4CH1/1C — June 2026 (Edexcel IGCSE Chemistry): Past Paper

Ammonium carbonate is a compound used in baking powders.

What is the formula of the ammonium ion?

What is the formula of the carbonate ion?

Explain why ammonium carbonate is a compound.

When heated, ammonium carbonate decomposes into ammonia and carbon dioxide.

Describe a test for carbon dioxide.

Calculate the relative molecular mass (Mr) of ammonia. Mr =

Using the relative molecular mass, determine the percentage by mass of nitrogen in ammonia. percentage = %

Explain why aqueous ammonia is an alkali and a base.

This question is about some Group 1 elements and their compounds.

A teacher adds a piece of sodium of mass 0.25 g to a trough of water.

Give two observations made when sodium reacts with water. 1 2

Give the word equation for this reaction.

Calculate the amount, in moles, of 0.25 g of sodium. Give your answer to two significant figures. amount = mol

The teacher adds a piece of potassium of mass 0.25 g to a different trough of water. Explain whether the volume of hydrogen produced in the reaction with potassium would be more than, less than or the same as the volume of hydrogen produced in the reaction with sodium.

The teacher then reacts sodium with oxygen.

Complete the equation for the reaction. Include state symbols Na ( ) + O₂ ( ) → Na₂O ( )

This passage is about the reaction between sodium and oxygen. Use words from the box to complete the passage. acidic basic complete covalent endothermic exothermic ionic maximum minimum molecular Sodium reacts with oxygen to form sodium oxide. To start the reaction, the sodium needs to be heated to overcome the activation energy. Activation energy is the energy needed to start the reaction. The enthalpy change for the reaction is negative, which means that the reaction is Sodium oxide contains bonding. It is a metal oxide that has properties.

A student does an experiment to investigate the decomposition of hydrogen peroxide in the presence of a catalyst. This is the equation for the decomposition. 2H₂O₂ → 2H₂O + O₂ The student collects the oxygen produced from the decomposition. They record the volume of oxygen every 20 seconds until 100 cm³ of oxygen has been produced. The student does the experiment twice, first with catalyst A and then with catalyst B.

Name a suitable piece of apparatus to measure the volume of oxygen collected.

Give two variables that the student must control to obtain valid results. 1 2

Give the test for oxygen gas.

Explain what is meant by the term catalyst.

The table shows the student’s results for catalyst A. Time in s 0 20 40 60 80 100 Volume of oxygen collected 0 54 79 91 96 100 in cm³

Plot the student’s results on grid 1.

Draw a curve of best fit. 120 100 Volume of oxygen 60 in cm³ 0 20 40 60 80 100 120 Time in s Grid 1

The student repeats the experiment using catalyst B. Grid 2 shows the results for catalyst B

On grid 2, draw a tangent to the curve for catalyst B at 60 s.

Use the tangent to determine the rate of reaction at 60 s. Include the units for the rate of reaction. rate of reaction = unit

Diagram 1 shows the displayed formula of isoprene

Explain why isoprene is a hydrocarbon.

Isoprene has this percentage composition by mass. C = 88.2 % H = 11.8 % Show by calculation that the empirical formula of isoprene is C₅H₈

Explain why isoprene does not have the same general formula as propene.

This is the equation for the complete combustion of isoprene. C₅H₈ + 7O₂ → 5CO₂ + 4H₂O Calculate the amount, in moles, of carbon dioxide produced when 50 g of isoprene undergoes complete combustion. amount = mol

Diagram 2 shows one of the reactions of isoprene with chlorine to give product X. H H H C H H C H Cl Cl H H H C C C C + Cl₂ C C C C H H H H H H H Product X Diagram 2

Name the type of reaction that occurs between isoprene and chlorine.

0.0500 mol of isoprene reacts with chlorine. 0.212 g of product X is produced. Calculate the percentage yield of product X. Give your answer to two decimal places. [for Product X Mr = 139] percentage yield =

Crude oil is a mixture of hydrocarbons.

Describe how useful hydrocarbons can be obtained from crude oil. Refer to fractional distillation and cracking in your answer.

State what is meant by the term fuel.

Explain how the combustion of an impurity in some hydrocarbon fuels causes an environmental problem.

This question is about ethane, C₂H₆

Explain a problem caused by a product of the incomplete combustion of ethane.

Draw a dot‑and‑cross diagram to show the outer shell electrons in a molecule of ethane.

No printed figure accompanies this part — in the paper you would draw the diagram (or label the apparatus) in the answer space provided.

Ethane has a boiling point of –89°C. Describe the arrangement and movement of particles of ethane at 25°C.

Explain why ethane has a lower boiling point than octane.

Ethane can react with bromine.

State the condition needed for ethane to react with bromine.

Give the displayed formula of each product. product 1 product 2

Explain why ethane does not have any isomers.

Anhydrous copper(II) sulfate reacts with water to produce hydrated copper(II) sulfate. This is the equation for the reaction. CuSO₄ + xH₂O ⇌ CuSO₄.xH₂O

A student does an experiment and determines that 1.75 mol of CuSO₄ reacts with 5.25 mol of H₂O Calculate the student’s value of x in the formula of hydrated copper(II) sulfate. x =

State what the ⇌ symbol shows about this reaction.

Describe two experiments to show that the ⇌ symbol is correct for this reaction. Include any relevant observations.

Hydrated copper(II) sulfate crystals can also be made by reacting copper(II) oxide with dilute sulfuric acid.

What is the colour of copper(II) oxide?

Give the chemical equation for the reaction between copper(II) oxide and sulfuric acid.

When making copper(II) sulfate using this method, excess copper(II) oxide is used. Explain why the copper(II) oxide is chosen as the reagent in excess.

Give a reason why copper metal cannot be used in this reaction.

Fluorine is an element found in Group 7 of the Periodic Table.

Give the electronic configuration of an atom of fluorine.

Which period does fluorine belong to?

Fluorine gas exists as the molecule F₂

Describe how two fluorine atoms combine to form a fluorine molecule.

One mole of fluorine gas contains 6.0 × 10²³ molecules. Calculate the number of molecules in 100 g of fluorine. Give your answer in standard form. number of molecules =

Fluorine forms fluoride ions when reacted with a metal.

Describe the changes in the electronic configurations of a lithium atom and a fluorine atom when they form lithium fluoride. fluorine lithium

Lithium fluoride has a giant ionic structure. Explain why lithium fluoride has a high melting point.

A student does an experiment to investigate the reactivity of metals. The diagram shows the set‑up for the experiment

What type of reaction occurs in beaker 1?

Give the chemical equation for the reaction that occurs in beaker 1.

Explain which species is the oxidising agent in beaker 1.

Explain why no changes are observed in beaker 2.

The student wants to confirm that both beakers contain sulfate ions. Before testing for sulfate ions, the student acidifies the solutions in the beakers.

Describe a test to show that the solutions in the beakers contain sulfate ions.

Explain why the student acidifies the solutions in the beakers before testing for sulfate ions.