IGCSE Chemistry: Structured Questions (Cambridge CIE)
IGCSE Chemistry: Structured Questions
This section contains 20 structured questions to test your knowledge of IGCSE Chemistry concepts. Read each question carefully and provide clear, concise answers.
Atomic Structure and Bonding
a) State the relative charge and mass of a proton, neutron, and electron.
b) An atom of element X has 17 protons and 18 neutrons. Write down its nucleon number and proton number.
c) Describe the formation of an ionic bond between sodium (Na) and chlorine (Cl) atoms, showing the electron transfer.
States of Matter and Separation Techniques
a) Describe the arrangement and movement of particles in a liquid.
b) Explain why a liquid has a fixed volume but no fixed shape.
c) Suggest a suitable method to separate a mixture of sand and salt, and outline the steps involved.
The Periodic Table
a) Explain the trend in reactivity of Group 1 elements down the group.
b) Describe two chemical properties of Group 7 elements (halogens).
c) What is a transition element? Give one common characteristic property.
Stoichiometry and Chemical Calculations
a) Calculate the relative formula mass of magnesium hydroxide, Mg(OH)₂. (Ar: Mg=24, O=16, H=1)
b) How many moles are present in 8.0 g of oxygen gas, O₂? (Ar: O=16)
c) Write a balanced chemical equation for the reaction between hydrogen and oxygen to form water.
Acids, Bases, and Salts
a) Define an acid in terms of proton transfer.
b) Name a strong acid and a weak acid.
c) Describe how to prepare a pure, dry sample of copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid.
Redox Reactions
a) Define oxidation in terms of oxygen transfer and electron transfer.
b) In the reaction 2Mg + O₂ → 2MgO, identify which substance is oxidised and which is reduced.
c) Explain what a reducing agent is.
Rates of Reaction
a) List two factors that affect the rate of a chemical reaction.
b) Explain how increasing the temperature affects the rate of reaction using collision theory.
c) What is a catalyst, and how does it work?
Energy Changes
a) Distinguish between an exothermic and an endothermic reaction.
b) Give an example of an exothermic reaction.
c) Draw a simple reaction profile diagram for an exothermic reaction, labelling the activation energy and enthalpy change.
Electrolysis
a) Define electrolysis.
b) Describe what happens at the anode and cathode during the electrolysis of molten lead(II) bromide.
c) State two industrial applications of electrolysis.
Metals
a) List three general physical properties of metals.
b) Explain why aluminium is extracted by electrolysis rather than reduction with carbon.
c) Describe the process of rusting and suggest two ways to prevent it.
Air and Water
a) State the approximate percentage of nitrogen and oxygen in dry air.
b) Name one common gaseous pollutant of air and explain one negative effect it has on the environment or human health.
c) Describe how potable water is produced from river water in a water treatment plant.
Organic Chemistry: Alkanes and Alkenes
a) State the general formula for alkanes.
b) Draw the full structural formula of propene.
c) Describe a test to distinguish between an alkane and an alkene, stating the expected observations.
Organic Chemistry: Alcohols and Carboxylic Acids
a) Give the functional group for alcohols and carboxylic acids.
b) Write the balanced chemical equation for the complete combustion of ethanol, C₂H₅OH.
c) Describe one chemical property of ethanoic acid, CH₃COOH.
Polymers
a) Define the term ‘monomer’ and ‘polymer’.
b) Explain the difference between addition polymerisation and condensation polymerisation.
c) Name one common addition polymer and one common condensation polymer.
Chemical Tests
a) Describe a chemical test for the presence of carbon dioxide gas, stating the expected observation.
b) How would you test for the presence of chloride ions (Cl⁻) in an aqueous solution?
c) Describe the test for sulfate ions (SO₄²⁻).
Reactivity Series
a) State the order of reactivity for potassium, zinc, and iron, from most reactive to least reactive.
b) Explain how the reactivity of a metal relates to its ability to displace another metal from a solution of its salt.
c) What is sacrificial protection? Give an example.
Equilibria
a) Explain what is meant by a reversible reaction.
b) State Le Chatelier's principle.
c) For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g) (exothermic), predict the effect of increasing temperature on the yield of ammonia.
Industrial Chemistry: Ammonia
a) State the raw materials for the Haber process.
b) Give the typical operating temperature and pressure for the Haber process.
c) Explain why a high pressure is used in the Haber process.
Industrial Chemistry: Sulfuric Acid
a) Name the industrial process used to manufacture sulfuric acid.
b) What is the catalyst used in the key step of this process?
c) Describe how sulfur trioxide is converted to sulfuric acid, avoiding direct addition to water.
Environmental Chemistry
a) What are greenhouse gases? Name two examples.
b) Explain how the burning of fossil fuels contributes to acid rain.
c) Describe one method of reducing pollution from vehicle exhaust gases.
Answer Key
Atomic Structure and Bonding
a) Proton: relative charge +1, relative mass 1; Neutron: relative charge 0, relative mass 1; Electron: relative charge -1, relative mass 1/1836 (or negligible).
b) Nucleon number = 17 + 18 = 35; Proton number = 17.
c) Sodium (2.8.1) loses its outer electron to become Na⁺ (2.8); Chlorine (2.8.7) gains this electron to become Cl⁻ (2.8.8). The oppositely charged ions are attracted to form an ionic bond.
States of Matter and Separation Techniques
a) Particles are close together but randomly arranged, able to slide past each other.
b) Particles are close and have strong forces of attraction, giving fixed volume. However, they can move past each other, taking the shape of the container.
c) Filtration followed by evaporation. Steps: 1. Add water to dissolve salt. 2. Filter to remove sand. 3. Heat the filtrate to evaporate water and obtain salt.
The Periodic Table
a) Reactivity increases down Group 1. Outer electron is further from nucleus, less attraction, easier to lose.
b) They are non-metals; exist as diatomic molecules; react with metals to form ionic halides; are oxidising agents.
c) An element in the d-block of the periodic table. Characteristic: form coloured compounds (or act as catalysts, have variable oxidation states).
Stoichiometry and Chemical Calculations
a) Mg(OH)₂ = 24 + 2(16+1) = 24 + 2(17) = 24 + 34 = 58.
b) Molar mass of O₂ = 2 * 16 = 32 g/mol. Moles = 8.0 g / 32 g/mol = 0.25 mol.
c) 2H₂(g) + O₂(g) → 2H₂O(l)
Acids, Bases, and Salts
a) An acid is a proton (H⁺) donor.
b) Strong acid: Hydrochloric acid (HCl); Weak acid: Ethanoic acid (CH₃COOH).
c) 1. Add excess copper(II) oxide to dilute sulfuric acid and warm. 2. Filter to remove unreacted copper(II) oxide. 3. Heat the filtrate to evaporate some water until saturated. 4. Allow to cool and crystallise. 5. Filter off crystals and dry them with filter paper.
Redox Reactions
a) Oxidation is the gain of oxygen or loss of electrons.
b) Mg is oxidised (gains oxygen). O₂ is reduced (gains electrons, forms O²⁻).
c) A reducing agent is a substance that causes another substance to be reduced (by being oxidised itself).
Rates of Reaction
a) Temperature, concentration, surface area, presence of a catalyst.
b) Increasing temperature increases the kinetic energy of particles, leading to more frequent collisions and more collisions having energy greater than or equal to the activation energy.
c) A catalyst is a substance that increases the rate of a chemical reaction without being chemically changed itself. It works by providing an alternative reaction pathway with a lower activation energy.
Energy Changes
a) Exothermic reactions release energy (heat) to the surroundings, causing temperature to rise. Endothermic reactions absorb energy (heat) from the surroundings, causing temperature to fall.
b) Combustion, neutralisation, respiration.
c) (Diagram shows reactants at higher energy than products, with an activation energy hump. Enthalpy change (ΔH) is negative, shown as difference between reactant and product energy levels.)
Electrolysis
a) Electrolysis is the decomposition of an ionic compound using electrical energy.
b) At the anode (+ve electrode): Br⁻ ions lose electrons (oxidised) to form bromine gas (2Br⁻ → Br₂ + 2e⁻). At the cathode (-ve electrode): Pb²⁺ ions gain electrons (reduced) to form lead metal (Pb²⁺ + 2e⁻ → Pb).
c) Extraction of reactive metals (e.g., aluminium), purification of metals (e.g., copper), electroplating, production of chlorine/sodium hydroxide.
Metals
a) Good conductors of heat and electricity, malleable, ductile, high melting points, high density, lustrous.
b) Aluminium is more reactive than carbon, so carbon cannot reduce its oxide. Electrolysis is required as it provides the necessary energy to overcome the strong ionic bonds in aluminium oxide.
c) Rusting is the corrosion of iron or steel, requiring both oxygen and water. Prevention: painting, oiling/greasing, galvanising, sacrificial protection.
Air and Water
a) Nitrogen approx. 78%; Oxygen approx. 21%.
b) Example: Carbon monoxide (CO). Effect: Binds to haemoglobin, reducing oxygen transport in blood (toxic). OR Sulfur dioxide (SO₂). Effect: Causes acid rain, respiratory problems.
c) Screening (removes large debris) → Sedimentation (allows suspended solids to settle) → Filtration (removes smaller suspended particles) → Chlorination (kills bacteria).
Organic Chemistry: Alkanes and Alkenes
a) CnH₂n+₂
b) CH₃-CH=CH₂ (carbon atoms in a chain, double bond between two carbons, H atoms to satisfy valency)
c) Test: Add aqueous bromine (bromine water). Observation: Alkene will decolourise brown bromine water immediately. Alkane will not decolourise bromine water in the dark (or slowly decolourises in UV light).
Organic Chemistry: Alcohols and Carboxylic Acids
a) Alcohols: -OH (hydroxyl group); Carboxylic acids: -COOH (carboxyl group).
b) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
c) It is a weak acid (reacts with bases, carbonates, reactive metals); undergoes esterification with alcohols.
Polymers
a) Monomer: A small molecule that can be joined together to form a polymer. Polymer: A large molecule made up of many repeating monomer units.
b) Addition polymerisation involves monomers adding to each other in such a way that the polymer contains all the atoms of the monomer (typically alkenes). Condensation polymerisation involves monomers joining together with the elimination of a small molecule (e.g., water) for each bond formed.
c) Addition polymer: Poly(ethene), PVC. Condensation polymer: Nylon, Terylene (polyester).
Chemical Tests
a) Bubble gas through limewater (aqueous calcium hydroxide). Observation: Limewater turns cloudy/milky (due to formation of insoluble calcium carbonate).
b) Add dilute nitric acid, then add aqueous silver nitrate. Observation: A white precipitate (AgCl) will form.
c) Add dilute hydrochloric acid, then add aqueous barium chloride. Observation: A white precipitate (BaSO₄) will form.
Reactivity Series
a) Potassium > Zinc > Iron
b) A more reactive metal will displace a less reactive metal from a solution of its salt because the more reactive metal loses electrons more easily (is more readily oxidised).
c) Sacrificial protection is a method of corrosion prevention where a more reactive metal is connected to the metal to be protected. The more reactive metal preferentially corrodes (is oxidised), protecting the other metal. Example: Galvanising (zinc coating on iron/steel), attaching magnesium blocks to steel pipelines.
Equilibria
a) A reversible reaction is one where the products can react to reform the original reactants.
b) If a system at equilibrium is subjected to a change, the system will adjust itself to counteract the effect of the change.
c) Increasing temperature will shift the equilibrium to the left (favouring the endothermic reverse reaction) to absorb the added heat, thus decreasing the yield of ammonia.
Industrial Chemistry: Ammonia
a) Nitrogen (from air) and hydrogen (from natural gas or steam reforming).
b) Temperature: 400-450°C; Pressure: 200-250 atmospheres (atm).
c) High pressure favours the side with fewer moles of gas (products in this case, 2 moles vs 4 moles of reactants), increasing the yield of ammonia according to Le Chatelier's principle.
Industrial Chemistry: Sulfuric Acid
a) The Contact Process.
b) Vanadium(V) oxide (V₂O₅).
c) Sulfur trioxide (SO₃) is dissolved in concentrated sulfuric acid to form oleum (H₂S₂O₇), which is then carefully diluted with water to produce concentrated sulfuric acid. Direct addition of SO₃ to water is too vigorous and forms a mist.
Environmental Chemistry
a) Greenhouse gases are gases in the atmosphere that absorb and emit radiant energy within the thermal infrared range, causing the greenhouse effect. Examples: Carbon dioxide (CO₂), Methane (CH₄), Water vapour (H₂O).
b) Burning fossil fuels releases sulfur dioxide and nitrogen oxides. These gases react with water, oxygen, and other chemicals in the atmosphere to form sulfuric acid and nitric acid, which then fall as acid rain.
c) Catalytic converters in vehicle exhausts convert harmful gases (CO, NOx, unburnt hydrocarbons) into less harmful ones (CO₂, N₂, H₂O). OR Use of low-sulfur fuels. OR Electrical/hybrid vehicles.