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

This question is about elements, compounds and mixtures.

The box gives the names of some substances. calcium fluorine helium neon petrol silicon water Choose a substance from the box to answer each of these questions.

Give the name of a compound.

Give the name of a mixture.

Give the name of a diatomic molecule.

Give the name of a metal element.

Name the technique used to separate crude oil into fractions.

Give one use of the kerosene fraction.

Magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen. The hydrogen is collected in a gas syringe. gas syringe magnesium dilute ribbon hydrochloric acid The reaction is exothermic and magnesium is in excess.

State what is meant by the term exothermic.

Complete the chemical equation for the reaction. Mg + 2HCl → +

Draw a sketch graph to show how the volume of hydrogen changes with time until the reaction has finished. Volume Time

Explain why increasing the temperature of the hydrochloric acid affects the rate of the reaction. Refer to collision theory in your answer.

Draw a reaction profile diagram for the reaction, showing ΔH and activation energy. Label the reactants and products. Energy

This question is about Group 2 elements and their compounds.

A sample of magnesium contains three isotopes. Mass number of isotope 24 25 26 Percentage abundance (%) 76.5 10.5 13.0

State, in terms of subatomic particles, what is meant by the term isotopes.

Calculate the relative atomic mass (Ar) of magnesium. Give your answer to one decimal place. Ar =

Which of these compounds is an insoluble solid?

Magnesium oxide is an ionic compound. The diagrams show the atoms of magnesium and oxygen. Mg O Draw diagrams to show the structure of each ion in magnesium oxide. Include the charge on each ion.

The table lists some substances and shows which substance conducts electricity. Substance Conducts electricity? water no solid magnesium chloride no aqueous magnesium chloride yes Explain these observations. Refer to structure and bonding in your answer.

A concentrated aqueous solution of magnesium chloride is electrolysed. Chlorine forms at the positive electrode.

Give the half‑equation for the reaction at the positive electrode.

Give a reason why this reaction is classified as oxidation.

This question is about the reactions of ethanol and ethanoic acid.

Ethanol reacts with potassium dichromate(VI) to form ethanoic acid. Name the other reagent needed in this reaction.

State the colour change that occurs when ethanol reacts with potassium dichromate(VI). from to

Ethanoic acid reacts with solid sodium carbonate.

Complete the chemical equation for this reaction. 2CH₃COOH + Na₂CO₃ → + +

State two observations seen in this reaction. 1 2

A student prepares the ester, ethyl ethanoate, by reacting ethanol with ethanoic acid. This is the student’s method.

• mix equal amounts of ethanol and ethanoic acid in a boiling tube
• add a few drops of concentrated sulfuric acid
• place the boiling tube in a hot water bath for several minutes

State the role of sulfuric acid in this reaction.

State why the student heats the mixture in a water bath instead of directly with a Bunsen burner flame.

State how the student would know that ethyl ethanoate has formed.

Draw the displayed formula of ethyl ethanoate.

A student does a titration to find the concentration of a solution of sulfuric acid. This is the student’s method.

• fill a burette with sulfuric acid and record the reading
• transfer 25.0 cm³ of potassium hydroxide solution to a conical flask
• add a few drops of methyl orange to the conical flask
• place the conical flask on a white tile
• swirl the flask continuously while adding sulfuric acid from the burette
• keep adding sulfuric acid until the end-point has been reached
• record the rough reading at the end-point

Name the most suitable piece of apparatus for measuring 25.0 cm³ of potassium hydroxide solution.

State why the student places the conical flask on a white tile.

The diagram shows the final burette reading. The initial burette reading is given in the table. Complete the table, giving both values to the nearest 0.05 cm³. final burette reading initial burette reading 4.15 volume of sulfuric acid added in cm³

The student repeats the titration more accurately four times. The table shows their results. titration number 1 2 3 4 volume of sulfuric acid added in cm³ 27.40 27.65 27.30 27.35 concordant results Concordant results are those within 0.20 cm³ of each other.

Place ticks (✓) in the table to show which results are concordant.

Use the concordant results to calculate the mean volume of sulfuric acid added. mean volume of sulfuric acid = cm³

Another student also does the titration.

The student uses 25.0 cm³ of potassium hydroxide solution with a concentration of 0.500 mol/dm³. The mean volume of sulfuric acid added is 26.50 cm³. This is the equation for the reaction. 2KOH(aq) + H₂SO₄(aq) → K₂SO₄(aq) + 2H₂O(l) Calculate the concentration of the sulfuric acid. concentration of sulfuric acid = mol/dm³

The student repeats the titration without the methyl orange indicator. They add exactly 26.50 cm³ of sulfuric acid to the potassium hydroxide solution. Describe how the student could obtain pure, dry potassium sulfate crystals from the reaction mixture.

Hydrogen reacts with iodine vapour to form hydrogen iodide, HI This is the equation for the reaction. H₂(g) + I₂(g) ⇌ 2HI(g) ΔH = +26 kJ/mol

Give the test for hydrogen.

State what the symbol ⇌ represents.

In a sealed container at equilibrium, the reaction conditions are 500°C and 2 atm.

The temperature of the reaction mixture is increased to 600°C, but the pressure is kept at 2 atm. Explain the effect, if any, on the yield of hydrogen iodide at equilibrium.

The pressure of the reaction mixture is decreased to 1 atm but the temperature is kept at 500°C. Explain the effect, if any, on the yield of hydrogen iodide at equilibrium.

An excess of hydrogen reacts with 50.8 g of iodine. At equilibrium, the yield of hydrogen iodide is 80%. Calculate the volume, in cm³, of hydrogen iodide produced at rtp. Give your answer in standard form. [at rtp, molar volume = 24 000 cm³] volume of hydrogen iodide = cm³