atom (17 electrons) that has gained one electron to give 18, so both have 18 electrons. Step 3: The aluminium ion has 13 − 3 = 10 electrons and the sodium ion has 11 − 1 = 10 electrons, so only particles 1 and 4 have the configuration 2,8,8.

Question 5 · Answer A

Step 1: The relative atomic mass is the weighted average: $(238 \times 66 + 244 \times 34) \div 100$. Step 2: This is $(15708 + 8296) \div 100 = 24004 \div 100 = 240.04$. Step 3: To three significant figures the relative atomic mass is 240.

Question 6 · Answer A

Step 1: Silicon(IV) oxide is a giant covalent solid in which silicon and oxygen atoms are joined throughout by covalent bonds. Step 2: Each silicon atom is bonded to four oxygen atoms in a tetrahedral arrangement like diamond, so that statement is correct. Step 3: It has no delocalised electrons (so it does not conduct), it is not a simple molecule, and its arrangement is like diamond, not graphite.

Question 7 · Answer A

Step 1: In the first experiment the 65 g of zinc exactly reacts with 32 g of sulfur to give 97 g of zinc sulfide, so this uses up all of both reactants. Step 2: Adding more sulfur (40 g) does not help because all 65 g of zinc has already reacted, so the zinc is the limiting reactant. Step 3: With no zinc left, the extra sulfur cannot react, so the mass of zinc sulfide stays at 97 g.

Question 8 · Answer A

Step 1: Iron(III) oxide is $\text{Fe}_2\text{O}_3$ and aluminium oxide is $\text{Al}_2\text{O}_3$, so these correct formulae must appear. Step 2: Balancing then needs 2 aluminium atoms on the left and 2 iron atoms on the right. Step 3: This gives $2\text{Al} + \text{Fe}_2\text{O}_3 \rightarrow \text{Al}_2\text{O}_3 + 2\text{Fe}$, which balances all the atoms.

Question 9 · Answer A

Step 1: Moles = concentration × volume in dm³ = 0.50 × (500 ÷ 1000) = 0.25 mol. Step 2: Mass = moles × relative formula mass = 0.25 × 40. Step 3: This gives a mass of 10 g of sodium hydroxide.

Question 10 · Answer A

Step 1: Molten zinc oxide contains only zinc ions and oxide ions, with no water present. Step 2: At the cathode the positive zinc ions gain electrons and form zinc metal, while at the anode the negative oxide ions lose electrons and form oxygen. Step 3: So oxygen is made at the anode and zinc at the cathode.

Question 11 · Answer A

Step 1: At the cathode positive ions gain electrons (reduction). Step 2: In dilute sodium chloride the hydrogen ions are discharged in preference to sodium ions, because hydrogen is less reactive than sodium. Step 3: So two hydrogen ions gain two electrons to form a hydrogen molecule: $2\text{H}^+ + 2\text{e}^- \rightarrow \text{H}_2$.

Question 12 · Answer A

Step 1: A fuel cell uses the reaction of hydrogen and oxygen to produce a voltage, so it converts chemical energy in the fuel into electrical energy. Step 2: The overall reaction is $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$, giving only water (no carbon dioxide). Step 3: Hydrogen is not a fossil fuel, so only the statement about chemical energy becoming electrical energy is correct.

Question 13 · Answer A

Step 1: The products are higher in energy than the reactants, so energy has been taken in from the surroundings, which makes the reaction endothermic. Step 2: Because the reaction absorbs energy from the surroundings, the surroundings lose energy and their temperature falls. Step 3: So the reaction is endothermic and the temperature of the surroundings decreases.

Question 14 · Answer A

Step 1: Forming bonds releases energy, so making bonds gives a negative (exothermic) enthalpy change. Step 2: Each methane molecule has four C–H bonds, so the energy released per mole is 4 × 413 = 1652 kJ. Step 3: Because the bonds are being formed, the enthalpy change is −1652 kJ.

Question 15 · Answer A

Step 1: A catalyst provides an alternative pathway with a lower activation energy, so it lowers $E_a$, it does not raise it. Step 2: A catalyst does not change the energies of the reactants or products, so the enthalpy change $\Delta H$ stays the same. Step 3: A catalyst does not lower the collision frequency or raise the particles’ kinetic energy, so the only correct statement is that $\Delta H$ is unchanged.

Question 16 · Answer A

Step 1: The Contact process uses vanadium(V) oxide as the catalyst, not iron (iron is used in the Haber process). Step 2: The key step is carried out at a temperature of about 450 °C and only a low pressure of about 2 atmospheres, because a higher pressure gives little extra yield and is expensive. Step 3: So the correct conditions are a vanadium(V) oxide catalyst, a low pressure and about 450 °C.

Question 17 · Answer A

Step 1: A reducing agent is the species that is itself oxidised, that is, it loses electrons (its oxidation state increases). Step 2: In equation 2 the iron goes from 0 in Fe to +2 in $\text{FeSO}_4$, and in equation 3 the iron goes from +2 in $\text{Fe}^{2+}$ to +3 in $\text{Fe}^{3+}$, so in both the iron is oxidised and acts as the reducing agent. Step 3: In equation 1 the iron in $\text{Fe}_2\text{O}_3$ is reduced (it gains electrons, so it is the oxidising agent), and in equation 4 the iron stays +2 throughout (no redox), so only equations 2 and 3 show the iron as a reducing agent.

Question 18 · Answer A

Step 1: A gas that turns damp red litmus paper blue is alkaline, and the common alkaline gas is ammonia. Step 2: Ammonia is released when an ammonium salt is warmed with a base, such as a basic oxide. Step 3: So the two substances are a basic oxide and an ammonium salt; potassium salts and acidic oxides do not release ammonia.

Question 19 · Answer A

Step 1: A strong acid is fully dissociated, so its equation uses a single forward arrow, while a weak acid is only partly dissociated, so its equation uses a reversible arrow. Step 2: Hydrochloric acid is strong, so $\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-$ has a forward arrow, and ethanoic acid is weak, so $\text{CH}_3\text{COOH} \rightleftharpoons \text{H}^+ + \text{CH}_3\text{COO}^-$ has a reversible arrow. Step 3: So the correct row gives HCl a full arrow and ethanoic acid a reversible arrow.

Question 20 · Answer A

Step 1: Acidic oxides are formed by non-metals, while metal oxides such as calcium oxide and sodium oxide are basic. Step 2: Carbon dioxide, nitrogen dioxide and sulfur dioxide are all non-metal oxides, so all three are acidic. Step 3: Any set containing CaO or $\text{Na}_2\text{O}$ includes a basic oxide, so only $\text{CO}_2$, $\text{NO}_2$ and $\text{SO}_2$ are all acidic.

Question 21 · Answer A

Step 1: Going down the noble gases both the density and the boiling point increase, so krypton’s values must lie between those of argon and xenon. Step 2: The density must be between 0.9 and 5.9 g/dm³, and the boiling point between −186 and −108 °C. Step 3: A density of 3.8 g/dm³ and a boiling point of −153 °C both fall in these ranges, so they are the correct predictions.

Question 22 · Answer A

Step 1: Like other metals, sodium is malleable, meaning it can be bent or hammered into shape. Step 2: As a Group I metal sodium is also a good conductor of electricity, has a low melting point and a low density. Step 3: So of the options given, only being malleable is a correct physical property of sodium.

Question 23 · Answer A

Step 1: Down Group VII the elements change from gases (fluorine, chlorine) to a liquid (bromine) to solids (iodine, astatine). Step 2: Tennessine lies below astatine, which is already a solid, so the trend predicts tennessine is also a solid. Step 3: So at room temperature and pressure tennessine is expected to be a solid.

Question 24 · Answer A

Step 1: Chlorine is more reactive than bromine because reactivity decreases down Group VII. Step 2: The more reactive chlorine takes the place of the less reactive bromine, forming chloride ions and releasing bromine: $\text{Cl}_2 + 2\text{Br}^- \rightarrow 2\text{Cl}^- + \text{Br}_2$. Step 3: So chlorine (the element) displaces bromine (the element) from the sodium bromide.

Question 25 · Answer A

Step 1: An alloy contains atoms of different sizes, which disrupt the regular layers of atoms in the metal. Step 2: The different-sized atoms in brass stop the layers from sliding over each other easily, so brass is harder than pure copper. Step 3: Brass is a mixture (not a compound) and still conducts, copper conducts because of its free electrons (not free atoms), and a pure metal is softer, so only the statement about brass being harder is correct.

Question 26 · Answer A

Step 1: The given equations show magnesium > zinc > copper > silver and that tin > copper, but the position of tin relative to zinc is still unknown. Step 2: If zinc reacts with $\text{Sn}^{2+}$ ions, then zinc is more reactive than tin, which fixes tin between zinc and copper. Step 3: This completes the order magnesium > zinc > tin > copper > silver, so the useful new information is that zinc reacts with $\text{Sn}^{2+}$ ions.

Question 27 · Answer A

Step 1: The zinc coating keeps out water and oxygen, so galvanising is a barrier method, making statement 1 correct. Step 2: Even if the zinc is scratched, the more reactive zinc still corrodes in preference to the iron, so the iron is protected and does not rust quickly, making statement 2 wrong and statement 3 (sacrificial protection) correct. Step 3: Zinc, being more reactive, loses (donates) electrons more readily rather than accepting them, so statement 4 is wrong, leaving 1 and 3.

Question 28 · Answer A

Step 1: In the blast furnace, carbon monoxide is the reducing agent that removes oxygen from the iron(III) oxide. Step 2: The carbon monoxide reduces the iron(III) oxide to iron, forming carbon dioxide: $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$. Step 3: Calcium is not used to reduce the ore, so the equations involving calcium do not represent the extraction of iron.

Question 29 · Answer A

Step 1: Anhydrous copper(II) sulfate is white and turns blue when water is added, which is the standard test for water. Step 2: Anhydrous cobalt(II) chloride is blue and turns pink when water is added, the other test for water. Step 3: So copper(II) sulfate goes white to blue and cobalt(II) chloride goes blue to pink.

Question 30 · Answer A

Step 1: A catalytic converter removes the harmful carbon monoxide and nitrogen monoxide from the exhaust. Step 2: It does this by reacting them together so that carbon monoxide is oxidised to carbon dioxide and nitrogen monoxide is reduced to nitrogen: $2\text{CO} + 2\text{NO} \rightarrow 2\text{CO}_2 + \text{N}_2$. Step 3: The other equations make harmful gases or carbon monoxide rather than removing them.

Question 31 · Answer A

Step 1: Carbon dioxide is a greenhouse gas that absorbs thermal energy radiated from the Earth, so statement 1 is correct, and burning fossil fuels has raised its atmospheric level, so statement 3 is correct. Step 2: By absorbing this energy it reduces the thermal energy lost to space, so statement 2 is wrong. Step 3: Other gases such as methane also cause global warming, so statement 4 is wrong, leaving statements 1 and 3.

Question 32 · Answer A

Step 1: Butan-2-ol has a chain of four carbon atoms (but-) and an –OH group (-ol) on carbon number 2. Step 2: Writing a four-carbon chain with the –OH on the second carbon gives $\text{CH}_3\text{CH}_2\text{CH(OH)CH}_3$. Step 3: So this is the structural formula of butan-2-ol.

Question 33 · Answer A

Step 1: An ester forms when the –OH of the alcohol reacts with the –COOH of the carboxylic acid, losing water and making a C(=O)–O ester linkage. Step 2: Ethanoic acid provides $\text{CH}_3\text{CO}{-}$ and methanol provides $-\text{OCH}_3$, which join to give methyl ethanoate, $\text{CH}_3{-}\text{C(=O)}{-}\text{O}{-}\text{CH}_3$. Step 3: So the correct displayed formula is the methyl ethanoate structure with the ester linkage in the right place.

Question 34 · Answer A

Step 1: Kerosene is the aircraft fuel fraction, so it is correctly used as jet fuel. Step 2: Bitumen is used to surface roads (not as a lubricant), naphtha is mainly a feedstock for making chemicals (not home heating), and refinery gas is used as a fuel for cooking and heating (not making chemicals). Step 3: So only kerosene matched with jet fuel is correct.

Question 35 · Answer A

Step 1: Ethane is a saturated alkane, so with chlorine and ultraviolet light it undergoes substitution, where a chlorine atom replaces one hydrogen atom. Step 2: One hydrogen of ethane is replaced by a chlorine, giving chloroethane, $\text{C}_2\text{H}_5\text{Cl}$, and the displaced hydrogen joins a chlorine to form hydrogen chloride, HCl. Step 3: So the products are $\text{C}_2\text{H}_5\text{Cl}$ and HCl.

Question 36 · Answer A

Step 1: The catalytic addition of steam to ethene is a fast, continuous process that gives pure ethanol. Step 2: Compared with fermentation, two clear advantages are that it produces a purer product and is a faster reaction. Step 3: Using renewable raw materials is an advantage of fermentation (ethene comes from finite petroleum), and using more energy is a disadvantage, so the correct pair is a purer product and a faster reaction.

Question 37 · Answer A

Step 1: The repeat unit contains amide linkages, –N(H)–C(=O)–, so it is a polyamide made from a diamine and a dicarboxylic acid. Step 2: The –N(H)–CH₂–CH₂–N(H)– part comes from a two-carbon diamine, $\text{H}_2\text{N}{-}\text{CH}_2\text{CH}_2{-}\text{NH}_2$, and the –C(=O)–CH₂–CH₂–C(=O)– part comes from a dicarboxylic acid, $\text{HOOC}{-}\text{CH}_2\text{CH}_2{-}\text{COOH}$. Step 3: So the correct monomers are this diamine and dicarboxylic acid, matching the chain lengths in the repeat unit.

Question 38 · Answer A

Step 1: A volume given to one decimal place, such as 26.3 cm³, needs apparatus with a fine, accurate scale. Step 2: A burette has a precise graduated scale and a tap, so it can deliver any accurate variable volume like 26.3 cm³. Step 3: A measuring cylinder is far less precise, and beakers and conical flasks only hold liquids, so the burette is the correct choice.

Question 39 · Answer A

Step 1: During filtration, the insoluble solid is trapped on the filter paper and is called the residue, so X is the residue. Step 2: The liquid that passes through the filter paper is called the filtrate, so Y is the filtrate. Step 3: The filtrate is the aqueous salt solution, not pure water, so X is the residue and Y is the filtrate.

Question 40 · Answer A

Step 1: Dissolving an impurity in a substance lowers its melting point and raises its boiling point. Step 2: So the melting point falls below −114 °C, to −116 °C, and the boiling point rises above 78 °C, to 79 °C. Step 3: So the impure ethanol melts at −116 °C and boils at 79 °C.