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Question 1

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 1.1: Solids, liquids and gases (Describe the effects of temperature and pressure on the volume of a gas)

▶️ Answer/Explanation

When a gas in a sealed, fixed-volume container is heated, the kinetic energy of its particles increases, making them move faster (statement 1 is correct). The faster-moving particles hit the walls more often and with greater force, leading to an increase in collision frequency (statement 2 is correct). Since the volume is fixed, this increased bombardment results in a rise in pressure, not a decrease, meaning statement 3 is incorrect. So, statements 1 and 2 are the correct ones.
✅ Answer: (A)

Question 2

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 1.1: Solids, liquids and gases (Explain changes of state in terms of kinetic particle theory, including the interpretation of heating and cooling curves)

▶️ Answer/Explanation

Looking at a typical heating curve, the flat horizontal sections (like between 4 and 5) represent changes of state where energy is absorbed to overcome intermolecular forces, but the temperature stays constant. The sloping section between 2 and 3 represents heating the liquid, so the energy absorbed there only increases the temperature. During boiling (4 to 5), much more energy is absorbed than during simple heating of the liquid (2 to 3), because latent heat of vaporization is larger than the specific heat capacity times temperature change. So, the statement that more energy is absorbed between 4 and 5 is indeed correct.
✅ Answer: (D)

Question 3

Which atom has an equal number of protons, neutrons and electrons?

(A) ⁴⁰Ar
(B) ¹H
(C) ²³Na
(D) ¹⁴N

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 2.2: Atomic structure and the Periodic Table (Define proton number/atomic number and mass number/nucleon number)

▶️ Answer/Explanation

For an atom to have an equal number of protons, neutrons, and electrons, its mass number must be exactly twice its atomic number (since protons = electrons = atomic number, and neutrons = mass number − atomic number). For ¹⁴N, the atomic number is 7, so it has 7 protons and 7 electrons, and its mass number is 14, meaning 14 − 7 = 7 neutrons. The other options, like ⁴⁰Ar, ¹H, or ²³Na, do not satisfy this condition.
✅ Answer: (D)

Question 4

The only naturally occurring isotopes in a sample of europium are ¹⁵¹Eu and ¹⁵³Eu. This sample of europium has a relative atomic mass, A_r, of 152. What is the percentage of ¹⁵¹Eu present in this sample to three significant figures?

(A) 0.987%
(B) 50.0%
(C) 76.0%
(D) 98.7%

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 2.3: Isotopes (Calculate the relative atomic mass of an element from the relative masses and abundances of its isotopes)

▶️ Answer/Explanation

We can solve this using the weighted average formula for relative atomic mass. Let the percentage of ¹⁵¹Eu be x%, so ¹⁵³Eu is (100 − x)%. Setting up the equation: 152 = (x × 151 + (100 − x) × 153) ÷ 100. Solving this gives 15200 = 151x + 15300 − 153x, which simplifies to 2x = 100, so x = 50.0%. Therefore, the sample contains exactly 50.0% of each isotope.
✅ Answer: (B)

Question 5

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 2.4: Ions and ionic bonds (Explain in terms of structure and bonding the properties of ionic compounds)

▶️ Answer/Explanation

Potassium chloride (KCl) is an ionic compound with a giant lattice structure, not covalent bonds (A is wrong). In the solid state, its ions are locked in place and cannot move, so it does not conduct electricity (B is wrong). When molten, the ionic lattice breaks down and the ions become free to move, allowing it to conduct electricity, which makes statement C correct. KCl is actually quite soluble in water, not insoluble (D is wrong).
✅ Answer: (C)

Question 6

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 2.5: Simple molecules and covalent bonds (Describe the formation of covalent bonds in simple molecules, including N₂)

▶️ Answer/Explanation

A nitrogen atom has 5 outer electrons. In a nitrogen molecule (N₂), the two nitrogen atoms share three pairs of electrons to form a triple covalent bond. This results in each nitrogen atom having one lone pair and three shared pairs, making a total of 8 electrons in its outer shell. The correct dot-and-cross diagram must show this triple bond with the remaining two electrons on each atom as a lone pair.
✅ Answer: (B)

Question 7

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 2.6: Giant covalent structures (Describe the giant covalent structure of silicon(IV) oxide, SiO₂)

▶️ Answer/Explanation

Silicon(IV) oxide (SiO₂) has a giant covalent structure, meaning it consists of atoms joined by covalent bonds, not ions (A is wrong). Like diamond, it does not conduct electricity, so it is not used in circuits (B is wrong). Each silicon atom forms four single covalent bonds to oxygen atoms, and each bond contains one shared pair of electrons, making statement C correct. Its structure is like diamond, not graphite, which has a layered arrangement (D is wrong).
✅ Answer: (C)

Question 8

Three organic molecules are described.

• The molecular formula of propanoic acid is CH₃CH₂COOH
• The molecular formula of lactic acid is CH₃CH(OH)COOH
• 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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 3.1: Formulae (Define the empirical formula of a compound as the simplest whole number ratio of the different atoms or ions in a compound)

▶️ Answer/Explanation

First, find the molecular formula for each. Propanoic acid is C₃H₆O₂, lactic acid is C₃H₆O₃, and glucose is C₆H₁₂O₆. The empirical formula is the simplest whole-number ratio. Propanoic acid’s ratio is C₃H₆O₂ (already simplest). Lactic acid simplifies to CH₂O, and glucose also simplifies to CH₂O. This means lactic acid and glucose share the same empirical formula, CH₂O, while propanoic acid does not.
✅ Answer: (D)

Question 9

Calcium carbonate reacts with dilute hydrochloric acid. The equation for the reaction is shown.

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

1.00 g of calcium carbonate is added to 50.0 cm³ of 0.0500 mol/dm³ hydrochloric acid. Which volume of carbon dioxide is made in this reaction?

(A) 30 cm³
(B) 60 cm³
(C) 120 cm³
(D) 240 cm³

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 3.3: The mole and the Avogadro constant (Calculate stoichiometric reacting masses, limiting reactants, volumes of gases at r.t.p.)

▶️ Answer/Explanation

Moles of CaCO₃ = 1.00 ÷ 100.1 ≈ 0.01 mol. Moles of HCl = 0.0500 × (50.0 ÷ 1000) = 0.0025 mol. HCl is the limiting reactant. From the equation, 2 mol HCl produce 1 mol CO₂, so 0.0025 mol HCl produce 0.00125 mol CO₂. At r.t.p., volume = 0.00125 × 24000 cm³ = 30 cm³.
✅ Answer: (A)

Question 10

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 4.1: Electrolysis (Identify the products formed at the electrodes … using copper electrodes)

▶️ Answer/Explanation

When electroplating a steel object with copper, the copper anode dissolves into the solution (becomes thinner), and copper deposits on the steel cathode, giving it a reddish-brown coating. Since copper ions leaving the anode are replaced by those plating out at the cathode, the concentration of copper sulfate solution stays the same — so the solution does not become paler. Therefore, statements 1 and 3 are correct, but 2 is incorrect.
✅ Answer: (C)

Question 11

Concentrated aqueous sodium chloride is electrolysed using inert electrodes.

Which equation shows the correct ionic half-equation for the reaction at the anode?

(A) Cl⁻ + e⁻ → Cl
(B) 2Cl⁻ → Cl₂ + 2e⁻
(C) H⁺ → H + e⁻
(D) 2H⁺ + 2e⁻ → H₂

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 4.1: Electrolysis (Construct ionic half-equations for reactions at the anode and at the cathode)

▶️ Answer/Explanation

At the anode in concentrated aqueous sodium chloride, chloride ions are discharged in preference to hydroxide ions. The anode reaction is oxidation, where electrons are lost. Two chloride ions give up two electrons to form a chlorine molecule. This is correctly represented by 2Cl⁻ → Cl₂ + 2e⁻. Option A shows a chlorine atom forming with gain of electrons (reduction), while C and D involve hydrogen ions, which are not discharged at the anode.
✅ Answer: (B)

Question 12

Which equation represents the overall reaction in a hydrogen-oxygen fuel cell?

(A) 2H₂ + O₂ → 2H₂O
(B) 2H₂O → 2H₂ + O₂
(C) H₂ + O₂ → H₂O₂
(D) H₂O₂ → H₂ + O₂

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 4.2: Hydrogen–oxygen fuel cells (State that a hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product)

▶️ Answer/Explanation

A hydrogen-oxygen fuel cell combines hydrogen and oxygen gas to produce electrical energy, with the only chemical product being water. The balanced equation for this overall reaction is 2H₂ + O₂ → 2H₂O. The reverse reaction (B) represents the electrolysis of water, while options C and D involve hydrogen peroxide, which is not the product in a typical fuel cell.
✅ Answer: (A)

Question 13

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?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 5.1: Exothermic and endothermic reactions (State that an exothermic reaction transfers thermal energy to the surroundings leading to an increase in the temperature of the surroundings)

▶️ Answer/Explanation

Since the test-tube becomes hot, thermal energy is being released to the surroundings, which is the definition of an exothermic reaction. In an exothermic reaction pathway diagram, the products have less energy than the reactants, so the line starts higher (reactants) and finishes lower (products), showing a net release of energy. This corresponds to the diagram where energy decreases from reactants to products.
✅ Answer: (C)

Question 14

The equation represents the reaction between ethanoic acid and ethanol.

CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O

Which type of reaction does this show?

(A) addition
(B) neutralisation
(C) reduction
(D) reversible

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 6.3: Reversible reactions and equilibrium (State that some chemical reactions are reversible as shown by the symbol ⇌)

▶️ Answer/Explanation

The reaction arrow shown is ⇌, which is the symbol specifically used to denote a reversible reaction. This reaction can proceed in both the forward direction (esterification) and the backward direction (hydrolysis) under the right conditions. While it is also technically a condensation reaction, the presence of the equilibrium arrows in the equation makes “reversible” the most directly applicable answer.
✅ Answer: (D)

Question 15

The graph shows the results of adding excess calcium carbonate to hydrochloric acid at 50 °C and at 30 °C. Only the temperature is changed.

Which row describes the reacting particles at 30 °C compared to those at 50 °C?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 6.2: Rate of reaction (Describe collision theory in terms of frequency of collisions and kinetic energy of particles)

▶️ Answer/Explanation

At a lower temperature of 30 °C, particles have less average kinetic energy compared to those at 50 °C. With less energy, they move more slowly, resulting in a lower frequency of collisions between reacting particles. Therefore, both the frequency of collisions and the average kinetic energy are lower at 30 °C than at the higher temperature. This matches row D exactly.
✅ Answer: (D)

Question 16

Industrially, ammonia is made by the Haber process. The equation is shown.

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = −92 kJ/mol

The conditions used are 450 °C and 200 atm. Which statements about the conditions are correct?

1. Temperatures below 450 °C give a lower rate of reaction.
2. Temperatures below 450 °C give a lower yield of ammonia.
3. Pressures above 200 atm give a lower yield of ammonia.
4. Pressures above 200 atm are too expensive to maintain.

(A) 1 and 2
(B) 1 and 4
(C) 2 and 3
(D) 3 and 4

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 6.3: Reversible reactions and equilibrium (Explain, in terms of rate of reaction and position of equilibrium, why the typical conditions stated are used in the Haber process)

▶️ Answer/Explanation

Statement 1 is correct: lower temperatures mean slower reactions. Statement 2 is incorrect: the forward reaction is exothermic, so lower temperatures would actually increase the yield of ammonia. Statement 3 is incorrect: higher pressure shifts the equilibrium towards fewer gas molecules, increasing ammonia yield. Statement 4 is correct: using very high pressures is costly due to the strong equipment and energy required to safely maintain them. So the correct pair is 1 and 4.
✅ Answer: (B)

Question 17

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?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 6.4: Redox (Identify redox reactions by the colour changes involved when using acidified aqueous potassium manganate(VII))

▶️ Answer/Explanation

Ethanol is oxidised to ethanoic acid by the powerful oxidising agent acidified potassium manganate(VII). During this reaction, the manganate(VII) ions (MnO₄⁻, which are purple) are reduced to colourless manganese(II) ions (Mn²⁺). This means the reaction mixture changes from purple to colourless, and ethanol undergoes oxidation. So the row with type ‘oxidation’ and colour change ‘purple to colourless’ is correct.
✅ Answer: (B)

Question 18

Two experiments involving acids R or S are done.

• 0.10 mol of acid R completely dissolves in 500 cm³ of water. 0.0048 mol of acid R is dissociated in the solution.
• 0.10 mol of acid S completely dissolves in 500 cm³ of water. 0.0179 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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 7.1: The characteristic properties of acids and bases (Define a strong acid as an acid that is completely dissociated in aqueous solution and a weak acid as an acid that is partially dissociated)

▶️ Answer/Explanation

The strength of an acid depends on its degree of dissociation. Both acid R and acid S are only partially dissociated; from 0.10 mol, only a small fraction (0.0048 mol and 0.0179 mol respectively) is dissociated. If either were a strong acid, nearly all of the 0.10 mol would be dissociated. Since both show only partial dissociation, they are both correctly classified as weak acids.
✅ Answer: (D)

Question 19

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 7.3: Preparation of salts (Describe the preparation of insoluble salts by precipitation)

▶️ Answer/Explanation

Insoluble salts like lead(II) sulfate are typically prepared by precipitation, where two soluble solutions are mixed and the insoluble salt forms as a solid precipitate. The mixture is then filtered, and the solid residue is dried. Crystallisation, however, is a technique used to obtain pure soluble salts from a solution by evaporating the solvent. So crystallisation is the process that is not used for making an insoluble salt.
✅ Answer: (A)

Question 20

The formulae of two hydrated salts are shown.

CuSO₄ • xH₂O
CoCl₂ • yH₂O

What are the values of x and y?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 7.3: Preparation of salts (Define the term water of crystallisation … including CuSO₄·5H₂O and CoCl₂·6H₂O)

▶️ Answer/Explanation

This is a recall question about common hydrated salts. Copper(II) sulfate crystals are well known to be hydrated with 5 water molecules, giving the formula CuSO₄·5H₂O, so x = 5. Cobalt(II) chloride crystals are hydrated with 6 water molecules, forming CoCl₂·6H₂O, meaning y = 6. So the correct pair of values is x = 5 and y = 6.
✅ Answer: (B)

Question 21

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 8.1: Arrangement of elements (Describe the change from metallic to non-metallic character across a period)

▶️ Answer/Explanation

As you move from left to right across Period 3, the elements change from metals on the left (like sodium, magnesium, aluminium) to non-metals on the right (like phosphorus, sulfur, chlorine). For example, sodium is a metallic solid, while argon is a non-metallic gas. The change is not from gases to solids, and the number of electron shells stays the same (3 shells) for all elements in Period 3.
✅ Answer: (C)

Question 22

Which property decreases down Group VII of the Periodic Table, from chlorine to iodine?

(A) atomic number
(B) density
(C) reactivity
(D) melting point

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 8.3: Group VII properties (Describe the Group VII halogens … with general trends down the group, limited to: decreasing reactivity)

▶️ Answer/Explanation

Going down Group VII from chlorine to bromine to iodine, the atomic number, density, and melting point all actually increase. However, the reactivity of the halogens decreases down the group because the atoms get larger and it becomes harder for them to attract an extra electron into their outer shell. So reactivity is the property that shows a decrease.
✅ Answer: (C)

Question 23

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 8.4: Transition elements (Describe transition elements as having ions with variable oxidation numbers) & TOPIC 9.1: Properties of metals

▶️ Answer/Explanation

Both iron and lithium are metals, so they share common metallic properties like good electrical conductivity (1) and malleability (3). However, lithium is a Group I alkali metal with a relatively low melting point and forms ions with only one oxidation number (+1). Iron, as a transition element, does have a high melting point and variable oxidation numbers (+2, +3), but these are not shared properties. So the correct shared properties are 1 and 3.
✅ Answer: (A)

Question 24

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 8.5: Noble gases (Describe the Group VIII noble gases as unreactive, monatomic gases and explain this in terms of electronic configuration)

▶️ Answer/Explanation

Statement 1 is incorrect: noble gases are famous for being extremely unreactive, not reactive. Statement 2, however, is entirely correct; they all possess a stable full outer electron shell, which is exactly why they are so unreactive. Since statement 1 is wrong and statement 2 is right, the correct choice is the one that identifies this. The full outer shell leads to their unreactivity, not reactivity.
✅ Answer: (D)

Question 25

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 9.2: Uses of metals (Describe the uses of metals in terms of their physical properties, including: copper in electrical wiring because of its good electrical conductivity and ductility)

▶️ Answer/Explanation

Copper’s primary use in electrical wiring is because it has excellent electrical conductivity and is highly ductile, meaning it can be drawn into thin wires without breaking. Option B is wrong because copper and tin make bronze, not brass. Option C is wrong because overhead cables usually use aluminium due to its lower density. Option D is wrong because aluminium, not copper, is typically used for takeaway containers.
✅ Answer: (A)

Question 26

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 9.4: Reactivity series (Describe the reactions, if any, of: magnesium with steam)

▶️ Answer/Explanation

The described properties point to magnesium. It reacts with acids to produce hydrogen gas, reacts very slowly with cold water but vigorously with steam to form magnesium oxide and hydrogen, and is a good thermal conductor. Potassium would react too explosively with water and acid, while gold and silver are unreactive with water, steam, and dilute hydrochloric acid. So magnesium fits perfectly.
✅ Answer: (B)

Question 27

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

The results are shown.

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 9.4: Reactivity series (Describe the relative reactivities of metals in terms of their tendency to form positive ions, by displacement reactions)

▶️ Answer/Explanation

A tick (✓) means a reaction occurred, proving the added metal has a greater tendency to form ions (is more reactive) than the metal ion in solution. J displaces K²⁺, so J > K. L displaces K²⁺ but not J²⁺, so the order is J > L > K. M reacts with nothing, so it is the least reactive. Therefore, J has a greater tendency to form positive ions than K, which makes statement A correct. Statements B, C, and D contradict this reactivity order.
✅ Answer: (A)

Question 28

Which process is used in the extraction of iron from hematite?

(A) electrolysis
(B) precipitation
(C) reduction
(D) fractional distillation

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 9.6: Extraction of metals (Describe the extraction of iron from hematite in the blast furnace, including the reduction of iron(III) oxide by carbon monoxide)

▶️ Answer/Explanation

Hematite is mainly iron(III) oxide (Fe₂O₃). In the blast furnace, this iron ore is converted to iron through a chemical process where carbon monoxide acts as a reducing agent and removes oxygen from the iron oxide. This is a classic example of a reduction reaction, where the iron(III) oxide is reduced to metallic iron. Electrolysis is used for more reactive metals like aluminium.
✅ Answer: (C)

Question 29

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 9.5: Corrosion of metals (Describe the use of zinc in galvanising as an example of a barrier method and sacrificial protection; Explain sacrificial protection in terms of electron loss)

▶️ Answer/Explanation

Galvanising is a process where iron is coated with zinc, not silver, so statement 1 is wrong. The zinc layer acts as a physical barrier, preventing oxygen and water from reaching the iron surface, making statement 2 correct. Crucially, zinc is more reactive than iron, so it loses electrons more readily and acts as a sacrificial protector even if the coating is scratched. Thus, statements 2 and 3 are correct.
✅ Answer: (C)

Question 30

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 10.2: Fertilisers (Describe the use of NPK fertilisers to provide the elements nitrogen, phosphorus and potassium for improved plant growth)

▶️ Answer/Explanation

To supply all three NPK elements, we need a mixture containing nitrogen (N), phosphorus (P), and potassium (K). Option A has ammonium phosphate (providing N and P) and potassium chloride (providing K). Option B lacks potassium. Option C lacks potassium. Option D has nitrogen and potassium from ammonium nitrate and potassium chloride, but contains no phosphorus at all. Therefore, only Option A provides all three elements.
✅ Answer: (A)

Question 31

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 10.3: Air quality and climate (Describe how the greenhouse gases carbon dioxide and methane cause global warming)

▶️ Answer/Explanation

Greenhouse gases like carbon dioxide allow the Sun’s short-wavelength radiation to pass through, but absorb the long-wavelength (thermal) radiation emitted by the Earth’s surface. Statement 1 is correct as gases like CO₂ and methane absorb this thermal energy. Some of this absorbed energy is re-radiated back toward the Earth’s surface, effectively trapping heat. Statement 4 also describes this heat-trapping mechanism correctly, making 1 and 4 the correct pair.
✅ Answer: (B)

Question 32

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.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 10.3: Air quality and climate (Explain how oxides of nitrogen form in car engines)

▶️ Answer/Explanation

Oxides of nitrogen (NOₓ) in car exhausts are not from the fuel itself but are produced when the high temperatures inside a car engine cause the normally unreactive nitrogen (N₂) and oxygen (O₂) gases from the intake air to directly react. Fuel does not contain significant nitrogen. Catalytic converters are actually designed to remove these oxides, not create them, so the correct formation mechanism is described in option A.
✅ Answer: (A)

Question 33

The structural formula of methyl ethanoate is CH₃COOCH₃. Which compounds are structural isomers of methyl ethanoate?

1. HCOOCHCH₃
2. CHCHCOOH
3. HOCHCHCHOH

(A) 1, 2 and 3
(B) 1 and 2 only
(C) 2 and 3 only
(D) 3 only

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 11.1: Formulae, functional groups and terminology (Define structural isomers as compounds with the same molecular formula, but different structural formulae)

▶️ Answer/Explanation

Methyl ethanoate has the molecular formula C₃H₆O₂. Structural isomers must have this same formula but different atom arrangements. Skeleton 1 (an ester formate) and skeleton 2 (an acid) can both be rearranged to C₃H₆O₂. However, skeleton 3 has three oxygen atoms attached to carbons, which gives it more than 6 hydrogens for a 3-carbon chain, so it does not match the target molecular formula. Only 1 and 2 are isomers.
✅ Answer: (B)

Question 34

What is the total number of covalent bonds in one molecule of propane?

(A) 8
(B) 9
(C) 10
(D) 11

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 11.4: Alkanes (State that the bonding in alkanes is single covalent)

▶️ Answer/Explanation

Propane is an alkane with the formula C₃H₈. In a displayed formula, it has a backbone of three carbon atoms. The C–C backbone has 2 single covalent bonds. Each of the 8 hydrogen atoms is connected by a single covalent C–H bond. Adding these together gives 2 carbon–carbon bonds + 8 carbon–hydrogen bonds, for a total of 10 covalent bonds in the molecule.
✅ Answer: (C)

Question 35

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 11.6: Alcohols (Describe the advantages and disadvantages of the manufacture of ethanol by fermentation and catalytic addition of steam to ethene)

▶️ Answer/Explanation

The fermentation process is a biological process using yeast to convert sugars to ethanol and operates around 25–35 °C. This is a relatively slow batch process. On the other hand, the reaction of ethene with steam involves heating with a catalyst (phosphoric acid) at high temperature and pressure, and it is a much faster, continuous industrial process. So “slow reaction” for fermentation and “fast reaction” for ethene + steam is correct.
✅ Answer: (C)

Question 36

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 11.7: Carboxylic acids (Describe the reaction of ethanoic acid with: carbonates)

▶️ Answer/Explanation

The clues clearly point to a carboxylic acid. Alkanes and alkenes are insoluble in water and are neutral. Alcohols are soluble and neutral, but do not react with calcium carbonate to produce carbon dioxide gas. Carboxylic acids are weak acids (pH around 3), and their acidic nature allows them to react with carbonates, fizzing and releasing CO₂. Their ability to form hydrogen bonds makes smaller ones liquid and soluble.
✅ Answer: (D)

Question 37

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?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 11.8: Polymers (Deduce the structure or repeat unit of a condensation polymer from given monomers)

▶️ Answer/Explanation

The monomers shown are a diamine (with two -NH₂ groups) and a dicarboxylic acid (with two -COOH groups). During condensation polymerization, water is eliminated and amide links (-CONH-) are formed. The repeat unit must show the carbon chains connected by an amide linkage. The correct structure is the one that accurately shows the amide bond in the middle, connecting the residues of the two monomers in an alternating fashion.
✅ Answer: (B)

Question 38

Which item of apparatus is used to measure 25.0cm³ of aqueous sodium hydroxide?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 12.1: Experimental design (Name appropriate apparatus for the measurement of … volume … including: burettes, volumetric pipettes, measuring cylinders)

▶️ Answer/Explanation

To measure a fixed, precise volume of a liquid like 25.0cm³, a volumetric pipette is the most accurate choice. It is specifically designed to deliver one particular volume with high precision. A burette is used for variable, accurate dispensing typically in titrations, and a measuring cylinder is for approximate measurements. The correct apparatus shown is the pipette, which matches the description for accurately measuring exactly 25.0cm³.
✅ Answer: (D)

Question 39

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

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 12.4: Separation and purification (Describe and explain methods of separation and purification using: crystallisation)

▶️ Answer/Explanation

To obtain solid crystals of copper(II) sulfate from its aqueous solution, you need to remove the water. First, the solution is heated to evaporate some of the water, creating a saturated, hot solution. Upon cooling, the solubility decreases, and crystals of hydrated copper(II) sulfate form. While the overall technique is crystallisation, the specific method used to initiate the process from a solution is evaporation of the solvent.
✅ Answer: (C)

Question 40

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_f value.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• TOPIC 12.3: Chromatography (Interpret simple chromatograms to identify pure and impure substances)

▶️ Answer/Explanation

Since the spots are visible, a locating agent must have been used (so A is wrong). If an amino acid were insoluble, it would stay on the baseline, showing no spot there, so B isn’t the reason. A common reason for seeing fewer spots than the number of substances in a mixture is that two components happen to have exactly the same affinity for the mobile and stationary phases, giving them identical R_f values and causing them to appear as a single combined spot on the chromatogram.
✅ Answer: (D)