0620_s25_qp

Question 1

An ice cube melts.

What happens to the molecules of water in the ice cube?

(A) They evaporate.
(B) They dissolve.
(C) They gain energy.
(D) They lose energy.

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

• TOPIC 1.1: Solids, liquids and gases (Describe changes of state in terms of melting, boiling, evaporating, freezing and condensing)

▶️ Answer/Explanation

Melting is the process where a solid turns into a liquid. For an ice cube to melt, it must absorb thermal energy from its surroundings. The water molecules in the ice use this energy to overcome the forces holding them in a fixed lattice, allowing them to move more freely. Therefore, the molecules gain energy during the melting process.
✅ Answer: (C)

Question 2

A sample of a liquid, X, is heated to a temperature above its boiling point.

X is then cooled, so that it condenses and then freezes.

Which graph describes the change in temperature of X over time?

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

The sample starts as a gas (above boiling point). As it cools, the temperature drops until it reaches the boiling point, where condensation occurs — the temperature stays constant while the gas becomes liquid. After all the gas condenses, the liquid cools further until it reaches the freezing point, where the temperature again stays constant as the liquid freezes. Finally, the solid cools. This produces a cooling curve with two horizontal plateaus: one at the boiling point and one at the freezing point.
✅ Answer: (D)

Question 3

Which row gives the number of protons, electrons and neutrons in an atom of zinc?

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

• TOPIC 2.2: Atomic structure and the Periodic Table (Define proton number/atomic number as the number of protons in the nucleus of an atom; Define mass number/nucleon number as the total number of protons and neutrons in the nucleus of an atom)

▶️ Answer/Explanation

Zinc has an atomic number of 30, which tells us it has 30 protons. In a neutral atom, the number of electrons equals the number of protons, so there are also 30 electrons. The mass number of the common zinc isotope is 65. The number of neutrons is found by subtracting the atomic number from the mass number: 65 − 30 = 35 neutrons.
✅ Answer: (A)

Question 4

Which particles have the electronic configuration 2,8,8?

an argon atom, Ar
an aluminium ion, Al³⁺
a sodium ion, Na⁺
a chloride ion, Cl⁻

(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 2.2: Atomic structure and the Periodic Table (Determine the electronic configuration of elements and their ions with proton number 1 to 20, e.g. 2,8,3)

▶️ Answer/Explanation

An argon atom has atomic number 18, giving it 18 electrons arranged as 2,8,8. A chloride ion (Cl⁻) forms when a chlorine atom (17 electrons, configuration 2,8,7) gains one electron, resulting in 18 electrons with configuration 2,8,8. An aluminium ion (Al³⁺) loses 3 electrons (from 13 to 10), giving 2,8. A sodium ion (Na⁺) loses 1 electron (from 11 to 10), also giving 2,8. So only 1 and 4 are correct.
✅ Answer: (B)

Question 5

A sample of element Q has two isotopes.

Their relative masses and abundances are shown.

What is the relative atomic mass of this sample of Q to three significant figures?

(A) 240
(B) 241
(C) 242
(D) 243

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

The relative atomic mass is calculated using the weighted average formula: A_r = ((238 × 66) + (244 × 34)) / 100 = (15708 + 8296) / 100 = 24004 / 100 = 240.04. When rounded to three significant figures, this becomes 240 since the fourth digit is 4, which does not round up the zero.
✅ Answer: (A)

Question 6

Which statement about silicon(IV) oxide, SiO₂, is correct?

(A) It conducts electricity because it contains delocalised electrons.
(B) It has a giant covalent structure with each silicon atom bonded to four oxygen atoms.
(C) It is a simple covalent molecule.
(D) Its structure is similar to that of 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; Describe the similarity in properties between diamond and silicon(IV) oxide, related to their structures)

▶️ Answer/Explanation

Silicon(IV) oxide has a giant covalent structure similar to diamond, where each silicon atom is bonded to four oxygen atoms in a tetrahedral arrangement. It does not contain delocalised electrons like graphite, so it does not conduct electricity. It is not a simple covalent molecule, and its structure is quite different from graphite’s layered structure.
✅ Answer: (B)

Question 7

When 65g of zinc reacts with 32g of sulfur, 97g of zinc sulfide is produced.

When 65g of zinc reacts with 40g of sulfur, the mass of zinc sulfide produced is still 97g.

Which statement explains this observation?

(A) Some of the zinc sulfide evaporates.
(B) The reaction rate is slow.
(C) The reaction stops before it is complete.
(D) Zinc is the limiting reactant.

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., volumes of solutions and concentrations of solutions expressed in g/dm³ and mol/dm³)

▶️ Answer/Explanation

In the first reaction, 65g of zinc reacts completely with 32g of sulfur to give 97g of zinc sulfide. When we use more sulfur (40g) with the same amount of zinc, the product mass doesn’t increase. This tells us that all the zinc is used up and some sulfur is left unreacted. Zinc is therefore the limiting reactant — it limits how much product can be formed, regardless of how much extra sulfur is present.
✅ Answer: (D)

Question 8

Aluminium reacts with iron(III) oxide to form aluminium oxide and iron.

Which chemical equation for the reaction between aluminium and iron(III) oxide is correct?

(A) Al + FeO → AlO + Fe
(B) 2Al + Fe₂O → Al₂O + 2Fe
(C) Al + Fe₂O₃ → Al₂O₃ + Fe
(D) 2Al + Fe₂O₃ → Al₂O₃ + 2Fe

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

• TOPIC 3.1: Formulae (Construct symbol equations with state symbols, including ionic equations)

• TOPIC 6.4: Redox (Identify redox reactions as reactions involving gain and loss of oxygen)

▶️ Answer/Explanation

Iron(III) oxide is Fe₂O₃ (iron has a +3 charge, oxide is −2, so the formula is Fe₂O₃). Aluminium oxide is Al₂O₃. The balanced equation needs 2 aluminium atoms and 1 formula unit of iron(III) oxide to produce 1 formula unit of aluminium oxide and 2 iron atoms: 2Al + Fe₂O₃ → Al₂O₃ + 2Fe. Options A and B have incorrect formulas, and option C is not balanced.
✅ Answer: (D)

Question 9

The concentration of a solution of aqueous sodium hydroxide is 0.50 mol/dm³.

Which mass of sodium hydroxide is used to make 500cm³ of this solution?

(A) 10g
(B) 20g
(C) 40g
(D) 160g

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

• TOPIC 3.3: The mole and the Avogadro constant (Use the relationship amount of substance (mol) = mass (g) / molar mass (g/mol) to calculate mass, molar mass, etc.)

▶️ Answer/Explanation

First convert the volume to dm³: 500 cm³ = 0.5 dm³. The number of moles needed is: moles = concentration × volume = 0.50 × 0.5 = 0.25 mol. The molar mass of NaOH is 23 + 16 + 1 = 40 g/mol. So the mass required is: mass = moles × molar mass = 0.25 × 40 = 10 g.
✅ Answer: (A)

Question 10

Molten zinc oxide is electrolysed using inert electrodes.

Which row identifies the product at each electrode?

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

• TOPIC 4.1: Electrolysis (Predict the identity of the products at each electrode for the electrolysis of a binary compound in the molten state)

▶️ Answer/Explanation

In molten zinc oxide (ZnO), the ions are Zn²⁺ and O²⁻. During electrolysis, positive zinc ions move to the cathode (negative electrode) and gain electrons to form zinc metal. Negative oxide ions move to the anode (positive electrode) and lose electrons to form oxygen gas. So oxygen is produced at the anode and zinc at the cathode.
✅ Answer: (C)

Question 11

Dilute aqueous sodium chloride is electrolysed using platinum electrodes. What is the half-equation for the reaction at the cathode?

(A) 2H⁺ + 2e⁻ → H₂
(B) Na⁺ + e⁻ → Na
(C) 2Cl⁻ → Cl₂ + 2e⁻
(D) 4OH⁻ → 2H₂O + O₂ + 4e⁻

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

• TOPIC 4.1: Electrolysis (Identify the products formed at the electrodes and describe the observations made during the electrolysis of concentrated aqueous sodium chloride)

▶️ Answer/Explanation

At the cathode, reduction occurs (gain of electrons). Although both Na⁺ and H⁺ ions are present in the solution, hydrogen ions are discharged in preference because hydrogen is less reactive than sodium. The H⁺ ions from water gain electrons to form hydrogen gas: 2H⁺ + 2e⁻ → H₂.
✅ Answer: (A)

Question 12

Hydrogen-oxygen fuel cells can be used to power vehicles.

Which statement about hydrogen-oxygen fuel cells is correct?

(A) The equation for the overall reaction is H₂ + O₂ → H₂O₂
(B) The only chemical products are water and carbon dioxide.
(C) Chemical energy in the fuel is converted into electrical energy.
(D) The hydrogen used in hydrogen-oxygen fuel cells is a fossil fuel.

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

In a hydrogen-oxygen fuel cell, hydrogen and oxygen react electrochemically to produce water and electricity. The key feature is that chemical energy is converted directly into electrical energy. The overall reaction is 2H₂ + O₂ → 2H₂O, not forming hydrogen peroxide. Water is the only chemical product (no carbon dioxide). Hydrogen is not a fossil fuel, though it may be produced from fossil fuels.
✅ Answer: (C)

Question 13

A reaction pathway diagram is shown.

Which row identifies the type of reaction and how the temperature of the surroundings changes during the 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; State that an endothermic reaction takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings)

▶️ Answer/Explanation

From the diagram, the products are at a higher energy level than the reactants. This means the reaction absorbs energy from the surroundings — it is endothermic. When a reaction absorbs thermal energy from its surroundings, the surroundings lose energy and their temperature decreases. So the reaction is endothermic and the surroundings’ temperature decreases.
✅ Answer: (A)

Question 14

The average bond energy for the C-H bond is 413 kJ/mol. What is the enthalpy change when 1.0 mol of methane molecules is formed from carbon and hydrogen atoms?

(A) −1652 kJ
(B) −413 kJ
(C) +413 kJ
(D) +1652 kJ

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

• TOPIC 5.1: Exothermic and endothermic reactions (State that bond breaking is an endothermic process and bond making is an exothermic process and explain the enthalpy change of a reaction in terms of bond breaking and bond making; Calculate the enthalpy change of a reaction using bond energies)

▶️ Answer/Explanation

Methane (CH₄) has four C-H bonds. When bonds are formed, energy is released — this is an exothermic process. The total energy released when forming four C-H bonds is 4 × 413 = 1652 kJ per mole of methane. Since forming bonds releases energy, the enthalpy change is negative: ΔH = −1652 kJ/mol.
✅ Answer: (A)

Question 15

Which statement describes the effect of adding a catalyst to a chemical reaction?

(A) The activation energy, E_a, of the reaction is increased.
(B) The enthalpy change, ΔH, of the reaction stays unchanged.
(C) The frequency of collisions between the particles is decreased.
(D) The kinetic energy of the particles is increased.

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

• TOPIC 6.2: Rate of reaction (State that a catalyst decreases the activation energy, E_a of a reaction; State that a catalyst increases the rate of a reaction and is unchanged at the end of a reaction)

▶️ Answer/Explanation

A catalyst provides an alternative reaction pathway with a lower activation energy, so option A is wrong. The enthalpy change (ΔH) depends only on the energy difference between reactants and products, which is not affected by a catalyst, so option B is correct. A catalyst does not change collision frequency or the kinetic energy of particles directly.
✅ Answer: (B)

Question 16

Which row describes the conditions used in the manufacture of sulfuric acid by the Contact process?

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

• TOPIC 6.3: Reversible reactions and equilibrium (State the typical conditions for the conversion of sulfur dioxide to sulfur trioxide in the Contact process as 450°C, 200 kPa / 2 atm and a vanadium(V) oxide catalyst)

▶️ Answer/Explanation

In the Contact process, the conversion of SO₂ to SO₃ uses a vanadium(V) oxide (V₂O₅) catalyst, not iron. The reaction is exothermic, so a lower temperature would give a higher yield, but to achieve a reasonable rate, a temperature of about 450°C (considered relatively high) is used. The pressure used is low (around 2 atm). So the correct combination is vanadium(V) oxide, low pressure, high temperature.
✅ Answer: (D)

Question 17

Which equations show the underlined species acting as a reducing agent?

Fe₂O₃ + 3CO → 2Fe + 3CO₂
Fe + CuSO₄ → FeSO₄ + Cu
5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O
Fe(OH)₂ + H₂SO₄ → FeSO₄ + 2H₂O

(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 6.4: Redox (Define a reducing agent as a substance that reduces another substance and is itself oxidised; Identify oxidising agents and reducing agents in redox reactions)

▶️ Answer/Explanation

A reducing agent is itself oxidised (loses electrons). In equation 2, Fe goes from oxidation state 0 to +2, so it loses electrons and acts as a reducing agent. In equation 3, Fe²⁺ goes to Fe³⁺, also losing an electron, so it is a reducing agent. In equation 1, the underlined species is Fe₂O₃ which is reduced (gains electrons), and equation 4 is an acid-base reaction, not redox.
✅ Answer: (C)

Question 18

A farmer incorrectly adds two substances to the soil at the same time.

They react together to form a gas which turns damp red litmus paper blue.

What are the two substances?

(A) a basic oxide and a potassium salt
(B) a basic oxide and an ammonium salt
(C) an acidic oxide and a potassium salt
(D) an acidic oxide and an ammonium salt

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

• TOPIC 7.1: The characteristic properties of acids and bases (Describe the characteristic properties of bases in terms of their reactions with ammonium salts)

• TOPIC 12.5: Identification of ions and gases (Describe tests to identify the gases: ammonia, NH₃, using damp red litmus paper)

▶️ Answer/Explanation

A gas that turns damp red litmus paper blue is ammonia (NH₃), which is an alkaline gas. Ammonia is produced when a base (such as a basic oxide) reacts with an ammonium salt. For example, calcium oxide (a basic oxide) reacts with ammonium chloride to produce ammonia, calcium chloride, and water. The other combinations would not produce ammonia gas.
✅ Answer: (B)

Question 19

Which row shows the equations for the dissociation of hydrochloric acid and of ethanoic acid in aqueous solution?

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

• TOPIC 7.1: The characteristic properties of acids and bases (State that hydrochloric acid is a strong acid, as shown by the symbol equation, HCl(aq) → H⁺(aq) + Cl⁻(aq); State that ethanoic acid is a weak acid, as shown by the symbol equation, CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻(aq))

▶️ Answer/Explanation

Hydrochloric acid is a strong acid, meaning it completely dissociates into ions in aqueous solution. This is shown by a single forward arrow (→). Ethanoic acid is a weak acid, meaning it only partially dissociates and the reaction is reversible, shown by the equilibrium arrow (⇌). Option A correctly shows complete dissociation for HCl and equilibrium for CH₃COOH.
✅ Answer: (A)

Question 20

Which three oxides are all acidic?

(A) CaO, NO₂, SO₂
(B) CaO, CO₂, Na₂O
(C) CO₂, NO₂, SO₂
(D) CO₂, Na₂O, SO₂

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

• TOPIC 7.2: Oxides (Classify oxides as acidic, including SO₂ and CO₂ or basic, including CuO and CaO, related to metallic and non-metallic character)

▶️ Answer/Explanation

Acidic oxides are typically oxides of non-metals. CO₂ (carbon dioxide), NO₂ (nitrogen dioxide), and SO₂ (sulfur dioxide) are all non-metal oxides that form acids when dissolved in water. CaO and Na₂O are metal oxides, which are basic oxides. Any option containing a metal oxide is incorrect, leaving only option C as the correct set of three acidic oxides.
✅ Answer: (C)

Question 21

The table shows some properties of noble gases.

Which row predicts the density and the boiling point of krypton?

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

Going down Group VIII, both density and boiling point increase due to increasing atomic mass and stronger intermolecular forces. Krypton is below argon, so its density must be higher than argon’s (1.8 g/dm³) and its boiling point higher than argon’s (−186°C). Option C shows a density of 3.8 (higher) and a boiling point of −153°C (higher), fitting the trend. The other options either show lower values or values that don’t follow the gradual trend.
✅ Answer: (C)

Question 22

Sodium is a Group I metal.

What is a physical property of sodium?

(A) non-conductor of electricity
(B) high melting point
(C) high density
(D) malleable

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

• TOPIC 8.2: Group I properties (Describe the Group I alkali metals, lithium, sodium and potassium, as relatively soft metals with general trends down the group)

• TOPIC 9.1: Properties of metals (Compare the general physical properties of metals and non-metals, including: malleability and ductility)

▶️ Answer/Explanation

Sodium is a metal, so it conducts electricity well (eliminating A). Group I metals are known for having relatively low melting points and low densities — sodium melts at about 98°C and floats on water (eliminating B and C). Sodium is very soft and can be cut with a knife, meaning it is malleable — it can be hammered or pressed into different shapes without breaking.
✅ Answer: (D)

Question 23

Tennessee (atomic number 117) is a manufactured element that is below astatine in Group VII of the Periodic Table.

What is the expected state of tennessine at room temperature and pressure?

(A) a diatomic gas
(B) a liquid
(C) a monatomic gas
(D) a solid

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

• TOPIC 8.3: Group VII properties (Predict the properties of other elements in Group VII, given information about the elements)

▶️ Answer/Explanation

In Group VII, melting and boiling points increase going down the group. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at room temperature. Astatine, below iodine, is expected to be a solid. Tennessine is even further down the group, so it will have an even higher melting and boiling point, making it a solid at room temperature and pressure.
✅ Answer: (D)

Question 24

When chlorine is bubbled into aqueous sodium bromide, a displacement reaction occurs.

Which description of this reaction is correct?

(A) Chloride displaces bromide.
(B) Chlorine displaces bromine.
(C) Chloride displaces bromine.
(D) Chlorine displaces bromide.

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

• TOPIC 8.3: Group VII properties (Describe and explain the displacement reactions of halogens with other halide ions)

▶️ Answer/Explanation

Chlorine is more reactive than bromine. When chlorine gas is bubbled into a solution of sodium bromide, the chlorine takes electrons from the bromide ions, causing them to become bromine molecules. The reaction is: Cl₂ + 2NaBr → 2NaCl + Br₂. So chlorine (the element) displaces bromine (the element) from the compound, not “chloride” which is already an ion.
✅ Answer: (B)

Question 25

Brass is an alloy of copper.

Which statement about brass or copper is correct?

(A) Brass does not conduct electricity because it is a compound.
(B) Copper conducts electricity because its atoms are free to move.
(C) Brass is harder than copper because its layers of atoms cannot easily slide over each other.
(D) Copper is stronger than brass because it is a pure metal.

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

• TOPIC 9.3: Alloys and their properties (Explain in terms of structure how alloys can be harder and stronger than the pure metals because the different sized atoms in alloys mean the layers can no longer slide over each other)

▶️ Answer/Explanation

Brass is an alloy of copper and zinc (a mixture, not a compound), and it still conducts electricity, so A is wrong. Copper conducts electricity because of delocalised electrons, not because its atoms are free to move, so B is wrong. In pure copper, atoms are arranged in regular layers that can slide over each other easily. In brass, zinc atoms of different size disrupt these layers, preventing easy sliding, making brass harder and stronger than pure copper. This makes C correct and D wrong.
✅ Answer: (C)

Question 26

The ionic equations for some reactions between metals and aqueous metal ions are shown.

Cu + 2Ag⁺ → 2Ag + Cu²⁺
Mg + Zn²⁺ → Mg²⁺ + Zn
Zn + Cu²⁺ → Cu + Zn²⁺
Sn + Cu²⁺ → Sn²⁺ + Cu

Which further information can be used to place copper, magnesium, silver, tin and zinc in order of their reactivity?

(A) Zinc reacts with Sn²⁺ ions.
(B) Copper does not react with Sn²⁺ ions.
(C) Magnesium reacts with Cu²⁺ ions.
(D) Magnesium reacts with Ag⁺ ions.

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, if any, with the aqueous ions of magnesium, zinc, iron, copper and silver)

▶️ Answer/Explanation

From the given equations, we know: Mg > Zn, Zn > Cu, Sn > Cu, and Cu > Ag. What we don’t know is the relative reactivity of Zn and Sn. Option A tells us zinc reacts with Sn²⁺ ions, meaning Zn > Sn. This gives the complete order: Mg > Zn > Sn > Cu > Ag. The other options provide information already known or don’t help complete the specific missing link in the reactivity chain.
✅ Answer: (A)

Question 27

Zinc is used to galvanise iron to prevent it from rusting.

Which statements are correct?

Galvanising is an example of a barrier method.
If the zinc is scratched, the iron will rust very quickly.
Galvanising is an example of sacrificial protection.
Zinc is more reactive than iron and so accepts electrons more readily.

(A) 1, 2 and 4
(B) 1 and 3
(C) 2, 3 and 4
(D) 2 and 3 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 the reactivity series and in terms of electron loss)

▶️ Answer/Explanation

Galvanising is the process of coating iron with a layer of zinc. This zinc layer acts as a barrier, preventing oxygen and water from reaching the iron (Statement 1 is correct). If the zinc is scratched, the iron does NOT rust quickly because zinc is more reactive and corrodes instead, acting as sacrificial protection (Statement 3 is correct, Statement 2 is wrong). Statement 4 is incorrect because zinc is more reactive and DONATES electrons more readily (not accepts them).
✅ Answer: (B)

Question 28

Which equation represents a reaction that occurs in a blast furnace during the extraction of iron from hematite?

(A) Ca + CO₂ → CaO + CO
(B) Fe₂O₃ + 3Ca → 2Fe + 3CaO
(C) Ca(OH)₂ → CaO + H₂O
(D) Fe₂O₃ + 3CO → 2Fe + 3CO₂

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

• TOPIC 9.6: Extraction of metals (State the symbol equations for the extraction of iron from hematite: Fe₂O₃ + 3CO → 2Fe + 3CO₂)

▶️ Answer/Explanation

In the blast furnace, iron is extracted from hematite (Fe₂O₃) by reduction using carbon monoxide gas. The carbon monoxide is produced from coke within the furnace. The key reduction reaction is: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Options A and B involve elemental calcium, which is not present in the blast furnace (limestone, CaCO₃, is used instead). Option C shows the decomposition of calcium hydroxide, which does not occur in the blast furnace.
✅ Answer: (D)

Question 29

Water is added separately to anhydrous copper(II) sulfate and to anhydrous cobalt(II) chloride. Which row shows the colour changes?

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

• TOPIC 10.1: Water (Describe chemical tests for the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate)

• TOPIC 6.3: Reversible reactions and equilibrium (Describe how changing the conditions can change the direction of a reversible reaction for: the effect of heat on hydrated compounds; the addition of water to anhydrous compounds limited to copper(II) sulfate and cobalt(II) chloride)

▶️ Answer/Explanation

Anhydrous copper(II) sulfate is a white powder. When water is added, it turns blue as it forms hydrated copper(II) sulfate (CuSO₄·5H₂O). Anhydrous cobalt(II) chloride is blue. When water is added, it turns pink as it forms hydrated cobalt(II) chloride (CoCl₂·6H₂O). So the colour changes are: white to blue for copper sulfate, and blue to pink for cobalt chloride.
✅ Answer: (C)

Question 30

Gases which cause acid rain form in car engines. These gases can be removed using a catalytic converter.

Which equation represents the removal of one of these gases using a catalytic converter?

(A) CO₂ + C → 2CO
(B) 2CO + 2NO → 2CO₂ + N₂
(C) N₂ + 2O₂ → 2NO₂
(D) 2NO + O₂ → 2NO₂

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

• TOPIC 10.3: Air quality and climate (Explain how oxides of nitrogen form in car engines and describe their removal by catalytic converters, e.g. 2CO + 2NO → 2CO₂ + N₂)

▶️ Answer/Explanation

Catalytic converters remove harmful pollutants from car exhaust gases. Nitrogen monoxide (NO) and carbon monoxide (CO) are two such pollutants. In the catalytic converter, they react together to form harmless nitrogen gas and carbon dioxide: 2CO + 2NO → 2CO₂ + N₂. Options C and D show the formation of nitrogen oxides, not their removal, and option A shows a reaction that would require extremely high temperatures.
✅ Answer: (B)

Question 31

Which statements about carbon dioxide are correct?

Carbon dioxide absorbs thermal energy from the Earth.
Carbon dioxide increases the thermal energy loss to space.
The level of carbon dioxide in the atmosphere has increased due to the burning of fossil fuels.
Carbon dioxide is the only gas that causes global warming.

(A) 1 and 2
(B) 1 and 3
(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, limited to: the absorption, reflection and emission of thermal energy; reducing thermal energy loss to space)

▶️ Answer/Explanation

Carbon dioxide is a greenhouse gas that absorbs infrared radiation (thermal energy) emitted from the Earth’s surface, trapping heat in the atmosphere (Statement 1 is correct). This process actually REDUCES thermal energy loss to space, so Statement 2 is incorrect. The burning of fossil fuels has significantly increased atmospheric CO₂ levels (Statement 3 is correct). CO₂ is not the only greenhouse gas — methane, water vapour, and others also contribute to global warming, so Statement 4 is incorrect.
✅ Answer: (B)

Question 32

What is the structural formula of butan-2-ol?

(A) CH₃CH₂CH₂OH
(B) CH₃CH(OH)CH₃
(C) CH₃CH₂CH₂CH₂OH
(D) CH₃CH₂CH(OH)CH₃

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

• TOPIC 11.2: Naming organic compounds (Name and draw the structural and displayed formulae of unbranched alcohols, including propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol)

▶️ Answer/Explanation

“Butan-” indicates a four-carbon chain, and “-2-ol” means the OH group is attached to the second carbon atom. CH₃CH₂CH(OH)CH₃ shows four carbon atoms with the OH group on carbon 2, which is butan-2-ol. Option A is propan-1-ol (3 carbons), option B is propan-2-ol (3 carbons), and option C is butan-1-ol (OH on carbon 1).
✅ Answer: (D)

Question 33

Methanol reacts with ethanoic acid to form an ester.

What is the displayed formula for this ester?

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

• TOPIC 11.7: Carboxylic acids (Describe the reaction of a carboxylic acid with an alcohol using an acid catalyst to form an ester)

• TOPIC 11.2: Naming organic compounds (Name and draw the displayed formulae of the unbranched esters which can be made from unbranched alcohols and carboxylic acids, each containing up to four carbon atoms)

▶️ Answer/Explanation

The reaction between methanol (CH₃OH) and ethanoic acid (CH₃COOH) produces the ester methyl ethanoate (CH₃COOCH₃) and water. The ester functional group is −COO−. The displayed formula must show the carbon-oxygen double bond (C=O) and the C−O single bond connecting the methyl group from the methanol. The correct structure has the ester linkage with the carbonyl group attached to a methyl group on one side and a methoxy group on the other.
✅ Answer: (C)

Question 34

Petroleum can be separated into useful fractions by fractional distillation.

Which row shows a correct use of the named fraction?

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

• TOPIC 11.3: Fuels (Name the uses of the fractions as: refinery gas fraction for gas used in heating and cooking; naphtha fraction as a chemical feedstock; kerosene/paraffin fraction for jet fuel; bitumen fraction for making roads)

▶️ Answer/Explanation

Kerosene (also called paraffin) is correctly used as jet fuel. Bitumen is used for road surfacing, not as a lubricant. Naphtha is used as a chemical feedstock (to make chemicals), not for home heating. Refinery gas is used as a fuel for heating and cooking, not for making chemicals. So only the pairing of kerosene with jet fuel in option C is completely correct.
✅ Answer: (C)

Question 35

Ethane reacts with chlorine in the presence of ultraviolet light.

Which products are formed?

(A) ClCH₂CH₂Cl and H₂
(B) 2CHCl and H₂
(C) C₂H₅Cl and HCl
(D) CH=CH₂ and 2HCl

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• TOPIC 11.4: Alkanes (Describe the substitution reaction of alkanes with chlorine as a photochemical reaction, with ultraviolet light providing the activation energy, $E_{\mathrm{a}}$, and draw the structural or displayed formulae of the products, limited to monosubstitution)

▶️ Answer/Explanation

Ethane ($\mathrm{C_2H_6}$) reacts with chlorine in the presence of UV light in a substitution reaction. One hydrogen atom from ethane is replaced by a chlorine atom, producing chloroethane ($\mathrm{C_2H_5Cl}$) and hydrogen chloride (HCl). This is a substitution, not an addition reaction, so the product retains a single bond between the carbon atoms. The other hydrogen and chlorine atom combine to form HCl, not $\mathrm{H_2}$ gas.
✅ Answer: (C)

Question 36

Ethanol can be made by the fermentation of aqueous glucose and by the catalytic addition of steam to ethene.

What are two advantages of making ethanol by the catalytic addition of steam to ethene rather than by the fermentation of aqueous glucose?

(A) faster reaction and renewable raw materials
(B) purer product and faster reaction
(C) renewable raw materials and continuous process
(D) uses more energy and forms a purer product

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 catalytic addition of steam to ethene ($\mathrm{C_2H_4 + H_2O \rightarrow C_2H_5OH}$) is a fast, continuous industrial process that produces very pure ethanol. Fermentation is slow and produces a dilute aqueous solution of ethanol that requires further purification. However, fermentation uses renewable resources (glucose from plants), while ethene comes from petroleum (non-renewable). So the two advantages of the steam/ethene method are that it yields a purer product and is faster.
✅ Answer: (B)

Question 37

The structure of a polymer repeat unit is shown.

Which pair of monomers is used to make this polymer?

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 and vice versa, limited to: polyamides from a dicarboxylic acid and a diamine)

▶️ Answer/Explanation

The polymer repeat unit contains an amide linkage (-CONH-), indicating it is a polyamide. The structure shows a repeating pattern with carbon chains of specific lengths from two monomers: a dicarboxylic acid and a diamine. By examining the repeat unit, we can see the diamine portion has 6 carbons and the diacid portion has 6 carbons. This matches the structure of nylon-6,6, formed from hexane-1,6-diamine and hexanedioic acid, which corresponds to option B.
✅ Answer: (B)

Question 38

Which item of apparatus is used to measure exactly $26.3cm^3$ of a liquid?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• TOPIC 12.1: Experimental design (Name appropriate apparatus for the measurement of time, temperature, mass and volume, including: burettes, volumetric pipettes, measuring cylinders)

▶️ Answer/Explanation

To measure exactly $26.3 \mathrm{cm^3}$ of a liquid, you need a burette. A burette is graduated in $0.1 \mathrm{cm^3}$ divisions and can deliver variable volumes of liquid with high precision. A measuring cylinder can only measure approximate volumes and cannot accurately deliver a volume to the decimal point. A pipette measures a fixed volume (like $25.0 \mathrm{cm^3}$). The burette (identified as A in the image) is the correct apparatus.
✅ Answer: (A)

Question 39

A mixture containing an aqueous salt and an insoluble salt is filtered.

Which row describes X and Y?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• TOPIC 12.1: Experimental design (Describe a: residue as a substance that remains after evaporation, distillation, filtration or any similar process; filtrate as a liquid or solution that has passed through a filter)

▶️ Answer/Explanation

During filtration, the mixture is poured through filter paper. The solid (insoluble salt) cannot pass through and is caught in the filter paper — this is the residue (X). The liquid (aqueous salt solution) passes through the filter paper and collects in the flask below — this is the filtrate (Y). So X is the residue and Y is the filtrate.
✅ Answer: (D)

Question 40

Pure ethanol has a melting point of $-114^{\circ}C$ and a boiling point of $78^{\circ}C$. What are the melting and boiling points of a sample of ethanol with glucose dissolved in it?

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• TOPIC 12.4: Separation and purification (Identify substances and assess their purity using melting point and boiling point information)

▶️ Answer/Explanation

When an impurity (like glucose) is dissolved in a pure solvent (like ethanol), the melting point of the solution decreases and the boiling point increases. This is due to colligative properties. Pure ethanol melts at -114°C, so with glucose dissolved, it will melt at a lower temperature (like -116°C). Pure ethanol boils at 78°C, so with an impurity, it will boil at a higher temperature (like 79°C). Option B correctly shows both effects.
✅ Answer: (B)