0620_s24_qp_11-hina

Question 1

The boiling point of sodium is 890°C. What happens to sodium atoms as the temperature of a sample of sodium changes from 950 °C to 900°C?
A The atoms move more quickly and bonds are formed.
B The atoms move more quickly and bonds are neither broken nor formed.
C The atoms move more slowly and bonds are formed.
D The atoms move more slowly and bonds are neither broken nor formed.

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); Explain changes of state in terms of kinetic particle theory, including the interpretation of heating and cooling curves (Supplement)

▶️ Answer/Explanation

At 950°C, sodium is above its boiling point (890°C), so it exists as a gas. When cooled to 900°C (still above the boiling point), it remains a gas; only the kinetic energy of the atoms decreases, causing them to move more slowly. No condensation (gas → liquid) occurs because the temperature is still above the boiling point, so no new metallic bonds are formed between atoms.
✅ Answer: (D)

Question 2

Which row shows the conditions for the particles of a gas colliding most frequently?

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 6.2: Rate of reaction — Describe collision theory in terms of number of particles per unit volume and frequency of collisions

▶️ Answer/Explanation

Collision frequency increases when particles are closer together (higher pressure) and when they move faster (higher temperature). High pressure reduces volume, increasing particle density; high temperature gives particles greater kinetic energy, increasing the speed and frequency of collisions. Looking at the table, row B shows both high pressure and high temperature, which provides the conditions for the most frequent collisions.
✅ Answer: B

Question 3

The diagram shows some properties of particles in an atom. To which labelled part of the diagram do electrons belong?

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

• 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)
• Topic 2.2: State the relative charges and relative masses of a proton, a neutron and an electron (Core)

▶️ Answer/Explanation

Electrons are negatively charged subatomic particles that are located outside the nucleus in shells. In the diagram, the part labelled with negative charge and very low mass (often indicated by a “–” symbol and very small relative mass) corresponds to electrons. The nucleus contains protons (positive, mass ~1) and neutrons (neutral, mass ~1), so electrons belong to the region far from the nucleus with negligible mass and negative charge.
✅ Answer: B

Question 4

Some properties of substances W, X, Y and Z are shown.

Which substances are ionic?

A. W, X and Y

B. W and Y only

C. W and Z

D. X and Z

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

• Topic 2.4: Ions and ionic bonds — Describe the properties of ionic compounds: (a) high melting points and boiling points (b) good electrical conductivity when aqueous or molten and poor when solid (Core)

▶️ Answer/Explanation

Ionic compounds are characterized by high melting points (due to strong electrostatic forces in the giant lattice) and the ability to conduct electricity only when molten or in solution (as ions are then free to move), not when solid. Examining the table: W has a high melting point and conducts only when molten (ionic). X has a low melting point (typical of simple molecular substances). Y has a high melting point but never conducts, which is consistent with a giant covalent structure (like diamond). Z has a high melting point and conducts when molten and solid (indicating metallic bonding). Therefore, only W and Z are ionic.
✅ Answer: (C) W and Z

Question 5

Atoms lose or gain electrons to become ions. Which row is correct?

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

▶️ Answer/Explanation

Magnesium (Mg) has 12 protons and loses 2 electrons to become Mg²⁺, which still has 12 protons but now 10 electrons. Fluorine (F) has 9 protons and gains 1 electron to become F⁻, resulting in 9 protons and 10 electrons. Evaluating each row: Row A (F: 9p, 9e) is incorrect (should be 10e); Row B (Mg: 12p, 10e) has electrons wrong; Row D (Mg: 12p, 12e) has electrons wrong. Only Row C correctly shows Mg²⁺ with 12 protons and 10 electrons, and F⁻ with 9 protons and 10 electrons.
✅ Answer: (C)

Question 6

A covalent molecule, M, contains four shared pairs of electrons. What is M?

A. ammonia, \(NH_3\)
B. hydrogen chloride, HCl
C. methane, \(CH_4\)
D. water, \(H_2O\)

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

• Topic 2.5: Simple molecules and covalent bonds — Describe the formation of covalent bonds in simple molecules, including H₂, Cl₂, H₂O, CH₄, NH₃ and HCl. Use dot-and-cross diagrams to show the electronic configurations in these and similar molecules (Core).

▶️ Answer/Explanation

Each shared pair of electrons represents one covalent bond. Methane (CH₄) has four single covalent bonds (C–H), each formed by sharing one electron pair from carbon with one from each hydrogen atom. In contrast, NH₃ has three shared pairs, HCl has one, and H₂O has two, making methane the only molecule with exactly four shared pairs.
✅ Answer: (C)

Question 7

Which substance has a giant covalent structure?
A sodium chloride
B sodium
C ethane
D diamond

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

A giant covalent structure consists of a network of atoms bonded by covalent bonds in a continuous lattice. Sodium chloride (A) is an ionic compound, sodium (B) is a metallic lattice, and ethane (C) is a simple molecular substance with weak intermolecular forces. Diamond (D) is an allotrope of carbon where each carbon atom forms four covalent bonds, creating a rigid three‑dimensional giant covalent network.
✅ Answer: D

Question 8

Iron(III) oxide is reduced by carbon monoxide to produce iron and carbon dioxide. What is the balanced equation for this reaction?
A \(Fe_2O_3 + 2CO → 2Fe + 2CO_2\)
B \(Fe_2O_3 + 3CO → 2Fe + 3CO_2\)
C \(2Fe_2O_3 + 6CO → 2Fe + 6CO_2\)
D \(2Fe_2O_3 + 3CO → 4Fe + 3CO_2\)

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

• Topic 9.6: Extraction of metals — Describe the extraction of iron from hematite in the blast furnace, limited to: (c) the reduction of iron(III) oxide by carbon monoxide (Core); State the symbol equations for the extraction of iron from hematite, e.g. Fe₂O₃ + 3CO → 2Fe + 3CO₂ (Supplement)

▶️ Answer/Explanation

In the blast furnace extraction of iron, carbon monoxide reduces iron(III) oxide. One formula unit of Fe₂O₃ contains two iron atoms and three oxygen atoms; removing all oxygen requires three CO molecules, producing three CO₂ molecules and leaving two Fe atoms. Option B correctly balances the atoms and charges. Options A, C, and D do not balance both iron and oxygen atoms correctly.
✅ Answer: (B)

Question 9

The equation for the reaction between magnesium and dilute hydrochloric acid is shown.
\(Mg + 2HCl \rightarrow MgCl_2 + H_2\)
Which mass of magnesium chloride is formed when 48.0 g of magnesium completely reacts with excess dilute hydrochloric acid?

A 23.8 g

B 47.5 g

C 95.0 g

D 190 g

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

• Topic 3.2: Relative masses of atoms and molecules — Calculate reacting masses in simple proportions. Calculations will not involve the mole concept (Core).
• Topic 3.3: The mole and the Avogadro constant — Calculate stoichiometric reacting masses (Supplement).

▶️ Answer/Explanation

First, calculate the moles of Mg: atomic mass of Mg = 24 g/mol, so moles = 48.0 g / 24 g/mol = 2.0 mol. From the balanced equation, 1 mol Mg produces 1 mol MgCl₂. Thus, 2.0 mol of MgCl₂ is formed. The molar mass of MgCl₂ = 24 + (2 × 35.5) = 95 g/mol. Therefore, mass of MgCl₂ = 2.0 mol × 95 g/mol = 190 g.
✅ Answer: (D) 190 g

Question 10

Dilute sulfuric acid and lead(II) bromide are electrolysed separately. Which statements are correct?

1 Colourless gases are produced when dilute sulfuric acid is electrolysed.
2 Lead(II) bromide can be electrolysed when molten.
3 Lead is formed at the positive electrode when lead(II) bromide is electrolysed.
4 Sulfate ions are produced at the negative electrode when dilute sulfuric acid is electrolysed.

A 1 and 2

B 1 and 3

C 2 and 3

D 3 and 4

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

• Topic 4.1: Electrolysis — Identify the products formed at the electrodes during the electrolysis of dilute sulfuric acid using inert electrodes (Core); Identify the products formed at the electrodes during the electrolysis of molten lead(II) bromide (Core); State that metals or hydrogen are formed at the cathode (Core).

▶️ Answer/Explanation

Statement 1 is correct: electrolysis of dilute H₂SO₄ produces colourless hydrogen and oxygen gases. Statement 2 is correct: lead(II) bromide must be molten for electrolysis as ions must be mobile. Statement 3 is incorrect: lead forms at the negative electrode (cathode), not the positive electrode. Statement 4 is incorrect: sulfate ions are negative and move to the positive electrode (anode), not the negative electrode.
✅ Answer: (A) 1 and 2

Question 11

Which statements about a hydrogen–oxygen fuel cell are correct?
1 The main form of energy released by the fuel cell is heat.
2 The reaction is a redox reaction.
3 An acidic gas is produced.
4 Water is the only chemical product.

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 4.2: 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); Describe the advantages and disadvantages of using hydrogen‑oxygen fuel cells in comparison with gasoline/petrol engines (Supplement)

▶️ Answer/Explanation

A hydrogen‑oxygen fuel cell converts chemical energy directly into electrical energy, so the main form of energy released is not heat (statement 1 is false). The overall reaction (2H₂ + O₂ → 2H₂O) involves both oxidation (H₂ → H⁺ + e⁻) and reduction (O₂ + 4e⁻ + 4H⁺ → 2H₂O), making it a redox reaction (statement 2 is true). The only chemical product is water, which is neutral, not an acidic gas (statement 3 is false, statement 4 is true). Therefore, the correct statements are 2 and 4.
✅ Answer: D

Question 12

Which row describes what happens during an endothermic reaction?

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).

▶️ Answer/Explanation

Detailed Solution: An endothermic reaction absorbs thermal energy from the surroundings. As energy is taken in, the temperature of the immediate surroundings decreases. The products of the reaction have more chemical energy stored in their bonds than the reactants did. Therefore, the correct row shows “heat taken in” and “temperature decrease”.
✅ Answer: A

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Question 13

Which diagram represents a chemical change?

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)
• Topic 2.5: Simple molecules and covalent bonds — Describe the formation of covalent bonds in simple molecules (Core)

▶️ Answer/Explanation

A chemical change involves the formation of new substances with different chemical properties, typically through the breaking and forming of chemical bonds. Diagram B shows two smaller molecules (represented by two circles) joining to form a single larger molecule; this represents a synthesis reaction, which is a chemical change. The other diagrams show physical changes: A shows dissolving, C shows pouring (a change of shape/container), and D shows mixing of gases, none of which create new chemical substances.
✅ Answer: (B)

Question 14

A method used to investigate the rate of reaction of calcium carbonate with dilute hydrochloric acid under different conditions is shown. Place 50 cm³
• of dilute hydrochloric acid in a conical flask.
• Add a known volume of water to the conical flask.
• Heat the conical flask to the required temperature.
• Add 1.0 g of calcium carbonate to the conical flask.
• Measure the time taken for the reaction to finish.
Which volume of water and which temperature give the shortest time taken for the reaction to finish?

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

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

▶️ Answer/Explanation

Adding more water dilutes the acid, lowering the concentration and decreasing the rate of reaction (fewer collisions per second). Higher temperature increases the rate (particles have more kinetic energy, more frequent and energetic collisions). To get the shortest time, we need the highest temperature (50°C) and the smallest added water volume (0 cm³) to keep acid concentration highest. Looking at the table, the combination with 0 cm³ water and 50°C gives the fastest reaction.
✅ Answer: B

Question 15

The rate of reaction between magnesium and hydrochloric acid is investigated. The total volume of hydrogen given off is measured at different times. A graph of the results is shown.

Which conclusions are correct?
1 The rate is fastest between 0 and 30 seconds.
2 The maximum volume of hydrogen given off is 22 cm³.
3 At 40 seconds, 20 cm³ of hydrogen is given off.

A. 1 and 2 only

B. 1 and 3 only

C. 2 and 3 only

D. 1, 2 and 3

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

• Topic 6.2: Rate of reaction — Interpret data, including graphs, from rate of reaction experiments (Core); Describe and explain the effect on the rate of reaction using collision theory (Supplement)

▶️ Answer/Explanation

✅ Answer: A (1 and 2 only)

Statement 1 is correct because the slope of the graph is steepest between 0 and 30 seconds, indicating the highest rate of hydrogen production. Statement 2 is correct as the graph flattens at 22 cm³, showing the reaction is complete. Statement 3 is incorrect because at 40 seconds, the graph clearly shows a volume of approximately 21 cm³, not 20 cm³.

Question 16

Water is added to anhydrous copper(II) sulfate. Which row describes the direction of energy change and the colour change of the mixture during the reaction?

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

• Topic 2.4: Ions and ionic bonds (hydrated/anhydrous salts)
• 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 (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

Correct answer: D

Adding water to anhydrous copper(II) sulfate (white solid) causes it to become hydrated copper(II) sulfate (blue crystals). This is an exothermic process, meaning heat energy is released to the surroundings, making the test tube feel warm. The colour change observed is from white to blue, which is also the standard chemical test for water.

Question 17

Which equation represents an oxidation reaction?

A \(CaCO_3 \rightarrow CaO + CO_2\)
B \(4FeO + O_2 \rightarrow 2Fe_2O_3\)
C \(2NO_2 \rightarrow N_2O_4\)
D \(2P_2O_5 \rightarrow P_4O_{10}\)

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

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

▶️ Answer/Explanation

Oxidation is defined as the gain of oxygen. In option B, iron(II) oxide (FeO) gains oxygen to form iron(III) oxide (Fe₂O₃), so this represents an oxidation reaction. Options A is a thermal decomposition, C is a combination without oxygen gain, and D involves no change in oxidation state of phosphorus from +5.
✅ Answer: (B)

Question 18

A farmer treats a field with calcium hydroxide to make it less acidic. When the farmer adds ammonium nitrate fertiliser to the field immediately after the calcium hydroxide, the two substances react. Why does this reaction make the fertiliser less effective?

A. It makes ammonia gas, so less nitrogen is absorbed by the soil.
B. It makes an acid, making the soil acidic again.
C. It makes nitrogen gas, so less nitrogen is absorbed by the soil.
D. It makes the fertiliser too strong, stopping the plants growing well.

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

• Topic 7.1: The characteristic properties of acids and bases — Define bases as proton acceptors (Supplement).
• Topic 10.2: Fertilisers — State that ammonium salts are used as fertilisers (Core).
• Topic 6.4: Redox (implicitly, via base reaction) and Topic 7.3 Preparation of salts.

▶️ Answer/Explanation

Calcium hydroxide (a base, Ca(OH)₂) reacts with ammonium nitrate (an ammonium salt, NH₄NO₃) to produce calcium nitrate, water, and ammonia gas (NH₃). This reaction causes loss of nitrogen from the fertiliser into the atmosphere as ammonia gas, thereby reducing the amount of nitrogen available for plant absorption from the soil.
✅ Answer: (A)

Question 19

Which statement about sodium oxide or nitrogen dioxide is correct?

A. Nitrogen dioxide is a solid at room temperature.
B. Nitrogen dioxide is acidic.
C. Sodium oxide has a lower melting point than nitrogen dioxide.
D. Sodium oxide is covalently bonded.

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

• Topic 7.1: The characteristic properties of acids and bases — Classify oxides as acidic or basic related to metallic and non-metallic character (Core)

• Topic 7.2: Oxides — Classify oxides as acidic (including SO₂ and CO₂) or basic (including CuO and CaO) (Core); Nitrogen dioxide (NO₂) is a non-metal oxide and thus acidic

▶️ Answer/Explanation

✅ Answer: B
Nitrogen dioxide (NO₂) is a non-metal oxide which dissolves in water to form an acidic solution (nitric and nitrous acids), making it an acidic oxide. Sodium oxide (Na₂O) is an ionic metal oxide with a very high melting point due to its giant ionic lattice, while NO₂ is a simple covalent molecule that is a gas at room temperature, so NO₂ has a much lower melting point than Na₂O, not the other way around. Therefore, only statement B is correct.

Question 20

A titration method is used to prepare a pure soluble sulfate salt from dilute sulfuric acid. What is the other reagent?

A. copper(II) oxide
B. magnesium
C. sodium hydroxide
D. zinc carbonate

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 by titration (Core)

▶️ Answer/Explanation

A titration method is specifically used when the reactant is a soluble base (alkali) and an acid, because it allows precise neutralisation without adding excess solid. Copper(II) oxide, magnesium, and zinc carbonate are all insoluble in water and would be better prepared using an excess solid method followed by filtration, not titration. Sodium hydroxide is a soluble alkali that reacts with dilute sulfuric acid in a titration to produce the soluble salt sodium sulfate and water.
✅ Answer: (C)

Question 21

Which row about elements in the Periodic Table is correct?

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

• Topic 8.1: Arrangement of elements — Describe the change from metallic to non-metallic character across a period; Explain similarities in chemical properties of elements in the same group in terms of their electronic configuration (Core)
• Topic 8.2: Group I properties — Describe alkali metals as relatively soft metals with trends down the group (Core)
• Topic 8.3: Group VII properties — Describe halogens as diatomic non-metals with trends down the group (Core)

▶️ Answer/Explanation

Detailed solution: Across a period from left to right, elements change from metallic to non-metallic character, so row A is correct. Down Group I, melting points decrease (not increase), so row B is incorrect. Down Group VII, reactivity decreases (not increases), so row C is incorrect. Elements in the same group have the same number of outer-shell electrons (not the same number of occupied shells, which increases down a group), so row D is incorrect.
✅ Answer: A

Question 22

The table gives some information about three elements in Group I of the Periodic Table.

Which row identifies the melting point and the density of rubidium?

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

• Topic 8.2: Group I properties — Describe the Group I alkali metals (lithium, sodium, potassium) as relatively soft metals with general trends down the group: decreasing melting point and increasing density (Core). Predict the properties of other elements in Group I, given information about the elements.

▶️ Answer/Explanation

Detailed Solution: Moving down Group I (from lithium to sodium to potassium), the melting point decreases significantly (from 180°C to 98°C to 63°C) and the density increases (from 0.53 to 0.97 to 0.86 g/cm³; note potassium is less dense than sodium, but the overall trend is increasing density with a slight anomaly). Rubidium is below potassium, so its melting point should be even lower than 63°C (option B: 39°C) and its density should be higher than 0.86 g/cm³ (option B: 1.53 g/cm³). Option A has a higher melting point, option C has a lower density, and option D has both melting point and density values inconsistent with the downward trend.

✅ Answer: (B)

Question 23

Which statement describes a transition element?

A. It is a dull grey metal that only forms white compounds.
B. It is a high-density metal with a high melting point that is used as a catalyst.
C. It is a low-density metal with a high melting point that reacts with steam to make hydrogen.
D. It is a soft, shiny silver metal that reacts vigorously with water.

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

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

▶️ Answer/Explanation

Transition elements are characterised by high densities, high melting points, and the ability to act as catalysts (e.g., iron in the Haber process, vanadium(V) oxide in the Contact process). They also typically form coloured compounds, not just white ones. The other options describe properties of non-transition metals (e.g., Group I or II metals), not transition elements.
✅ Answer: (B)

Question 24

The electronic configurations of helium, neon and argon are shown.

Which row describes these gases?

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)

• Topic 2.2: Atomic structure and the Periodic Table — State that Group VIII noble gases have a full outer electron shell (Core)

▶️ Answer/Explanation

Helium, neon, and argon are noble gases (Group VIII). They are all monatomic (exist as single atoms) and unreactive because they have full outer electron shells (2 for He, 8 for Ne and Ar). This corresponds to row D, which correctly states both properties.
✅ Answer: D

Question 25

X is a shiny silver-coloured solid at room temperature and pressure. X is a good conductor of heat and electricity when solid. Which statement about X is correct?

A. X is an ionic compound or a metallic element.
B. X is a metallic element or a non-metallic element.
C. X is an alloy or a metallic element.
D. X is an alloy or a non-metallic element.

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

• Topic 9.1: Properties of metals — Compare the general physical properties of metals and non-metals, including electrical conductivity, thermal conductivity, malleability and ductility, melting points and boiling points.
• Topic 9.3: Alloys and their properties — Describe an alloy as a mixture of a metal with other elements, and state that alloys can be harder and stronger than the pure metals.

▶️ Answer/Explanation

The properties described—shiny, solid at room temperature, and good conduction of heat and electricity—are characteristic of metals. Both pure metallic elements (like copper or silver) and alloys (mixtures of metals, like brass or steel) exhibit these properties. Ionic compounds do not conduct electricity when solid, and non-metallic elements are typically not shiny or good conductors. Therefore, X must be either an alloy or a metallic element.
✅ Answer: (C)

Question 26

Which elements can be combined to produce an alloy?
1 magnesium and aluminium
2 nitrogen and oxygen
3 iron and carbon
4 copper and zinc

A 1, 3 and 4

B 1 and 2

C 2 and 3

D 4 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 brass as a mixture of copper and zinc, stainless steel as a mixture of iron and other elements such as chromium, nickel and carbon (Core)

▶️ Answer/Explanation

An alloy is a mixture of a metal with at least one other element (metal or non-metal). Magnesium and aluminium are both metals and can form alloys (e.g., Magnalium). Iron and carbon together make steel (an alloy). Copper and zinc make brass (an alloy). Nitrogen and oxygen are both non-metals and do not form an alloy. Therefore, combinations 1, 3, and 4 are correct.
✅ Answer: (A) 1, 3 and 4

Question 27

Three metals, L, M and N, are added separately to dilute hydrochloric acid and cold water. The results are shown.

What is the order of reactivity of the metals?

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

• Topic 9.4: Reactivity series — Describe the reactions of metals with dilute hydrochloric acid and cold water, and deduce an order of reactivity from experimental results.
• Topic 9.4: Supplement — Describe the relative reactivities of metals in terms of their tendency to form positive ions, by displacement reactions.

▶️ Answer/Explanation

Metal M reacts vigorously with cold water and rapidly with dilute HCl, placing it highest in the reactivity series (similar to Na or Ca). Metal L does not react with cold water but reacts rapidly with dilute HCl, so it is less reactive than M but more reactive than N. Metal N does not react with cold water and reacts slowly with dilute HCl, making it the least reactive. Therefore the order of reactivity is M > L > N.
✅ Answer: C

Question 28

Which reaction produces carbon dioxide?

A. cracking of large hydrocarbon molecules
B. photosynthesis
C. reaction of a base with a carbonate
D. thermal decomposition of calcium carbonate

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 carbonates (Core)
• Topic 9.6: Extraction of metals — Describe the thermal decomposition of calcium carbonate/limestone to produce calcium oxide (Core)
• Topic 11.5: Alkenes — Describe the manufacture of alkenes and hydrogen by the cracking of larger alkane molecules (Core)
• Topic 10.3: Air quality and climate — Photosynthesis word equation (Core)

▶️ Answer/Explanation

Cracking breaks large alkanes into smaller alkenes and hydrogen (no CO₂). Photosynthesis consumes CO₂ to produce glucose and oxygen. A base reacting with a carbonate produces a salt, water, and carbon dioxide — this is a correct method to produce CO₂. Thermal decomposition of calcium carbonate (CaCO₃ → CaO + CO₂) also produces carbon dioxide. Since the question asks which reaction produces CO₂, both C and D are correct in general chemistry, but in IGCSE context, the most direct and unambiguous answer is the reaction of a base with a carbonate as a standard laboratory test for carbonates producing CO₂.
✅ Answer: (C)

Question 29

A sample of air containing four gases only is analysed. 99.0% of the sample contains the two main gases in the same percentages as in clean, dry air. The remaining 1.0% of the sample contains argon and carbon dioxide. The gas that makes up 0.1% of the sample turns limewater milky. Which row shows the percentage composition of the sample of air?

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

• Topic 10.3: Air quality and climate — State the composition of clean, dry air as approximately 78% nitrogen, N₂, 21% oxygen, O₂ and the remainder as a mixture of noble gases and carbon dioxide, CO₂ (Core)

• Topic 12.5: Identification of ions and gases — Describe tests to identify the gases: carbon dioxide, CO₂, using limewater (Core)

▶️ Answer/Explanation

Clean, dry air is 78% nitrogen and 21% oxygen, totalling 99%. The remaining 1% is argon and CO₂. The gas that turns limewater milky is CO₂, given as 0.1%. Therefore, argon = 1.0% – 0.1% = 0.9%. The full composition is: N₂ = 78%, O₂ = 21%, Ar = 0.9%, CO₂ = 0.1%.
✅ Answer: (A)

Question 30

Which substance contains two elements that are found in NPK fertilisers?

A. ammonium chloride
B. calcium hydroxide
C. potassium nitrate
D. sodium phosphate

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

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

▶️ Answer/Explanation

NPK fertilisers contain the essential elements Nitrogen (N), Phosphorus (P), and Potassium (K). Potassium nitrate (KNO₃) contains both potassium (K) from the ‘K’ in NPK and nitrogen (N) from the ‘N’. Ammonium chloride (NH₄Cl) contains nitrogen but not phosphorus or potassium; calcium hydroxide (Ca(OH)₂) contains none of the three; sodium phosphate (Na₃PO₄) contains phosphorus but lacks potassium.
✅ Answer: C

Question 31

Which statement about sulfur is correct?
A When sulfur is burned, it produces a substance that causes acid rain.
B Sulfur is produced by the thermal decomposition of limestone.
C Compounds of sulfur make up approximately 1% of unpolluted air.
D Sulfur is a member of the family of elements called halogens.

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

• Topic 10.3: Air quality and climate — sulfur dioxide from the combustion of fossil fuels which contain sulfur compounds (Core); adverse effect: acid rain (Core)
• Topic 8.2/8.3: Group I / Group VII — sulfur is not a halogen; halogens are Group VII (Core)
• Topic 9.6: Extraction of metals — limestone decomposes to calcium oxide, not sulfur (Core)

▶️ Answer/Explanation

When sulfur is burned in air, it reacts with oxygen to form sulfur dioxide (SO₂). Sulfur dioxide is released into the atmosphere and dissolves in rainwater to form sulfurous acid, leading to acid rain. Limestone decomposition produces calcium oxide and carbon dioxide, not sulfur. Unpolluted air is about 78% nitrogen and 21% oxygen, with noble gases and CO₂ making up the remainder; sulfur compounds are not 1%. Halogens are Group VII (fluorine, chlorine, etc.); sulfur is in Group VI.
✅ Answer: (A)

Question 32

Questions 32

What are two adverse effects of particulates in the air?
1 acid rain
2 cancer
3 photochemical smog
4 respiratory problems
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 — particulates: increased risk of respiratory problems and cancer (Core)

▶️ Answer/Explanation

The syllabus clearly states that particulates from incomplete combustion cause increased risk of respiratory problems (effect 4) and cancer (effect 2). Acid rain (effect 1) is caused by sulfur dioxide and oxides of nitrogen, not particulates. Photochemical smog (effect 3) is mainly due to oxides of nitrogen and volatile organic compounds. Therefore, the correct pair of adverse effects from particulates is cancer and respiratory problems.
✅ Answer: (D)

Question 33

Which formula represents a compound that is a member of the homologous series of alkanes?
A \(C_2H_4\)

B \(C_3H_6\)

C \(C_4H_8\)

D \(C_5H_{12}\)

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

• Topic 11.1: Formulae, functional groups and terminology — Write and interpret general formulae of compounds in the same homologous series, limited to alkanes, \(C_nH_{2n+2}\) (Core)
• Topic 11.2: Naming organic compounds — State the type of compound present, given a molecular formula (Core)

▶️ Answer/Explanation

Alkanes are saturated hydrocarbons with the general formula \(C_nH_{2n+2}\). For \(n = 5\), the formula becomes \(C_5H_{12}\), which fits this pattern. Options A, B and C follow the alkene general formula \(C_nH_{2n}\) (or cycloalkane), not alkanes. Therefore, only D represents an alkane.
✅ Answer: (D) \(C_5H_{12}\)

Question 34

Which statement about ethane is correct?
A It rapidly decolourises aqueous bromine.
B It does not burn.
C It forms long-chain compounds called polymers.
D It only contains single bonds between its atoms.

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

• Topic 11.4: Alkanes — State that the bonding in alkanes is single covalent and that alkanes are saturated hydrocarbons.

▶️ Answer/Explanation

Ethane is an alkane (C₂H₆), meaning it is a saturated hydrocarbon containing only carbon-carbon single bonds. It does not decolourise aqueous bromine under normal conditions (unlike alkenes), does burn (combustion), and does not polymerise. Therefore, the only correct statement is that it only contains single bonds between its atoms.
✅ Answer: (D)

Question 35

Which raw material is used to make ethanol by fermentation?

A. carbon dioxide
B. ethene
C. glucose
D. natural gas

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

• Topic 11.6: Alcohols — Describe the manufacture of ethanol by fermentation of aqueous glucose at 25–35°C in the presence of yeast and in the absence of oxygen (Core).

▶️ Answer/Explanation

Fermentation is an anaerobic process where yeast converts sugars into ethanol and carbon dioxide. The most common sugar used is glucose. Ethene (B) is used to make ethanol via catalytic hydration (an industrial process, not fermentation). Carbon dioxide (A) and natural gas (D) are not raw materials for fermentation.
✅ Answer: (C)

Question 36

Which statement about ethanoic acid is correct?
A It contains a –COOH group.
B It has a pH greater than pH 7.
C It reacts with sodium carbonate to form hydrogen gas.
D It reacts with copper to form copper(II) ethanoate.

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

• Topic 11.7: Carboxylic acids — Describe the reaction of ethanoic acid with metals, bases, carbonates including names and formulae of the salts produced (Core).
• Topic 7.1: The characteristic properties of acids and bases — Define acids as proton donors; state that aqueous solutions of acids contain H⁺ ions (Supplement).

▶️ Answer/Explanation

Ethanoic acid (CH₃COOH) is a carboxylic acid, and all carboxylic acids contain the functional group –COOH, so statement A is correct. Ethanoic acid is a weak acid, so its pH is below 7, not above (B is wrong). It reacts with sodium carbonate to produce carbon dioxide gas, not hydrogen (C is wrong). Copper is below hydrogen in the reactivity series and does not react with dilute acids like ethanoic acid, so D is wrong.
✅ Answer: (A)

Question 37

Which statement explains why the disposal of plastic waste leads to environmental problems?
A. Plastic waste forms toxic gases when it is burned.
B. Plastic waste contains many small molecules.
C. Plastic waste rapidly dissolves in the oceans.
D. Plastic waste reacts with both acids and bases.

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

• Topic 11.8: Polymers — Describe the environmental challenges caused by plastics, limited to: disposal in landfill sites, accumulation in oceans, formation of toxic gases from burning (Core)

▶️ Answer/Explanation

Burning plastic waste (especially chlorinated plastics like PVC) releases toxic gases such as hydrogen chloride, dioxins, and furans, which harm human health and the environment. Plastics do not rapidly dissolve in oceans (they persist for hundreds of years) and are generally unreactive toward acids/bases. They are made of long-chain polymers, not many small molecules. Therefore, option A correctly explains an environmental problem caused by plastic disposal.
✅ Answer: A

Question 38

Substance X and four known substances, P, Q, R and S, are analysed by chromatography. The chromatogram produced is shown.

Which statement about X is correct?
A It is a mixture of P, Q and S.
B It contains P and S only.
C It contains P, S and another unknown substance.
D It is a mixture of Q, R and S.

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

• Topic 12.3: Chromatography — Interpret simple chromatograms to identify unknown substances by comparison with known substances (Core)

▶️ Answer/Explanation

In paper chromatography, each component moves up the paper by a characteristic distance. Comparing the spots of substance X with known substances P, Q, R and S, X shows a spot at the same height as P, a spot at the same height as S, and an additional spot that does not match any of the four known substances. This means X contains P, S and another unknown substance.
✅ Answer: (C)

Question 39

Copper is insoluble in water. Copper(II) oxide is a solid that is insoluble in water but reacts with dilute hydrochloric acid. Which method is used to separate copper from a mixture of copper and copper(II) oxide?

A. dissolve the mixture in water then filter
B. dissolve the mixture in water then crystallise
C. react the mixture with dilute hydrochloric acid then filter
D. react the mixture with dilute hydrochloric acid then crystallise

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 excess metal, excess insoluble base, or excess insoluble carbonate (Core)
• Topic 12.4: Separation and purification — Describe and explain methods of separation and purification using filtration (Core)

▶️ Answer/Explanation

Detailed Solution: Copper(II) oxide reacts with dilute hydrochloric acid to form soluble copper(II) chloride and water, while copper metal remains unreacted because it is below hydrogen in the reactivity series and does not react with dilute acids. Filtration after this reaction will separate the insoluble copper as the residue from the solution containing the reacted copper compound. Dissolving in water alone (options A and B) fails because both substances are insoluble in water. Crystallisation (option D) would not separate the two solids.

✅ Answer: (C)

Question 40

A salt, S, is dissolved in water and three tests are carried out on the solution formed.

What is the identity of S?
A copper(II) chloride
B copper(II) sulfate
C iron(II) chloride
D iron(II) sulfate

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

• Topic 12.2: Acid-base titrations (Note: This question primarily tests ion identification, which falls under Topic 12.5). Topic 12.5: Identification of ions and gases — Describe tests using aqueous sodium hydroxide and aqueous ammonia to identify the aqueous cations including copper(II) and iron(II); Describe tests to identify the anion sulfate, SO₄²⁻, by acidifying with dilute nitric acid and then adding aqueous barium nitrate.

▶️ Answer/Explanation

The light blue precipitate with both NaOH and aq. ammonia (soluble in excess ammonia) identifies the cation as copper(II) (Cu²⁺). The white precipitate with acidified barium nitrate confirms the presence of sulfate ions (SO₄²⁻). Therefore, the salt is copper(II) sulfate. Options A and C are incorrect because chloride would not give a precipitate with barium nitrate. Option D is incorrect because iron(II) forms a green, not light blue, precipitate.
✅ Answer: (B) copper(II) sulfate