0620_s24_qp_12-hina

Question 1

Which statement about gases is correct?
A Gases are difficult to compress when pressure is applied.
B The particles in gases are close together.
C The particles in gases have a random arrangement.
D The particles in gases move slowly past each other.

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

• Topic 1.1: Solids, liquids and gases — State the distinguishing properties of solids, liquids and gases (Core); Describe the structures of solids, liquids and gases in terms of particle separation, arrangement and motion (Core).

▶️ Answer/Explanation

Gases are easily compressible because their particles are far apart, not close together. Particles in a gas are in constant rapid random motion and have a random arrangement with no fixed positions. Therefore the correct statement is that gas particles have a random arrangement.
✅ Answer: (C)

Question 2

A sample of argon gas is heated in a closed container. Which row describes what happens to the pressure and the size of the argon atoms?

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)
• Topic 2.2: Atomic structure and the Periodic Table — Describe the structure of the atom as a central nucleus containing neutrons and protons surrounded by electrons in shells (Core)

▶️ Answer/Explanation

Answer: D

According to the kinetic particle theory, heating a gas in a closed container increases the average kinetic energy of its particles. This leads to more frequent and forceful collisions with the container walls, causing the pressure to increase (eliminating rows B and C). However, the size of individual argon atoms is a fixed property of the element and does not change with temperature; only the space between atoms or their speed changes. Therefore, both increased pressure and unchanged atomic size are correctly described in row D.

Question 3

Which statement is correct?
A. Air is a mixture of gaseous elements only.
B. Alloys are formed when a metal is ionically bonded to other elements.
C. Carbon dioxide is a mixture of carbon and oxygen.
D. Potassium bromide is an ionic compound.

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

• Topic 2.1: Elements, compounds and mixtures — Describe the differences between elements, compounds and mixtures (Core).
• Topic 2.4: Ions and ionic bonds — Describe the formation of ionic bonds between elements from Group I and Group VII (Core).

▶️ Answer/Explanation

Detailed Solution: Air is a mixture of both elements (e.g., nitrogen, oxygen, noble gases) and compounds (e.g., carbon dioxide, water vapor), making option A incorrect. Alloys are mixtures of a metal with other elements, held together by metallic bonding, not ionic bonding, so option B is false. Carbon dioxide is a compound formed by chemically combining carbon and oxygen, not a mixture, thus option C is wrong. Potassium bromide (KBr) consists of a metal (potassium, Group I) and a non-metal (bromine, Group VII), which transfer electrons to form strong electrostatic attractions between oppositely charged ions, making it an ionic compound. Therefore, option D is correct.
✅ Answer: D

Question 4

Which row identifies methods of testing the purity of a compound?

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 (Core)
• Topic 12.3: Chromatography — Interpret simple chromatograms to identify pure and impure substances (Core)

▶️ Answer/Explanation

A pure substance has a sharp, fixed melting point and a fixed boiling point, while impurities cause these to change (lower melting point, broader range). Chromatography can also assess purity: a pure substance produces only one spot on the chromatogram, whereas an impure sample shows multiple spots. Therefore, both melting point measurement and chromatography are valid methods for testing purity, as shown in row D.
✅ Answer: D

Question 5

Which row shows the number of protons, neutrons and electrons in the ion \( _{8}^{18}\textrm{O}^{2-}\)?

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 (Core).
• Topic 2.4: Ions and ionic bonds — Describe the formation of positive ions, known as cations, and negative ions, known as anions (Core).

▶️ Answer/Explanation

The atomic number (Z) = 8 = number of protons. The mass number (A) = 18, so neutrons = A – Z = 18 – 8 = 10. The neutral atom has 8 electrons; the 2- charge means it has gained 2 electrons, so electrons = 8 + 2 = 10. This matches the values in Row D (protons = 8, neutrons = 10, electrons = 10).
✅ Answer: D

Question 6

Isotopes of the same element have some features that are the same and some that are different. Which row shows the features that are the same and those that are different?

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

• Topic 2.3: Isotopes — Define isotopes as different atoms of the same element that have the same number of protons but different numbers of neutrons (Core); State that isotopes of the same element have the same chemical properties because they have the same electronic configuration (Supplement).

▶️ Answer/Explanation

Answer: B

Isotopes have the same number of protons (and hence electrons) but different numbers of neutrons. The number of electrons determines chemical properties, so chemical properties are the same. The different mass number affects physical properties like density and mass. Row B correctly identifies the same chemical properties and different physical properties.

Question 7

The electronic configurations of four atoms, W, X, Y and Z, are shown.

Which atoms form an ion with a charge of 2– when they react?
A W and Y
B W only
C X and Z
D Y only

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 (Core).
• Topic 2.4: Ions and ionic bonds — Describe the formation of negative ions, known as anions (Core).

▶️ Answer/Explanation

Atoms form a 2– ion by gaining two electrons to achieve a full outer shell (stable octet or duet). W has 2 electrons in its outer shell (already full, likely group II) and would lose electrons to become a 2+ ion, not gain. X has 6 outer electrons (group VI) and gains 2 electrons to become X²⁻. Y has 1 outer electron (group I) and loses it to become Y⁺. Z has 6 outer electrons (group VI) and gains 2 electrons to become Z²⁻. Therefore, only X and Z form a 2– ion.
✅ Answer: (C)

Question 8

Which statement about bonding is correct?
A All the atoms in \(CH_4\), \(NH_3\) and \(H_2O\) molecules have noble gas electronic configurations.
B Calcium chloride is a covalent molecule.
C Group I metals gain electrons when they bond with Group VII elements.
D Oxide ions in calcium oxide are positively charged.

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

• Topic 2.2 & 2.4 & 2.5: Atomic structure and the Periodic Table; Ions and ionic bonds; Simple molecules and covalent bonds — formation of covalent bonds leading to noble gas configurations; formation of ionic bonds between Group I and Group VII

▶️ Answer/Explanation

In CH₄, NH₃ and H₂O, each atom (C, H, N, O) achieves a full outer electron shell like a noble gas through electron sharing: H has 2 electrons (like He), C has 8, N has 8, O has 8. Calcium chloride is ionic, not covalent. Group I metals lose (not gain) electrons when bonding with Group VII. Oxide ions (O²⁻) are negatively charged. Therefore, option A is correct.
✅ Answer: A

Question 9

Which statement about diamond is correct?

A. It is a giant covalent structure consisting of carbon atoms and each atom is bonded to four other atoms.
B. It is a giant covalent structure consisting of flat sheets of carbon atoms.
C. It is a structure held together by ionic bonds and each ion is bonded to four other ions.
D. It is a structure held together by ionic bonds and each ion is bonded to three other ions.

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

• Topic 2.6: Giant covalent structures — Describe the giant covalent structures of graphite and diamond (Core).

▶️ Answer/Explanation

Diamond is a giant covalent structure (not ionic), where each carbon atom forms four strong covalent bonds with four other carbon atoms in a tetrahedral arrangement. This rigid three-dimensional network makes it extremely hard. Option B describes graphite (flat sheets), while options C and D incorrectly describe ionic bonding. Therefore, only option A accurately describes diamond’s structure and bonding.
✅ Answer: (A)

Question 10

Which row shows the correct formulae of lead(II) bromide and butane?

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

• Topic 3.1: Formulae — Deduce the formula of a simple compound from the relative numbers of atoms present in a model or a diagrammatic representation (Core).
• Topic 11.2: Naming organic compounds — Name and draw the displayed formulae of methane and ethane (Core); butane is an alkane with formula C₄H₁₀ (Extension of understanding from alkanes CₙH₂ₙ₊₂, Topic 11.1).

▶️ Answer/Explanation

✅ Answer: (B)

Lead(II) bromide is an ionic compound. Lead (Pb) in the +2 oxidation state forms the ion Pb²⁺, and bromine forms the ion Br⁻. To balance the charges, one Pb²⁺ requires two Br⁻ ions, giving the formula PbBr₂. Butane is a saturated hydrocarbon (alkane) with four carbon atoms. The general formula for alkanes is CₙH₂ₙ₊₂, so for n=4, the formula is C₄H₁₀. Only row B correctly pairs PbBr₂ and C₄H₁₀.

Question 11

Calcium phosphate forms when calcium chloride and sodium phosphate solutions react together.
\(x CaCl_2 + y Na_3PO_4 → 2Ca_3(PO_4)_2 + 12NaCl\)
Which values of x and y balance the equation?

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

• Topic 3.1: Formulae — Construct symbol equations, including ionic equations (Supplement).
• Topic 3.3: The mole and the Avogadro constant — Calculate stoichiometric reacting masses (Supplement).

▶️ Answer/Explanation

To balance the equation, first balance calcium (Ca): the right side has 2 × 3 = 6 Ca atoms (from Ca₃(PO₄)₂), so left needs 6 Ca, meaning x = 6 (since each CaCl₂ has 1 Ca). Next balance chlorine (Cl): left has 6 × 2 = 12 Cl, right has 12 Cl (from 12 NaCl), so Cl is balanced. Now balance phosphate (PO₄): right has 2 × 2 = 4 PO₄ groups, left needs 4 PO₄; since each Na₃PO₄ gives 1 PO₄, y = 4. Option D shows x=6 and y=4, which correctly balances all atoms (Na also balances: left 4×3=12 Na, right 12 Na).
✅ Answer: D

Question 12

What is the definition of relative molecular mass, \(M_r\)?
A It is the average mass of the isotopes in a compound.
B It is the sum of the atomic numbers in a compound.
C It is the sum of the relative atomic masses in a compound.
D It is the total number of atoms in a compound.

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

• Topic 3.2: Relative masses of atoms and molecules — Define relative molecular mass, \(M_r\) as the sum of the relative atomic masses (Core)

▶️ Answer/Explanation

Relative molecular mass (\(M_r\)) is defined as the sum of the relative atomic masses (\(A_r\)) of all the atoms present in one molecule of a compound. It has no units because it is a ratio. Option C correctly matches this definition, while options A, B, and D describe different incorrect concepts (isotope averages, atomic numbers, or atom counts).
✅ Answer: (C)

Question 13

In an experiment, a molten compound is broken down using electricity. Which row identifies the negative electrode and the general name for the molten compound being broken down?

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

• Topic 4.1: Electrolysis — Define electrolysis as the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current; Identify in simple electrolytic cells: (c) the electrolyte as the molten or aqueous substance that undergoes electrolysis; (b) the cathode as the negative electrode

▶️ Answer/Explanation

In electrolysis, the negative electrode is called the cathode (where positive ions gain electrons). The process of breaking down a compound using electricity is electrolysis, and the molten compound that conducts electricity and decomposes is the electrolyte. Therefore, the correct row must have ‘cathode’ for the negative electrode and ‘electrolyte’ as the general name for the molten compound.
✅ Answer: C

Question 14

Hydrogen–oxygen fuel cells can be used to power vehicles. What is produced by the fuel cells?

1 carbon dioxide
2 electricity
3 water

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 4.2: 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

In a hydrogen-oxygen fuel cell, hydrogen gas reacts with oxygen gas in an electrochemical process that does not involve combustion. The chemical reaction produces electrical energy (electricity) and water as the only product, with no carbon dioxide emissions. Therefore, items 2 and 3 are correct, making option D the right choice.
✅ Answer: D (2 and 3 only)

Question 15

Three reactions are described.
1 An acid is added to substance H. Rapid fizzing happens and the temperature decreases.
2 When substance J is ignited, it produces large quantities of heat.
3 Substance K reacts slowly with air and becomes warmer.
Which reactions are endothermic?
A 1, 2 and 3

B 1 and 2 only

C 1 only

D 2 and 3 only

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 (Core)

▶️ Answer/Explanation

Reaction 1 shows a temperature decrease, which is the key sign of an endothermic reaction (absorbing heat from surroundings). Reaction 2 releases large quantities of heat upon ignition, making it exothermic. Reaction 3 becomes warmer as it reacts, also indicating an exothermic process (releasing heat). Therefore, only reaction 1 is endothermic.
✅ Answer: (C) 1 only

Question 16

Which of the processes produces a physical change?
A thermal decomposition of calcium carbonate
B addition of sodium chloride to water
C addition of magnesium to hydrochloric acid
D combustion of sodium

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 does not produce a new substance and is usually reversible. Dissolving sodium chloride in water is a physical change because the salt can be recovered by evaporation and no chemical reaction occurs. Thermal decomposition (A) produces new substances (CaO and CO₂), adding magnesium to acid (C) produces hydrogen gas and a salt, and combustion of sodium (D) produces sodium oxide — all are chemical changes.
✅ Answer: (B)

Question 17

A known mass of gaseous ammonia and excess gaseous hydrogen chloride react together to make solid ammonium chloride. Line X shows the total mass of ammonium chloride produced over time. The reaction is repeated at a higher pressure. All other conditions are kept the same. Line Y shows the total mass of ammonium chloride produced over time at the higher pressure. Which diagram is correct?

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 pressure of gases (Core)
• Topic 6.2 (Supplement): Describe and explain the effect on the rate of reaction of changing the pressure of gases using collision theory
• Topic 6.3: Reversible reactions and equilibrium — Predict and explain how changing pressure affects the position of equilibrium (Supplement)

▶️ Answer/Explanation

Increasing the pressure on a gaseous reaction increases the concentration of reactant particles per unit volume, leading to more frequent successful collisions and a faster rate of reaction. This means the same final mass of product (since the mass of ammonia is fixed and hydrogen chloride is in excess) is reached in a shorter time. Therefore, line Y (higher pressure) must reach the same horizontal plateau as line X but more quickly. Among the diagrams, the one showing both curves leveling off at the same final mass, with Y rising more steeply and reaching the plateau earlier, corresponds to option D.
✅ Answer: (D)

Question 18

The equation for the hydration of anhydrous copper(II) sulfate is shown.
\(CuSO_4 + 5H_2O \rightarrow CuSO_4 \cdot 5H_2O\)
Which colour change is observed in this reaction?
A. blue to white
B. white to blue
C. pink to blue
D. blue to pink

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

• Topic 6.3: Reversible reactions and equilibrium — Describe how changing the conditions can change the direction of a reversible reaction for: the addition of water to anhydrous compounds limited to copper(II) sulfate (Core)
• 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 copper(II) sulfate (Core)

▶️ Answer/Explanation

Anhydrous copper(II) sulfate (CuSO₄) is white. When water is added, it becomes hydrated copper(II) sulfate (CuSO₄·5H₂O), which is blue. The reaction shown is hydration, so the colour change is from white to blue. Option B is correct; option A describes the reverse (dehydration) change; options C and D involve cobalt compounds or incorrect transitions.
✅ Answer: (B)

Question 19

Which of the reactions show the underlined substance being reduced?
1 \(\underline{CuO} + H_2 → Cu + H_2O\)
2 \(2Mg + \underline{O_2} → 2MgO\)
3 \(\underline{MgO} + 2HCl → MgCl_2 + H_2O\)
A 1 and 2

B 1 only

C 2 and 3

D 3 only

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

• Topic 6.4: Redox — Define reduction as loss of oxygen or gain of electrons (Core) and in terms of decrease in oxidation number (Supplement)

▶️ Answer/Explanation

In reaction 1, CuO loses oxygen to become Cu, so CuO is reduced (and H₂ is oxidised). In reaction 2, O₂ gains electrons (oxidation number 0 → -2) so O₂ is reduced; therefore the underlined O₂ is reduced. However, the question asks for the underlined substance being reduced. In reaction 3, MgO has no change in oxidation numbers (Mg²⁺, O²⁻ remain same) and no loss/gain of oxygen, so it is not reduced. Thus reactions 1 and 2 show the underlined substance being reduced, giving answer A.
✅ Answer: (A)

Question 20

Four different solutions are separately tested with blue litmus and with methyl orange. Each solution is known to be either acidic or alkaline. The results are shown.

Which statement is correct?
A Solutions 1 and 4 are acidic.
B Solutions 1 and 2 are alkaline.
C Solutions 3 and 4 are acidic.
D Solutions 3 and 4 are alkaline.

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 and methyl orange; Describe alkalis in terms of their effect on litmus and methyl orange (Core)

▶️ Answer/Explanation

Blue litmus turns red in acidic conditions and stays blue in alkaline conditions. Methyl orange is yellow in alkaline solutions and red/pink in acidic solutions. Solution 3 turns blue litmus red (acidic) but methyl orange yellow (alkaline) — this is a mismatch, so it must be neutral or an error? Actually, re-check: methyl orange is yellow in alkaline, red in acid. Solution 3: blue litmus → red (acid), methyl orange → yellow (alkaline) — impossible, so likely the question expects standard results: Solution 1 (blue litmus red = acid; methyl orange red = acid) so acid. Solution 2 (blue litmus blue = alkaline; methyl orange yellow = alkaline) so alkaline. Solution 3 (blue litmus red = acid; methyl orange yellow? Wait that would be alkaline) — inconsistent, but if we trust table: maybe Solution 3 is acid? No — methyl orange yellow means alkaline, so Solution 3 is alkaline. Solution 4: blue litmus blue = alkaline, methyl orange yellow = alkaline. Therefore Solutions 3 and 4 are alkaline. Statement D is correct.
✅ Answer: (D)

Question 21

Which statement about sulfur dioxide or calcium oxide is correct?
A Calcium oxide is an acid.
B Calcium oxide turns thymolphthalein yellow.
C Sulfur dioxide is a base.
D Sulfur dioxide turns thymolphthalein colourless.

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

• Topic 7.1: The characteristic properties of acids and bases — Describe alkalis in terms of their effect on litmus, thymolphthalein, methyl orange (Core)
• Topic 7.2: Oxides — Classify oxides as acidic (including SO₂) or basic (including CaO) related to metallic and non-metallic character (Core)

▶️ Answer/Explanation

Calcium oxide (CaO) is a basic oxide (not an acid), so A is false. Thymolphthalein is blue in alkaline conditions and colourless in acidic/neutral conditions; CaO in water forms an alkaline solution (turns thymolphthalein blue, not yellow), so B is false. Sulfur dioxide (SO₂) is an acidic oxide (not a base), so C is false. Sulfur dioxide dissolves in water to form an acidic solution (sulfurous acid), which turns thymolphthalein colourless, making D correct.
✅ Answer: (D)

Question 22

Which substances can be used to make pure crystals of sodium sulfate?

A. potassium sulfate and sodium hydroxide
B. sodium carbonate and sulfuric acid
C. sodium nitrate and magnesium sulfate
D. sulfuric acid and sodium chloride

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

• Topic 7.3: Preparation of salts — Describe the preparation, separation and purification of soluble salts by reaction of an acid with an alkali, excess metal, excess insoluble base, or excess insoluble carbonate (Core)

▶️ Answer/Explanation

Sodium sulfate is a soluble salt. It can be prepared by reacting a suitable acid (sulfuric acid) with a sodium compound that is either an alkali, carbonate, or metal. In option B, sodium carbonate reacts with sulfuric acid: Na₂CO₃ + H₂SO₄ → Na₂SO₄ + CO₂ + H₂O, producing a solution from which pure crystals of sodium sulfate can be obtained by crystallisation. The other options do not yield sodium sulfate as the intended pure product.
✅ Answer: (B)

Question 23

Which statements describe changes that occur from left to right across a period of the Periodic Table?

1 The atomic number of the elements increases.
2 The metallic character of the elements decreases.
3 The physical state of the elements changes from gas to solid.

A 2 only

B 1 and 2

C 1 and 3

D 2 and 3

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; Describe the change from metallic to non-metallic character across a period (Core)

▶️ Answer/Explanation

Detailed Solution: Statement 1 is correct because atomic (proton) number increases by one for each element moving left to right across a period. Statement 2 is also correct as metallic character decreases across a period, transitioning from metals on the left to non-metals on the right. Statement 3 is incorrect because the physical state across a period varies and does not follow a consistent gas-to-solid change (e.g., period 3 starts with solid sodium and ends with gaseous argon). Therefore, statements 1 and 2 are correct.
✅ Answer: (B) 1 and 2

Question 24

Part of the Periodic Table is shown. Which element is the most reactive non-metal?

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

• Topic 8.3: Group VII properties — Describe the Group VII halogens, chlorine, bromine and iodine, with general trends down the group, limited to decreasing reactivity (Core).

▶️ Answer/Explanation

In Group VII (halogens), reactivity decreases down the group because the outer shell of electrons is further from the nucleus, making it harder to gain an electron. Fluorine (not shown) is the most reactive, but among the elements displayed, chlorine (Cl) is higher up than bromine (Br) and iodine (I). Therefore, chlorine is the most reactive non-metal in the provided section.
✅ Answer: D

Question 25

An alloy contains aluminium, copper, magnesium, manganese, silver and zirconium. Which row identifies the number of transition elements in the alloy and the relative density of the transition elements compared to sodium?

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

• Topic 8.4 (Transition Elements): Describe the transition elements as metals that: (a) have high densities, (b) have high melting points, (c) form coloured compounds, (d) often act as catalysts.
• Topic 9.1 (Properties of Metals): Compare the general physical properties of metals and non-metals, including density.

▶️ Answer/Explanation

From the list (aluminium, copper, magnesium, manganese, silver, zirconium), the transition elements are copper, manganese, silver, and zirconium — that is 4 elements. Transition metals are characterised by high density compared to Group I metals like sodium, so the density is greater than sodium. Row A correctly shows 4 transition elements and “greater” density.

✅ Answer: (A)

Question 26

Which statement about the halogens and their compounds is correct?
A The colour of the element gets lighter going down Group VII.
B The elements get less dense going down Group VII.
C When chlorine is added to sodium iodide solution, iodine is formed.
D When iodine is added to sodium bromide solution, bromine is formed.

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 8.3: Group VII properties — State the appearance of halogens at r.t.p. and describe general trends down the group (Core).

▶️ Answer/Explanation

Answer: C

Detailed Solution: In Group VII (halogens), reactivity decreases down the group. A more reactive halogen (chlorine) will displace a less reactive halogen (iodine) from its salt (sodium iodide), producing iodine. Thus, when chlorine is added to sodium iodide solution, iodine is formed (solution turns brown). Option A is incorrect because colours get darker (paler yellow-green to dark grey-black). Option B is incorrect because density increases down the group. Option D is incorrect because iodine is less reactive than bromine and cannot displace it.

Question 27

Which row describes an element in Group VIII of the Periodic Table?

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 (Core)

▶️ Answer/Explanation

Group VIII (also called Group 0 or noble gases) elements are chemically unreactive because they have a full outer shell of electrons. They exist as monatomic gases (single atoms) at room temperature and pressure, not as diatomic molecules or reactive solids. Therefore, the correct row must show a monatomic gas that is unreactive. Among the options, the row stating “monatomic gas” and “unreactive” is correct.
✅ Answer: B

Question 28

Magnesium reacts with dilute hydrochloric acid. Which gas is given off in this reaction?
A carbon dioxide
B chlorine
C hydrogen
D oxygen

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

• Topic 9.4: Reactivity series — Describe the reactions of metals with dilute hydrochloric acid.
• Topic 7.1: Characteristic properties of acids — Reaction of acids with metals.

▶️ Answer/Explanation

Magnesium is a reactive metal above hydrogen in the reactivity series. When it reacts with dilute hydrochloric acid, it displaces hydrogen from the acid, forming magnesium chloride and hydrogen gas. The other gases (carbon dioxide, chlorine, oxygen) are not produced in this typical metal–acid reaction.
✅ Answer: C (hydrogen)

Question 29

Which statement about aluminium is correct?
A Aluminium is easy to extract from its ore because it is near the bottom of the reactivity series.
B Aluminium is formed when aluminium oxide is heated with carbon.
C Bauxite is an important ore of aluminium.
D Hematite is an important ore of aluminium.

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

• Topic 9.6: Extraction of metals — State that the main ore of aluminium is bauxite and that aluminium is extracted by electrolysis (Core).

▶️ Answer/Explanation

Aluminium is extracted by electrolysis, not by carbon reduction, because it is high in the reactivity series. Bauxite is the main ore of aluminium (option C), while hematite is an ore of iron. Heating aluminium oxide with carbon does not yield aluminium due to the strong bond between aluminium and oxygen.
✅ Answer: (C)

Question 30

Which statement shows that a liquid is pure water?
A It boils at 100°C.
B It has a pH value of 7.
C It turns blue cobalt(II) chloride pink.
D It turns white copper(II) sulfate blue

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

• Topic 12.5: Identification of ions and gases — Describe tests to identify the gases.
• Topic 10.1: Water — Describe chemical tests for the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate; Explain how to test for the purity of water using melting point and boiling point.

▶️ Answer/Explanation

The boiling point of pure water at standard atmospheric pressure is exactly 100°C; impurities raise or lower the boiling point, so a liquid boiling at 100°C indicates it is pure water. A pH of 7 only shows neutrality, not purity. Tests C and D confirm the presence of water (not purity), as cobalt(II) chloride turns from blue to pink and white copper(II) sulfate turns blue in the presence of any water, pure or impure.
✅ Answer: (A)

Question 31

Which compound can be added to ammonium sulfate to make an NPK fertiliser?

A. \((NH_4)_3PO_4\)
B. \(KNO_3\)
C. \(K_3PO_4\)
D. \(CO(NH_2)_2\)

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.

▶️ Answer/Explanation

Ammonium sulfate, \((NH_4)_2SO_4\), already provides nitrogen (N) and sulfur. To make an NPK fertiliser, we must add a source of phosphorus (P) and potassium (K). \(K_3PO_4\) (potassium phosphate) supplies both potassium and phosphorus. \((NH_4)_3PO_4\) supplies N and P but lacks K; \(KNO_3\) supplies N and K but lacks P; \(CO(NH_2)_2\) (urea) supplies only N. Therefore, \(K_3PO_4\) is the correct additive to provide the missing P and K for a complete NPK formulation.
✅ Answer: (C)

Question 32

Four gases found in air are listed.
1 carbon dioxide
2 carbon monoxide
3 methane
4 sulfur dioxide
Which gases lead directly to global warming when their concentrations are increased?
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 the adverse effect of air pollutants: carbon dioxide and methane: higher levels leading to increased global warming (Core).

▶️ Answer/Explanation

Carbon dioxide (1) and methane (3) are greenhouse gases that absorb and re-emit infrared radiation, trapping heat in the atmosphere and directly causing global warming. Carbon monoxide (2) is toxic but not a greenhouse gas, while sulfur dioxide (4) causes acid rain but not direct global warming.
✅ Answer: A

Question 33

The structures of four organic compounds are shown.

Which compounds are members of the same homologous series?
A 1, 2 and 3

B 1 and 2 only

C 1 and 3 only

D 3 and 4

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 displayed formula.

▶️ Answer/Explanation

Compound 1 is an alcohol (ethanol, –OH functional group). Compound 2 is a carboxylic acid (ethanoic acid, –COOH functional group). Compound 3 is an alcohol (propan-2-ol, –OH functional group). Compound 4 is an alkane (butane, only C–C and C–H single bonds). Alcohols (1 and 3) share the same –OH functional group and general formula CₙH₂ₙ₊₁OH, so they belong to the same homologous series. Carboxylic acids and alkanes are different series.
✅ Answer: (C)

Question 34

Which of the statements about propene are correct?
1 Propene contains only single bonds.
2 Propene decolourises aqueous bromine.
3 Propene is obtained by cracking large alkanes.
4 Propene is a hydrocarbon.

A 1, 3 and 4

B 1 only

C 2, 3 and 4

D 2 and 4 only

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

• Topic 11.5: Alkenes — State that the bonding in alkenes includes a double carbon-carbon covalent bond and that alkenes are unsaturated hydrocarbons; Describe the test to distinguish between saturated and unsaturated hydrocarbons by their reaction with aqueous bromine; Describe the manufacture of alkenes by the cracking of larger alkane molecules.

▶️ Answer/Explanation

Propene is an alkene containing one carbon-carbon double bond, so statement 1 is false (it does not contain only single bonds). The double bond reacts with aqueous bromine, decolourising it (statement 2 correct). Propene is produced industrially by cracking large alkanes (statement 3 correct). Propene contains only carbon and hydrogen, so it is a hydrocarbon (statement 4 correct). Therefore statements 2, 3 and 4 are correct.
✅ Answer: (C) 2, 3 and 4

Question 35

Petroleum is a mixture. Which method is used to separate petroleum into its components?
A chromatography
B cracking
C filtration
D fractional distillation

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

• Topic 11.3: Fuels — Describe the separation of petroleum into useful fractions by fractional distillation (Core)

▶️ Answer/Explanation

Petroleum (crude oil) is a complex mixture of hydrocarbons with different boiling points. Fractional distillation separates these components by heating the mixture in a fractionating column; hydrocarbons with lower boiling points rise to the top and condense, while those with higher boiling points remain lower. Chromatography separates mixtures based on solubility, cracking breaks down large hydrocarbons, and filtration separates solids from liquids — none of these are used for petroleum refining into fractions.
✅ Answer: D (fractional distillation)

Question 36

The equation for a reaction that produces ethanol is shown.
ethene + steam → ethanol
Which type of reaction does the equation represent?
A. addition
B. combustion
C. fermentation
D. polymerisation

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

• Topic 11.5: Alkenes — Describe the properties of alkenes in terms of addition reactions with steam in the presence of an acid catalyst (Supplement)
• Topic 11.6: Alcohols — Describe the manufacture of ethanol by catalytic addition of steam to ethene at 300°C and 6000 kPa in the presence of an acid catalyst (Core)

▶️ Answer/Explanation

This reaction converts ethene (an unsaturated hydrocarbon with a double bond) into ethanol by adding the elements of water (H and OH) across the double bond. This fits the definition of an addition reaction, where two or more molecules combine to form a single product without losing any atoms. Fermentation uses glucose and yeast, polymerisation forms long chains, and combustion requires oxygen, making A the correct choice.
✅ Answer: (A)

Question 37

Four statements about ethene or poly(ethene) are listed.
1 Poly(ethene) is produced by an addition reaction.
2 Ethene is a monomer.
3 Poly(ethene) is a monomer.
4 Poly(ethene) decolourises aqueous bromine.
Which statements are correct?
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 11.8: Polymers — Define polymers as large molecules built up from many smaller molecules called monomers; Describe the formation of poly(ethene) as an example of addition polymerisation using ethene monomers (Core). Also relates to alkenes and addition reactions.

▶️ Answer/Explanation

Poly(ethene) is formed from ethene monomers via addition polymerisation (statement 1 is correct). Ethene is the small repeating unit (monomer) that polymerises (statement 2 is correct). Poly(ethene) itself is a polymer, not a monomer, and it contains no carbon-carbon double bonds (saturated), so it does not decolourise aqueous bromine (statements 3 and 4 are incorrect).
✅ Answer: (A) 1 and 2

Question 38

Sea water contains dissolved sodium chloride. Which method is used to obtain pure water from sea water?

A. chromatography
B. distillation
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 simple distillation.

▶️ Answer/Explanation

Distillation is the correct method because it involves boiling the sea water to evaporate the water, then condensing the steam back into pure water, leaving the dissolved sodium chloride behind. Chromatography separates mixtures based on solubility, evaporation would leave the salt behind but not collect pure water, and filtration only removes insoluble solids, not dissolved salts.
✅ Answer: (B)

Question 39

Which piece of apparatus is used to measure exactly 21.4 cm³ of water?

A. a 25 cm³ beaker
B. a 25 cm³ pipette
C. a 50 cm³ burette
D. a 50 cm³ measuring cylinder

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 (Core).
• Topic 4: Details of the assessment — Candidates should be able to take readings from apparatus with appropriate precision and select the most appropriate apparatus or method for the task.

▶️ Answer/Explanation

A 25 cm³ beaker (A) is not accurate for exact volumes. A 25 cm³ pipette (B) measures only one fixed volume (25 cm³), not 21.4 cm³. A 50 cm³ measuring cylinder (D) has graduation intervals too large (typically 1 cm³) and is not precise enough to measure to 0.1 cm³. A 50 cm³ burette (C) has fine graduations (0.1 cm³) and allows any volume up to 50 cm³ to be delivered exactly, including 21.4 cm³.
✅ Answer: (C)

Question 40

An aqueous solution of compound M is tested. The results are shown.
• a lilac colour in a flame test
• a white precipitate when tested with acidified barium nitrate
What is compound M?
A copper(II) chloride
B copper(II) sulfate
C potassium carbonate
D potassium sulfate

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

• Topic 12.5: Identification of ions and gases — flame test to identify cations (potassium gives lilac flame); test for sulfate ions (acidified barium nitrate gives white precipitate).

▶️ Answer/Explanation

A lilac flame test indicates the presence of potassium ions (K⁺). A white precipitate with acidified barium nitrate confirms the presence of sulfate ions (SO₄²⁻), because barium sulfate is insoluble in acid. Copper(II) compounds give a blue-green flame, not lilac, and carbonates produce effervescence with acid, not a white precipitate with barium nitrate. Therefore compound M must be potassium sulfate.
✅ Answer: D (potassium sulfate)