4CH1/2C — January 2022 (Edexcel IGCSE Chemistry): Past Paper

This question is about the unsaturated hydrocarbon, ethene. The displayed formula of ethene is

State the meaning of the term hydrocarbon.

Give the reason why ethene is described as unsaturated.

Ethene is bubbled through bromine water until there is no further colour change. Which of these is the appearance of the solution formed?

Ethanol is produced industrially by the reaction between ethene and steam. The equation for the reaction is CH₂CH₂(g) + H₂O(g) → CH₃CH₂OH(l)

State the temperature and pressure used in this reaction. temperature pressure

Give the molecular formula of ethanol.

This question is about gases in the air. The pie chart represents the percentages of gases in dry, unpolluted air. Gases with percentages of less than 1% in air are called trace gases

Which of these is gas Z?

Which of these is the approximate percentage of oxygen in dry, unpolluted air?

One of the trace gases is carbon dioxide.

Identify two reactions that produce carbon dioxide by placing a tick (✓) in two boxes. cracking an alkane complete combustion of an alkane reaction between magnesium and hydrochloric acid rusting of iron thermal decomposition of copper(II) carbonate

Name an environmental problem that is caused by the percentage of carbon dioxide increasing in the atmosphere.

Name the trace gas with the highest percentage in dry, unpolluted air.

Rainwater is acidic because carbon dioxide dissolves in water to form carbonic acid. Acid rain is more acidic than rainwater because acidic pollutant gases also dissolve in water.

Give the name of the acid that forms when nitrogen dioxide dissolves in water.

Name another pollutant gas that also forms acid rain.

This question is about solubility.

The graph shows the solubilities of copper(II) chloride and sodium chloride at different temperatures

Determine the temperature at which copper(II) chloride and sodium chloride have the same solubility. Show on the graph how you obtained your answer. temperature = °C

A saturated solution of copper(II) chloride in 100 g of water is cooled from 40 °C to 10 °C. Determine the mass, in grams, of copper(II) chloride that crystallises. mass of copper(II) chloride = g

A student uses this method to determine the solubility of potassium chloride in water at room temperature.

• record the mass of an empty evaporating basin
• pour some saturated potassium chloride solution into the evaporating basin
• record the mass of the evaporating basin and saturated potassium chloride solution
• heat the evaporating basin to remove all the water
• record the mass of the evaporating basin and the dry potassium chloride The table shows the student’s results. Mass in grams evaporating basin 58.1 evaporating basin and saturated 78.2 potassium chloride solution evaporating basin and dry 63.2 potassium chloride

Calculate the mass of dry potassium chloride obtained. mass = g

Calculate the mass of water removed. mass = g

Calculate the solubility of potassium chloride in grams per 100 grams of water. solubility = g per 100 g of water

Suggest why the student’s method is not suitable for determining the solubility of hydrated copper(II) sulfate.

This question is about the reactions of Group 1 metals with water.

A teacher adds a piece of sodium to some water containing universal indicator. piece of sodium water containing universal indicator The equation for this reaction is 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) The sodium floats on the surface of the water and the universal indicator changes colour because an alkaline solution is formed.

Give two other observations. 1 2

Give the final colour of the universal indicator.

The diagram represents an atom of lithium and an atom of sodium. lithium sodium

Give a reason why lithium and sodium have similar reactions with water.

Explain why lithium is less reactive than sodium.

The teacher adds 0.150 g of lithium to an excess of water and collects the hydrogen gas produced. The equation for the reaction is 2Li(s) + 2H₂O(l) → 2LiOH(aq) + H₂(g) The teacher collects 254 cm³ of hydrogen gas at room temperature and pressure (rtp). Show by calculation that 1 mol of hydrogen gas has a volume of approximately 24 000 cm³ at rtp.

Hydrogen peroxide solution decomposes to give water and oxygen gas. The equation for this reaction is 2H₂O₂(aq) → 2H₂O(l) + O₂(g)

Three different solids are catalysts for the decomposition of hydrogen peroxide solution. A student is given hydrogen peroxide solution and a sample of each of the solid catalysts. The student has a timer, a measuring cylinder, a balance and the apparatus shown in the diagram. Describe a method the student could use to find which of the three solids is the most effective catalyst for the decomposition of hydrogen peroxide solution.

The diagram shows the reaction profile for the decomposition of hydrogen peroxide without a catalyst. hydrogen peroxide Energy water + oxygen

Label the diagram to show the activation energy (Ea ) and the enthalpy change (ΔH) for this reaction.

On the diagram, draw a curve to show the reaction profile for the same reaction when a catalyst is used.

This question is about the electrolysis of copper(II) sulfate solution.

The diagram shows the apparatus used for the electrolysis. power supply + − lamp positive electrode negative electrode copper(II) sulfate solution A student records the total increase in mass of the negative electrode every minute for 8 minutes. The table shows the results. Total increase in mass of Time in minutes the negative electrode in grams 0 0.00 1 0.15 2 0.27 3 0.34 4 0.39 5 0.41 6 0.42 7 0.42 8 0.42

Plot the student’s results.

Draw a curve of best fit. 0.50 0.40 0.30 Increase in mass in grams 0.20 0.10 0 1 2 3 4 5 6 7 8 Time in minutes

Explain the shape of the graph.

The product at the positive electrode is oxygen gas.

The student repeats the electrolysis using different apparatus. positive electrode negative electrode Describe how the student should collect a sample of pure oxygen at the positive electrode.

Give an ionic half-equation for the formation of oxygen.

The wire used to connect the power supply to the electrodes is made of copper metal. The diagram shows the arrangement of the ions in a metal. + + + + + + + + + + + + + + + metal ion + + + + + + + + + + + + + +

Metals that are malleable can also be stretched to form long, thin wires. Suggest why metals can be stretched to form wires.

Explain why metals conduct electricity.

This question is about esters. Ester A reacts with water to form ethanoic acid and ethanol. The displayed formulae of the reactants and products are shown in this equation H O H H H H H O H C C O + ⇌ H C C + H C C O H O C C H H H H O H H H H H H ester A The molar enthalpy change (ΔH) for the reaction is 0 kJ/mol.

Draw a ring around the functional group in ester A.

Give the name of ester A.

Describe a chemical test, other than using an indicator, to show that the reaction mixture contains ethanoic acid.

Explain why the molar enthalpy change (ΔH) for the reaction between ester A and water is 0 kJ/mol. In your answer, refer to the bonds broken and the bonds formed.

A mixture of ester A and water is left in a sealed container until the reaction mixture reaches dynamic equilibrium.

Describe what is meant by dynamic equilibrium.

Explain why adding a catalyst does not change the position of equilibrium.

The ethanoic acid produced in the reaction is completely neutralised by 22.75 cm³ of 0.150 mol/dm³ barium hydroxide solution. The equation for the neutralisation reaction is 2CH₃COOH + Ba(OH)₂ → Ba(CH₃COO)₂ + 2H₂O Calculate the amount, in moles, of ethanoic acid neutralised. Give your answer to 3 significant figures. amount = mol

The structures of two organic compounds are shown. These compounds react together to form a polymer. Give the repeat unit of the polymer formed.