Cambridge IGCSE Chemistry: Structured Questions Exam Practice
Cambridge IGCSE Chemistry
Structured Questions Practice
This section contains 20 structured questions to help you prepare for your Cambridge IGCSE Chemistry examination. Read each question carefully and provide clear, detailed answers.
Question 1
The element X has an atomic number of 17 and a mass number of 35. State the number of protons, neutrons, and electrons in an atom of X. Predict the charge on an ion of X and write its electronic configuration.
Question 2
Describe the difference between ionic bonding and covalent bonding, giving one example of a compound formed by each type of bonding.
Question 3
A student carries out an experiment to determine the empirical formula of an oxide of copper. They heat 4.00 g of copper powder in air until it is completely converted to copper oxide, producing 5.00 g of the oxide. Calculate the empirical formula of the copper oxide. (Ar: Cu=63.5, O=16).
Question 4
Explain why diamond is hard and does not conduct electricity, while graphite is soft and conducts electricity, both being allotropes of carbon.
Question 5
State the observations when aqueous sodium hydroxide is added dropwise until in excess to separate solutions of: (a) iron(III) sulfate, (b) zinc nitrate.
Question 6
Describe the test for hydrogen gas and state the expected result.
Question 7
Explain what is meant by a homologous series. Give two characteristics of a homologous series.
Question 8
Magnesium reacts with dilute hydrochloric acid. Write a balanced chemical equation for this reaction. Describe how the rate of this reaction could be increased without changing the concentration of the acid.
Question 9
Explain the term 'oxidation' in terms of electron transfer and in terms of oxygen gain/loss. Give an example for each explanation.
Question 10
Describe the process of fractional distillation used to separate crude oil into useful fractions, stating one common use for two of these fractions.
Question 11
Sulfuric acid is a strong acid. Explain what is meant by a strong acid. Describe how to prepare a pure, dry sample of zinc sulfate crystals from zinc oxide and dilute sulfuric acid.
Question 12
State the general trend in: (a) metallic character, (b) electronegativity, across a period in the Periodic Table.
Question 13
Calcium carbonate decomposes on heating. Write a balanced chemical equation for this reaction. State one industrial use of calcium oxide.
Question 14
Explain how electrolysis can be used to purify copper. Mention the materials used for the anode, cathode, and electrolyte, and describe what happens at each electrode.
Question 15
A sample of gas occupies 240 cm3 at room temperature and pressure (r.t.p.). Calculate the number of moles of gas present. (Molar gas volume at r.t.p. is 24 dm3/mol).
Question 16
Describe how a precipitation reaction can be used to prepare a pure, dry sample of silver chloride from aqueous silver nitrate and aqueous sodium chloride.
Question 17
Explain the conditions required for the rusting of iron to occur. Describe one method to prevent rusting, explaining its mechanism.
Question 18
Ethene can be converted into poly(ethene). (a) Name the type of reaction involved. (b) Draw the displayed formula of ethene and a section of poly(ethene) showing two repeat units.
Question 19
State the observations when ethanol is oxidized by acidified potassium manganate(VII) solution.
Question 20
Describe the chemical test for the presence of sulfate ions in an aqueous solution, stating the reagents used and the expected positive result.
Answer Key
Protons: 17, Neutrons: 18, Electrons: 17. Charge on ion: 1- (Cl-). Electronic configuration: 2,8,7.
Ionic bonding involves the electrostatic attraction between oppositely charged ions formed by the transfer of electrons from a metal to a non-metal (e.g., NaCl). Covalent bonding involves the sharing of electrons between non-metal atoms (e.g., H2O).
Mass of Cu = 4.00 g. Moles of Cu = 4.00 / 63.5 = 0.06299 mol. Mass of O = 5.00 - 4.00 = 1.00 g. Moles of O = 1.00 / 16 = 0.0625 mol. Ratio Cu:O = 0.06299 : 0.0625 ≈ 1:1. Empirical formula is CuO.
Diamond has a giant covalent structure where each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement, making it very strong and hard. All valence electrons are used in bonding, so there are no delocalised electrons to conduct electricity. Graphite has a layered structure where each carbon atom is covalently bonded to three other carbon atoms, forming hexagonal rings in layers. Weak intermolecular forces exist between layers, allowing them to slide over each other (soft). Each carbon atom has one delocalised electron not involved in bonding, which can move freely within the layers, allowing graphite to conduct electricity.
(a) Iron(III) sulfate: Green precipitate formed, insoluble in excess. (Incorrect, should be reddish-brown. Let's correct this: Reddish-brown precipitate, insoluble in excess.)
Correction: (a) Iron(III) sulfate: Reddish-brown precipitate formed, insoluble in excess. (b) Zinc nitrate: White precipitate formed, soluble in excess to form a colourless solution.
Test for hydrogen gas: Place a lit splint at the mouth of the test tube. Expected result: A 'pop' sound is heard.
A homologous series is a family of organic compounds with the same general formula, similar chemical properties, and consecutive members differing by a -CH2- group. Two characteristics: same general formula, gradual change in physical properties (e.g., boiling point) as molecular mass increases.
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g). The rate could be increased by: increasing the temperature, increasing the surface area of magnesium (e.g., using powder), or using a catalyst (though not common for this specific reaction under IGCSE context for rate increase without changing concentration).
Oxidation in terms of electron transfer: loss of electrons (e.g., Fe2+ → Fe3+ + e-). Oxidation in terms of oxygen gain/loss: gain of oxygen (e.g., C + O2 → CO2) or loss of hydrogen.
Crude oil is heated and vaporised, then enters a fractionating column. The column is hotter at the bottom and cooler at the top. Vapours rise and condense at different temperatures according to their boiling points, with fractions having lower boiling points condensing higher up the column. Examples: Bitumen (used for road surfacing), Petrol/Gasoline (fuel for cars).
A strong acid is an acid that completely ionises (dissociates) in aqueous solution to produce hydrogen ions (H+). To prepare pure, dry zinc sulfate crystals: Add zinc oxide (an insoluble base) to dilute sulfuric acid. Stir until no more zinc oxide dissolves (ensuring excess zinc oxide). Filter off the unreacted zinc oxide. Heat the filtrate (zinc sulfate solution) to evaporate some water until saturation (crystallisation point). Allow the solution to cool slowly for crystals to form. Filter off the crystals and wash with a small amount of cold distilled water. Dry the crystals between filter papers.
(a) Metallic character: Decreases across a period. (b) Electronegativity: Increases across a period.
CaCO3(s) → CaO(s) + CO2(g). Industrial use of calcium oxide: Neutralising acidic soils or in the manufacture of steel.
Electrolysis can be used to purify copper. Anode: Impure copper. Cathode: Pure copper. Electrolyte: Aqueous copper(II) sulfate. At the anode, impure copper oxidises, releasing Cu2+ ions into the solution and other more reactive metals also oxidise. Less reactive impurities fall to the bottom as anode sludge. At the cathode, Cu2+ ions from the electrolyte gain electrons and are deposited as pure copper (Cu2+ + 2e- → Cu).
Volume of gas = 240 cm3 = 0.240 dm3. Number of moles = Volume / Molar gas volume = 0.240 dm3 / 24 dm3/mol = 0.01 mol.
To prepare silver chloride (an insoluble salt): Mix aqueous silver nitrate with aqueous sodium chloride. A white precipitate of silver chloride will form. Filter the precipitate to separate it from the solution. Wash the precipitate with distilled water to remove soluble impurities. Dry the silver chloride by placing it in a warm oven or between filter papers.
Conditions for rusting: Presence of both oxygen (from air) and water. Prevention method: Painting. Mechanism: The paint forms a barrier between the iron surface and oxygen/water, preventing contact and thus preventing rusting.
(a) Addition polymerisation. (b) Ethene: H2C=CH2. Poly(ethene): -[CH2-CH2]n- (Displayed formula shows all bonds, with 'n' indicating repetition and extending bonds at ends).
Observations: The purple solution of acidified potassium manganate(VII) turns colourless (or decolourises).
Chemical test for sulfate ions: Add aqueous barium nitrate (or barium chloride) solution followed by dilute nitric acid (or hydrochloric acid) to the sample. Expected positive result: A white precipitate forms, which is insoluble in the dilute acid.