OCR GCSE Combined Science A (Gateway) Chemistry Paper 4 Foundation June 2025 question paper J250/04

Which part of the Periodic Table contains the least reactive non-metals?

Which gas in the atmosphere causes acid rain?

A Carbon monoxide

B Hydrogen

C Oxygen

D Sulfur dioxide

When is electrolysis used to extract a metal from its ore?

A The metal dissolves in water.

B The metal has a high melting point.

C The metal is in high demand.

D The metal is very reactive.

When marble chips react with an acid, they produce a colourless solution and a gas.

Which method is used to determine the rate of reaction?

A A disappearing cross experiment

B Gas chromatography

C Measuring the mass loss using a balance

D Measuring the volume of solution produced

Which Group 7 element is a red-brown liquid at room temperature?

A Fluorine

B Chlorine

C Bromine

D Iodine

Desalination is the removal of salt from seawater to produce drinking water.

The seawater is heated and the water vapour condensed and collected.

Which separation technique is used to produce drinking water in desalination?

A Chromatography

B Crystallisation

C Distillation

D Filtration

The equation shows a reaction that has reached dynamic equilibrium.

Which statement explains why this reaction is a dynamic equilibrium?

A N₂ and H₂ are gases.

B The rates of the forward and reverse reactions are equal.

C The reaction has stopped.

D The reaction produces a 100% yield of NH₃.

The graph shows the volume of gas produced during a reaction.

A tangent has been drawn at 50 seconds. The gradient of the tangent gives the rate of reaction.

What is the rate of reaction, in cm³ / s, at 50 seconds?

A 0.56

B 0.70

C 1.1

D 1.4

Crude oil is a source of hydrocarbons.

Which chemical is a hydrocarbon?

Tick (✓) one box.

Complete the sentences about crude oil.

Use words from the list.

cracking filtration fractional distillation neutralisation reduction

The hydrocarbons in crude oil are separated by........

Some of these hydrocarbons are made more useful by........

The table shows the description of three resources A, B and C.

Which resource is crude oil?

Explain your choice using information from the table.

Crude oil is resource........

Reason........

Scientists think that increased levels of carbon dioxide are causing global warming.

Which statements about the potential effects of global warming are true and which are false ?

Tick (✓) one box in each row.

This question is about elements in Group 1 and Group 7 of the Periodic Table.

Sodium is below lithium in Group 1.

Table 12.1 describes the observations when small pieces of lithium and sodium are placed in water.

Table 12.1

Describe how these observations show how the reactivity of the elements increases going down Group 1.

Potassium is below sodium in Group 1.

Describe one observation when a small piece of potassium is placed in water.

Use information from Table 12.1.

When sodium reacts with water, it forms sodium hydroxide and hydrogen.

Complete the word equation for the reaction of potassium with water.

The equation for sodium, Na, reacting with a Group 7 element, X, is:

Sodium is a solid at room temperature.

Complete the equation by writing in the missing state symbol for sodium.

State the name of element X.

A more reactive Group 7 element displaces a less reactive Group 7 element from a solution of one of its salts.

Chlorine reacts with potassium bromide as chlorine is more reactive than bromine.

Bromine reacts with potassium iodide as bromine is more reactive than iodine.

Iodine does not react with potassium chloride as iodine is less reactive than chlorine.

Table 12.2 shows the results of mixing three Group 7 elements and solutions of their salts.

Table 12.2

Key ✓ = reaction ✗ = no reaction

Complete Table 12.2 by putting a tick (✓) or cross (✗) in the three answer spaces.

The Earth’s early atmosphere may have been mainly carbon dioxide, nitrogen and water vapour.

The pie chart shows the relative amounts of each gas in the Earth’s early atmosphere.

Calculate the percentage of nitrogen in the Earth’s early atmosphere.

Some of the gases in the Earth’s atmosphere today are called greenhouse gases.

What effect do greenhouse gases have in the Earth’s atmosphere?

Tick (✓) one box.

Which of these gases is a greenhouse gas?

Tick (✓) one box.

14* Containers for drinks are made from aluminium or glass.

Aluminium can Glass bottle

The table shows some information about the containers.

State which container you would choose to produce as a container for drinks.

Explain your choice using information from the table. Include an advantage and a disadvantage of your chosen container in your answer.

Fig. 15.2 shows the thermometer when the metal powder is magnesium.

Fig. 15.2

Draw a line on the thermometer in the circle to show the highest temperature for magnesium.

Describe how the highest temperature changes as the reactivity of the metals increases.

The student repeats the experiment with another metal from the reactivity series shown above.

The highest temperature measured is 49 °C.

Suggest the name of this metal.

The student repeats the experiment with magnesium.

This table shows all their results.

Calculate the mean highest temperature.

Give your answer to 2 significant figures.

Describe one variable the student must control when they repeat this experiment.

The student thinks that the highest temperatures are lower than they should be.

Suggest one improvement the student could make so the highest temperatures are more accurate.

Hydrogen peroxide solution, H₂O₂(aq), decomposes to make water and oxygen gas.

Complete the balanced symbol equation for the reaction.

Describe a test and its result which shows that the gas produced in the reaction is oxygen.

Test........

Result........

A hydrogen peroxide solution produces oxygen gas slowly.

A student adds a piece of potato to the hydrogen peroxide solution. The potato contains a biological catalyst.

What name is given to biological catalysts?

Describe and explain the effect of adding the piece of potato to the hydrogen peroxide solution.

Include ideas about rate of reaction and activation energy.

The student measures the total volume of oxygen produced in the reaction with and without the piece of potato.

With the potato, the total volume is: increased, decreased, stays the same.

Tick (✓) one box.

The piece of potato added to the hydrogen peroxide solution is a six-sided cube.

Calculate the surface area of the piece of potato in cm². (i)

A student thinks that cutting the potato into smaller pieces will make the catalyst more effective.

Explain why the student is correct.

Tick (✓) one box.

The student measures the rate of reaction when the piece of potato is added to the hydrogen peroxide.

The rate of reaction is 1.5 cm³ / s.

They then measure the rate of reaction again with an increased concentration of hydrogen peroxide.

What would the rate of reaction be now?

Tick (✓) one box.