IGCSE Chemistry Recap: Topics 1–9

Choose the best answer for each question. Each question carries one mark.

1. A pure solid is heated at a constant rate. Its temperature rises from 20°C to 65°C, remains constant for four minutes, and then rises again. Which statement explains the period at 65°C?
   1. The particles stop moving while the solid melts.
   2. The energy supplied is used to overcome attractive forces between particles.
   3. The particles lose kinetic energy as the solid changes into a liquid.
   4. The energy supplied increases the average speed of the particles.
2. A fixed mass of gas is sealed in a flexible container. Its temperature is increased while the external pressure remains constant. Why does the volume increase?
   1. The gas particles become larger.
   2. The number of gas particles increases.
   3. The particles move faster and become farther apart while maintaining the same pressure.
   4. The attractive forces between the gas particles become much stronger.
3. Hydrogen chloride gas and ammonia gas are released simultaneously at opposite ends of a long tube. A white ring forms closer to the hydrogen chloride end. What is the best explanation?
   1. Hydrogen chloride particles are smaller than ammonia particles.
   2. Ammonia has a lower relative molecular mass and diffuses faster.
   3. Hydrogen chloride has a higher concentration and diffuses faster.
   4. Ammonia molecules are more strongly attracted to the walls of the tube.
4. A gas occupies 120 cm³ at a particular temperature and pressure. Its pressure is doubled at constant temperature. Which volume is expected?
   1. 60 cm³ because particles collide with the walls more frequently in a smaller volume.
   2. 60 cm³ because half of the gas particles escape.
   3. 240 cm³ because the particles move twice as fast.
   4. 240 cm³ because the spaces between the particles double.
5. Four particles are represented below.

   Particle	Protons	Neutrons	Electrons
   P	16	16	18
   Q	16	18	16
   R	18	22	18
   S	17	18	18

   Which statement is correct?
   1. P and Q are isotopes of the same element.
   2. Q and R are atoms of the same element.
   3. P and S have the same charge.
   4. R and S are isotopes of the same element.
6. An element has three naturally occurring isotopes.

   Relative isotopic mass	Percentage abundance
   24	Unknown
   25	10%
   26	15%

   Its relative atomic mass is 24.40. What is the abundance of the isotope with mass 24?
   1. 65%
   2. 70%
   3. 75%
   4. 80%
7. Substance X has a high melting point. It does not conduct electricity when solid but conducts when molten. Which description is correct?
   1. It is a simple molecular substance containing weak covalent bonds.
   2. It is an ionic compound containing ions that become mobile when molten.
   3. It is a metal containing positive ions that become mobile when molten.
   4. It is a giant covalent substance containing delocalised electrons.
8. Element M has the electron arrangement 2,8,2. Element N has the electron arrangement 2,7. Which formula and bonding are expected?
   1. MN, covalent
   2. MN₂, ionic
   3. M₂N, ionic
   4. M₂N₇, covalent
9. Aluminium reacts with chlorine.
   2Al + 3Cl₂ → 2AlCl₃
   A mixture contains 5.4 g of aluminium and 14.2 g of chlorine. What is the maximum mass of aluminium chloride formed?

   Use: A_r(Al) = 27 and A_r(Cl) = 35.5.

   1. 8.9 g
   2. 13.4 g
   3. 17.8 g
   4. 26.7 g
10. Calcium carbonate reacts with excess hydrochloric acid.
    CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
    What volume of carbon dioxide at r.t.p. is produced from 5.0 g of pure calcium carbonate?

    Use: M_r(CaCO₃) = 100; molar gas volume = 24 dm³.

    1. 0.60 dm³
    2. 1.20 dm³
    3. 2.40 dm³
    4. 4.80 dm³
11. A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its relative molecular mass is 180. What is its molecular formula?
    1. CH₂O
    2. C₂H₄O₂
    3. C₃H₆O₃
    4. C₆H₁₂O₆
12. 25.0 cm³ of sodium hydroxide is neutralised by 20.0 cm³ of 0.150 mol/dm³ sulfuric acid.
    H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
    What is the concentration of sodium hydroxide?
    1. 0.120 mol/dm³
    2. 0.150 mol/dm³
    3. 0.240 mol/dm³
    4. 0.300 mol/dm³
13. Molten lead(II) bromide is electrolysed using inert electrodes. Which products form?

    Option	Cathode	Anode
    A	Bromine	Lead
    B	Lead	Bromine
    C	Hydrogen	Oxygen
    D	Lead	Oxygen

    1. Pair A
    2. Pair B
    3. Pair C
    4. Pair D
14. Aqueous copper(II) sulfate is electrolysed using inert graphite electrodes. Which changes occur?
    1. Copper forms at the cathode, oxygen at the anode, and the blue colour becomes paler.
    2. Hydrogen forms at the cathode, copper at the anode, and the blue colour becomes darker.
    3. Copper forms at both electrodes, and the concentration remains unchanged.
    4. Oxygen forms at both electrodes, and the solution becomes neutral.
15. Concentrated aqueous sodium chloride is electrolysed using inert electrodes. Which products form?

    Option	Cathode	Anode	Substance remaining in solution
    A	Sodium	Chlorine	Hydrochloric acid
    B	Hydrogen	Chlorine	Sodium hydroxide
    C	Hydrogen	Oxygen	Sodium chloride only
    D	Sodium	Oxygen	Sodium hydroxide

    1. Pair A
    2. Pair B
    3. Pair C
    4. Pair D
16. Aqueous copper(II) sulfate is electrolysed using copper electrodes. Which statement is correct?
    1. The cathode loses mass and the anode gains mass.
    2. Both electrodes gain mass.
    3. The anode loses mass, the cathode gains mass, and the Cu²⁺ concentration remains approximately constant.
    4. Oxygen forms at the anode and the blue colour fades rapidly.
17. In a reaction pathway, the reactants are at 80 kJ/mol, the products at 20 kJ/mol and the maximum point at 140 kJ/mol. Which values are correct?

    Option	Forward activation energy	Enthalpy change
    A	60 kJ/mol	−60 kJ/mol
    B	60 kJ/mol	+60 kJ/mol
    C	120 kJ/mol	−60 kJ/mol
    D	140 kJ/mol	+20 kJ/mol

    1. Pair A
    2. Pair B
    3. Pair C
    4. Pair D
18. Hydrogen reacts with chlorine.
    H₂ + Cl₂ → 2HCl
    Bond energies are: H–H = 436 kJ/mol, Cl–Cl = 243 kJ/mol and H–Cl = 431 kJ/mol. What is the enthalpy change?
    1. −183 kJ/mol
    2. −110 kJ/mol
    3. +183 kJ/mol
    4. +679 kJ/mol
19. A catalyst is added to an exothermic reaction. Which statement is correct?
    1. It makes the enthalpy change more negative.
    2. It lowers the activation energy of both forward and reverse reactions.
    3. It increases the energy level of the products.
    4. It increases the energy released per mole.
20. An instant cold pack becomes cold when a salt dissolves in water. Which statement is correct?
    1. The process is exothermic because bond breaking releases energy.
    2. The process is exothermic because energy transfers to the surroundings.
    3. The process is endothermic because it takes in thermal energy from the surroundings.
    4. The process is endothermic because the products have less energy than the reactants.
21. Calcium carbonate reacts with excess dilute hydrochloric acid. The experiment is repeated using the same mass of smaller calcium carbonate particles. Which change is expected?
    1. A lower initial rate and more carbon dioxide.
    2. A higher initial rate and the same final volume of carbon dioxide.
    3. A higher initial rate and more carbon dioxide.
    4. The same initial rate, but the reaction finishes sooner.
22. A catalyst increases reaction rate because it:
    1. increases reactant concentration.
    2. increases the energy released by successful collisions.
    3. provides an alternative pathway with a lower activation energy.
    4. increases the kinetic energy of every reactant particle.
23. The following equilibrium is established in a closed container.
    N₂O₄(g) ⇌ 2NO₂(g)
    The forward reaction is endothermic. Which changes favour NO₂ formation?
    1. Decrease temperature and increase pressure.
    2. Decrease temperature and decrease pressure.
    3. Increase temperature and increase pressure.
    4. Increase temperature and decrease pressure.
24. Iron(III) oxide is reduced by carbon monoxide.
    Fe₂O₃ + 3CO → 2Fe + 3CO₂
    Which statement is correct?
    1. Iron(III) oxide is oxidised because it loses oxygen.
    2. Carbon monoxide is reduced because it gains oxygen.
    3. Iron(III) oxide is reduced and carbon monoxide is oxidised.
    4. Iron and carbon dioxide are both reducing agents.
25. A solution of pH 2 is diluted with a large volume of water. Which statement is correct?
    1. Its pH decreases because it contains more water.
    2. Its pH increases, but the solution normally remains acidic.
    3. Its pH immediately becomes 7 because water is neutral.
    4. Its hydrogen-ion concentration increases.
26. Which method is most suitable for preparing pure, dry copper(II) sulfate crystals?
    1. Add excess copper to dilute sulfuric acid and evaporate to dryness.
    2. Add excess copper(II) oxide to warm dilute sulfuric acid, filter, concentrate and crystallise.
    3. Mix copper(II) chloride solution with sodium sulfate solution and filter.
    4. Titrate copper(II) oxide with sulfuric acid using an indicator.
27. Which pair of aqueous solutions produces a precipitate when mixed?
    1. Sodium nitrate and potassium chloride
    2. Hydrochloric acid and sodium hydroxide
    3. Barium nitrate and sodium sulfate
    4. Ammonium chloride and sodium nitrate
28. An ammonium salt is warmed with aqueous sodium hydroxide. Which observation and conclusion are correct?
    1. A colourless gas turns damp red litmus paper blue; ammonia is produced.
    2. A colourless gas turns damp blue litmus paper red; carbon dioxide is produced.
    3. A green precipitate forms; ammonium ions are present.
    4. A white precipitate forms; hydroxide ions are present.
29. Element X has the electron arrangement 2,8,7. Which statement is correct?
    1. X is in Group VII and Period 3 and tends to gain one electron.
    2. X is in Group VII and Period 2 and tends to lose one electron.
    3. X is in Group III and Period 7 and tends to gain three electrons.
    4. X is in Group VIII and Period 3 and is unreactive.
30. Which trends are observed down Group I?
    1. Atomic radius decreases, melting point increases and reactivity decreases.
    2. Atomic radius increases, melting point generally decreases and reactivity increases.
    3. Atomic radius increases, melting point increases and reactivity decreases.
    4. Atomic radius decreases, melting point decreases and reactivity increases.
31. Chlorine water is added separately to aqueous potassium bromide and aqueous potassium iodide. Which statement is correct?
    1. Chlorine displaces bromine only because iodine is more reactive.
    2. Chlorine displaces iodine only because bromine is more reactive.
    3. Chlorine displaces both bromine and iodine because chlorine is more reactive.
    4. No reaction occurs because halogens cannot displace halide ions.
32. Which property is characteristic of transition elements but not Group I metals?
    1. They form only colourless compounds.
    2. They have low densities and low melting points.
    3. They form ions with only a +1 charge.
    4. They may form coloured compounds and act as catalysts.
33. Metal X is below carbon but above hydrogen in the reactivity series.

    1. X can be extracted from its oxide using carbon.

    2. X reacts with dilute hydrochloric acid.

    3. X can be extracted from an aqueous solution of its salt by electrolysis only.

    Which statements are correct?
    1. 1 and 2 only
    2. 1 and 3 only
    3. 2 and 3 only
    4. 1, 2 and 3
34. Four iron nails are treated as shown.

    Nail	Conditions
    P	Dry air only
    Q	Boiled water covered with oil
    R	Air and water
    S	Salt water exposed to air

    Which order shows increasing rate of rusting?
    1. P = Q < R < S
    2. P < Q < S < R
    3. R < S < P = Q
    4. Q < R < P < S
35. Why is an alloy usually harder than the pure metal from which it is made?
    1. The alloy contains no delocalised electrons.
    2. Different-sized atoms distort the layers and make sliding more difficult.
    3. The atoms in the alloy form simple molecules.
    4. The alloy contains weaker metallic bonds that break less easily.
36. Magnesium, zinc and copper are separately added to cold water, steam and dilute hydrochloric acid. Which statement is correct?
    1. Copper reacts with dilute hydrochloric acid to form hydrogen.
    2. Zinc reacts rapidly with cold water but not with steam.
    3. Magnesium reacts with steam and dilute hydrochloric acid.
    4. All three metals react with cold water to form hydroxides.

A pure substance is heated at a constant rate. The results are shown.

1. State the melting point of the substance. [1]
2. Describe the arrangement and movement of the particles:
   1. before heating begins;
   2. during the constant-temperature section;
   3. after the substance has completely melted.
   [5]
3. Explain why the temperature remains constant from 6 to 10 minutes even though heating continues. [2]
4. The liquid is heated until it becomes a gas. Explain why the gas occupies the whole container. [2]
5. The gas is compressed at constant temperature. Explain, in terms of particles, why its pressure increases. [2]
6. Gas X diffuses more slowly than gas Y under the same conditions. What can be concluded about their relative molecular masses? Explain your answer. [2]

Element X has a proton number of 13. It has two naturally occurring isotopes, X-27 and X-29. Its relative atomic mass is 27.2.

1. Complete the table. [6]

   Particle	Protons	Neutrons	Electrons
   X-27 atom
   X-29 atom
   X3+ ion formed from X-27

2. Define the term isotope. [2]
3. Calculate the percentage abundance of X-29. [3]
4. Write the electron arrangement of:
   1. an atom of X;
   2. an X³⁺ ion.
   [2]
5. Element Y has the electron arrangement 2,8,7.
   1. Explain how X and Y form ions.
   2. Deduce the formula of the compound formed.
   3. State the type of bonding present.
   [4]
6. Explain why the compound formed between X and Y has a high melting point and conducts electricity when molten but not when solid. [4]

Magnesium reacts with dilute hydrochloric acid.

A student adds 3.60 g of magnesium to hydrochloric acid containing 0.200 mol of HCl. Use A_r(Mg) = 24 and a molar gas volume of 24 dm³ at r.t.p.

1. Calculate the amount, in moles, of magnesium used. [2]
2. Determine the limiting reactant. Show your working. [3]
3. Calculate the amount, in moles, of hydrogen formed. [1]
4. Calculate the volume of hydrogen produced at r.t.p. [2]
5. Calculate the mass of the reactant remaining when the reaction is complete. [3]
6. The actual volume of hydrogen collected is 2.16 dm³. Calculate the percentage yield. [2]
7. A 4.00 g sample of impure magnesium reacts with excess hydrochloric acid and produces 3.60 dm³ of hydrogen at r.t.p. Calculate the percentage purity of the magnesium sample. [4]

Aqueous copper(II) sulfate is electrolysed in two experiments. Experiment 1 uses graphite electrodes. Experiment 2 uses copper electrodes.

1. Define electrolysis. [2]
2. For Experiment 1:
   1. state the product at the cathode;
   2. state the product at the anode;
   3. describe the observation at each electrode;
   4. describe the change in the colour of the solution.
   [5]
3. Write an ionic half-equation for the reaction at:
   1. the cathode;
   2. the anode.
   [4]
4. For Experiment 2:
   1. describe the change in mass of each electrode;
   2. explain why the concentration of Cu²⁺ remains approximately constant.
   [4]
5. A steel spoon is electroplated with silver. State:
   1. which electrode the spoon should form;
   2. a suitable material for the other electrode;
   3. a suitable electrolyte;
   4. one reason for electroplating.
   [4]
6. State one advantage and one disadvantage of using hydrogen–oxygen fuel cells rather than petrol engines in vehicles. [2]

Methane burns completely in oxygen.

1. State what is meant by:
   1. an exothermic reaction;
   2. activation energy.
   [3]
2. Calculate the total energy needed to break all the bonds in the reactants. [3]
3. Calculate the total energy released when all the bonds in the products form. [3]
4. Calculate the enthalpy change. Include its sign and unit. [3]
5. Explain the sign of the enthalpy change in terms of bond breaking and bond making. [2]
6. Sketch a labelled reaction pathway diagram showing the reactants, products, activation energy and enthalpy change. [4]
7. On the same diagram, show the pathway when a catalyst is used. Explain why the catalyst increases reaction rate but does not change the enthalpy change. [3]

A student investigates the reaction between calcium carbonate and dilute hydrochloric acid.

1. Which experiment has the greatest initial rate? Explain using collision theory. [4]
2. Compare Experiments 1 and 2.
   1. Which finishes first?
   2. Do they produce the same final volume of carbon dioxide?
   3. Explain both answers.
   [4]
3. Explain how increasing temperature increases reaction rate. Refer to particle speed, collision frequency, activation energy and successful collisions. [4]
4. The following equilibrium is established in a closed container:
   N₂O₄(g) ⇌ 2NO₂(g)
   The forward reaction is endothermic. Predict and explain the effect of:
   1. increasing temperature;
   2. increasing pressure.
   [4]
5. For the reaction below, identify the substance oxidised, the substance reduced and the reducing agent.
   Fe₂O₃ + 3CO → 2Fe + 3CO₂
   [3]

A student prepares hydrated copper(II) sulfate crystals using copper(II) oxide and dilute sulfuric acid.

1. Write the word equation and balanced symbol equation for the reaction. [3]
2. Explain why copper metal is not normally used to prepare copper(II) sulfate directly from dilute sulfuric acid. [1]
3. The student warms the acid, adds copper(II) oxide, filters the mixture, heats the filtrate, cools the solution, and filters and dries the crystals. Explain:
   1. why copper(II) oxide is added until some remains unreacted;
   2. why the mixture is filtered;
   3. why the filtrate is not heated to complete dryness;
   4. why the concentrated solution is cooled.
   [5]
4. 25.0 cm³ of sodium hydroxide is neutralised by 18.0 cm³ of 0.250 mol/dm³ sulfuric acid.
   H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
   Calculate the concentration of sodium hydroxide. [4]
5. A student wants to prepare pure, dry barium sulfate. Name two suitable aqueous solutions and describe the procedure. [4]
6. Write:
   1. the ionic equation for neutralisation;
   2. the ionic equation for barium sulfate formation.
   [2]
7. Describe a test for ammonium ions and give the positive result. [2]

1. Identify P, Q and R. [3]
2. State the group and period of P and Q. [4]
3. Explain why R is very unreactive. [2]
4. Predict how the reaction of T with water differs from the reaction of P with water. Explain using occupied electron shells, shielding, nuclear attraction and loss of the outer electron. [5]
5. Chlorine, bromine and iodine are added separately to solutions containing halide ions.
   1. State the order of reactivity of the three halogens.
   2. State which halogen displaces bromide ions but not chloride ions.
   3. Write an ionic equation for chlorine reacting with iodide ions.
   [4]
6. Describe two characteristic properties of transition elements illustrated by S. [2]
7. State the trend in the colour of the halogens down Group VII and explain why their melting and boiling points increase. [3]

1. Arrange W, X, Y and Z in decreasing order of reactivity. Explain your reasoning. [4]
2. Which metal could be:
   1. potassium;
   2. zinc;
   3. copper?
   Give a reason for each answer. [3]
3. Explain why highly reactive metals are extracted by electrolysis, whereas less reactive metals may be extracted by reducing their oxides with carbon. [3]
4. Iron is extracted from iron(III) oxide using carbon monoxide.
   1. Write the balanced equation.
   2. Identify the substance oxidised.
   3. Identify the substance reduced.
   [3]
5. Explain why aluminium is used in aircraft bodies, overhead electrical cables and food containers. [3]
6. Explain, in terms of structure, why an alloy is generally harder than a pure metal. [3]
7. State the two substances required for iron to rust. Explain why iron rusts faster in salt water than in pure water. [3]
8. Describe two different methods of preventing iron from rusting and explain how each method works. [4]