A2 LEVEL CHEMISTRY

ARENES

ASSESSED HOMEWORK

Answer all questions
Max 64 marks

	
Name		…………………………………………………………..

Mark		……../64	……....%	Grade ………

1.	Diphenylethanedione is a pale yellow colour, which disappears when it is reduced.
	The colour results from the arrangement of the delocalised p-bond electrons.
	Explain what is meant by the term delocalised π-bond electrons.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
[Total 2 marks]

2.	The nitration of benzene is a very important industrial reaction.
(a)	Name two types of commercially important material whose manufacture involves the nitration of benzene.
........................................................................................................................
........................................................................................................................
[2]
(b)	State the conditions required for the nitration of benzene using nitric acid and sulphuric acid.
........................................................................................................................
........................................................................................................................
[2]
(c)	Write a balanced equation for the nitration of benzene.

[2]

(d)	The mechanism for the reaction is given below.
	Step 1: formation of the electrophile, NO2+, from HNO3 and H2SO4
		HNO3   +   H2SO4   ®   H2O   +   NO2+   +   HSO4−
	Steps 2 and 3: substitution of NO2+ into the benzene ring

	Step 4: protonation of the HSO4−
		H+   +   HSO4–   ®   H2SO4
(i)	Explain what a curly arrow  represents in this type of mechanism.
...............................................................................................................
...............................................................................................................
[2]
(ii)	State why the NO2+ is described as an electrophile in this mechanism.
...............................................................................................................
...............................................................................................................
[1]
(iii)	State why this mechanism is described as substitution.
...............................................................................................................
[1]
(iv)	How does the mechanism show that the sulphuric acid is acting as a catalyst?
...............................................................................................................
...............................................................................................................
[1]

(e)	In this question, one mark is available for the quality of spelling, punctuation and grammar.
	The benzene ring and the ring in the intermediate formed after step 2 have different structures shown below. Both structures have p-bonds.

	Deduce how many electrons are involved in the π-bonding in each structure and describe how their arrangements are different.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
[5]
Quality of Written Communication [1]
[Total 17 marks]

3.	Benzene reacts with chlorine in the presence of a halogen carrier, such as AlCl3.
(a)	(i)	Write the equation for the reaction of benzene with chlorine.

[1]
(ii)	How does the halogen carrier allow the reaction to take place?
...............................................................................................................
...............................................................................................................
[1]
(iii)	Outline a mechanism for this reaction.
	Include curly arrows and relevant dipoles.

[4]
(iv)	State the name of this mechanism.
...............................................................................................................
[1]
(b)	In contrast to benzene, the reaction of an alkene with bromine does not need a halogen carrier.
	Compare the different reactivities of benzene and alkenes towards chlorine.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
[3]
[Total 10 marks]
4.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
	Phenol reacts much more readily with bromine than benzene does.
•	Describe, with the aid of a diagram, the bonding in benzene.
•	Explain why electrophiles, such as bromine, react much more readily with phenol than with benzene.

.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
[7]
Quality of Written Communication [1]
[Total 8 marks]

5.	Salicylic acid is used in the manufacture of aspirin tablets. In the UK around 3500 tonnes of salicylic acid are manufactured per year.
	
	Salicylic acid is manufactured from phenol in three stages.
(a)	Phenol is first converted to sodium phenoxide, C6H5O–Na+.
(i)	State a reagent that could be used for this reaction.
...............................................................................................................
[1]
(ii)	Write a balanced equation for this reaction.

[1]

(b)	The phenoxide ion is then combined with carbon dioxide under high pressure to form the salicylate ion.

	This reaction is an electrophilic substitution reaction, which occurs by the incomplete mechanism shown below. Carbon dioxide acts as the electrophile.

(i)	Add partial charges d+ and d– to show the polarisation of the C=O bonds in the carbon dioxide molecule above.
[1]
(ii)	Complete the mechanism by adding curly arrows to show the movement of electron pairs in step 1 to give the intermediate shown.
[2]
(iii)	Carbon dioxide is normally a very poor electrophile. However, this reaction does occur because the benzene ring in the phenoxide ion is activated.
	Explain how the benzene ring in the phenoxide ion is activated.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
[3]

(c)	In the final stage of this process, the salicylate ion is acidified to give salicylic acid.
	Assuming an overall yield by mass of 45% for this three stage process, calculate the mass of phenol that is needed to produce the annual UK output of 3500 tonnes of salicylic acid.
	Mr of phenol = 94.0; 1 tonne = 106 g

mass of phenol = ....................... tonnes
[4]
[Total 12 marks]

6.	Phenol reacts readily with dilute nitric acid at room temperature in a nitration reaction to produce a mixture of products as shown below.

(a)	Suggest the structure of another organic product that is likely to be formed in the nitration of phenol.

[1]

(b)	Assuming a yield by mass of 27% for 4-nitrophenol, calculate the mass of 4-nitrophenol that would be produced from 100 g of phenol. Show your working.
	Give your answer to an appropriate number of significant figures.

mass of 4-nitrophenol = …………………… g
[4]

(c)	In this question, one mark is available for the quality of spelling, punctuation and grammar.
	Compare the reagents and conditions for the nitration of phenol with those used for the nitration of benzene.
	State and explain the effect of the –OH group on the reactivity of the benzene ring in phenol.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
[7]
Quality of Written Communication [1]
[Total 13 marks]

7.	4-Nitrophenol can be converted into a range of useful organic chemicals. Draw the structures of the organic products formed in the following reactions.

[Total 2 marks]