IGCSE Chemistry 0620 Paper 21, May/June 2025

A gas is placed in a sealed container with a fixed volume. The gas is heated. Which statements are correct? 1 The gas molecules move around faster. 2 The gas particles collide with the walls of the container more frequently. 3 The pressure in the container decreases. A 1 and 2 B 1 only C 2 and 3 D 2 only

A sample of ethanol is heated at a constant rate. The heating curve for this sample is shown. Which statement about the heating curve is correct? A Ethanol changes its physical state between 3 and 4. B Ethanol condenses between 2 and 3. C Energy is absorbed between 3 and 4 but not absorbed between 4 and 5. D More energy is absorbed between 4 and 5 than between 2 and 3.

Which atom has an equal number of protons, neutrons and electrons? A ${}^{40}\mathrm{A}\mathrm{r}$ B ${}^1\mathrm{H}$ C ${}^{23}\mathrm{N}\mathrm{a}$ D ${}^{14}\mathrm{N}$

The only naturally occurring isotopes in a sample of europium are ${}^{151}\mathrm{E}\mathrm{u}$ and ${}^{153}\mathrm{E}\mathrm{u}$. This sample of europium has a relative atomic mass, $A_{\text{r}}$, of 152. What is the percentage of ${}^{151}\mathrm{E}\mathrm{u}$ present in this sample to three significant figures? A 0.987% B 50.0% C 76.0% D 98.7%

Which statement about potassium chloride is correct? A It has a high melting point because it is a giant structure with strong covalent bonds. B It conducts electricity when solid because of its oppositely charged ions. C It conducts electricity when molten because its ions can move. D It is insoluble in water because of its strong bonding.

Which dot-and-cross diagram shows the outer shell electron arrangement in a molecule of nitrogen? A B C D

Which statement about silicon(IV) oxide is correct? A It contains silicon ions and oxide ions arranged in a giant lattice. B It is used in electrical circuits because it can conduct electricity. C Its bonds each contain one shared pair of electrons. D Its atoms are arranged in the same way as the atoms in graphite.

Three organic molecules are described. ● The molecular formula of propanoic acid is $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$. ● The molecular formula of lactic acid is $\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{H}(\mathrm{O}\mathrm{H})\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$. ● A glucose molecule consists of 6 carbon atoms, 6 oxygen atoms and 12 hydrogen atoms only. Which molecules have the same empirical formula? A propanoic acid, lactic acid and glucose B propanoic acid and lactic acid only C propanoic acid and glucose only D lactic acid and glucose only

Calcium carbonate reacts with dilute hydrochloric acid. The equation for the reaction is shown. $$\mathrm{C}\mathrm{a}\mathrm{C}{\mathrm{O}}_3+2\mathrm{H}\mathrm{C}\mathrm{l}\to \mathrm{C}\mathrm{a}\mathrm{C}{\mathrm{l}}_2+{\mathrm{H}}_2\mathrm{O}+\mathrm{C}{\mathrm{O}}_2$$ $1.00\text{ g}$ of calcium carbonate is added to $50.0{\text{ cm}}^3$ of $0.0500\text{ mol}\mathrm{/}{\text{dm}}^3$ hydrochloric acid. Which volume of carbon dioxide is made in this reaction? A $30{\text{ cm}}^3$ B $60{\text{ cm}}^3$ C $120{\text{ cm}}^3$ D $240{\text{ cm}}^3$

The diagram shows the electroplating of a steel object. A student makes three statements. 1 The steel object turns a reddish-brown colour. 2 The aqueous copper(II) sulfate changes to a paler blue colour. 3 The copper electrode becomes thinner. Which statements are correct? A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only

Concentrated aqueous sodium chloride is electrolysed using inert electrodes. Which equation shows the correct ionic half-equation for the reaction at the anode? A $\mathrm{C}{\mathrm{l}}^{-}+{\mathrm{e}}^{-}\to \mathrm{C}\mathrm{l}$ B $2\mathrm{C}{\mathrm{l}}^{-}\to \mathrm{C}{\mathrm{l}}_2+2{\mathrm{e}}^{-}$ C ${\mathrm{H}}^{+}\to \mathrm{H}+{\mathrm{e}}^{-}$ D $2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2$

Which equation represents the overall reaction in a hydrogen–oxygen fuel cell? A $2{\mathrm{H}}_2+{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}$ B $2{\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{H}}_2+{\mathrm{O}}_2$ C ${\mathrm{H}}_2+{\mathrm{O}}_2\to {\mathrm{H}}_2{\mathrm{O}}_2$ D ${\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{H}}_2+{\mathrm{O}}_2$

Water is added to anhydrous copper(II) sulfate in a test-tube. The mixture becomes hot. Which type of reaction and reaction pathway diagram apply to this reaction? A endothermic B endothermic C exothermic D exothermic

The equation represents the reaction between ethanoic acid and ethanol. $$\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}+\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{O}\mathrm{H}\rightleftharpoons \mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3+{\mathrm{H}}_2\mathrm{O}$$ Which type of reaction does this show? A addition B neutralisation C reduction D reversible

The graph shows the results of adding excess calcium carbonate to hydrochloric acid at $50{}^{\circ }\text{C}$ and at $30{}^{\circ }\text{C}$. Only the temperature is changed. Which row describes the reacting particles at $30{}^{\circ }\text{C}$ compared to those at $50{}^{\circ }\text{C}$?

Industrially, ammonia is made by the Haber process. The equation is shown. $${\mathrm{N}}_2(\mathrm{g})+3{\mathrm{H}}_2(\mathrm{g})\rightleftharpoons 2\mathrm{N}{\mathrm{H}}_3(\mathrm{g})\mathrm{\Delta }H=-92\text{ kJ/mol}$$ The conditions used are $450{}^{\circ }\text{C}$ and $200\text{ atm}$. Which statements about the conditions are correct? 1 Temperatures below $450{}^{\circ }\text{C}$ give a lower rate of reaction. 2 Temperatures below $450{}^{\circ }\text{C}$ give a lower yield of ammonia. 3 Pressures above $200\text{ atm}$ give a lower yield of ammonia. 4 Pressures above $200\text{ atm}$ are too expensive to maintain. A 1 and 2 B 1 and 4 C 2 and 3 D 3 and 4

Ethanol is warmed with acidified aqueous potassium manganate(VII). Which row describes the type of reaction of the ethanol and the colour change observed in the reaction mixture?

Two experiments involving acids R or S are done. ● $0.10\text{ mol}$ of acid R completely dissolves in $500{\text{ cm}}^3$ of water. $0.0048\text{ mol}$ of acid R is dissociated in the solution. ● $0.10\text{ mol}$ of acid S completely dissolves in $500{\text{ cm}}^3$ of water. $0.0179\text{ mol}$ of acid S is dissociated in the solution. Which statement about acids R and S is correct? A Acid R is a strong acid, and acid S is a weak acid. B Acid R is a weak acid, and acid S is a strong acid. C Acid R and acid S are both strong acids. D Acid R and acid S are both weak acids.

Lead(II) sulfate is an insoluble salt. Which process is not used to prepare a pure sample of this salt? A crystallisation B drying C filtration D precipitation

The formulae of two hydrated salts are shown. ● $\mathrm{C}\mathrm{u}\mathrm{S}{\mathrm{O}}_4\cdot x{\mathrm{H}}_2\mathrm{O}$ ● $\mathrm{C}\mathrm{o}\mathrm{C}{\mathrm{l}}_2\cdot y{\mathrm{H}}_2\mathrm{O}$ What are the values of $x$ and $y$?

The properties of the elements change from left to right across the Periodic Table. Which statement describes how the properties change across Period 3? A Elements change from gases to solids. B Elements change from non-conductors to electrical conductors. C Elements change from metal to non-metal. D Elements have a decreasing number of electron shells.

Which property decreases down Group VII of the Periodic Table, from chlorine to iodine? A atomic number B density C reactivity D melting point

Some properties of elements are listed. 1 They have good electrical conductivity. 2 They have high melting points. 3 They are malleable. 4 They have ions with variable oxidation numbers. Which properties are correct for both iron and lithium? A 1 and 3 B 1 and 4 C 2 and 3 D 2 and 4

Two statements about noble gases are listed. 1 Noble gases are reactive, monatomic gases. 2 Noble gases all have a full outer shell of electrons. Which statements about noble gases are correct? A Both statements are correct, and statement 2 explains statement 1. B Both statements are correct but statement 2 does not explain statement 1. C Statement 1 is correct but statement 2 is not correct. D Statement 2 is correct but statement 1 is not correct.

Which statement about the properties and uses of copper is correct? A It is used in electrical wiring, and it is ductile. B It is mixed with tin to make the alloy brass. C It is used in overhead electrical cables because it has a low density. D It is used in takeaway food containers because of its resistance to corrosion.

Three statements about solid Z are listed. ● It reacts with dilute hydrochloric acid to produce hydrogen. ● It reacts very slowly with cold water and quickly with steam. ● It is a good thermal conductor. What is solid Z? A gold B magnesium C potassium D silver

Four metals J, K, L and M are added separately to aqueous solutions of their ions. The results are shown.

key ✓ = reaction ✗ = no reaction Which statement about the metals is correct? A J has a greater tendency to form positive ions than K. B L has a greater tendency to form positive ions than J. C K has a greater tendency to form positive ions than L. D M has a greater tendency to form positive ions than K.

Which process is used in the extraction of iron from hematite? A electrolysis B precipitation C reduction D fractional distillation

Galvanising prevents iron from rusting. Which statements about galvanising are correct? 1 Galvanising involves coating the iron with silver. 2 Galvanising prevents oxygen and water from coming into contact with the iron. 3 Galvanising works because the metal coating loses electrons more readily than iron. A 1, 2 and 3 B 1 and 3 only C 2 and 3 only D 2 only

Nitrogen, phosphorus and potassium are essential elements for improved plant growth. Which mixture provides all three essential elements?

Which statements help explain why an increasing amount of carbon dioxide or methane in the atmosphere causes global warming? 1 Carbon dioxide absorbs thermal energy from the Earth. 2 Methane does not absorb thermal energy from the Sun. 3 Carbon dioxide does not reflect thermal energy from the Sun to the Earth. 4 Methane reflects thermal energy from the Earth back to the Earth. A 1 and 3 B 1 and 4 C 2 and 3 D 2 and 4

The exhaust gases from cars contain oxides of nitrogen. How are these oxides of nitrogen formed? A Nitrogen and oxygen from the air react together at the high temperatures in the engine. B Nitrogen and oxygen from the petrol react together in the car exhaust. C Nitrogen from the petrol reacts with oxygen at the high temperatures in the engine. D Nitrogen reacts with oxygen from the air in the catalytic converter.

The structural formula of methyl ethanoate is $\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{C}{\mathrm{H}}_3$. Which compounds are structural isomers of methyl ethanoate? 1 $\mathrm{H}\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$ 2 $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$ 3 $\mathrm{H}\mathrm{O}\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{O}\mathrm{H}$ A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 3 only

What is the total number of covalent bonds in one molecule of propane? A 8 B 9 C 10 D 11

Industrially, ethanol is produced by fermentation or by the reaction of ethene with steam. Which row is correct?

Some properties of an organic compound, J, are listed. ● It is a liquid at room temperature. ● It is soluble in water. ● A solution of J reacts with calcium carbonate to form carbon dioxide. ● A solution of J has a pH of 3. In which homologous series does J belong? A alkane B alkene C alcohol D carboxylic acid

The structures of two monomers that are used to make a condensation polymer are shown. Which structure represents one repeat unit of the condensation polymer formed? A B C D

Which item of apparatus is used to measure $25.0{\text{ cm}}^3$ of aqueous sodium hydroxide? A B C D

Which method is used to obtain copper(II) sulfate crystals from an aqueous solution of copper(II) sulfate? A chromatography B condensation C evaporation D filtration

A mixture of four different colourless amino acids is analysed by paper chromatography. The final chromatogram is shown. Why does the chromatogram only show three spots? A A locating agent is not used. B One of the amino acids is insoluble in the solvent. C The solvent front is too near the top of the paper. D Two of the amino acids have the same $R_{\text{f}}$ value.