4CH1/2CR — June 2025 (Edexcel IGCSE Chemistry): Past Paper

This question is about gases.

The box gives the names of some gases. carbon dioxide carbon monoxide helium neon nitrogen oxygen Choose gases from the box to answer questions (i) to (iv). You may use each gas once, more than once or not at all.

Identify two gases in Group 0 of the Periodic Table.

Identify the gas that makes up about 21% of the atmosphere.

Identify a greenhouse gas.

Identify the toxic gas formed by incomplete combustion of a hydrocarbon.

Describe a test to show that a gas is carbon dioxide.

Crude oil is a mixture of hydrocarbons.

Name the process used to separate crude oil into fractions.

Give one use for the bitumen fraction.

The diagram shows the displayed formula of one of the alkanes in the refinery gases fraction. H H H H H C C C C H H H H H

Determine the molecular formula of this alkane.

Name this alkane.

Give the general formula of the homologous series of alkanes.

This question is about a compound called potassium permanganate.

A teacher makes a saturated solution of potassium permanganate using this method. The teacher adds 25 cm³ of water at 50 °C to a beaker. The teacher then adds solid potassium permanganate one spatula at a time, while stirring, until the solution is saturated.

Give the meaning of the term saturated solution.

Give a reason why crystals form when the saturated solution cools from 50 °C to room temperature.

The teacher pours 25 cm³ of a saturated solution of potassium permanganate at room temperature into an evaporating dish. The teacher leaves the solution until all the water has evaporated. The teacher records the mass of the evaporating dish and the mass of the evaporating dish with the dry crystals. mass of evaporating dish = 64.10 g mass of evaporating dish with dry crystals = 65.35 g Calculate the solubility of potassium permanganate in grams per 100 g of water. [1.00 cm³ of water has a mass of 1.00 g] solubility = g per 100 g of water

The equation shows the thermal decomposition of potassium permanganate. 2KMnO₄ → K₂MnO₄ + MnO₂ + O₂

Describe a test to show that oxygen gas is produced.

Calculate the Mr of K₂MnO₄ Mr =

Potassium permanganate is an oxidising agent. Give a reason why potassium permanganate is an oxidising agent.

This question is about Group 1 metals.

A teacher adds a small piece of lithium metal to a trough containing water.

Complete the equation for the reaction between lithium and water by adding the state symbols. 2Li( ) + 2H₂O( ) → 2LiOH( ) + H₂( )

Give two observations made when the lithium is added to the water. 1 2

The reaction produces 375 cm³ of hydrogen gas at room temperature and pressure (rtp). Show, by calculation, that the mass of lithium added is between 0.20 g and 0.30 g. [1 mol of gas has a volume of 24 000 cm³ at rtp] [for lithium, Ar = 7]

Potassium is more reactive than lithium. The diagram shows the electronic structure of an atom of lithium and an atom of potassium. Lithium Potassium

Give one observation that is different when a small piece of potassium, instead of lithium, is added to water.

Explain why potassium is more reactive than lithium. Refer to the electronic structure of lithium and of potassium in your answer.

This question is about metals and metal compounds.

The method used to extract a metal depends on the reactivity of the metal. Explain which method is used to extract sodium metal from sodium chloride.

The diagram shows the arrangement of particles in a pure metal. Explain why pure metals are soft.

The diagram shows the electronic structure of an atom of sodium and an atom of oxygen. Sodium Oxygen Describe, in terms of electrons, what happens when sodium reacts with oxygen.

The table shows the melting points of sodium and sodium oxide. Melting point in °C Sodium 98 Sodium oxide 1132 Explain why sodium and sodium oxide have different melting points. In your answer you should refer to: • the structures of sodium and sodium oxide • the forces between the particles

A student does a titration to find the volume of phosphoric acid solution (H₃PO₄) needed to neutralise a sample of potassium hydroxide solution (KOH). One of the products of the reaction is potassium phosphate. This is the student’s method.

• use a measuring cylinder to transfer 25 cm³ of potassium hydroxide solution to a conical flask
• add two drops of an indicator
• fill a burette with phosphoric acid solution and record the initial reading on the burette
• add the acid to the conical flask
• record the final burette reading when the indicator changes colour This is the equation for the reaction. H₃PO₄(aq) + 3KOH(aq) → K₃PO₄(aq) + 3H₂O(l)

Explain two improvements to the student’s method that would give more accurate results. 1 2

The student repeats the titration correctly. The potassium hydroxide solution has a concentration of 0.150 mol / dm³ . The phosphoric acid solution has a concentration of 0.0400 mol / dm³ . Calculate the volume, in cm³ , of phosphoric acid solution needed to neutralise 25.0 cm³ of 0.150 mol / dm³ potassium hydroxide solution. Give your answer to three significant figures. volume of phosphoric acid solution = cm³

Potassium phosphate solution reacts with calcium chloride solution. One of the products is the insoluble solid, calcium phosphate.

Complete the equation for the reaction. 2K₃PO₄(aq) + CaCl₂(aq) → Ca₃(PO₄)₂(s) + KCl(aq)

The student reacts a solution containing 0.0400 mol of potassium phosphate with an excess of calcium chloride solution. The student obtains 5.70 g of calcium phosphate. Show that the percentage yield for the reaction is about 90% [for Ca₃(PO₄)₂ Mr = 310]

Describe how the student can obtain a pure, dry sample of calcium phosphate from the mixture at the end of the reaction.

This question is about ethanol, C₂H₅OH , which can be used as a fuel. Ethanol can be produced by the fermentation of glucose solution.

Name the substance that is added that causes the fermentation of glucose solution.

Which temperature is most suitable for fermentation?

Explain why fermentation is done in the absence of air.

This is the equation for the combustion of ethanol. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O The equation shows the displayed formulae of the reactants and products. O H H O O H H O C O H C C O H + O O + O O C O H H H H O O O H H The table shows some bond energies. Bond Bond energy in kJ / mol C H 414 C C 346 C O 358 O H 463 O O 498 C O 804

Use the bond energies to show that the molar enthalpy change, ΔH , is about −1300 kJ / mol.

Complete the energy level diagram for the reaction between C₂H₅OH and O₂ energy

Explain, in terms of bonds broken and bonds made, why this reaction is exothermic.

Ethanol reacts with compound A to produce ester B and compound C. This is the equation for the reaction. H H H O H C C O H + compound A H C C H H + compound C H H H O C C H H H ester B

Draw the displayed formula for compound A and for compound C. compound A compound C

Name ester B.