OCR GCSE Chemistry B (21st Century) Paper 4 June 2025 question paper

Potassium, sodium and lithium are metals in Group 1 of the Periodic Table.

A student watches a video of the reaction of potassium with water.

Fig. 1.1 shows a diagram of the experiment.

Fig. 1.1

The table shows information about this reaction.

The student then watches a video of the reaction of sodium with water.

Predict the products of the reaction of sodium with water and describe the observations you expect.

Products........ and........

Observations........

Fig. 1.2 shows the arrangement of electrons in a lithium atom and a fluorine atom.

Lithium and fluorine belong to different groups of the Periodic Table.

Explain how the arrangement of electrons in lithium and fluorine is related to their groups in the Periodic Table.

Explain how Fig. 1.2 shows that lithium and fluorine are in the same period of the Periodic Table.

Lithium fluoride is an ionic compound that has lithium ions and fluoride ions.

Fig. 1.3 shows a dot and cross diagram of these ions. The diagram is not complete.

Complete Fig. 1.3.

You need to:

• show the arrangement of electrons in the fluoride ion

• show the charges on both ions.

Which statement gives a correct limitation of using a complete dot and cross diagram to represent ionic bonding?

Tick (✓) one box.

It does not show that the ions are different sizes.

It does not show the correct ratio of numbers of ions.

It does not show the total number of electrons.

It only shows shared electrons.

A student does an electrolysis experiment.

They pass electricity through dilute aqueous copper(II) sulfate using inert electrodes.

The diagram shows the apparatus they set up.

Oxygen gas forms at the positive electrode.

Which two statements give correct reasons why oxygen forms at the positive electrode?

Tick (✓) two boxes.

Copper reacts with water to form oxygen.

Hydroxide ions from water react to form oxygen.

Non-metals usually form at the positive electrode.

The electricity causes water to evaporate around the electrode.

The student wants to find the rate that oxygen gas forms by measuring the volume of gas produced.

Suggest one change to the apparatus so that the volume of oxygen gas can be measured.

Describe how the student uses the new apparatus and a stop watch to find the rate that oxygen gas forms.

Include in your answer:

• what results they need to collect

• how they use their results to find the rate.

The student measures the mass of the electrodes before and after the electrolysis.

The table shows their results.

Explain what happens to the mass of each electrode during the experiment.

Positive electrode........

Negative electrode........

Water for drinking can be separated from sea water by distillation.

The diagram shows a laboratory apparatus that can be used for the distillation of sea water.

Complete the labels on the diagram.

Use all of the words from the list.

Heat Pure water Sea water Water in Water out

Sea water contains dissolved sodium chloride.

A student adds dilute acidified silver nitrate to the sea water before distillation and to the water collected after distillation.

Complete the table to show the observations that the student makes.

Typhoid fever is a disease that causes death. It is caused by harmful microorganisms in water.

Chlorine was added to drinking water in the United States in 1908.

The graph shows the death rate from typhoid fever in the United States before and after chlorine was first added to drinking water.

Chlorine was not added to water in all areas of the United States at the same time.

A student says that the time taken for all areas to have chlorine added to their drinking water was ~ 40 years.

Explain why the student is correct.

Include data from the graph in your answer.

Some people think that chlorine should not be added to drinking water because it causes other health issues such as allergies in some people.

Suggest why chlorine should be added to drinking water.

Include in your answer:

• ideas about risk and benefit

• data from the graph.

The effect of adding chlorine to drinking water was an important scientific discovery.

Today, information about important scientific discoveries is published for peer review.

Information about important scientific discoveries is also published in newspapers.

Explain the differences between publishing information for peer review and in newspapers.

Pure iron corrodes easily and is too weak for some uses.

When iron corrodes it reacts with oxygen to make iron(III) oxide.

Complete the balanced symbol equation for the reaction.

Include state symbols.

Steel is a mixture of iron and other elements.

Table 4.1 shows the effect of different elements on the properties of steel.

Table 4.1

A type of steel contains 2% carbon and 98% iron.

Explain why this steel has a limited range of uses.

Use Table 4.1 to help you answer.

Another type of steel is used to make electrical wires for use in the engine of a ship.

The engine gets very hot.

This steel contains iron mixed with three other metals and a small amount of carbon.

Complete Table 4.2 by:

• suggesting which three metals have been added to this steel to make it most suitable for this use

• predicting a value for the percentage of each metal in this steel.

Use Table 4.1 to help you answer.

Table 4.2

Nitrogen and hydrogen react together to make ammonia in the Haber process.

Ammonia is used in fertilisers.

Which statements about fertilisers are true and which are false ?

Tick (✓) one box in each row.

* The diagram shows a flow chart for the substances that enter and leave the reactor in the Haber process.

The table shows the main conditions used.

Explain why the conditions in the table are chosen for this process.

Include in your answer:

• the effect each condition has on the rate of reaction and on the yield

• why higher or lower values of temperature and pressure are not used.

Methanol (CH₃OH) and hydrogen can both be used as fuels.

Burning hydrogen has a different impact on the Earth’s climate to burning methanol.

Explain why.

Equation 1 shows the reaction of methane with steam which is used in industry to manufacture hydrogen.

Equation 1

The carbon dioxide produced in the reaction is used to make methanol, CH₃OH.

In the process shown in Equation 1, carbon dioxide is considered a by-product and not a waste product.

Explain the difference between a by-product and a waste product.

Complete Table 6.1 by calculating the relative formula mass for carbon dioxide.

Use the Periodic Table.

Calculate the atom economy of the reaction of methane with steam to make hydrogen.

Give your answer to 1 decimal place.

Scientists did some experiments and collected data about the yield of the products made when 1000 kg of methane reacts with steam.

Table 6.2 shows the data they collected.

Table 6.2

Calculate the percentage yield of hydrogen.

Use data from Table 6.2.

Methanol can be made by reacting carbon dioxide with hydrogen.

Equation 2 shows this reaction.

Equation 2

Explain how Equation 2 shows that the percentage yield of methanol is not 100%.

Explain how Equation 2 shows that the atom economy of the reaction to make methanol is not 100%.

Buckyballs are a type of nanoparticle. They consist of carbon atoms joined in a ball with a hollow centre.

The diagram shows the structure of a buckyball.

A buckyball has a diameter of 1 nm.

1 nm = 1 × 10^–9 m

Which of these is the best estimate for the diameter of a carbon atom?

Tick (✓) one box.

1 × 10^–8 m

1 × 10^–10 m

10 nm

1 × 10¹⁰ nm

The radius of a buckyball is half its diameter.

The surface area to volume ratio of a buckyball can be calculated using this formula: surface area to volume ratio = (r is the radius of the buckyball in nm).

Calculate the surface area to volume ratio of a buckyball that has a diameter of 1 nm.

Scientists are developing ways of using nanoparticles such as buckyballs to carry medicines into the human body.

Describe two reasons why buckyballs are suitable to carry medicines into the human body.

Explain one possible risk of using nanoparticles to carry medicines into the human body.

* A student does some experiments to investigate the trends in energy changes when ionic compounds dissolve in water.

The diagram shows the apparatus the student uses.

The student follows this method:

• Add the same amount of each compound to the same volume of water.

• Stir until the compound is fully dissolved.

• Record the change in temperature.

The table shows their results.

What conclusions can you make about the trends in energy changes when compounds containing Group 1 ions and Group 7 ions dissolve in water?

Use the information in the table.

In your answer you should:

• identify exothermic and endothermic changes

• discuss trends for ions down Group 1 and Group 7.

Fig. 8.1 shows a reaction profile diagram for a catalysed and an uncatalysed reaction.

Complete Fig. 8.1 by drawing labelled arrows to show:

• the activation energy for the uncatalysed reaction, E_a

• the activation energy for the catalysed reaction, E_acat

• the energy change of reaction, E.

Aqueous sodium hydroxide reacts with dilute nitric acid in a neutralisation reaction.

Table 9.1 shows the relative formula masses for the compounds in the equation.

Table 9.1

Explain how the equation and the data in Table 9.1 show that this reaction obeys the principle of conservation of mass.

Include data from Table 9.1 in your answer.

In the reaction, hydrogen ions from the acid react with hydroxide ions from the sodium hydroxide.

Write the ionic equation for this reaction.

Complete Table 9.2 by working out the missing information.

25.0 cm³ samples of each dilute acid are used in a titration with aqueous sodium hydroxide. (ii) The concentration of the aqueous sodium hydroxide was the same for each titration.

Which dilute acid, 1, 2, 3 or 4, needs the largest volume of aqueous sodium hydroxide for neutralisation?

Explain your answer.

Dilute acid........

Explanation........

The concentration of hydrogen ions is the same as the concentration of acid for some dilute acids but different for others.

Explain why.

Use examples from Table 9.2 in your answer.