0620_s24_qp_22-hina

Question 1

Which gas has the slowest rate of diffusion?

A. \(H_2\)
B. \(NH_3\)
C. \(CH_4\)
D. \(CO_2\)

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

• Topic 1.2: Diffusion — Describe and explain the effect of relative molecular mass on the rate of diffusion of gases (Supplement)

▶️ Answer/Explanation

According to Graham’s law of diffusion, the rate of diffusion of a gas is inversely proportional to the square root of its relative molecular mass. Therefore, the gas with the highest relative molecular mass diffuses slowest. Among the options, \(CO_2\) has the highest relative molecular mass (44), followed by \(NH_3\) (17), \(CH_4\) (16), and \(H_2\) (2). Hence, carbon dioxide diffuses slowest.
✅ Answer: (D)

Question 2

Which statements about the position of the elements in the Periodic Table are correct?
1 Elements in the same group have similar chemical properties.
2 Elements in the same period have similar chemical properties.
3 Elements in the same group have the same number of electron shells.
4 Elements in the same group have the same number of outer shell electrons.
A 1 and 3

B 1 and 4

C 2 and 3

D 2 and 4

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

• Topic 8.1: Arrangement of elements — Explain similarities in the chemical properties of elements in the same group of the Periodic Table in terms of their electronic configuration (Core).
• Topic 2.2: Atomic structure and the Periodic Table — State that the number of outer shell electrons is equal to the group number in Groups I to VII, and the number of occupied electron shells is equal to the period number (Core).

▶️ Answer/Explanation

Answer: B (1 and 4)

Statement 1 is correct because elements in the same group have the same number of outer shell electrons, which governs their chemical reactions. Statement 2 is incorrect; elements in the same period show a gradual change in properties and do not have similar chemical properties. Statement 3 is incorrect; elements in the same group have increasing numbers of electron shells as you go down, while elements in the same period have the same number of shells. Statement 4 is correct as the group number (for Groups I to VII) equals the number of outer shell electrons.

Question 3

Which statements about isotopes are correct?

1 Isotopes are atoms of different elements with the same number of protons.
2 Isotopes of the same element have the same chemical properties.
3 Isotopes are atoms with the same relative atomic mass.
4 Isotopes of the same element have the same electronic configuration.

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 2.3: Isotopes — Define isotopes as different atoms of the same element that have the same number of protons but different numbers of neutrons; State that isotopes of the same element have the same chemical properties because they have the same number of electrons and therefore the same electronic configuration.

▶️ Answer/Explanation

Statement 1 is false: isotopes are atoms of the same element (same proton number), not different elements. Statement 2 is true: having the same electronic configuration means they have identical chemical properties. Statement 3 is false: isotopes have different mass numbers, so their relative atomic masses differ. Statement 4 is true: isotopes of an element have the same number of electrons and thus the same electronic configuration. Therefore, only statements 2 and 4 are correct.
✅ Answer: C (2 and 4)

Question 4

Which diagram shows the arrangement of the outer shell electrons in a molecule of water?

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 H₂O, using dot-and-cross diagrams to show the electronic configurations (Core).

▶️ Answer/Explanation

A water molecule (H₂O) has one oxygen atom bonded to two hydrogen atoms. Oxygen has 6 outer electrons and needs 2 more to complete its octet, while each hydrogen has 1 electron and shares it with oxygen. Diagram C correctly shows the oxygen atom with 8 outer electrons (2 lone pairs and 4 shared in two single covalent bonds), and each hydrogen atom achieves a duplet with the shared pair. Options A, B, and D do not satisfy the octet rule for oxygen or show incorrect electron sharing and arrangement.
✅ Answer: (C)

Question 5

The structures of three substances are shown.

Which substances are hard and have a high melting point?
A 1, 2 and 3

B 1 only

C 2 only

D 2 and 3 only

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

• Topic 2.5: Simple molecules and covalent bonds — low melting points and boiling points (Core)
• Topic 2.6: Giant covalent structures — hard, high melting point (e.g., diamond, graphite, SiO₂)
• Topic 2.4: Ions and ionic bonds — high melting points and boiling points (Core)

▶️ Answer/Explanation

Structure 1 shows simple molecular (covalent) molecules with weak intermolecular forces — these are soft, low melting point. Structures 2 and 3 show giant covalent network (diamond-like) and giant ionic lattice respectively; both have strong bonds throughout the structure, making them hard and with very high melting points.
✅ Answer: D (2 and 3 only)

Question 6

Information about four substances, W, X, Y and Z, is shown.

W, X, Y and Z are graphite, poly(ethene), sodium chloride and silicon(IV) oxide but not in that order. What are W, X, Y and Z?

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

• Topic 2.6: Giant covalent structures — Describe the giant covalent structures of graphite and diamond; Describe the giant covalent structure of silicon(IV) oxide, SiO₂.
• 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.
• Topic 11.8: Polymers — Describe the formation of poly(ethene) as an example of addition polymerisation using ethene monomers; State that plastics are made from polymers.

▶️ Answer/Explanation

Detailed Solution:
Substance W has a very high melting point (conducts electricity) — this matches graphite, a giant covalent structure with delocalised electrons.
Substance X has a very high melting point (does not conduct) — this matches silicon(IV) oxide, a giant covalent structure with no free charge carriers.
Substance Y has a high melting point (conducts when molten) — this matches sodium chloride, an ionic compound.
Substance Z has a low melting point (does not conduct) — this matches poly(ethene), a simple molecular polymer.
This sequence (W=graphite, X=SiO₂, Y=NaCl, Z=polyethene) corresponds to option D.

✅ Answer: D

Question 7

The structure of glycine is shown.

Which row is correct?

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

• Topic 11.7: Carboxylic acids — Describe the reaction of a carboxylic acid with an alcohol using an acid catalyst to form an ester (Supplement)
• Topic 11.8: Polymers — Describe proteins as natural polyamides formed from amino acid monomers (Supplement)

▶️ Answer/Explanation

Glycine is the simplest amino acid, containing both a basic amino group (–NH₂) and an acidic carboxyl group (–COOH). In aqueous solution, the carboxyl group donates a proton to the amino group, forming a zwitterion with –NH₃⁺ and –COO⁻. This zwitterion is overall neutral. Among the rows, the correct combination is: functional groups = amine and carboxylic acid; formula = C₂H₅NO₂; nature of aqueous solution = neutral (since the positive and negative charges balance).
✅ Answer: B

Question 8

The incomplete equation for photosynthesis is shown.

Compound P is a product of the reaction. Which row describes the values of w, x and y and gives the empirical formula of compound P?

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

• Topic 10.3: Air quality and climate — Photosynthesis as the reaction between carbon dioxide and water to produce glucose and oxygen (Core); State the symbol equation for photosynthesis, 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (Supplement)

▶️ Answer/Explanation

The balanced symbol equation for photosynthesis is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Therefore w = 6, x = 6, and y = 6, making compound P (oxygen) O₂. The empirical formula of O₂ is O because it simplifies to the smallest whole‑number ratio of atoms. Only row A has w=6, x=6, y=6 and empirical formula O.
✅ Answer: (A)

Question 9

The concentration and volume of an aqueous alkali are known. Which additional information is required to calculate the number of moles of acid needed to neutralise the aqueous alkali?

A. the concentration of the acid
B. the equation for the acid–alkali reaction
C. the formula of the acid
D. the volume of the acid required for neutralisation

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

• Topic 7.1: The characteristic properties of acids and bases — Describe the neutralisation reaction between an acid and an alkali to produce water, H⁺(aq) + OH⁻(aq) → H₂O(l) (Core); Define acids as proton donors and bases as proton acceptors (Supplement)

• Topic 3.3: The mole and the Avogadro constant — Use experimental data from a titration to calculate the moles of solute, or the concentration or volume of a solution (Supplement)

▶️ Answer/Explanation

Knowing only the concentration and volume of the alkali gives the moles of alkali (moles = concentration × volume). To find the moles of acid needed for neutralisation, the balanced chemical equation is required because it provides the stoichiometric mole ratio between acid and alkali (e.g., 1:1 for HCl/NaOH, but 1:2 for H₂SO₄/NaOH). Without this ratio, the acid moles cannot be calculated from the alkali moles.
✅ Answer: (B)

Question 10

Which statement about electrolysis is correct?
A. Electrons move through the electrolyte from the cathode to the anode.
B. Electrons move in the external circuit towards the cathode.
C. Negative ions move in the external circuit towards the anode.
D. Positive ions move through the electrolyte towards the anode.

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

• Topic 4.1: Electrolysis — Identify in simple electrolytic cells: the anode as the positive electrode, the cathode as the negative electrode (Core); Describe the transfer of charge during electrolysis to include: the movement of electrons in the external circuit, the loss or gain of electrons at the electrodes, the movement of ions in the electrolyte (Supplement)

▶️ Answer/Explanation

In electrolysis, electrons travel through the external circuit, not through the electrolyte. They move from the anode (where oxidation occurs) towards the cathode (where reduction occurs) because electrons are released at the anode and attracted to the positive terminal of the power supply, then flow to the cathode. Negative ions (anions) move through the electrolyte towards the anode, not in the external circuit. Positive ions (cations) move through the electrolyte towards the cathode, not the anode. Hence only statement B is correct.
✅ Answer: (B)

Question 11

Aqueous copper(II) sulfate is electrolysed using copper electrodes. What is the half-equation for the reaction at the cathode?
A \(2H^+ + 2e^– → H_2\)
B \(4OH^– → O_2 + 2H_2O + 4e^–\)
C \(Cu → Cu^{2+} + 2e^–\)
D \(Cu^{2+} + 2e^– → Cu\)

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 aqueous copper(II) sulfate using inert carbon/graphite electrodes and when using copper electrodes (Supplement); Construct ionic half-equations for reactions at the anode (to show oxidation) and at the cathode (to show reduction) (Supplement)

▶️ Answer/Explanation

With copper electrodes, copper ions (Cu²⁺) from the solution are preferentially reduced at the cathode because copper is less reactive than hydrogen. The half-equation shows copper(II) ions gaining two electrons to deposit as copper metal. Options A and B involve H⁺ or OH⁻, which are not the main reaction here, and option C is oxidation occurring at the anode.
✅ Answer: (D) Cu²⁺ + 2e⁻ → Cu

Question 12

Three statements about activation energy, \(E_a\), are listed.
1 Colliding particles must have at least Ea before they can react.
2 \(E_a\) for exothermic reactions is always greater than for endothermic reactions.
3 \(E_a\) is always endothermic.
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 5.1: Exothermic and endothermic reactions — Define activation energy, \(E_{\mathrm{a}}\) as the minimum energy that colliding particles must have to react (Supplement).

• Topic 6.2: Rate of reaction — Describe collision theory in terms of kinetic energy of particles and activation energy, \(E_{\mathrm{a}}\) (Supplement).

▶️ Answer/Explanation

Statement 1 is correct because activation energy is the minimum kinetic energy colliding particles need to start a reaction. Statement 2 is incorrect; \(E_a\) is independent of reaction type (exothermic or endothermic) and can vary widely. Statement 3 is correct; breaking bonds (required to reach the transition state) always absorbs energy, making the activation process endothermic.
✅ Answer: (C) 1 and 3 only

Question 13

A student adds excess magnesium ribbon to \(10 \, \text{cm}^3\) of \(0.5 \, \text{mol} / \text{dm}^3\) sulfuric acid. The hydrogen gas produced is collected and its total volume is measured every 10 seconds.
The experiment is repeated with \(5 \, \text{cm}^3\) of \(0.5 \, \text{mol} / \text{dm}^3\) sulfuric acid added to \(5 \, \text{cm}^3\) of water using the same mass of magnesium ribbon. Which line on the graph shows the results of the second experiment?

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 (Core); Describe and explain the effect on the rate of reaction using collision theory (Supplement)

▶️ Answer/Explanation

Answer: D

In the second experiment, the sulfuric acid is diluted from 10 cm³ to 10 cm³ total volume (5 cm³ acid + 5 cm³ water), halving the concentration. The rate of reaction decreases because there are fewer H⁺ ions per unit volume, reducing collision frequency. However, the amount (moles) of acid is half, so the total volume of hydrogen gas produced is also halved. Line D shows both a slower initial rate (less steep slope) and a lower final gas volume compared to the original experiment.

Question 14

The equation represents the reversible reaction between ethene and steam.
\(C_2H_4 (g) + H_2O(g) ⇌ C_2H_5OH(g)\) ∆H is negative
Which row describes the conditions that produce the greatest yield of ethanol?

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

• Topic 6.3: Reversible reactions and equilibrium — Predict and explain, for a reversible reaction, how the position of equilibrium is affected by changing temperature and pressure (Supplement).
• Topic 11.5: Alkenes — Describe the properties of alkenes in terms of addition reactions with steam in the presence of an acid catalyst (Supplement).

▶️ Answer/Explanation

Since ΔH is negative, the forward reaction (ethene + steam → ethanol) is exothermic. For an exothermic reversible reaction, a lower temperature favours the forward reaction (increases yield). The reaction also involves a decrease in the number of gas moles (2 moles of gas → 1 mole of gas), so higher pressure favours the forward reaction. Therefore, the greatest yield is achieved at low temperature and high pressure, which corresponds to option C.
✅ Answer: (C)

Question 15

Which row identifies the pressure and the catalyst used for the conversion of sulfur dioxide to sulfur trioxide in the Contact process?

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

• Topic 6.3: Reversible reactions and equilibrium — State the typical conditions for the conversion of sulfur dioxide to sulfur trioxide in the Contact process as 450°C, 200 kPa / 2 atm and a vanadium(V) oxide catalyst (Supplement)
• Topic 8.4: Transition elements — Describe transition elements as metals that often act as catalysts as elements and in compounds (Core)

▶️ Answer/Explanation

According to the Cambridge IGCSE Chemistry syllabus (Section 6.3), the Contact process converts sulfur dioxide to sulfur trioxide using a vanadium(V) oxide catalyst (V₂O₅) at a typical pressure of about 200 kPa (approximately 2 atm) and a temperature of 450°C. Examining the table, Row B correctly lists a pressure of 200 kPa and vanadium(V) oxide as the catalyst, matching these exact specifications. The other rows either use an incorrect catalyst (such as iron, which is for the Haber process) or an incorrect pressure.

✅ Answer: B

Question 16

Which equation represents a redox reaction?
A \(AgNO_3 + NaCl \rightarrow AgCl + NaNO_3\)
B \(PCl_5 + 4H_2O \rightarrow H_3PO_4 + 5HCl\)
C \(3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2\)
D \(MgCO_3 + 2HCl \rightarrow MgCl_2 + CO_2 + H_2O\)

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 by changes in oxidation number (Supplement)

▶️ Answer/Explanation

A redox reaction involves both oxidation and reduction. In option C, iron (Fe) is oxidised to Fe₃O₄ (oxygen gain) and hydrogen in water (H₂O) is reduced to H₂ (oxygen loss). Options A, B, and D are non-redox reactions: A and D are double displacement / acid–carbonate reactions with no change in oxidation states; B is a hydrolysis reaction where oxidation numbers do not change.
✅ Answer: (C)

Question 17

The equation for the reaction between aluminium and copper(II) oxide is shown.
\(2Al + 3CuO → Al_2O_3 + 3Cu\)
Which statements about this equation are correct?
1 The oxidation number of the aluminium reactant is +2.
2 The oxidation number of the aluminium in the product is +6.
3 The oxidation number of the copper in the reactant is +2.
4 The oxidation number of the copper product is 0.
A 1, 2 and 3

B 1 and 2 only

C 3 and 4

D 4 only

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

• Topic 6.4: Redox — Define oxidation in terms of increase in oxidation number and reduction as a decrease in oxidation number; Identify redox reactions by changes in oxidation number.

▶️ Answer/Explanation

For statement 1: Aluminium reactant (Al) is an uncombined element, so its oxidation number is 0, not +2. Statement 2: In \(Al_2O_3\), oxygen is -2, so aluminium is +3 (since \(2x + 3(-2)=0\) gives \(x=+3\)), not +6. Statement 3: In \(CuO\), oxygen is -2, so copper is +2 (correct). Statement 4: The copper product (Cu) is an uncombined element, so its oxidation number is 0 (correct). Therefore, only statements 3 and 4 are correct.
✅ Answer: (C) 3 and 4

Question 18

What is the colour of thymolphthalein in dilute hydrochloric acid?
A blue
B red
C yellow
D 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); Describe how to compare hydrogen ion concentration using universal indicator (Core).

▶️ Answer/Explanation

Thymolphthalein is a pH indicator that is colourless in acidic and neutral solutions and turns blue in alkaline conditions. Dilute hydrochloric acid is strongly acidic (pH < 7), so thymolphthalein remains colourless. Therefore, options A (blue), B (red – typical for litmus or methyl orange in acid, not thymolphthalein), and C (yellow – methyl orange colour in acid) are incorrect.
✅ Answer: D (colourless)

Question 19

Two acids, P and Q, with the same concentration and volume are reacted separately with the same mass of magnesium ribbon. The reactions produce the same total volume of hydrogen gas but acid Q reacts much more slowly than acid P. Which explanation for the difference between P and Q is correct?

A. Acid P has a higher pH than acid Q.
B. Acid P has a lower concentration of hydrogen ions.
C. Acid Q is partially dissociated and acid P is fully dissociated.
D. Acid Q is a proton acceptor.

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

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

▶️ Answer/Explanation

Since both acids have the same concentration and volume and produce the same total volume of hydrogen, the total amount of H⁺ available is the same. However, acid Q reacts slower, meaning it has a lower concentration of free H⁺ ions at any given time. This occurs if acid Q is a weak acid (partially dissociated) and acid P is a strong acid (fully dissociated). The slower reaction rate is due to the gradual dissociation of the weak acid.
✅ Answer: C (Acid Q is partially dissociated and acid P is fully dissociated).

Question 20

Which process is not used in the preparation of an insoluble salt?
A. filtration
B. washing
C. crystallisation
D. drying

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

• Topic 7.3: Preparation of salts — Describe the preparation of insoluble salts by precipitation (Supplement)

▶️ Answer/Explanation

Insoluble salts are prepared by precipitation, where two soluble reactants are mixed to form the solid salt. The solid is then separated by filtration (A), washed with distilled water to remove soluble impurities (B), and dried by leaving it in a warm oven or between filter papers (D). Crystallisation (C) is used to obtain soluble salts from a solution by evaporating the solvent, but it is not used for an insoluble salt because the product is already a solid precipitate and does not need to be crystallised from a solution.
✅ Answer: (C) crystallisation

Question 21

Lithium and potassium are metals in Group I of the Periodic Table. Lithium has a melting point of 181 °C and a density of \(0.53 g / cm^3\). Which row describes the melting point and density of potassium?

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

• Topic 8.2: Group I properties — Describe the Group I alkali metals, lithium, sodium and potassium, as relatively soft metals with general trends down the group, limited to: (a) decreasing melting point (b) increasing density (c) increasing reactivity (Core)

▶️ Answer/Explanation

Down Group I (from lithium to potassium), the melting point decreases due to weaker metallic bonding from larger ions, while density increases because the increase in atomic mass outweighs the increase in atomic volume. Potassium is below lithium, so it has a lower melting point (63 °C) and a higher density (0.86 g/cm³). Therefore, the correct row shows melting point lower than 181 °C and density higher than 0.53 g/cm³.
✅ Answer: (B)

Question 22

Which statements about transition elements are correct?
1 They have a low density.
2 They form ions with variable oxidation numbers.
3 They have a high melting point.
4 They form only colourless compounds.
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 8.4: Transition elements — Describe 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).
• Topic 8.4 (Supplement): Describe transition elements as having ions with variable oxidation numbers, including iron(II) and iron(III).

▶️ Answer/Explanation

Transition elements are hard metals with high densities and high melting points (statement 3 is correct). A key chemical property is their ability to form ions with variable oxidation numbers (e.g., Fe²⁺ and Fe³⁺), so statement 2 is also correct. Statement 1 is false because they have high, not low, density. Statement 4 is false because they typically form coloured compounds (e.g., blue Cu²⁺, green Fe²⁺).
✅ Answer: (C) 2 and 3

Question 23

Which statements describe the elements in Group VIII of the Periodic Table?
1 Their atoms have full outer electron shells.
2 They are unreactive metals.
3 They are monatomic gases.
4 They are diatomic gases.
A 1 and 3

B 1 and 4

C 2 and 3

D 2 and 4

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

• Topic 8.5: 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 elements (noble gases) have a full outer electron shell, making them very stable and unreactive. They exist as monatomic gases, meaning they consist of single atoms rather than diatomic molecules. Statement 2 is incorrect because they are non‑metals, not metals. Statement 4 is incorrect because they are monatomic, not diatomic.
✅ Answer: A (1 and 3)

Question 24

Four metals, Q, R, S and T, are each added to separate samples of water, steam and dilute hydrochloric acid. The results are shown.

Which statements are correct?
1 R is the least reactive metal.
2 T could be potassium.
3 S is more reactive than Q and R.
4 Metals generally react faster with steam than they react with water.
A 1, 2 and 4

B 1 and 2 only

C 2 and 3

D 3 and 4

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

• Topic 9.4: Reactivity series — Describe the reactions of metals with water, steam and dilute acids; Deduce an order of reactivity from experimental results.
• Topic 6.2: Rate of reaction — Effect of increasing temperature (steam vs water) on reaction rate.

▶️ Answer/Explanation

From the table: R reacts with nothing → least reactive (statement 1 correct). T reacts with water vigorously (like K, Na, Ca) → could be potassium (statement 2 correct). S reacts with steam but not cold water, while Q reacts with dilute acid but not steam/water → S is more reactive than Q and R? No: S (reacts steam) is less reactive than Q (reacts acid) because metals that react with acid are above H₂, but comparing S and Q: Q reacts with acid (more reactive than S which only reacts with steam). So statement 3 is false. Steam is hotter than water → faster reaction (statement 4 correct). Correct statements: 1, 2, 4 → answer A.
✅ Answer: (A) 1, 2 and 4

Question 25

Metal X acts as a sacrificial metal to prevent iron from corroding. Metal X does not act as a sacrificial metal to prevent aluminium from corroding. What is X?

A. copper
B. magnesium
C. silver
D. zinc

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

• Topic 9.5: Corrosion of metals — Describe the use of zinc in galvanising as an example of a barrier method and sacrificial protection (Supplement).
• Topic 9.4: Reactivity series — Describe the relative reactivities of metals in terms of their tendency to form positive ions.

▶️ Answer/Explanation

Detailed Solution: A sacrificial metal must be more reactive than the metal it protects. Zinc is more reactive than iron but less reactive than aluminium. Thus, zinc protects iron by corroding preferentially, but does not protect aluminium (aluminium already has a protective oxide layer and is more reactive). Magnesium is more reactive than both, silver and copper are less reactive.
✅ Answer: D (zinc)

Question 26

Which equation represents the reduction of a compound found in hematite in the blast furnace?
A \(2Al_2O_3 → 4Al + 3O_2\)
B \(CaO + SiO_2 → CaSiO_3\)
C \(2FeO + CO → Fe_2O_3 + C\)
D \(Fe_2O_3 + 3CO → 2Fe + 3CO_2\)

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

• Topic 9.6: Extraction of metals — Reduction of iron(III) oxide by carbon monoxide in the blast furnace (Core); Symbol equations for the extraction of iron from hematite (Supplement)

▶️ Answer/Explanation

In the blast furnace, hematite (\(Fe_2O_3\)) is reduced by carbon monoxide (\(CO\)) to produce molten iron (\(Fe\)) and carbon dioxide (\(CO_2\)). Reduction is the loss of oxygen, so \(Fe_2O_3\) loses oxygen to become Fe. Option A is electrolysis of alumina (not reduction in a blast furnace), option B is slag formation (no reduction), and option C is incorrect and not balanced for the blast furnace process.
✅ Answer: (D)

Question 27

Which statements about the treatment of domestic water supplies are correct?
1 Filtration is used to remove insoluble substances from the water.
2 Sedimentation is used to remove soluble substances from the water.
3 Carbon is used to remove tastes and odours from the water.
4 Chlorine is used to lower the pH of the water.
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 10.1: Water — Describe the treatment of the domestic water supply in terms of: (a) sedimentation and filtration to remove solids (b) use of carbon to remove tastes and odours (c) chlorination to kill microbes (Core)

▶️ Answer/Explanation

Filtration removes insoluble solids (statement 1 correct). Sedimentation removes suspended solids, not soluble substances (statement 2 wrong). Carbon adsorbs tastes and odours (statement 3 correct). Chlorine disinfects (kills microbes) and does not primarily lower pH (statement 4 wrong). Hence correct statements are 1 and 3.
✅ Answer: A (1 and 3)

Question 28

Which statement about water is correct?

A. It turns anhydrous copper(II) sulfate from pink to blue.
B. It turns anhydrous copper(II) sulfate from white to blue.
C. It turns cobalt(II) chloride paper from blue to white.
D. It turns cobalt(II) chloride paper from pink to blue.

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

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

▶️ Answer/Explanation

Detailed Solution: The test for water using anhydrous copper(II) sulfate results in a color change from white to blue as the compound becomes hydrated (CuSO₄ + 5H₂O → CuSO₄·5H₂O). Cobalt(II) chloride paper changes from blue to pink in the presence of water. Therefore, option B is correct.
✅ Answer: B

Question 29

Cupronickel is used to make coins. The arrangement of atoms in cupronickel is shown.

Which kind of substance is cupronickel?
A an alloy
B an isotope
C a compound
D a transition element

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 (Core)

▶️ Answer/Explanation

The diagram shows a mixture of two different types of atoms (copper and nickel) arranged randomly in a metallic lattice. This is characteristic of an alloy, not a pure metal, compound, or isotope. Cupronickel is an alloy of copper and nickel, widely used for coins because of its hardness and corrosion resistance.
✅ Answer: (A) an alloy

Question 30

Which physical properties are typical of all metals?

1 good heat conductivity
2 low density
3 malleability

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

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: thermal conductivity, electrical conductivity, malleability and ductility, melting points and boiling points (Core)

▶️ Answer/Explanation

All metals are good conductors of heat (due to delocalised electrons) and are malleable (layers of ions can slide). However, not all metals have low density; many, such as iron and copper, have high density. Therefore only properties 1 and 3 are typical of all metals.
✅ Answer: (B) 1 and 3

Question 31

Which oxide is used to neutralise acidic gases in flue gas desulfurisation?
A. calcium oxide
B. carbon dioxide
C. nitrogen oxide
D. sulfur dioxide

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

• Topic 10.3: Air quality and climate — State and explain strategies to reduce environmental issues, including flue gas desulfurisation with calcium oxide (Core).

▶️ Answer/Explanation

Flue gas desulfurisation removes acidic sulfur dioxide (SO₂) from industrial exhaust. Calcium oxide (CaO, quicklime) is a base that reacts with and neutralises acidic SO₂ to form calcium sulfite or sulfate. Carbon dioxide and nitrogen oxide are not used for neutralisation; sulfur dioxide is the pollutant being removed, not the neutralising agent.
✅ Answer: (A)

Question 32

Some information about three gases, P, Q and R, is listed.
• Gas P forms when magnesium reacts with dilute hydrochloric acid.
• Gas Q makes up 78% of the air.
• Gas R forms when gas P reacts with gas Q.
What is gas R?
A ammonia
B methane
C nitrogen dioxide
D water vapour

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

• Topic 9.4: Reactivity series — Reactions of metals with dilute hydrochloric acid (Core)
• Topic 10.3: Air quality and climate — Composition of clean, dry air (Core)
• Topic 6.4: Redox — Reactions involving nitrogen and oxygen (Supplement)
• Topic 8.1: Arrangement of elements — Predicting properties from position in Periodic Table (Core)

▶️ Answer/Explanation

Magnesium reacts with dilute hydrochloric acid to produce hydrogen gas, so gas P is hydrogen. Gas Q makes up 78% of air, which is nitrogen. When hydrogen reacts with nitrogen under suitable conditions (Haber process), ammonia is produced. Therefore, gas R is ammonia. Methane and water vapour are not formed from hydrogen and nitrogen, and nitrogen dioxide requires oxygen, not hydrogen.
✅ Answer: A (ammonia)

Question 33

Which formula represents an alkene?
A \(CH_4\)

B \(C_2H_4\)

C \(C_2H_6\)

D \(C_2H_5OH\)

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 (Core)
• Topic 11.2: Naming organic compounds — Name and draw displayed formulae of ethene (Core)
• Topic 11.1: Formulae, functional groups and terminology — Write and interpret general formulae of alkenes, CₙH₂ₙ (Core)

▶️ Answer/Explanation

Alkenes are unsaturated hydrocarbons containing at least one carbon‑carbon double bond, with the general formula CₙH₂ₙ. Methane (CH₄) is an alkane, ethane (C₂H₆) is an alkane, and ethanol (C₂H₅OH) is an alcohol. Only ethene (C₂H₄) fits CₙH₂ₙ (n=2) and contains a double bond, so it is an alkene.
✅ Answer: B

Question 34

The structures of two compounds used to make an ester are shown.

What is the name of the ester?
A ethyl propanoate
B propyl ethanoate
C ethyl ethanoate
D propyl propanoate

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

• Topic 11.7: Carboxylic acids — Describe the reaction of a carboxylic acid with an alcohol using an acid catalyst to form an ester (Supplement)
• Topic 11.2: Naming organic compounds — Name and draw the displayed formulae of the products of the reactions (Core)

▶️ Answer/Explanation

The left structure shows propanoic acid (3 carbons), and the right structure shows ethanol (2 carbons). In esterification, the alcohol provides the first part of the name (‘ethyl’) and the carboxylic acid provides the second part (‘propanoate’), forming ethyl propanoate. The reaction involves removing water (H₂O) to join the two molecules via an ester link.
✅ Answer: (A) ethyl propanoate

Question 35

Which statement about a homologous series is correct?
A All members have the same general formula.
B All members have the same molecular formula.
C All members have similar physical properties.
D Members show a trend in their chemical properties.

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

• Topic 11.1: Formulae, functional groups and terminology — State that a homologous series is a family of similar compounds with similar chemical properties due to the presence of the same functional group (Core); Describe the general characteristics of a homologous series as: having the same functional group, having the same general formula, differing by a –CH₂– unit, displaying a trend in physical properties, sharing similar chemical properties (Supplement)

▶️ Answer/Explanation

A homologous series is a family of organic compounds with the same functional group and the same general formula (e.g., alkanes CₙH₂ₙ₊₂). Members differ by a –CH₂– unit, show a gradual trend in physical properties (e.g., boiling point), but share very similar chemical properties due to the same functional group. Option A is correct; B is wrong (molecular formula changes); C is wrong (physical properties are similar but show a trend, not identical); D is wrong (chemical properties are similar, not a trend).
✅ Answer: (A)

Question 36

Which statements about aqueous ethanoic acid are correct?

1 It contains the functional group –COOH.
2 It reacts with carbonates to produce hydrogen.
3 It turns universal indicator paper blue.
4 It has a pH lower than pH 7.

A 1 and 2

B 1 and 3

C 1 and 4

D 2 and 4

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 have a pH below 7; Describe the characteristic properties of acids in terms of their reactions with carbonates.
• 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 (carboxylic acids contain -COOH).

▶️ Answer/Explanation

Ethanoic acid is a weak carboxylic acid. Statement 1 is correct because its functional group is -COOH. Statement 4 is correct because all acids, including weak ones like ethanoic acid, have a pH lower than 7. Statement 2 is incorrect because it reacts with carbonates to produce carbon dioxide gas, not hydrogen. Statement 3 is incorrect because universal indicator turns red/orange in acidic conditions, not blue.
✅ Answer: C (1 and 4)

Question 37

Alkenes react with steam in an addition reaction. Some alkenes produce only one alcohol product. Some alkenes produce two different alcohols which are structural isomers.

Which row gives the number of alcohol isomers formed when ethene reacts with steam and when propene reacts with steam?

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 and draw the structural or displayed formulae of the products (Supplement).
• Topic 11.1: Formulae, functional groups and terminology — Define structural isomers as compounds with the same molecular formula, but different structural formulae (Supplement).

▶️ Answer/Explanation

Detailed Solution:
Ethene (C₂H₄) is a symmetrical alkene. When it reacts with steam (hydration), water adds across the double bond. Because both carbon atoms in the double bond are identical, the addition can only produce one alcohol: ethanol (CH₃CH₂OH).

Propene (C₃H₆) is an unsymmetrical alkene. The double bond is between carbon 1 and carbon 2. Following Markovnikov’s rule, the hydrogen from water (H-OH) can attach to the less substituted carbon (carbon 1), giving propan-2-ol (major product). However, the addition can also occur the other way, producing propan-1-ol. These two products, propan-1-ol and propan-2-ol, have the same molecular formula (C₃H₈O) but different structural arrangements of atoms, making them structural isomers.

Therefore, ethene forms 1 alcohol isomer and propene forms 2 alcohol isomers.
✅ Answer: Option B (Ethene: 1, Propene: 2)

Question 38

What is an advantage of manufacturing ethanol by fermentation rather than by the addition of steam to ethene?
A No gases that cause global warming are produced.
B The ethanol that is produced is pure.
C Fermentation is a fast process.
D Fermentation uses renewable raw materials.

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

• Topic 11.6: Alcohols — Describe the manufacture of ethanol by fermentation of aqueous glucose (Core) and by catalytic addition of steam to ethene (Core); Describe the advantages and disadvantages of the manufacture of ethanol by fermentation and by catalytic addition of steam to ethene (Supplement)

▶️ Answer/Explanation

Fermentation uses glucose from renewable crops (e.g., sugar cane or corn) as the raw material, whereas the catalytic addition of steam to ethene uses ethene derived from non‑renewable fossil fuels (crude oil). Therefore, fermentation is more sustainable. Fermentation does produce CO₂ (a greenhouse gas) and is slow, and the ethanol obtained requires purification, so options A, B and C are incorrect.
✅ Answer: (D)

Question 39

The diagram shows the structure of a polymer.

Which structure represents the monomer for this polymer?

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

• Topic 11.8: Polymers — Describe the formation of poly(ethene) as an example of addition polymerisation using ethene monomers (Core); Deduce the structure or repeat unit of an addition polymer from a given alkene and vice versa (Supplement)

▶️ Answer/Explanation

The polymer shown has a carbon backbone with a methyl (CH₃) group and an ethyl (CH₂CH₃) group branching alternately from every other carbon. This repeating pattern indicates it is an addition polymer formed from an alkene monomer. To find the monomer, identify the two-carbon unit with the substituents that repeat; breaking the double bond between these two carbons gives the monomer. The repeating unit is –CH(CH₃)–CH(CH₂CH₃)–, so the monomer must be the corresponding alkene with a methyl and an ethyl group on the double-bonded carbons. Option C correctly shows CH₂=C(CH₃)(CH₂CH₃) (2-methylbut-1-ene or a similar isomer), which polymerizes to give the shown structure. Option A has only one substituent, B has a chlorine atom, and D has a longer chain that does not match the repeating pattern.
✅ Answer: (C)

Question 40

Which piece of apparatus is used to measure \(24.5 \, \text{cm}^3\) of gas produced during a reaction?

A. beaker
B. conical flask
C. measuring cylinder
D. volumetric pipette

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 gas syringes, measuring cylinders (Core)

▶️ Answer/Explanation

A measuring cylinder (C) is the appropriate apparatus for measuring a specific volume of gas, as it can be used to collect gas via water displacement and read the volume directly. Beakers and conical flasks are not calibrated for precise gas volume measurement, and a volumetric pipette is designed for accurate measurement of liquids, not gases.
✅ Answer: C