OCR GCSE Combined Science B (21st Century) Paper 2 June 2023 question paper

11 questions

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Question

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(a)

Give the symbols of the two elements shown in the diagram which are not in order of atomic mass.

[1]

Answer

(b)

Mendeleev left gaps for elements that had not been discovered.

(b)(i)

Name the two elements that had not been discovered when Mendeleev wrote his Periodic Table.

Use the diagram and the Data Sheet.

[2]

Answer

(b)(ii)

Describe how the discovery of new elements supported Mendeleev’s decision to leave gaps.

[1]

Answer

(c)

The table shows the atomic number and electron arrangement of some of the elements in Group 1 of the modern Periodic Table.

Element	Atomic number	Electron arrangement
Lithium	3	2.1
Sodium	11	2.8.1
Potassium	19	2.8.8.1

Which two statements explain how the reactions of lithium, sodium and potassium are related to their electron arrangements and so to their atomic number?

Tick (✓) two boxes.

$Question 1, shown as an image$

[2]

Answer

(d)

Lithium reacts with cold water to produce hydrogen gas and a solution of lithium hydroxide.

(d)(i)

Complete the equation by adding the state symbols.

$Question 1, shown as an image$

[2]

Answer

(d)(ii)

Describe an experiment to show that the reactivity of the Group 1 elements increases down the group.

[2]

Answer

(a)

Sodium is a metal and sodium chloride is an ionic compound.

Draw lines to connect sodium and sodium chloride with the correct structure and nature of their chemical bonds.

[3]

Answer

(b)

Complete the sentences to explain the electrical conductivity of sodium and sodium chloride.

$Question 2, shown as an image$

Sodium is a good conductor of electricity when solid because its atoms / electrons / ions are fixed / mobile.

Sodium chloride conducts electricity when liquid because its atoms / electrons / ions are fixed / mobile but does not conduct when solid because they are fixed / mobile.

[3]

Answer

(c)

Complete the sentences to explain the difference in melting points of sodium and sodium chloride.

$Question 2, shown as an image$

The melting point of sodium chloride is higher / lower / the same compared to the melting point of sodium.

This is because the forces of attraction between the particles in sodium chloride are higher / lower / the same compared to those in sodium and so the energy needed to separate the particles is higher / lower / the same.

[2]

Answer

(d)

The diagram shows the structure of potassium oxide.

What is the chemical formula of potassium oxide?

Tick (✓) one box.

$Question 2, shown as an image$

[1]

Answer

Acids react with alkalis to form salt and water. This reaction is called neutralisation.

An example is shown:

$Question 3, shown as an image$

(a)

Complete the sentence to describe neutralisation in terms of ions.

Use the ions and formulae.

H⁺ Na⁺ OH^– NO₃^– NaNO₃ H₂O HNO₃ NaOH

Neutralisation is when........ ions from an acid react with........ ions from an

alkali to form........ molecules.

[2]

Answer

(b)

Felix wants to find the concentration of some dilute nitric acid using a titration.

He finds this simple method in a book:

• measure 25.0 cm³ sodium hydroxide solution into a conical flask using a measuring cylinder

• add dilute nitric acid from a burette to the sodium hydroxide solution until neutralisation

• write down the volume of acid used.

(b)(i)

The method does not say how he will know when neutralisation has occurred.

Explain what should be added to the method so that he knows when to stop adding acid.

[2]

Answer

(b)(ii)

[2]

Answer

(c)

The table shows the results of Felix’s experiment.

	Rough Repeat 1 Repeat 2 Repeat 3
Second reading on burette (cm³)	27.6 23.4 46.9 23.9
First reading on burette (cm³)	0.0 0.0 23.4 0.5
Volume used (cm³)	27.6 23.4 23.5 23.4

(c)(i)

Complete the sentence to evaluate the quality of his repeated results.

$Question 3, shown as an image$

These results are high / low quality because the repeated results are

close together / far apart / the same.

[1]

Answer

(c)(ii)

Calculate the mean of the repeated results.

Give your answer to 1 decimal place.

[3]

Answer

The halogens are in Group 17(7) of the Periodic Table.

(a)

The halogens are all molecules with two atoms joined together by covalent bonds.

(a)(i)

Complete the sentence to explain covalent bonding.

$Question 4, shown as an image$

The atoms in a covalent bond are held together when electrons are gained / lost / shared.

[1]

Answer

(a)(ii)

Fig. 4.1 shows the electron arrangement of a fluorine atom.

Complete Fig. 4.2 to show the dot and cross diagram for F₂. Show outer shell electrons only.

[2]

Answer

(b)

The halogens all react with iron wool.

The reactivity of the halogens decreases down Group 17(7).

The table shows the reactions when iron wool is put into jars containing each gaseous

Predict the reaction of bromine with iron wool.

[1]

Answer

(c)

Aqueous solutions of the halogens react with aqueous solutions of less reactive halides.

Alex plans an experiment to find the order of reactivity of some halogens.

The table shows the solutions they use.

Aqueous halogens	Aqueous halides
Cl₂(aq)	KCl (aq)
Br₂(aq)	KBr(aq)
I₂(aq)	KI(aq)

The halogens all have different colours in aqueous solution. The halide solutions are all colourless.

Which two statements describe how Alex can find the order of reactivity of these halogens?

Tick (✓) two boxes.

$Question 4, shown as an image$

[2]

Answer

Ammonia is manufactured by reacting nitrogen and hydrogen gases together.

(a)

The reaction to produce ammonia is reversible.

(a)(i)

Complete the equation with the symbol to show that it is reversible.

N₂(g) + 3H₂(g)........ 2NH₃(g)

[1]

Answer

(a)(ii)

Why does this reaction not give a 100% yield?

[1]

Answer

(a)(iii)

If the nitrogen and hydrogen are left in a closed container, eventually the reaction will reach a dynamic equilibrium.

Complete the sentence to describe when a dynamic equilibrium occurs in the reaction.

$Question 5, shown as an image$

When the rate of the forward reaction is faster / slower / the same compared to the rate of the reverse reaction.

[1]

Answer

(b)

A catalyst of iron is used when ammonia is manufactured.

What effect does a catalyst have on a reaction?

Tick (✓) two boxes.

$Question 5, shown as an image$

[2]

Answer

Crude oil is a mixture of hydrocarbons.

(a)(i)

Give one reason why modern life depends on crude oil.

[1]

Answer

(a)(ii)

Give one reason why we cannot depend on crude oil in the future.

[1]

Answer

(b)

Carbon bonds covalently with more carbons and with other elements to form lots of different compounds.

(b)(i)

How many covalent bonds does each carbon atom form?

[1]

Answer

(b)(ii)

Which statement explains why carbon can form so many different compounds?

Tick (✓) one box.

$Question 6, shown as an image$

[1]

Answer

(c)

Hydrocarbons are compounds of carbon and hydrogen.

Alkanes are one type of hydrocarbon. They have the general formula C_nH_2n+2.

(c)(i)

What is the formula of the alkane with five carbons?

[1]

Answer

(c)(ii)

Hexane has the formula C₆H₁₄.

What is its empirical formula?

[1]

Answer

(d)

The table gives some information about ethene, poly(ethene) and diamond.

	Ethene	Poly(ethene)	Diamond
Formula	C₂H₄	(C₂H₄)_n	C
Bonding	..............................	Covalent	..............................
Structure	.............................. ..............................	Large molecule	.............................. ..............................
Melting point (°C)	–169	Approximately 110	Approximately 4000

(d)(i)

Complete the table.

[3]

Answer

(d)(ii)

Explain why the melting point of poly(ethene) is higher than the melting point of ethene.

Use ideas about chain length and forces between the particles in your answer.

[2]

Answer

(e)

Umi wants to check the melting point of the poly(ethene).

They have a sample of solid poly(ethene) in a test tube.

Describe how they can measure the melting point of the solid poly(ethene).

[2]

Answer

(a)

What is the total volume of carbon dioxide collected?

[1]

Answer

(b)

How long does it take for the reaction to finish?

[1]

Answer

(c)

Draw a tangent to the curve and use it to find the rate of reaction at 40 seconds.

Rate of reaction =........ cm³ / s

[4]

Answer

Atoms are too small to see with the naked eye.

Models can be used to help show the size of atoms compared with objects that we can see.

(a)

What is the typical size of atoms and small molecules?

$Question 8, shown as an image$

1 × 10^–10 m 1 × 10^–6 m 1 × 10^–2 m 1 m

[1]

Answer

(b)

[3]

Answer

The diagram shows how aluminium is extracted from its ore by electrolysis of molten aluminium oxide.

It is carried out at high temperature with carbon electrodes.

(a)(i)

Complete the balanced symbol equation for the decomposition of aluminium oxide by electrolysis.

$Question 9, shown as an image$

[2]

Answer

(a)(ii)

During electrolysis, reactions take place at the positive and negative electrodes.

Complete the table to explain the reactions at each electrode.

Use the diagram and the symbol equation to help you.

[2]

Answer

(a)(iii)

Explain why carbon dioxide is also produced.

[1]

Answer

(b)

Zinc is extracted from its oxide using carbon:

$Question 9, shown as an image$

Which two statements explain why aluminium must be extracted by electrolysis and not by reaction with carbon?

Tick (✓) two boxes.

$Question 9, shown as an image$

[2]

Answer

(c)

[6]

Answer

The combustion of fossil fuels for energy produces harmful substances.

(a)(i)

[2]

Answer

(a)(ii)

Explain one problem caused by increased amounts of sulfur dioxide in the atmosphere.

[2]

Answer

(a)(iii)

Describe one method that is used to decrease the amount of harmful substances put into the atmosphere by petrol cars.

[1]

Answer

(b)

The combustion of fossil fuels produces carbon dioxide. Most scientists now accept that recent climate change can be explained by increased carbon dioxide emissions.

Fig. 10.1 shows the change in concentration of CO₂ in the atmosphere over time.

Fig. 10.1

Fig. 10.2 shows the change in world carbon dioxide emissions from fossil fuels over time.

Fig. 10.2

Fig. 10.3 shows the change in global average temperature over time.

Fig. 10.3

Describe the trends in Fig. 10.1 and Fig. 10.2 and explain how this can be used with Fig. 10.3 to show that human activity is causing the global temperature to increase.

[4]

Answer

A company called Healthyfood make food colourings.

The diagram shows the label from one of their food colourings.

Healthyfood

Orange food colouring

All ingredients natural and tested

Ingredients: dye 1, dye 2, solvent

(a)

A representative for Healthyfood says that the food colouring is pure.

A scientist says that it is not pure.

Explain the different meanings of the word ‘pure’ used by the Healthyfood representative and the scientist.

Healthyfood representative........

[2]

Answer

(b)

The table shows the melting points of some substances.

Substance	Melting point (°C)
A	42
B	60–66
C	92–98
D	104

Which two substances are chemically pure?

[1]

Answer

(c)

The dyes in the food colouring can be separated using paper chromatography.

The diagram shows the apparatus used to separate the dyes and the chromatogram that is produced.

(c)(i)

Draw lines to connect each letter with its correct label.

[2]

Answer

(c)(ii)

Which property causes the dyes in the food colouring to separate?

Tick (✓) one box.

$Question 11, shown as an image$

[1]

Answer

(d)

The chromatogram can be used to find the Rf values for the dyes.

(d)(i)

Measure the distance moved by dye 1 and by the solvent.

Use a ruler.

[2]

Answer

(d)(ii)

Calculate the Rf value of dye 1.

Use this formula.

$Question 11, shown as an image$

[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

Question 10

Question 11