4CH1/2C — November 2023 (Edexcel IGCSE Chemistry): Past Paper

This question is about Group 7, the halogens.

What is the total number of electrons in one fluorine atom?

What is the charge on a bromide ion?

Which of these describes the element iodine at room temperature?

When a halogen is added to a solution containing halide ions, a displacement reaction may occur. The table shows whether a reaction occurs. Chloride ion Bromide ion Iodide ion Halogen added in solution in solution in solution chlorine reaction reaction bromine no reaction reaction iodine no reaction no reaction Using information from the table, explain the order of reactivity of the three halogens.

This question is about gases in the atmosphere. A teacher uses this apparatus to determine the percentage of oxygen in air. stopper magnesium air ribbon bell jar basin water The teacher removes the stopper, ignites the magnesium ribbon and immediately replaces the stopper. The magnesium reacts with oxygen to form magnesium oxide. During the reaction the water level in the bell jar rises. When the flame goes out, some magnesium remains in the basin.

Give the appearance of the magnesium oxide.

Give a chemical equation for the reaction of magnesium with oxygen.

Explain why the water in the bell jar rises.

The volume of air in the bell jar at the start of the reaction is 2000 cm³. When the reaction ends, the apparatus cools down to room temperature. Calculate the expected volume of gas in the bell jar at room temperature. volume of gas = cm³

State why the gas remaining in the bell jar at the end of the reaction is approximately 99% nitrogen.

This question is about aluminium.

State why aluminium cannot be extracted by heating aluminium oxide with carbon.

Aluminium is a metal with many uses. Aluminium is malleable, a good conductor of heat and electricity, and has a low density compared to most other metals. Explain two uses of aluminium that are related to its properties. 1 2

The diagram represents the structure of pure aluminium, and the structure of an alloy of aluminium. Pure aluminium Alloy of aluminium Use the diagram to explain why the alloy is harder than pure aluminium.

A student uses this method to investigate the reaction between sodium hydroxide solution and dilute hydrochloric acid.

• pour 25 cm³ of dilute hydrochloric acid into a glass beaker
• measure the temperature of the acid
• add 5 cm³ of sodium hydroxide solution and stir the mixture
• record the highest temperature reached
• continue to add further 5 cm³ portions of sodium hydroxide solution until a total of 40 cm³ has been added
• record the temperature after adding each 5 cm³ portion of sodium hydroxide solution

State two factors that the student must keep constant to make this a valid investigation. 1 2

Explain how using a polystyrene cup, instead of a glass beaker, would increase the accuracy of the results.

The graph shows the student’s results

Use the graph to determine the maximum temperature change in °C. maximum temperature change = °C

Explain the shape of the graph.

The student repeats the experiment using a polystyrene cup. These are the student’s results. Maximum temperature change 35 °C Volume of hydrochloric acid 25 cm³ Volume of sodium hydroxide solution added for complete reaction 22 cm³ Calculate the heat energy change (Q) in kJ. [for the solution, 1.0 cm³ has a mass of 1.0 g c = 4.2 J / g / °C] Q = kJ

This question is about carboxylic acids and esters.

Ethanoic acid reacts with magnesium to form two products.

Complete the equation for this reaction + → (CH₃COO)₂Mg +

Give two observations that could be made during this reaction. 1 2

Propanoic acid reacts with methanol to form an ester.

Give the name of a suitable catalyst for this reaction.

What is the structural formula of the ester that forms?

A polyester can be made by reacting ethanedioic acid with ethanediol. These are the displayed formulae of the two reactants. O O H H H O C C O H H O C C O H H H ethanedioic acid ethanediol

Give the name for this type of polymerisation.

Give the name of the other product of this reaction.

Draw the displayed formula for the repeat unit of the polyester that forms.

State what is meant by the term biopolyester.

The diagram shows two pieces of apparatus used in a titration. cm³ cm³ Not to scale X Y Give the names of these pieces of apparatus. X Y

Give the name of a suitable indicator that can be used in an acid-alkali titration.

A student does a titration using sodium carbonate solution and dilute nitric acid. This is the equation for the reaction. Na₂CO₃ + 2HNO₃ → 2NaNO₃ + CO₂ + H₂O The table shows the concentrations of the two solutions and the volume of sodium carbonate used in the titration. Concentration of nitric acid in mol / dm³ 0.350 Concentration of sodium carbonate solution in mol / dm³ 0.220 Volume of sodium carbonate solution in cm³ 25.0 Use the equation and the data in the table to answer these questions.

Calculate the volume of dilute nitric acid that the student would need to neutralise the sodium carbonate solution. volume of nitric acid = cm³

Calculate the volume, in cm³, of carbon dioxide gas at rtp that would be produced from the 25.0 cm³ of the sodium carbonate solution. [at rtp, molar volume = 24 000 cm³] volume of carbon dioxide = cm³

Describe a test to show that sodium carbonate solution contains carbonate ions.

Sodium chloride is an ionic compound. Explain why sodium chloride conducts electricity when it is molten or in solution, but not when it is solid.

A solution of sodium chloride can be electrolysed using this apparatus. P Q sodium chloride solution + – power supply

If the solution is dilute, a significant amount of oxygen collects at P. Complete the ionic half-equation for this reaction H₂O → H+ + O₂ + e–

If the solution is concentrated, chlorine is the main product that collects at P. This is the ionic half-equation for the reaction. 2Cl⁻ → Cl₂ + 2e– State why this is an oxidation reaction.

The gas that collects at Q is hydrogen.

Give a test for hydrogen.

Explain how hydrogen gas forms at the negative electrode.

Hydrogen reacts with oxygen to form water. The equation shows the covalent bonds in the molecules. 2H H + O O → 2H O H The table gives the bond energies

Use the equation and the values in the table to calculate the enthalpy change, ΔH , for the reaction. Include a sign in your answer. ΔH = kJ

Complete the diagram to show the energy levels of the reactants and products, and the enthalpy change, ΔH . Energy