OCR GCSE Combined Science A (Gateway) Chemistry Paper 3 Foundation June 2019 question paper J250/03

Which of these processes is an example of a physical change?

A Combustion

B Freezing

C Neutralisation

D Oxidation

The equation shows the reaction of sodium with water.

Sodium hydroxide and hydrogen are made.

Two of the state symbols are missing.

What are the missing state symbols?

A (l), (l)

B (s), (g)

C (aq), (g)

D (l), (g)

A student tests which gas is produced in a reaction using a glowing splint. The gas re-lights the glowing splint.

What is the name of the gas?

A Carbon dioxide

B Chlorine

C Hydrogen

D Oxygen

What is the relative formula mass of sulfuric acid, H₂SO₄?

The relative atomic mass, A_r, of H is 1.0, of S is 32.1 and of O is 16.0.

A 49.1

B 81.2

C 98.1

D 129.2

Fluorine is in Group 7 of the Periodic Table.

Which statement best describes fluorine?

A It has a full outer shell of electrons

B It is a metal

C It is a non-metal

D It is a solid at room temperature and pressure

Calcium carbonate, CaCO₃, decomposes when heated. Calcium oxide, CaO, and carbon dioxide, CO₂, are made.

Look at the equation for the reaction.

In an experiment, 20.0 g of CaCO₃ are used. 11.2 g of CaO are made.

What is the mass of CO₂ made?

A 8.8 g

B 11.2 g

C 20.0 g

D 31.2 g

The molecular formula of a compound is C₁₂H₂₆.

What is its empirical formula ?

A C₂H₄

B C₂H₆

C C₄H₆

D C₆H₁₃

Phosphorus sulfide, P₄S₃, has a relative formula mass of 220.3.

What is the percentage, by mass, of phosphorus in P₄S₃?

Use the Periodic Table to help you.

A 6.8

B 14.1

C 27.2

D 56.3

Which statement best describes an atom?

A The nucleus is small compared to the atom and contains little of the atom’s mass.

B The nucleus is large compared to the atom and contains little of the atom’s mass.

C The nucleus is small compared to the atom and contains most of the atom’s mass.

D The nucleus is large compared to the atom and contains most of the atom’s mass.

Atoms are made of particles called protons, neutrons and electrons.

Complete the table to show the relative charges of protons, neutrons and electrons.

Sodium is a metal in the Periodic Table.

Sodium is an example of an atom that can form an ion.

Describe what happens to a sodium atom when it becomes an ion.

Look at this statement about the Periodic Table.

‘Atoms are placed in groups according to the total number of electrons they have.’

Explain why this statement is incorrect.

A new element has been discovered and has these properties:

• a high melting point

• reacts with oxygen to form oxides

• conducts electricity

• solid at room temperature.

Suggest what type of bonding the new element has.

Explain your answer.

What is the melting point of substance X ?

What is the state of matter of substance X at 70 °C?

Tick (✓) one box.

In which state of matter do the particles of X have the most energy?

Tick (✓) one box.

Another substance, Y, is heated.

Substance Y is an ionic compound.

Substance Y has a much higher melting point than substance X.

Substance X is a simple covalent compound.

Which substance, X or Y, is made up of molecules ?

Tick (✓) one box.

Explain your answer.

Explain the difference between the melting points of substances X and Y.

Use ideas about the forces between the particles.

A student tests three solutions A, B and C. He wants to identify which solution is acidic.

The student adds a metal carbonate to each solution.

Table 13.1 shows his results.

Which solution, A, B or C, is acidic?

Tick (✓) one box.

Suggest a pH value for the acidic solution.

Write down two other tests the student could use to identify that the solution is acidic.

The student adds the acidic solution to a solution of sodium hydroxide. A neutralisation reaction takes place.

He records the pH of the mixture.

Table 13.2 shows his results.

Describe the relationship between the volume of acidic solution added and the pH of the mixture.

Sodium hydroxide is an alkali.

Which ion do solutions of alkalis contain?

H⁺ Na⁺ OH^– SO₄^2–

In a different neutralisation reaction sulfuric acid, H₂SO₄, reacts with sodium hydroxide, NaOH.

Complete the balanced symbol equation for this reaction.

Aspirin is a widely used painkiller and is sold as tablets.

One of the chemicals in aspirin is salicylic acid. The structure of salicylic acid is shown below.

Salicylic acid

What is the empirical formula of salicylic acid?

It is important that aspirin is pure for it to be safely used in tablets.

Explain the meaning of the term pure.

Three students, A, B and C make aspirin and check its purity. The students test the purity of the aspirin by measuring the melting point.

Their results are shown in the table.

The melting point of pure aspirin is in the range 138–140 °C.

Which student made pure aspirin?

Tick (✓) one box.

Another method of checking the purity of a substance is paper chromatography.

Look at the diagram of the apparatus used for paper chromatography.

Label the chromatography diagram.

Choose your labels from the list.

active phase

inactive phase

gas phase

mobile phase

stationary phase

* This is the method the students follow for the paper chromatography experiment.

1. Draw a pen line near the bottom of the paper.

2. Put a spot of the substance to be tested onto the line.

3. Stand the paper in the solvent. The solvent should be at the same level as the spot.

4. Cover the beaker.

5. Remove the paper from the beaker before the solvent reaches the top.

6. Calculate the R_f value of the substance by using this equation:

Their teacher notices some mistakes with this method.

Describe and explain the mistakes in the method and suggest improvements that could be made.

A student does an experiment to identify an unknown metal M.

The student weighs metal M. Then the student adds metal M to a solution of copper sulfate, CuSO₄(aq).

A reaction takes place forming copper metal, Cu:

The student separates the copper and then weighs the copper.

These are the student’s results: Mass of metal M = 8.10 g Mass of copper = 21.2 g

How could the student separate the copper from the solution?

Use your answer from (b)(i) and the Periodic Table to identify the metal M.

A student investigates three reactions.

She wants to find out if the reactions are exothermic or endothermic.

Look at her results.

Which reaction, X, Y or Z, is endothermic ?........

Explain your answer.

Draw a labelled reaction profile for an endothermic reaction.

Use the following labels on your reaction profile:

• products

• energy change

• activation energy.

Another student repeats the same reactions.

The student does the experiment in a polystyrene cup instead of a beaker.

Explain why using a polystyrene cup is an improvement to the method.

The reaction between iron oxide and aluminium is very exothermic.

Look at the equation for the reaction.

During this reaction the aluminium is oxidised.

Explain what is meant by the term oxidised.

Pure iron metal is produced in the reaction.

Draw a diagram to show the bonding in a metal.

Label your diagram clearly.