Edexcel GCSE Combined Science Paper 4: Chemistry 2 Higher June 2025 question paper 1SC0/2CH

When solutions P and Q are mixed together, a purple mixture forms. This mixture slowly becomes colourless.

A student pours 25 cm³ of solution P into a conical flask and then adds 25 cm³ of solution Q.

The student uses a beaker to measure out these volumes.

Name a piece of apparatus that could be used to measure these volumes more accurately.

The student investigates this reaction using the apparatus shown in Figure 1. The student measures the time taken for the cross to become visible. The experiment is repeated at different temperatures.

Figure 2 shows the results.

The concentrations of the solutions are kept constant in each experiment.

State one other variable that should be kept constant.

State, and explain in terms of particles, how the time taken for the cross to become visible would change if a temperature of 80 °C was used.

The concentration of solution Q is 26.8 g dm^–3.

Calculate the mass of solid Q present in 25 cm³ of solution Q.

mass of solid Q =_........ g

The student repeats the experiment at 20 °C, with the addition of a catalyst.

Explain how the addition of a catalyst will affect the rate of reaction.

Crude oil is a mixture of hydrocarbons.

The majority of hydrocarbons in crude oil belong to one homologous series.

Give the name of this series.

When hydrocarbons undergo combustion, water is produced.

Draw a dot and cross diagram of a molecule of water.

One compound in crude oil contains 0.96 g of carbon atoms combined with 0.32 g of hydrogen atoms.

Calculate the empirical formula of this compound.

(relative atomic masses: C = 12, H = 1.0)

empirical formula of this compound =_........

Group 1 elements are known as the alkali metals.

Which row gives two physical properties of the alkali metals?

The alkali metals react with water.

A teacher adds a small piece of potassium to water.

Give two observations that would be seen.

The reaction of lithium with water is much less vigorous than the reaction of potassium with water.

Explain why, in terms of their electronic configurations.

When sodium reacts with water, a solution of sodium hydroxide is formed.

When the solution is left in air, the hydroxide ions react with carbon dioxide, forming carbonate ions, CO₃^2–, and one other product.

Complete the ionic equation for this reaction.

_........ OH^– +_........ CO₃^2– +_........

The relative atomic mass of caesium is 132.905.

Calculate the average mass of one atom of caesium

(Avogadro constant = 6.02 × 10²³)

mass =_........ g

This question is about the noble gas xenon.

Xenon is unreactive.

Explain, in terms of its electronic configuration, why xenon is unreactive.

Under extreme conditions, xenon can be made to react with fluorine to form xenon tetrafluoride, XeF₄.

Write the balanced equation for this reaction.

Some information about xenon tetrafluoride is shown in Figure 3.

State and explain, with reasons, the type of structure and bonding in xenon tetrafluoride.

Under extreme conditions, xenon reacts with fluorine to form xenon hexafluoride.

The reaction is exothermic. The energy change for the reaction is –400 kJ mol^–1.

On Figure 4

• add a label to the y‑axis

• draw the reaction profile for this reaction

• label the energy change and the activation energy for the reaction.

This question is about carbon and some carbon compounds.

Two forms of pure carbon are graphite and Buckminsterfullerene.

Explain why graphite is used as a lubricant.

Calculate the mass, in kg, of five moles of Buckminsterfullerene, C₆₀.

(relative atomic mass: C = 12)

mass =_........ kg

A molecule in an homologous series has the formula C₉H₂₁N.

What is the formula of the next molecule in this homologous series?

A Bunsen burner burns methane gas, CH₄.

A student investigates the time taken to heat up a beaker of water using this Bunsen burner.

Figure 5 shows the apparatus used.

The student sees that a large amount of carbon forms as a black solid on the underside of the gauze.

The teacher said that the investigation would be improved if no carbon forms.

Explain what the student should do to stop carbon forming on the underside of the gauze.

*(d) Natural processes and human activities change the amount of carbon dioxide in the atmosphere.

Figure 6 shows the concentration of carbon dioxide in the atmosphere measured in one location and the mean global temperature from 1960 to 2000.

Evaluate whether the data in Figure 6 shows that the change in the amount of carbon dioxide is leading to climate change.

Your answer should include

• the natural processes that change the amount of carbon dioxide in the atmosphere

• the human activities that change the amount of carbon dioxide in the atmosphere

• how carbon dioxide contributes to the greenhouse effect and climate change.

This question is about molecules containing two atoms.

In an experiment, hydrochloric acid is reacted with zinc.

The volume of gas produced is measured by collecting the gas in an upturned measuring cylinder over water.

Give a method of collecting and measuring the gas that would give a more accurate volume of gas.

Iodine has an atomic number of 53 and a mass number of 127.

How many electrons are there in an iodine molecule, I₂?

Iodine reacts with hydrogen to form hydrogen iodide, H I.

Explain whether or not a solution of hydrogen iodide in water conducts electricity.

Chlorine gas is bubbled through a colourless solution of potassium bromide, KBr. The mixture turns orange.

Give the name of the substance that causes the orange colour.

Write the balanced equation for this reaction.

Hydrogen iodide reacts with oxygen to form water and iodine.

The equation for this reaction is

Calculate the energy change for this reaction using the bond energies in Figure 7.

Include a sign and unit in your answer.

energy change =_........