OCR GCSE Combined Science B (21st Century) Paper 2 June 2025 question paper

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Many everyday products are based on the chemistry of acid reactions.

(a)

Complete the sentences to describe how to show that a solution is acidic.

$Question 1, shown as an image$

Add a few drops of alkali / universal indicator / water to a small amount of the solution.

If the solution is acidic, the solution will turn blue / green / red.

[2]

Answer

(b)

Acids react with some metals to form a salt and hydrogen.

The table shows some information about the reactions between some metals and acids.

(b)(i)

[2]

Answer

(b)(ii)

Pieces of zinc metal react with dilute sulfuric acid to form a solution of zinc sulfate and hydrogen gas.

Complete the state symbols in the balanced symbol equation.

$Question 1, shown as an image$

[2]

Answer

(c)

[3]

Answer

Nanoparticles are very small particles. They have many important uses.

(a)

Fullerene and graphene are nanoparticles made from carbon.

The diagrams show their structures.

$Question 2, shown as an image$

(a)(i)

Complete the table to show which statements are true for fullerenes only, graphene only, both or neither.

Tick (✓) one box in each row.

[4]

Answer

(a)(ii)

Graphene is a very good conductor of electricity.

Complete the sentence to explain why.

$Question 2, shown as an image$

Graphene is a good conductor of electricity because the atoms / electrons / ions

within graphene can evaporate / move / vibrate.

[2]

Answer

(a)(iii)

Fullerene can be used to carry drugs into the body.

Which two properties of the structure makes this possible?

Tick (✓) two boxes.

$Question 2, shown as an image$

[2]

Answer

(b)

Some scientists are worried about the use of fullerenes to carry drugs into the body.

State one benefit and one risk of using fullerenes in this way.

Benefit........

Risk........

[2]

Answer

The elements in Group 7 of the periodic table are called the halogens.

(a)

Draw lines to connect each element with its colour at room temperature.

[2]

Answer

(b)

[2]

Answer

(c)

The halogens also react with metals to form metal halides.

(c)(i)

Complete the balanced symbol equation for the reaction between sodium and bromine to form sodium bromide.

$Question 3, shown as an image$

[1]

Answer

(c)(ii)

[3]

Answer

(d)

Chlorine has the electron arrangement 2.8.7.

Complete the dot and cross diagram for a chlorine molecule, Cl₂.

Show the outer shell electrons only.

[2]

Answer

Energy is transferred when reactants change into products in a chemical reaction.

(a)

When solid ammonium chloride dissolves in water, energy is transferred from the surroundings to the reaction mixture.

(a)(i)

Suggest a simple experiment to show that this reaction is endothermic, and describe the results expected.

Experiment........

Results........

[2]

Answer

(a)(ii)

Complete the reaction profile for an endothermic reaction.

Include labels for:

• the products

• the activation energy.

[3]

Answer

(b)

A student does an experiment to find out the change in thermal energy when a fuel burns.

They use this apparatus.

They burn the fuel to heat some water.

The table shows their results.

(b)(i)

Describe how the mass of fuel burned is measured.

[2]

Answer

(b)(ii)

Calculate the change in the thermal energy of the water.

Use the formula:

Change in thermal energy (J) = mass of water (g) maths symbol 4.2 temperature change (C)

[3]

Answer

(b)(iii)

Calculate the change in thermal energy of the water if only 1 g of fuel was burned.

Use your answer to (b)(ii).

Give your answer to 2 significant figures.

[3]

Answer

Drinking water in the UK can be obtained from rivers. Rivers are a type of surface water.

(a)

* The diagram shows some stages of the treatment to make surface water more suitable for drinking.

Surface water contains impurities including:

• large objects such as branches or leaves

• other insoluble items such as grit, sand and soil

• harmful microorganisms

• dissolved minerals

• other pollutants.

Explain which impurities are removed at each stage of the process shown and why the treated water is now more suitable for drinking but is still not considered scientifically pure.

[6]

Answer

(b)

Some countries get their drinking water from seawater. Seawater contains dissolved salts such as sodium chloride.

A student plans to use distillation to separate the salt from the water, using this apparatus:

(b)(i)

[4]

Answer

(b)(ii)

Complete the sentences to explain how distillation separates the salt from the water.

$Question 5, shown as an image$

The separation occurs because the salt and water have different boiling / freezing / melting

points. The salt / solution / water evaporates and the vapour passes through the condenser

where it is cooled / heated / stirred. The salt / solution / water condenses and is collected in

the beaker.

[4]

Answer

The compounds found in crude oil are mostly in the alkane homologous series.

(a)

State one way in which modern life is dependent upon hydrocarbons.

[1]

Answer

(b)

The alkanes are all hydrocarbons with a general formula C_nH_2n+2.

What is the molecular formula of the alkane with 8 carbon atoms?

[2]

Answer

(c)

The table shows some information about some alkanes.

Number of carbon atoms	Melting point (C)	Boiling point (C)
5	–130	36
6	–95	69
7	–91	98
9	–54	151
10	–30	174

(c)(i)

Describe the trend in melting points shown in the table.

[1]

Answer

(c)(ii)

The alkane with 6 carbons has a melting point of – 95 maths symbol C and a boiling point of 69 C.

Predict the state of this alkane at 20 maths symbol C.

[1]

Answer

(c)(iii)

Plot the results from the table on the graph.

Three points have already been plotted.

[2]

Answer

(c)(iv)

Draw a straight line of best fit.

[1]

Answer

(c)(v)

Use the graph to estimate the boiling point of the alkane with 8 carbon atoms.

$Question 6, shown as an image$

[1]

Answer

A student investigates the rate of reaction between calcium carbonate and dilute hydrochloric acid.

$Question 7, shown as an image$

(a)

[2]

Answer

(b)

The student repeats the experiment under different conditions.

The student plots a graph with their results.

(b)(i)

What is the time taken for the reaction to finish?

[1]

Answer

(b)(ii)

What is the volume of carbon dioxide collected when the reaction has finished?

[1]

Answer

(b)(iii)

Calculate the average rate of reaction from the start to the end of the reaction.

$Question 7, shown as an image$

Give your answer to 2 decimal places.

Average rate of reaction =........ cm³ / s

[3]

Answer

(b)(iv)

Describe the changes in the gradient of the graph and the rate of reaction shown in the graph.

[4]

Answer

In the 1800s, Dalton did experiments to help produce a model for the atom.

(a)

Later discoveries led to scientists suggesting new models for the atom.

Draw lines to connect each discovery with the model it led to.

[2]

Answer

(b)

The modern model of the atom consists of electrons, neutrons and protons.

Which statements about the modern model of the atom are true and which are false ?

Tick (✓) one box in each row.

[3]

Answer

(c)

[2]

Answer

(d)

The atomic number and mass number can be used to find the number of protons, neutrons and electrons in an atom.

The table shows information about an argon atom and a potassium atom.

Complete the table.

	Argon atom	Potassium atom
Atomic number	18	......................
Mass number	40	......................
Number of electrons	......................	19
Number of neutrons	......................	20
Number of protons	......................	19

[4]

Answer

Zinc is extracted from its ore by separating the zinc compounds from the waste rock and then converting the zinc compounds into zinc.

(a)

A company wants to extract 5.5 kg of zinc from an ore which contains 8.5% zinc.

Calculate the mass of ore needed.

$Question 9, shown as an image$

Give your answer to 3 significant figures.

[4]

Answer

(b)

The zinc compounds are heated strongly to produce zinc oxide. The zinc oxide is then heated with carbon to produce zinc and carbon monoxide.

$Question 9, shown as an image$

Explain which substance is oxidised and which is reduced in this reaction.

Oxidised........

Reduced........

[2]

Answer

(c)

Many metals cannot be extracted using carbon.

Explain why zinc can be extracted using carbon but aluminium cannot.

Zinc........

Aluminium........

[2]

Answer

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OCR J260 · Paper 2

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9