4CH1/2C — November 2020 (Edexcel IGCSE Chemistry): Past Paper

A student is given a mixture of salt solution and sand. She wants to obtain pure water from the mixture.

She separates the sand from the salt solution. Which method of separation should she use?

The student then uses this apparatus to obtain pure water from the salt solution. X water out Y water in flask Z salt solution heat

Name the pieces of apparatus labelled X, Y and Z. X Y Z

State what remains in the flask when the separation is complete.

In a chromatography experiment a student uses samples of three pure food dyes, blue (B), red (R) and yellow (Y). He also uses samples of four unknown substances, S, T, U and V. The student puts a small drop of each substance on the pencil line. The diagram shows the student’s chromatogram at the end of the experiment

Which of the unknown substances contains only one food dye?

Explain which pure food dyes are in substance V.

Calculate the Rf value of the yellow food dye Y. Rf =

State how the chromatogram suggests that the yellow food dye Y is less soluble in the solvent than the red food dye R.

The box gives the names of some metals. calcium copper iron magnesium silver zinc

Identify the metal from the box that burns with a bright white flame.

In the Earth, metals are found either in ores or as uncombined elements. Explain which metal from the box is most likely to be found as an uncombined element.

This is the order of reactivity of four metals. most reactive aluminium iron lead least reactive copper The method used to obtain a metal from its oxide depends on the reactivity of the metal. Two possible methods are Method 1 heating the metal oxide with carbon Method 2 electrolysis Explain which method should be used to obtain lead from lead(II) oxide, PbO Include an equation for the formation of lead in your answer.

The diagram shows the arrangement of the particles in a pure metal. Metals are often made into alloys to make them harder. Explain why alloys are harder than pure metals. Draw a diagram to support your answer.

Alcohols contain the functional group —OH

Give the structural formula of the alcohol that contains one carbon atom.

Ethanol (C₂H₅OH) is an alcohol that can be obtained from glucose (C₆H₁₂O₆).

Name the process that converts glucose into ethanol.

Explain why this process is carried out in the absence of air and at a temperature below 40 °C.

The table gives information about some organic compounds in the same homologous series

Complete the table by giving the missing information.

Name the homologous series that contains these compounds.

The compounds in the table can react with alcohols to form esters. When preparing esters, a small amount of concentrated sulfuric acid is also used.

State the purpose of the acid.

Draw the displayed formula of the ester that forms when propanoic acid reacts with ethanol.

Esters have particular uses that depend on their properties. Give an example of a property and use of esters. property use

The organic compound butadiene is a colourless gas used in the manufacture of synthetic rubber for tyres. The displayed formula of butadiene is

Explain why butadiene is described as an unsaturated hydrocarbon.

Butadiene reacts with bromine water. State the colour change that occurs during this reaction. from to

The equation for the reaction between butadiene and bromine can be shown using displayed formulae. H H C C H H H H H H C C + 2Br Br → H C C C C H H H Br Br Br Br The table gives some bond energies. Bond C—H C= C Br—Br C—C C—Br Bond energy in kJ/mol 412 612 193 348 276 Use this information to calculate the enthalpy change, ΔH, for the reaction. Include a sign in your answer. ΔH = kJ/mol

A scientist does an investigation to find out if butadiene would be a good fuel. He burns a sample of butadiene gas and observes that carbon forms as black soot.

Complete the equation to explain the scientist’s observation. 2C₄H₆ + 7O₂ → C + 4CO + 2CO₂ + H₂O

Explain how one of the products, other than carbon, may cause a problem.

The equation for the combustion of butadiene in excess oxygen is 2C₄H₆ + 11O₂ → 8CO₂ + 6H₂O The enthalpy change for this reaction, ΔH, is – 3446 kJ/mol. Complete the energy profile diagram for the reaction. Label the enthalpy change for this reaction, ΔH, and the activation energy. Energy 2C₄H₆ + 11O₂

A student is provided with a bottle containing a colourless solution X. Solution X is thought to be dilute sulfuric acid of concentration 0.10 mol/dm³. The student does some experiments on samples of solution X to try to show that it is dilute sulfuric acid. The student adds a few drops of litmus to a sample of solution X. The litmus turns red.

The student knows that the products of the electrolysis of dilute sulfuric acid are hydrogen and oxygen. She carries out the electrolysis using this apparatus. oxygen hydrogen solution X graphite anode graphite cathode + − power supply

Suggest why the student does not use zinc electrodes in her experiment.

State what is observed at both the anode and the cathode during the electrolysis.

Which of these tests shows that the gas formed at the cathode is hydrogen?

Describe a test to show that solution X contains sulfate ions.

The student then does a titration to see if the concentration of the dilute sulfuric acid is 0.10 mol/dm³. She measures 25.0 cm³ of potassium hydroxide solution into a conical flask, and then adds a few drops of indicator solution.

Name the piece of apparatus the student should use to measure 25.0 cm³ of the potassium hydroxide solution.

The concentration of potassium hydroxide in the solution is 0.125 mol/dm³. Calculate the amount, in mol, of KOH in 25.0 cm³ of this solution. amount = mol

The equation for the reaction in the titration is H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O Calculate the volume, in cm³, of 0.10 mol/dm³ sulfuric acid needed to neutralise 25.0 cm³ of the potassium hydroxide solution. volume of sulfuric acid = cm³

This question is about reactions involving gases.

Potassium carbonate reacts with dilute hydrochloric acid to produce carbon dioxide gas. The equation for the reaction is K₂CO₃(s) + 2HCl(aq) → 2KCl(aq) + H₂O(l) + CO₂(g) Calculate the volume, in cm³, of carbon dioxide gas produced when 6.9 g of potassium carbonate reacts with excess dilute hydrochloric acid. [Mr of K₂CO₃ = 138] [molar volume of CO₂ at rtp = 24 dm³ ] volume = cm³

This reaction involving gases is in dynamic equilibrium at a temperature of 225 °C. H₂(g) + CO₂(g) ⇌ CO(g) + H₂O(g) ΔH = + 41 kJ/mol

Predict the effect on the yield of CO(g) at equilibrium when the temperature is increased without changing the pressure. Give a reason for your answer.

Predict the effect on the yield of CO(g) at equilibrium when the pressure is increased without changing the temperature. Give a reason for your answer.