Syllabus Edition

First teaching 2020

Last exams 2024

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Hydrocarbons (A Level Only) (CIE A Level Chemistry)

Exam Questions

2 hours10 questions
1a2 marks

Benzene undergoes substitution reactions. State the equation for the reaction of benzene with nitric acid to produce nitrobenzene and water.

1b2 marks

The structure of methylbenzene is shown below in Fig. 1.1.

a2c33069-43fc-46b0-af04-465fc1e6e6d1
Fig. 1.1

Draw the structures of the two isomers of choromethylbenzene formed from the reaction of methyl benzene and Cl2 in the presence of AlCl3

1c1 mark

State the type of reaction that benzene will typically undergo.

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2a1 mark

This question is about the bromination of benzene.

State the name of the mechanism that benzene will undergo if reacted with bromine in the presence of a halogen carrier to form bromobenzene, C6H5Br. 

2b2 marks

Write an equation to show how the halogen carrier generates the Br+ ion in order to allow the reaction in part (a) to occur. 

2c3 marks

Complete the mechanism in Fig. 2.1 for the formation of bromobenzene. Include relevant charges where appropriate. 

6-1_q2c-ocr-a-as--a-level-easy-sq
Fig. 2.1

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3a1 mark

This question is about the reactions of methylbenzene.

Draw the structure of compound A in Fig. 3.1.


7-2-3a-e-compound-a-cie-7-2-q3-a
Fig. 3.1
3b1 mark

Draw the structure of compound B in Fig. 3.2.

7-2-3b-e-compound-b-cie-7-2-q3-a
Fig. 3.2
3c3 marks

State the reagents and conditions required for reaction 1 in Fig. 3.3 for the formation of benzoic acid from methylbenzene.

7-2-3c-e-benzoic-acid-cie-7-2-q3
Fig. 3.3

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1a3 marks

The nitration of benzene is the first important step in manufacturing dyes and explosives. 

i)
Write the equation for the generation of the electrophile.
 
[1]
 
ii)
State which reactant acting as a Brønsted-Lowry base and justify your answer.
 
[1]
 
iii)
Identify the conjugate acid in the reaction.
 
[1]
1b5 marks

Compound B is produced in two steps as outlined in Fig. 1.1.

7-2-1b-h-benzene-pathway-1 

Fig. 1.1

i)
Outline the reagents and conditions required for the production of compound A drawn in Fig. 1.1.
 
[2]
 
ii)
Using curly arrows, describe the mechanism for step 1.
 
[3]
1c2 marks

Draw the dot-and-cross diagram for the structure of the catalyst, once the electrophile has been generated in part (b).

1d4 marks

Explain why benzene can generally only undergo substitution reactions.

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2a2 marks

Fig. 2.1 shows the formation of a ketone followed by an alcohol. 

7-2-2a-h-benzene-to-ketone-to-alcohol-1

Fig. 2.1

Draw the mechanism to show the formation of the catalyst responsible for step 1.

2b5 marks

Draw the mechanism for the formation of the ketone, including the regeneration of the catalyst required.

2c2 marks

State the reagents required for step 2.

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3a4 marks

Benzene can be converted into cyclohexane as shown in Fig. 3.1.

7-2-3a-h--benzene-to-cyclohexane

Fig. 3.1

i)
For this reaction, name the type of reaction and identify the reagent and conditions needed.
 
type of reaction ................................................................................
 
reagent and conditions ................................................................................
 
[2]
 
ii)
State the bond angles in benzene and cyclohexane.
 
bond angle in benzene ..............................
 
bond angle in cyclohexane ..............................
 
Explain your answers.
 
[2]
3b4 marks

When benzene reacts with SO3, as shown in Fig. 3.2, benzenesulfonic acid is produced.

7-2-3b-h-fig--3-2-benzenesulfonic-acid-fig--3-3-benzenesulfonic-acid-1

Fig. 3.2

The mechanism of this reaction is similar to that of the nitration of benzene. Concentrated H2SO4 is used in an initial step to generate the SO3H+ electrophile as shown.

SO3 + H2SO4 → SO3H+ + HSO4 

i)
Draw a mechanism for the reaction of benzene with SO3H+ ions in Fig. 3.3. Include all necessary curly arrows and charges.
 
7-2-3b-h-fig--3-2-benzenesulfonic-acid-fig--3-3-benzenesulfonic-acid-2
 
Fig. 3.3
 
[3]
 
ii)
Write an equation to show how the H2SO4 catalyst is reformed.
 
[1]
3c5 marks

3-aminobenzoic acid can be synthesised from methylbenzene in three steps as shown in Fig. 3.4.

7-3-3c-h-fig--3-4-pathway

Fig. 3.4

i)
Draw the structures of M and N in the boxes.
 
[2]
 
ii)
Suggest reagents and conditions for each step of the synthesis.
 
step 1 ................................................................................
 
step 2 ................................................................................
 
step 3 ................................................................................
 
[3]

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