0620_s24_qp_13-hina

Question 1

Which two processes are required to change ice into steam?
A boiling and melting
B boiling and freezing
C condensing and melting
D condensing and freezing

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 (Core)

▶️ Answer/Explanation

To change ice (solid water) into steam (gaseous water), the ice must first be melted into liquid water (melting), and then the liquid water must be boiled to become steam (boiling). Freezing and condensing are processes that move in the opposite direction (towards liquid or solid). Therefore, the correct pair of processes is melting followed by boiling.
✅ Answer: (A)

Question 2

Which row describes how the volume of a gas changes when the temperature increases, or when the pressure increases?

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 (Core); Explain, in terms of kinetic particle theory, the effects of temperature and pressure on the volume of a gas (Supplement)

▶️ Answer/Explanation

According to kinetic particle theory, increasing temperature gives gas particles more kinetic energy, causing them to collide harder and more often, so volume increases (if pressure is constant). Increasing pressure (by applying force) compresses the gas, forcing particles closer together, so volume decreases (if temperature is constant). Row C correctly shows volume increases with temperature and decreases with pressure.
✅ Answer: C

Question 3

Four substances in a mixture are listed.
• calcium nitrate
• iron(II) sulfate
• oxygen
• water
Which statement describes the mixture?
A It contains 6 elements.
B It contains 3 compounds and 1 element.
C It contains 2 compounds and 2 elements.
D It contains 4 compounds.

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

• Topic 2.1: Elements, compounds and mixtures — Describe the differences between elements, compounds and mixtures (Core)

▶️ Answer/Explanation

Calcium nitrate (Ca(NO₃)₂), iron(II) sulfate (FeSO₄), and water (H₂O) are compounds because they contain two or more different elements chemically bonded. Oxygen (O₂) is an element (a diatomic molecule). The mixture therefore contains three compounds and one element. Option A is incorrect because the mixture contains a total of 5 distinct elements (Ca, N, O, Fe, S, H), not 6. Options C and D are incorrect as they miscount the number of compounds and elements.
✅ Answer: (B)

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Question 4

An ion is represented by the symbol \( _{8}^{18}\textrm{O}^{2-}\). Which statements about this ion are correct?

1 The ion contains 8 electrons.
2 The ion contains 10 neutrons.
3 The ion contains 8 protons.

A 1 and 2

B 1 and 3

C 2 only

D 2 and 3

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

• Topic 2.2: Atomic structure and the Periodic Table — State the relative charges and relative masses of a proton, a neutron and an electron; 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.
• Topic 2.3: Isotopes — Interpret and use symbols for atoms and ions.

▶️ Answer/Explanation

The bottom number (8) is the atomic number, which equals the number of protons (statement 3 is correct). The top number (18) is the mass number (protons + neutrons), so neutrons = 18 − 8 = 10 (statement 2 is correct). The 2− charge means it has gained 2 electrons; a neutral oxygen atom has 8 electrons, so this ion has 8 + 2 = 10 electrons, not 8 (statement 1 is incorrect). Therefore, statements 2 and 3 are correct, which corresponds to option D.
✅ Answer: D

Question 5

What is the meaning of the term nucleon number?
A the number of neutrons in the nucleus of an atom
B the number of protons in the nucleus of an atom
C the total number of protons and electrons in the nucleus of an atom
D the total number of protons and neutrons in the nucleus of an atom

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

• Topic 2.2: Atomic structure and the Periodic Table — Define mass number/nucleon number as the total number of protons and neutrons in the nucleus of an atom (Core)

▶️ Answer/Explanation

The term “nucleon” refers to the particles found inside the nucleus of an atom, which are protons and neutrons. Therefore, the nucleon number (also known as the mass number) is the sum of the number of protons and the number of neutrons. This is a fundamental definition of atomic structure.
✅ Answer: (D) the total number of protons and neutrons in the nucleus of an atom

Question 6

Which row describes the electrical conductivity of covalent and ionic compounds when solid and when molten?

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

• Topic 2.5: Simple molecules and covalent bonds — Describe in terms of structure and bonding the properties of simple molecular compounds: low melting points and boiling points, poor electrical conductivity (Core)
• Topic 2.4: Ions and ionic bonds — Describe the properties of ionic compounds: high melting points and boiling points, good electrical conductivity when aqueous or molten and poor when solid (Core)

▶️ Answer/Explanation

Covalent compounds (simple molecular) have no mobile charged particles when solid or molten because they consist of neutral molecules with weak intermolecular forces, so they do not conduct electricity in either state. Ionic compounds have fixed ions in a lattice when solid (no conduction), but when molten the ions become free to move and carry charge. Therefore the correct row is the one showing covalent: no / no and ionic: no / yes.
✅ Answer: (A)

Question 7

Which statement about the bonding in sodium chloride is correct?
A The sodium and chlorine atoms share pairs of electrons.
B The chlorine atoms give electrons to the sodium atoms to form positive and negative ions.
C There is covalent bonding between sodium and chlorine.
D The positive and negative ions have noble gas electronic configurations.

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

• Topic 2.4: Ions and ionic bonds — Describe the formation of positive ions, known as cations, and negative ions, known as anions (Core); Describe the formation of ionic bonds between elements from Group I and Group VII, including the use of dot- and- cross diagrams (Core); Describe the giant lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions (Supplement)

▶️ Answer/Explanation

In sodium chloride (NaCl), sodium atoms lose one electron to form Na⁺ ions and chlorine atoms gain one electron to form Cl⁻ ions. Both resulting ions achieve stable noble gas electronic configurations (Na⁺ like neon, Cl⁻ like argon). Option A describes covalent bonding (sharing), option B has the direction of electron transfer wrong (chlorine does not give electrons to sodium), and option C is false because NaCl is ionic, not covalent.
✅ Answer: D

Question 8

The diagram shows the arrangement of carbon atoms in a giant covalent structure.

Which row identifies the substance and describes a use of this substance?

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

• Topic 2.6: Giant covalent structures — Describe the giant covalent structures of graphite and diamond; Relate the structures and bonding of graphite and diamond to their uses (Core)

▶️ Answer/Explanation

The diagram shows a tetrahedral arrangement of carbon atoms where each carbon is bonded to four others, which is the structure of diamond, not graphite. Diamond is extremely hard due to its strong covalent network, making it suitable for cutting tools, whereas graphite is soft and conducts electricity. Therefore, the correct row identifies diamond with the use in cutting tools (Row B).
✅ Answer: (B)

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Question 9

Which statement is the correct definition for molecular formula?
A an atom or group of atoms that determine the chemical properties of a compound
B a structure which shows all the atoms and all the bonds in a compound
C the number and arrangement of different atoms in one gram of a compound
D the number and type of different atoms in one molecule of a compound

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

• Topic 3.1: Formulae — Define the molecular formula of a compound as the number and type of different atoms in one molecule (Core)

▶️ Answer/Explanation

A molecular formula tells you exactly how many atoms of each element are present in a single molecule of a compound, but it does not show the arrangement or bonding (that is a displayed formula). It also does not refer to one gram of the compound. Option A describes a functional group, and Option B describes a displayed or structural formula. Therefore, the correct definition is the number and type of different atoms in one molecule of a compound.
✅ Answer: (D)

Question 10

A compound, T, has the formula \(CH_3Cl\). Three statements about this compound are listed.
1 A molecule of the compound contains five atoms.
2 A molecule of the compound contains five different elements.
3 The relative molecular mass of the compound is 50.5.
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 3.1: Formulae — Define the molecular formula of a compound as the number and type of different atoms in one molecule (Core); Construct word equations and symbol equations (Core).
• Topic 3.2: Relative masses of atoms and molecules — Define relative molecular mass, \(M_{r}\) as the sum of the relative atomic masses (Core).
• Topic 2.2: Atomic structure and the Periodic Table — Interpret and use symbols for atoms and ions (Core).

▶️ Answer/Explanation

Statement 1 is correct because one molecule of CH₃Cl contains 1 carbon, 3 hydrogen, and 1 chlorine atom, totalling 5 atoms. Statement 2 is incorrect as the compound contains only three different elements (C, H, Cl), not five. Statement 3 is correct: the relative molecular mass (M_r) is 12 + (3×1) + 35.5 = 50.5. Hence, statements 1 and 3 are correct.
✅ Answer: (C) 1 and 3 only

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Question 11

Iron water taps are often electroplated with a layer of chromium. Which statements explain why iron water taps are electroplated?

1 It improves the appearance of the taps.
2 It increases the strength of the taps.
3 It prevents the corrosion of the taps.
4 It improves the electrical conductivity of the taps.

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 4.1: Electrolysis — State that metal objects are electroplated to improve their appearance and resistance to corrosion (Core)

▶️ Answer/Explanation

Electroplating serves two main purposes on iron taps: a decorative finish and corrosion protection. Chromium provides a shiny, attractive surface (improving appearance) and acts as a barrier layer that prevents oxygen and water from reaching the iron, thus stopping rust (corrosion). It does not significantly increase the strength of the taps nor improve their electrical conductivity, as taps are not used for conducting electricity.
✅ Answer: (A) 1 and 3

Question 12

Molten caesium bromide 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 — Identify the products formed at the electrodes and describe the observations made during the electrolysis of molten lead(II) bromide (Core); Predict the identity of the products at each electrode for the electrolysis of a binary compound in the molten state (Core)

▶️ Answer/Explanation

In the electrolysis of molten caesium bromide (CsBr), the compound dissociates into Cs⁺ and Br⁻ ions. Cs⁺ ions are attracted to the negative cathode, where each gains one electron to form caesium metal. Br⁻ ions are attracted to the positive anode, where each loses one electron to form bromine molecules (Br₂). Therefore, the correct row shows caesium at the cathode and bromine at the anode.
✅ Answer: A

Question 13

Which equation represents the overall reaction in a hydrogen–oxygen fuel cell?
A \(4H + O_2 → 2H_2O\)
B \(2H_2 + O_2 → 2H_2O\)
C \(H_2 + O_2 → H_2O\)
D \(2H + O → H_2O\)

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 (Core).

▶️ Answer/Explanation

A hydrogen–oxygen fuel cell combines hydrogen gas and oxygen gas to produce electrical energy and water. The overall reaction must balance both hydrogen and oxygen atoms: each water molecule contains two hydrogen atoms, so two H₂ molecules (four H atoms total) react with one O₂ molecule to produce two H₂O molecules. Options A and D show atomic hydrogen (H or 2H), which is not the fuel gas; option C is unbalanced. Therefore, the correct balanced equation is 2H₂ + O₂ → 2H₂O.
✅ Answer: (B)

Question 14

Which statements about endothermic reactions are correct?

1 The energy of the products is greater than the energy of the reactants.
2 The energy of the reactants is greater than the energy of the products.
3 The temperature of the surroundings increases during the reaction.
4 The temperature of the surroundings decreases during the reaction.

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 5.1: Exothermic and endothermic reactions — State that an endothermic reaction takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings (Core); Interpret reaction pathway diagrams showing exothermic and endothermic reactions (Core)

▶️ Answer/Explanation

In an endothermic reaction, thermal energy is absorbed from the surroundings, causing the temperature of the surroundings to decrease (statement 4 correct, statement 3 incorrect). This absorbed energy increases the chemical potential energy of the system, meaning the products have a higher total energy than the reactants (statement 1 correct, statement 2 incorrect). Therefore, the correct combination is statements 1 and 4.
✅ Answer: (B)

Question 15

Which process is a physical change?
A firework exploding
B burning wood
C chocolate melting
D iron rusting

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

• Topic 6.1: Physical and chemical changes — Identify physical and chemical changes, and describe the differences between them (Core)

▶️ Answer/Explanation

A physical change is a change of state or appearance that does not form a new chemical substance. Melting chocolate is a reversible change of state from solid to liquid where the chemical composition (fats and cocoa solids) remains unchanged. In contrast, exploding fireworks, burning wood, and iron rusting are all chemical changes because they produce new substances (gases, ash, and hydrated iron(III) oxide respectively) through chemical reactions.
✅ Answer: (C) chocolate melting

Question 16

Magnesium reacts with dilute hydrochloric acid, HCl, to produce hydrogen gas. Which row identifies the reaction conditions that give the fastest rate of reaction?

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

• Topic 6.2: Rate of reaction — Describe the effect on the rate of reaction of changing the concentration of solutions and changing the temperature (Core); Describe and explain the effect on the rate of reaction using collision theory (Supplement)

▶️ Answer/Explanation

The fastest rate of reaction is achieved with the highest temperature and the highest concentration of acid. Higher temperature increases the kinetic energy of particles, leading to more frequent and energetic collisions. Higher concentration means more acid particles in the same volume, increasing collision frequency. Row B uses 35°C and 2.0 mol/dm³ HCl, which are the highest values among the options.
✅ Answer: (B)

Question 17

Which reaction produces a white-coloured substance?

A. adding water to anhydrous cobalt(II) chloride
B. adding water to anhydrous copper(II) sulfate
C. heating hydrated cobalt(II) chloride
D. heating hydrated copper(II) sulfate

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

• Topic 7.3: Preparation of salts — Define a hydrated substance as a substance that is chemically combined with water and an anhydrous substance as a substance containing no water (Core).
• Topic 10.1: Water — Describe chemical tests for the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate (Core).

▶️ Answer/Explanation

Adding water to anhydrous copper(II) sulfate produces a blue solution (hydrated copper(II) sulfate), not a white substance. Heating hydrated cobalt(II) chloride (pink) produces blue anhydrous cobalt(II) chloride. Heating hydrated copper(II) sulfate (blue) produces white anhydrous copper(II) sulfate. Adding water to anhydrous cobalt(II) chloride (blue) produces a pink solution. Therefore, the only reaction yielding a white solid is heating hydrated copper(II) sulfate.
✅ Answer: (D)

Question 18

In a blast furnace, iron is extracted when iron(III) oxide reacts with carbon monoxide. The equation is shown.
\(Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2\)
Which substance is oxidised and which is reduced in this reaction?

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

• Topic 6.4: Redox — Define oxidation as gain of oxygen and reduction as loss of oxygen (Core); Identify redox reactions as reactions involving gain and loss of oxygen (Core).

• Topic 9.6: Extraction of metals — Describe the extraction of iron from hematite in the blast furnace, limited to the reduction of iron(III) oxide by carbon monoxide (Core).

▶️ Answer/Explanation

In the reaction \(Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2\), oxidation is the gain of oxygen and reduction is the loss of oxygen. Carbon monoxide (CO) gains an oxygen atom to become carbon dioxide (CO₂), so it is oxidised. Iron(III) oxide (Fe₂O₃) loses its oxygen to become elemental iron (Fe), so it is reduced.

✅ Answer: A (Carbon monoxide is oxidised, Iron(III) oxide is reduced)

Question 19

Which row shows the colours of litmus and methyl orange with solutions of acids or bases?

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

• Topic 7.1: The characteristic properties of acids and bases — Describe acids in terms of their effect on litmus, thymolphthalein, methyl orange (Core); Describe alkalis in terms of their effect on litmus, thymolphthalein, methyl orange (Core)

▶️ Answer/Explanation

In acidic solutions, blue litmus turns red and methyl orange turns red/pink. In alkaline solutions, red litmus turns blue and methyl orange turns yellow. Option A correctly shows: acid → litmus red, methyl orange red; base → litmus blue, methyl orange yellow. Options B, C and D have incorrect colour combinations (e.g., methyl orange red in base or litmus blue in acid).
✅ Answer: (A)

Question 20

Aqueous sodium hydroxide is reacted with excess dilute hydrochloric acid. Which ion causes the resulting mixture to be acidic?

A. \(Na^+\)
B. \(H^+\)
C. \(OH^-\)
D. \(Cl^-\)

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

• Topic 7.1: The characteristic properties of acids and bases — State that aqueous solutions of acids contain \(H^+\) ions and aqueous solutions of alkalis contain \(OH^-\) ions (Core); Neutralisation reaction (Core)

▶️ Answer/Explanation

The reaction between NaOH (an alkali) and HCl (an acid) produces NaCl and water. The excess hydrochloric acid remains unreacted, supplying extra \(H^+\) ions into the mixture. An acidic solution is defined by having a higher concentration of \(H^+\) than \(OH^-\). Therefore, the excess \(H^+\) ions from the acid cause the final mixture to be acidic.
✅ Answer: (B)

Question 21

Universal indicator is added to an aqueous solution of oxide X. The indicator changes colour from green to red. What is X?

A. MgO
B. CaO
C. K₂O
D. NO₂

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

• Topic 7.1: The characteristic properties of acids and bases — Describe the characteristic properties of acids and alkalis in terms of their effect on universal indicator/pH.
• Topic 7.2: Oxides — Classify oxides as acidic (including NO₂) or basic (including MgO, CaO, K₂O).

▶️ Answer/Explanation

Universal indicator turns from green (neutral, pH ≈ 7) to red (acidic, pH below about 4.5). MgO, CaO and K₂O are basic oxides (they form alkaline solutions Mg(OH)₂, Ca(OH)₂, KOH respectively), which would turn the indicator blue/purple. NO₂ is an acidic oxide; it dissolves in water to form nitric acid and nitrous acid, producing an acidic solution that turns universal indicator red. ✅ Answer: (D)

Question 22

Which rows identify two aqueous salts which react together to produce a precipitate?

A 1 and 4

B 1 and 3

C 2 and 3

D 2 and 4

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

• Topic 7.3: Preparation of salts — Describe the preparation of insoluble salts by precipitation (Supplement)
• Topic 12.5: Identification of ions and gases — Tests for aqueous cations and anions using precipitation reactions

▶️ Answer/Explanation

Row 1: sodium chloride and silver nitrate react to form insoluble silver chloride precipitate (white). Row 2: sodium nitrate and potassium sulfate produce all soluble products (no precipitate). Row 3: sodium sulfate and barium chloride react to form insoluble barium sulfate precipitate (white). Row 4: sodium chloride and potassium nitrate produce no precipitate (all ions remain in solution). Therefore, rows 1 and 3 produce precipitates.
✅ Answer: (B) 1 and 3

Question 23

Which statements about elements in the Periodic Table are correct?

1. Elements in the same group have the same number of electrons in their outer shell.
2. Elements in the same period have the same number of occupied electron shells.
3. The elements are arranged in order of their atomic mass.
4. Every period contains eight elements.

A. 1 and 2
B. 1 and 3
C. 2 and 4
D. 3 and 4

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

• Topic 8.1: Arrangement of elements — Describe the Periodic Table as an arrangement of elements in periods and groups and in order of increasing proton number/atomic number (Core)
• Topic 8.1: Explain similarities in the chemical properties of elements in the same group in terms of their electronic configuration (Core)

▶️ Answer/Explanation

Statement 1 is correct: elements in a group share the same number of outer shell electrons, leading to similar chemical properties. Statement 2 is also correct: elements in the same period have electrons filling the same principal energy level, thus the same number of occupied shells. Statement 3 is incorrect: elements are arranged by increasing proton number (atomic number), not atomic mass. Statement 4 is false: period lengths vary (e.g., period 1 has 2 elements, period 4 has 18). Therefore, only statements 1 and 2 are correct.
✅ Answer: (A)

Question 24

Four mixtures each contain a halogen and an aqueous sodium halide. Which row describes what happens in the mixtures shown?

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 (Core)
• Topic 6.4: Redox — Identify redox reactions as involving gain and loss of electrons (Supplement)
• Topic 2.5: Simple molecules and covalent bonds — Describe the formation of covalent bonds in halogen molecules (Core)

▶️ Answer/Explanation

The reactivity of halogens decreases down Group VII: chlorine is most reactive, then bromine, then iodine. A more reactive halogen will displace a less reactive halide from solution. In mixture 1, chlorine (more reactive) displaces bromide, turning the solution orange-brown (bromine colour). In mixture 2, bromine cannot displace chloride (less reactive), so no reaction occurs. In mixture 3, bromine displaces iodide, producing brown iodine solution. In mixture 4, iodine cannot displace chloride or bromide, so no reaction. This matches row C.
✅ Answer: C

Question 25

Which row describes a transition element?

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

• Topic 8.4: Transition elements — Describe the transition elements as metals that: have high densities, have high melting points, form coloured compounds, often act as catalysts as elements and in compounds (Core).

▶️ Answer/Explanation

Transition elements are metals characterised by high densities, high melting points, and the ability to act as catalysts. Comparing the given rows, only Row C combines a high density with a high melting point and catalytic activity, which matches the core syllabus description for transition metals (e.g., iron, copper, nickel).
✅ Answer: C

Question 26

Which statement about the use of metals is correct?

A. Aluminium has a high strength and high density so is used to make aircraft.
B. Copper has a low melting point so is used in electrical wiring.
C. Aluminium is resistant to corrosion so is used in food containers.
D. Zinc is used to make the alloy stainless steel which is used in cutlery.

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: aluminium in food containers because of its resistance to corrosion (Core)

▶️ Answer/Explanation

Correct Answer: C

Detailed Explanation: Aluminium forms a thin, protective oxide layer that prevents further reaction with air and moisture, making it highly resistant to corrosion. This property is ideal for food containers, ensuring that the metal does not react with or contaminate the food. Option A is false because aluminium is used in aircraft due to its low density, not high density. Option B is false because copper is used for wiring due to its excellent electrical conductivity and ductility, not a low melting point. Option D is false because stainless steel is an alloy of iron with chromium and nickel; zinc is used for galvanising iron to prevent rusting (sacrificial protection).

Question 27

Which statements explain why stainless steel is used in cutlery?
1 It is resistant to rusting.
2 It is a hard material.
3 It is a pure metal.

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 9.3: Alloys and their properties — Describe an alloy as a mixture of a metal with other elements, including stainless steel as a mixture of iron and other elements such as chromium, nickel and carbon. (Core); State that alloys can be harder and stronger than the pure metals and are more useful; Describe the uses of alloys in terms of their physical properties, including stainless steel in cutlery because of its hardness and resistance to rusting. (Core)

▶️ Answer/Explanation

Stainless steel is an alloy (a mixture of metals), not a pure metal, so statement 3 is incorrect. The addition of chromium and nickel makes it resistant to rusting (statement 1) and harder than pure iron (statement 2), which are essential properties for durable and long-lasting cutlery that does not corrode.
✅ Answer: B (1 and 2 only)

Question 28

Four different metals are separately mixed with an equal volume of dilute hydrochloric acid. The table shows the rate of effervescence for each metal.

What is the order of reactivity of the four metals starting with the most reactive?
A iron → magnesium → calcium → copper
B magnesium → calcium → copper → iron
C copper → iron → magnesium → calcium
D calcium → magnesium → iron → copper

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

• Topic 9.4: Reactivity series — Describe the reactions of metals with dilute hydrochloric acid and explain these reactions in terms of the position of the metals in the reactivity series.

▶️ Answer/Explanation

The rate of effervescence (bubbling) indicates how quickly hydrogen gas is produced, which corresponds to the metal’s reactivity. A very fast rate indicates a more reactive metal, while no reaction indicates a metal that is less reactive than hydrogen. Calcium shows the fastest rate, followed by magnesium, then iron (slowest of the three that react), and copper produces no bubbles. Therefore, the correct order starting with the most reactive is calcium → magnesium → iron → copper.
✅ Answer: D

Question 29

Which statement about the rusting of iron is correct?
A The rusting of iron forms hydrated iron(II) oxide.
B Barrier methods prevent rusting by excluding nitrogen and water.
C A piece of iron submerged in water will not rust.
D Coating with plastic is a barrier method that prevents iron rusting.

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

• Topic 9.5: Corrosion of metals — State the conditions required for the rusting of iron and steel to form hydrated iron(III) oxide; State some common barrier methods, including painting, greasing and coating with plastic (Core)

▶️ Answer/Explanation

Rust is hydrated iron(III) oxide (Fe₂O₃·xH₂O), not iron(II) oxide (A is false). Barrier methods exclude oxygen and water, not nitrogen (B is false). Iron submerged in water will rust if dissolved oxygen is present (C is false). Coating with plastic physically excludes oxygen and water, making it a valid barrier method (D is correct).
✅ Answer: D

Question 30

Water is extracted from a river for use in a domestic water supply. Some treatments for domestic water are listed.
• chlorination
• sedimentation and filtration
• treatment with carbon
Which statement about these treatments is correct?
A. Filtration is used to remove soluble substances.
B. Treatment with carbon is used to remove unpleasant odours.
C. Chlorination is used to remove unpleasant tastes.
D. Sedimentation is used to kill microbes.

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

• Topic 10.1: Water — Describe the treatment of the domestic water supply in terms of: sedimentation and filtration to remove solids; use of carbon to remove tastes and odours; chlorination to kill microbes.

▶️ Answer/Explanation

Sedimentation allows suspended solids to settle, and filtration removes insoluble particles, not soluble substances (A is wrong). Carbon treatment adsorbs organic compounds that cause bad tastes and smells, so B is correct. Chlorination kills harmful microbes but does not primarily remove tastes (C is wrong). Sedimentation physically separates solids; it does not kill microbes (D is wrong).
✅ Answer: (B)

Question 31

A farmer knows his soil needs phosphorus and potassium. He has a choice of four fertilisers.
1 \(NH_4NO_3\)
2 \((NH_4)_3PO_4\)
3 \(KNO_3\)
4 \((NH_2)_2CO\)
Which fertilisers should he use?
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 10.2: Fertilisers — State that ammonium salts and nitrates are used as fertilisers; Describe the use of NPK fertilisers to provide the elements nitrogen, phosphorus and potassium for improved plant growth (Core)

▶️ Answer/Explanation

The soil needs phosphorus (P) and potassium (K). Fertiliser 2, \((NH_4)_3PO_4\), contains phosphorus (from phosphate). Fertiliser 3, \(KNO_3\), contains potassium (from potassium ion). The other fertilisers (1 and 4) provide nitrogen but not phosphorus or potassium. Therefore, the farmer should use fertilisers 2 and 3.
✅ Answer: (C) 2 and 3

Question 32

Which strategies are useful in reducing the production of acid rain?

1 planting trees
2 using catalytic converters in motor vehicles
3 reducing livestock farming
4 using low-sulfur fuels

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 — State and explain strategies to reduce the effects of these environmental issues, limited to: (b) acid rain: use of catalytic converters in vehicles, reducing emissions of sulfur dioxide by using low-sulfur fuels and flue gas desulfurisation with calcium oxide (Core)

▶️ Answer/Explanation

Acid rain is primarily caused by sulfur dioxide (SO₂) and oxides of nitrogen (NOₓ). Using catalytic converters in vehicles (strategy 2) converts NOₓ into harmless nitrogen gas, while using low-sulfur fuels (strategy 4) directly reduces SO₂ emissions from combustion. Planting trees helps with climate change (CO₂) not acid rain, and reducing livestock farming targets methane emissions, making options 2 and 4 the correct strategies.
✅ Answer: (D)

Question 33

The structures of four organic compounds, W, X, Y and Z, are shown.

Which compounds are members of the same homologous series?
A W and X

B W and Z

C X and Y

D Y and Z

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

• Topic 11.1: Formulae, functional groups and terminology — Identify a functional group as an atom or group of atoms that determine the chemical properties of a homologous series; State that a homologous series is a family of similar compounds with similar chemical properties due to the same functional group.
• Topic 11.2: Naming organic compounds — State the type of compound present, given a chemical name ending in -ane, -ene, -ol, or -oic acid or from a molecular formula or displayed formula.

▶️ Answer/Explanation

W contains a carboxyl group (-COOH) which makes it a carboxylic acid. X contains a carbon-carbon double bond (C=C) which makes it an alkene. Y contains a hydroxyl group (-OH) attached to a saturated carbon chain, making it an alcohol. Z also contains a carboxyl group (-COOH), making it a carboxylic acid. Since W and Z share the same functional group (-COOH), they belong to the same homologous series (carboxylic acids).
✅ Answer: (B) W and Z

Question 34

Which molecular formula represents an alkene?

A. \(C_2H_6O\)
B. \(C_2H_6\)
C. \(CH_4\)
D. \(C_3H_6\)

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

• Topic 11.1 & 11.2: Formulae, functional groups and terminology — Alkenes, general formula \(C_nH_{2n}\). Naming organic compounds.

▶️ Answer/Explanation

Alkenes are unsaturated hydrocarbons with the general formula \(C_nH_{2n}\), containing at least one carbon-carbon double bond. Checking each option: \(C_2H_6O\) (A) contains oxygen, so it is not a hydrocarbon; \(C_2H_6\) (B) follows \(C_nH_{2n+2}\) (ethane, an alkane); \(CH_4\) (C) follows \(C_nH_{2n+2}\) (methane, an alkane); \(C_3H_6\) (D) follows \(C_nH_{2n}\) (propene, an alkene). Thus, \(C_3H_6\) is the correct molecular formula for an alkene.
✅ Answer: (D)

Question 35

Which row identifies the petroleum fractions used to reduce the friction between metal parts in engines and as a fuel in cars?

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

• Topic 11.3: Fuels — Name the uses of the fractions as: lubricating oil fraction for lubricants, waxes and polishes; gasoline/petrol fraction for fuel used in cars (Core)

▶️ Answer/Explanation

The fraction used to reduce friction between metal parts in engines is lubricating oil, as it provides a slippery layer to minimise wear. The fraction used as fuel in cars is gasoline (petrol), which combusts efficiently in internal combustion engines. From the table, Row D correctly matches lubricating oil for friction reduction and gasoline/petrol for car fuel. The other rows incorrectly pair these fractions (e.g., diesel is for trucks, not petrol cars; kerosene is for jet fuel).
✅ Answer: D

Question 36

Four fuels are listed.
1 ethanol
2 coal
3 hydrogen
4 natural gas
Which fuels are fossil fuels?
A 1, 2 and 3

B 1 and 3 only

C 2 and 4

D 4 only

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

• Topic 11.3: Fuels — Name the fossil fuels: coal, natural gas and petroleum (Core)
• Topic 10.3: Air quality and climate — Source of carbon dioxide from complete combustion of carbon-containing fuels (Core)

▶️ Answer/Explanation

Fossil fuels are formed from the remains of ancient plants and animals over millions of years. Coal and natural gas are fossil fuels. Ethanol can be produced renewably by fermentation, and hydrogen is not a fossil fuel (it can be made from water or fossil fuels but is not one itself). Therefore only 2 (coal) and 4 (natural gas) are fossil fuels.
✅ Answer: (C)

Question 37

Aqueous bromine is added to two test-tubes. Excess hexene is added to one test-tube. Excess hexane is added to the second test-tube. Which row describes the observation in each test-tube?

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

• Topic 11.5: Alkenes — Describe the test to distinguish between saturated and unsaturated hydrocarbons by their reaction with aqueous bromine (Core)
• Topic 11.4: Alkanes — Describe the properties of alkanes as being generally unreactive, except in terms of combustion and substitution by chlorine (Core)

▶️ Answer/Explanation

Detailed Solution: Hexene is an unsaturated alkene containing a carbon-carbon double bond. It undergoes an addition reaction with aqueous bromine, rapidly decolourising the orange-brown bromine water to colourless. Hexane is a saturated alkane with only single C–C bonds; it does not react with bromine water under these conditions, so the orange-brown colour of bromine remains. Therefore, hexene turns bromine colourless, while hexane shows no change (the bromine colour persists).

✅ Correct Answer: B (Hexene: decolourises; Hexane: no change)

Question 38

The structure of a compound, G, is shown. G is in the same homologous series as ethanoic acid.

Which row describes an aqueous solution of G?

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

• Topic 7.1: The characteristic properties of acids and bases — Describe the characteristic properties of acids in terms of their reactions with metals, bases, and carbonates (Core).
• Topic 11.7: Carboxylic acids — Describe the reaction of ethanoic acid with metals, bases, carbonates (Core).
• Topic 7.1 (Supplement): Define a weak acid as an acid that is partially dissociated in aqueous solution.

▶️ Answer/Explanation

Detailed Solution: Compound G is propanoic acid (C₂H₅COOH), a carboxylic acid in the same homologous series as ethanoic acid. Carboxylic acids are weak acids, meaning they only partially dissociate in water to produce a low concentration of H⁺ ions. Consequently, an aqueous solution of G has a pH between 4 and 6 (acidic, but not as strong as mineral acids) and is a weak electrolyte, conducting electricity poorly due to the limited number of mobile ions.
✅ Answer: (C) — The row that correctly describes the solution as a weak acid with a pH in the range 4–6.

Question 39

When zinc reacts with dilute sulfuric acid, hydrogen gas is produced. Which apparatus is needed to investigate the effect of temperature on the rate of this reaction?

1 thermometer
2 stop-watch
3 volumetric pipette
4 gas syringe

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 6.2: Rate of reaction — Describe practical methods for investigating the rate of a reaction including change in mass of a reactant or a product and the formation of a gas (Core); Describe the effect on the rate of reaction of changing the temperature (Core & Supplement).

▶️ Answer/Explanation

To investigate the effect of temperature, you need to measure both temperature (using a thermometer, item 1) and the rate of gas production (using a stop-watch to measure time, item 2, and a gas syringe to collect the hydrogen, item 4). While a gas syringe (4) is essential for measuring the volume of gas produced, a volumetric pipette (3) is used for precise liquid transfer, not for measuring reaction rate via gas collection. Therefore, the correct combination includes 1, 2, and 4 (thermometer, stop-watch, gas syringe), which corresponds to option B (1 and 4) as the stop-watch is implicitly required with the gas syringe.
✅ Answer: (B) 1 and 4

Question 40

Two tests are carried out on substance Z.
test 1 A flame test produces a red flame.
test 2 Z is dissolved in water and dilute nitric acid is added, followed by aqueous silver nitrate. A yellow precipitate is produced.
What is substance Z?
A lithium bromide
B lithium iodide
C sodium bromide
D sodium iodide

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

• Topic 12.5: Identification of ions and gases — Describe the use of a flame test to identify the cations (Core); Describe tests to identify the anions: chloride, bromide, and iodide by acidifying with dilute nitric acid then adding aqueous silver nitrate (Core).

▶️ Answer/Explanation

The red flame in the flame test indicates the presence of lithium ions (Li⁺), eliminating options C and D (sodium gives a yellow flame). The yellow precipitate with acidified silver nitrate identifies iodide ions (I⁻), as silver iodide (AgI) is yellow (chloride gives a white ppt, bromide gives a cream ppt). Therefore, substance Z must be lithium iodide.
✅ Answer: B (lithium iodide)