4CH1/2CR — June 2024 (Edexcel IGCSE Chemistry): Past Paper

This question is about sulfur.

The diagram represents the electronic configuration of an atom of sulfur.

Which period of the Periodic Table contains sulfur?

What is the charge on a sulfide ion?

When a mixture of sulfur and zinc is heated to a high temperature a reaction occurs, forming the compound zinc sulfide, ZnS

Give a reason why the mixture of sulfur and zinc needs heating before a reaction occurs.

Calculate the relative formula mass (Mr) of zinc sulfide. [for Zn, Ar = 65 for S, Ar = 32] Mr =

The diagram represents an atom of an element. + + + W +

What is the name of the particle labelled W?

What is the mass number of this atom?

These are the symbols for the two isotopes of lithium. 6 7 Li Li 3 3

In terms of sub-atomic particles, give one similarity and one difference between the two isotopes. similarity difference

A sample of lithium contains 7.5% of 63Li and 92.5% of 73Li Calculate the relative atomic mass (Ar) of this sample of lithium. Ar =

This question is about magnesium metal and its compounds.

The diagram represents the structure of magnesium. Complete the diagram by adding the labels.

Explain why magnesium is malleable.

Magnesium burns in oxygen gas to form solid magnesium oxide.

Complete the chemical equation for the reaction by balancing the equation and adding the state symbols Mg(s) + O₂( ) → MgO( )

Give a reason why magnesium is oxidised in this reaction.

A student uses this method to make a solution of magnesium chloride. Step 1 measure 25 cm³ of dilute hydrochloric acid into a beaker Step 2 add magnesium powder a little at a time Step 3 keep adding magnesium powder until it is in excess Step 4 remove the excess magnesium powder by filtration This is the equation for the reaction. Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Give a reason why the student uses magnesium powder rather than magnesium ribbon.

Give a reason why the student adds an excess of magnesium in step 3.

Calculate the minimum mass of magnesium needed to react with 25.0 cm³ of 2.00 mol / dm³ hydrochloric acid. [for Mg, Ar = 24] mass = g

This question is about the manufacture of ethanol by the fermentation of glucose.

Fermentation needs to be done in the absence of air. Give two other conditions needed for fermentation. 1 2

Explain why fermentation needs to be done in the absence of air.

Complete the equation for fermentation. C₆H₁₂O₆ → 2C₂H₅OH + 2

A mixture containing 500 mol of glucose is fermented. A mass of 5750 g of ethanol is obtained. Calculate the percentage yield. [for ethanol, Mr = 46] percentage yield = %

Sodium sulfate can be prepared by the reaction between sodium hydroxide solution and sodium hydrogensulfate (NaHSO₄) solution. This is the equation for the reaction. NaOH(aq) + NaHSO₄(aq) → Na₂SO₄(aq) + H₂O(l) Sodium hydrogensulfate solution is acidic. A student adds 25.0 cm³ of sodium hydroxide solution to a conical flask and adds two drops of indicator. The student does a titration.

Name a piece of apparatus that should be used to add 25.0 cm³ of sodium hydroxide solution to the conical flask.

Describe the method the student should use to find the accurate volume of sodium hydrogensulfate solution needed to neutralise the 25.0 cm³ of sodium hydroxide solution.

The student repeats the titration without the indicator and forms a solution of sodium sulfate. Describe how the student can obtain pure, dry crystals of hydrated sodium sulfate from the solution.

Crystals of hydrated sodium sulfate decompose when heated. This is the equation for the decomposition. Na₂SO₄.xH₂O → Na₂SO₄ + xH₂O A student uses this apparatus to find the value of x. hydrated sodium sulfate heat ice water The student heats the crystals until the decomposition is complete. The table shows the student’s results. mass of empty test tube in g 25.12 mass of test tube and Na₂SO₄.xH₂O in g 31.56 mass of test tube and Na₂SO₄ in g 27.96 Use the results to calculate the value of x. [for Na₂SO₄ , Mr = 142 for H₂O, Mr = 18] value of x =

This question is about electrolysis.

This apparatus is used to collect the gases produced when an electric current passes through dilute sulfuric acid. dilute sulfuric acid oxygen hydrogen inert electrode inert electrode + – power supply

Name a suitable material for the inert electrodes.

Give a test to show that the gas produced at the positive electrode is oxygen.

Give a test to show that the gas produced at the negative electrode is hydrogen.

Give an ionic half-equation for the formation of hydrogen at the negative electrode.

The oxygen gas in the tube has a volume of 17.8 cm³ at rtp. Calculate the mass, in grams, of oxygen gas in the tube. Give your answer to 3 significant figures. [for O₂ at rtp, molar volume = 24 000 cm³] mass of oxygen = g

This apparatus is used to electrolyse a concentrated solution of sodium chloride. chlorine hydrogen concentrated solution of sodium chloride – power + supply

Give a reason why sodium chloride solution conducts electricity.

The positive ions in the solution are H+ and Na+. Give a reason why hydrogen forms at the negative electrode rather than sodium.

A sample of the solution is taken from near the negative electrode. The sample is tested with universal indicator. Explain the final colour of the universal indicator.

Gaseous ethanol is manufactured by reacting ethene gas with steam. This is the equation for the reaction. C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g)

The pressure on an equilibrium mixture of the three gases is decreased. All the other conditions are kept the same. Predict the effect of this change on the yield of ethanol at equilibrium, giving a reason for your answer.

Predict the effect of adding a catalyst on the yield of ethanol at equilibrium, giving a reason for your answer.

The equation shows the displayed formulae for the reactants and products. H H H H O C C + ⇌ H C C O H H H H H H H The table gives the bond energies

Using the data in the table and the equation, show that the enthalpy change, ΔH , is approximately –40 kJ / mol.

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

Draw an energy level diagram for the reaction between ethene and steam. Label the enthalpy change, ΔH . Energy

Ethanoic acid reacts with ethanol to form ester A and water.

Complete the equation by adding the displayed formula of ester A.

Give the name of ester A.