2023 Edexcel IGCSE Chemistry Practice Paper with Answers

A student carries out an experiment to find the empirical formula of an oxide of titanium. (a) Describe how the student could heat a sample of titanium metal in a crucible with oxygen to ensure complete reaction. (4 marks) (b) In the experiment, 1.44 g of titanium reacted with oxygen to form 2.40 g of titanium oxide. Calculate the empirical formula of the titanium oxide. [Ar values: Ti = 48, O = 16] (4 marks) (c) Write a balanced chemical equation for this reaction. (1 mark) (d) Calculate the mass of titanium required to produce exactly 15.0 g of this titanium oxide. (2 marks)

A student investigates the displacement reaction between zinc and copper(II) sulfate. (a) The student adds excess zinc powder to 50.0 cm\(^3\) of 0.200 mol/dm\(^3\) copper(II) sulfate solution in a polystyrene cup. Explain why a polystyrene cup is used instead of a glass beaker. (2 marks) (b) The temperature of the mixture increases from 18.5 °C to 24.3 °C. Calculate the heat energy change (Q) in Joules. [Assume mass of solution is 50.0 g and specific heat capacity is 4.18 J/g/°C] (3 marks) (c) Calculate the number of moles of copper(II) sulfate used in this experiment. (2 marks) (d) Use your answers to (b) and (c) to calculate the molar enthalpy change (\(\Delta H\)) for the reaction in kJ/mol. Include a sign in your final answer. (4 marks)

This question is about the thermal decomposition of copper(II) carbonate. (a) State the color change observed when green copper(II) carbonate solid is heated strongly. (2 marks) (b) Write a chemical equation for this thermal decomposition, including state symbols. (3 marks) (c) A student collects 72 cm\(^3\) of carbon dioxide gas at room temperature and pressure. Calculate the amount, in moles, of carbon dioxide gas collected. [Molar volume of gas at rtp = 24 dm\(^3\)] (3 marks) (d) Carbon dioxide is a greenhouse gas. Describe how greenhouse gases contribute to global warming. (3 marks)

Crude oil is a complex mixture of hydrocarbons that must be processed to produce useful fuels. (a) Explain how fractional distillation separates crude oil into useful fractions. (4 marks) (b) A long-chain alkane, hexadecane (\(\text{C}_{16}\text{H}_{34}\)), is cracked to form octane (\(\text{C}_8\text{H}_{18}\)), butene (\(\text{C}_4\text{H}_8\)), and one other alkene. Write a balanced chemical equation for this reaction. (2 marks) (c) In an industrial cracking reactor, a student cracks 500 g of hexadecane. The theoretical yield of octane is 252 g. If the actual yield of octane obtained is 189 g, calculate the percentage yield of octane. (3 marks) (d) State the catalyst and temperature range used in industrial catalytic cracking. (2 marks)

An unknown ionic solid, compound X, is analyzed using chemical tests. (a) Describe how to perform a flame test on a solid sample. (3 marks) (b) Compound X does not produce a flame color. When sodium hydroxide solution is added to an aqueous solution of X, a brown precipitate forms. Identify the cation present in X and write an ionic equation for this reaction. (3 marks) (c) To another portion of the solution of X, dilute hydrochloric acid is added followed by barium chloride solution. A white precipitate forms. Identify the anion present in X and write an ionic equation for this reaction. (3 marks) (d) A student dissolves 1.60 g of anhydrous compound X in water to make 100 cm\(^3\) of solution. Calculate the concentration of the cation in this solution in mol/dm\(^3\). [Mr of compound X = 400] (2 marks)

A student performs a titration to find the concentration of a sodium hydroxide solution. They titrate 25.0 cm\(^3\) of sodium hydroxide solution with 0.150 mol/dm\(^3\) sulfuric acid. The mean volume of sulfuric acid needed for neutralization is 18.40 cm\(^3\). (a) Write a balanced chemical equation for the reaction. (2 marks) (b) Calculate the amount, in moles, of sulfuric acid used. (2 marks) (c) Calculate the concentration of the sodium hydroxide solution in mol/dm\(^3\). (4 marks) (d) Calculate the concentration of the sodium hydroxide solution in g/dm\(^3\). [Ar values: Na = 23, O = 16, H = 1] (3 marks)

An experiment is set up to determine the percentage by volume of oxygen in the air. A student places wet iron wool in the bottom of a 100 cm\(^3\) measuring cylinder and inverts it in a trough of water. (a) State the percentage by volume of the two most abundant gases in clean, dry air. (2 marks) (b) Describe how the student should use this setup over the course of a week to find the volume of oxygen that has reacted. (3 marks) (c) At the start of the experiment, the volume of air inside the cylinder is 84 cm\(^3\). After one week, the water level stops rising and the remaining gas volume is 67 cm\(^3\). Calculate the percentage of oxygen in this sample of air. (3 marks) (d) State why this reaction occurs slowly, and suggest how the student could accelerate the rusting process without changing the temperature or main reactants. (3 marks)

This question is about energetics and bond calculations. (a) Explain how you would identify an exothermic reaction from a reaction profile (energy level diagram), stating what the labels \(\Delta H\) and \(E_a\) represent on such a diagram. (4 marks) (b) Methane burns in oxygen according to the equation: \(\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g)\). Use the following bond energies to calculate the enthalpy change (\(\Delta H\)) for this reaction in kJ/mol: C-H = 413 kJ/mol, O=O = 498 kJ/mol, C=O = 805 kJ/mol, O-H = 464 kJ/mol. (5 marks) (c) State whether the reaction is endothermic or exothermic, and explain this in terms of the energy associated with bond breaking and bond making. (2 marks)

A student performs an experiment to determine the formula of hydrated cobalt(II) chloride, \(\text{CoCl}_2 \cdot x\text{H}_2\text{O}\), by heating a sample to remove the water of crystallisation. (a) State why the crucible is heated, cooled and reweighed multiple times during this experiment. [2 marks] (b) Describe the colour change when hydrated cobalt(II) chloride is heated. [2 marks] (c) A student heats a sample of hydrated cobalt(II) chloride in a crucible. The following results are obtained: mass of empty crucible = 22.40 g; mass of crucible + hydrated cobalt(II) chloride = 27.16 g; mass of crucible + anhydrous cobalt(II) chloride = 25.00 g. Calculate the value of \(x\) in \(\text{CoCl}_2 \cdot x\text{H}_2\text{O}\). Show your working. (\(A_r\): \(\text{Co} = 59\), \(\text{Cl} = 35.5\), \(\text{H} = 1\), \(\text{O} = 16\)) [5 marks] (d) The student noticed some condensation forming on the upper inside walls of the crucible which disappeared upon stronger heating. Explain how the calculated value of \(x\) would be affected if this condensation did not completely evaporate before weighing. [2 marks]

A student uses a polystyrene cup calorimeter to determine the enthalpy change (\(\Delta H\)) for the displacement reaction: \(\text{Zn(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Cu(s)}\). (a) Explain why a polystyrene cup is used instead of a copper beaker in this experiment. [2 marks] (b) In an experiment, a student adds excess zinc powder to \(50.0\text{ cm}^3\) of \(0.400\text{ mol/dm}^3\) copper(II) sulfate solution. The initial temperature of the solution is \(19.5\text{ }^\circ\text{C}\) and the maximum temperature reached is \(30.7\text{ }^\circ\text{C}\). Calculate the heat energy change (\(Q\)) in joules for this reaction. Assume the density of the solution is \(1.00\text{ g/cm}^3\) and its specific heat capacity is \(4.18\text{ J/g/}^\circ\text{C}\). [4 marks] (c) Use your answer to part (b) to calculate the enthalpy change (\(\Delta H\)) for this reaction in kJ/mol. Include a sign in your final answer. If you could not calculate \(Q\), use a value of \(2500\text{ J}\). [4 marks] (d) Suggest one source of error, other than heat loss, that could lead to an inaccurate value of \(\Delta H\). [1 mark]

A student designs an experiment to determine the enthalpy change of displacement for the reaction between zinc and copper(II) sulfate solution.\
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\( \text{Zn(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Cu(s)} \)\
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The student uses a polystyrene cup as a calorimeter. They place \( 50.0\text{ cm}^3 \) of \( 0.200\text{ mol/dm}^3 \) copper(II) sulfate solution in the cup and record its initial temperature. They then add an excess of zinc powder and stir the mixture, recording the maximum temperature reached. The temperature of the solution increases by \( 10.5\text{ }^\circ\text{C} \).\
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(a) Calculate the heat energy released, in joules, during this reaction. (Assume the specific heat capacity of the solution is \( 4.18\text{ J/g/}^\circ\text{C} \) and its density is \( 1.00\text{ g/cm}^3 \)). [2 marks]\
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(b) Calculate the number of moles of copper(II) sulfate used in this experiment. [1 mark]\
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(c) Calculate the molar enthalpy change (\( \Delta H \)) for this displacement reaction in \( \text{kJ/mol} \). State the correct sign and express your final answer to 3 significant figures. [3 marks]\
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(d) Explain why a polystyrene cup is preferred over a glass beaker for this experiment, and why it is important to use an excess of zinc. [2 marks]\
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(e) The student's experimental value is less exothermic than the accepted data book value. Suggest two changes to the apparatus or procedure (excluding using a polystyrene cup) that would improve the accuracy of the results. [2 marks]

A student uses heated copper to determine the percentage by volume of oxygen in a sample of air.\
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(a) Describe how the student can use two gas syringes and heated copper wire to determine the percentage by volume of oxygen in a sample of air. Your description should include the observations made during the experiment. [4 marks]\
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(b) In an experiment, the initial volume of air in one syringe is \( 80.0\text{ cm}^3 \). After heating the copper and passing the air over it until the volume remains constant, the apparatus is allowed to cool. The final volume of gas is \( 63.6\text{ cm}^3 \).\
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(i) Explain why the gas must be cooled to room temperature before measuring the final volume. [2 marks]\
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(ii) Calculate the percentage by volume of oxygen in this sample of air. [2 marks]\
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(iii) Name the copper compound formed on the surface of the copper wire and write a balanced chemical equation for its formation. [2 marks]

Crude oil is a complex mixture of hydrocarbons that is separated into fractions using fractional distillation. Shorter-chain alkanes and alkenes are then obtained from heavier fractions by catalytic cracking.\
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(a) Explain how the properties of fractions change from the top to the bottom of a fractional distillation column. Refer to boiling point, viscosity, and flammability in your answer. [3 marks]\
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(b) Catalytic cracking is used to break down larger alkanes into smaller, more useful molecules.\
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(i) State the catalyst and temperature range used in industrial catalytic cracking. [2 marks]\
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(ii) Explain why cracking is an economically vital process in the oil industry. [2 marks]\
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(c) A molecule of decane, \( \text{C}_{10}\text{H}_{22} \), undergoes cracking to form one molecule of propene, one molecule of but-1-ene, and one molecule of an alkane \( X \).\
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(i) State the molecular formula of alkane \( X \). [1 mark]\
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(ii) Write a balanced chemical equation for this cracking reaction. [1 mark]\
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(iii) Draw the displayed formula of but-1-ene. [1 mark]

An unknown solid compound, \( Y \), contains one metal cation and one halide anion. A student carries out tests to identify these ions.\
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(a) The student carries out a flame test on solid \( Y \) and observes a lilac flame. Identify the cation present. [1 mark]\
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(b) The student dissolves solid \( Y \) in deionised water to form a solution. They split the solution into two portions.\
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(i) To the first portion, the student adds dilute nitric acid followed by silver nitrate solution. A cream precipitate forms. Identify this precipitate and write an ionic equation, including state symbols, for its formation. [3 marks]\
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(ii) Identify compound \( Y \). [1 mark]\
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(iii) State why dilute nitric acid is added before the silver nitrate solution. [2 marks]\
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(c) If compound \( Y \) were instead replaced with ammonium bromide, \( \text{NH}_4\text{Br} \):\
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(i) Describe the tests and observations you would make to confirm the presence of the ammonium ion. [2 marks]\
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(ii) Write a balanced chemical equation for the reaction that occurs when ammonium bromide is heated with sodium hydroxide solution. [1 mark]

A student determines the formula of hydrated magnesium sulfate, \( \text{MgSO}_4 \cdot x\text{H}_2\text{O} \), by heating a sample in a crucible to drive off the water of crystallisation.\
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(a) Describe how the student should carry out this experiment to ensure that all the water of crystallisation has been removed. [3 marks]\
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(b) The student records the following data:\
- Mass of empty crucible = \( 22.45\text{ g} \)\
- Mass of crucible + hydrated magnesium sulfate = \( 24.91\text{ g} \)\
- Mass of crucible + anhydrous magnesium sulfate = \( 23.65\text{ g} \)\
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(i) Calculate the mass of anhydrous magnesium sulfate, \( \text{MgSO}_4 \), obtained. [1 mark]\
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(ii) Calculate the mass of water of crystallisation lost. [1 mark]\
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(iii) Calculate the value of \( x \) in the formula \( \text{MgSO}_4 \cdot x\text{H}_2\text{O} \). Show your working. (Relative formula masses: \( \text{MgSO}_4 = 120.4 \), \( \text{H}_2\text{O} = 18.0 \)). [4 marks]\
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(c) Suggest why the calculated value of \( x \) would be lower than the true value if the sample were not heated to constant mass. [1 mark]

This question is about the thermal decomposition of calcium carbonate, \( \text{CaCO}_3 \).\
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(a) Write a balanced chemical equation, including state symbols, for the thermal decomposition of calcium carbonate. [2 marks]\
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(b) A student heats \( 5.00\text{ g} \) of pure calcium carbonate until it completely decomposes.
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(i) Calculate the maximum theoretical volume, in \( \text{dm}^3 \), of carbon dioxide gas produced. Assume the reaction takes place at room temperature and pressure (rtp), where 1 mole of gas occupies \( 24.0\text{ dm}^3 \). (Relative formula mass: \( \text{CaCO}_3 = 100.1 \)). [3 marks]\
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(ii) In the experiment, the student collects \( 1.08\text{ dm}^3 \) of carbon dioxide gas. Calculate the percentage yield of carbon dioxide. [2 marks]\
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(c) The student performs the decomposition in an open crucible on a balance.\
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(i) State and explain the change in mass of the crucible and its contents during the reaction. [1 mark]\
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(ii) Sketch a graph to show how the mass of the crucible and its contents changes with time from the moment heating begins until the reaction is complete. Label the axes. [2 marks]

A student determines the concentration of a sample of hydrochloric acid by titrating it against a standard solution of sodium hydroxide.\
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(a) First, the student prepares a standard solution by dissolving \( 2.00\text{ g} \) of solid sodium hydroxide, \( \text{NaOH} \), in deionised water to make exactly \( 250\text{ cm}^3 \) of solution.\
Calculate the concentration, in \( \text{mol/dm}^3 \), of this sodium hydroxide solution. (Relative formula mass: \( \text{NaOH} = 40.0 \)). [3 marks]\
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(b) The student transfers \( 25.0\text{ cm}^3 \) of the sodium hydroxide solution to a conical flask.\
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(i) Describe the practical steps to carry out the titration to find the volume of hydrochloric acid needed to neutralise the sodium hydroxide. Name the piece of apparatus used to measure the sodium hydroxide solution, the apparatus containing the acid, and state the color change of a suitable indicator. [4 marks]\
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(ii) The average titre of the hydrochloric acid used is \( 21.50\text{ cm}^3 \). The equation for the reaction is:\
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\( \text{HCl(aq)} + \text{NaOH(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)} \)\
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Calculate the concentration, in \( \text{mol/dm}^3 \), of the hydrochloric acid. Give your answer to 3 significant figures. [3 marks]