AS Chemistry
Unit 2 Practice Exam Questions – Test 7

Name………………………………………………………..

1.	Hexane reacts with Br2 in the presence of ultraviolet light.
	C6H14 + Br2 ® C6H13Br + HBr
(i)	State the type of reaction.
.........................................................................................................................
[1]
 
(ii)	Identify the three possible structural isomers of the product, C6H13Br, that could be formed from this reaction with hexane.

	
[3]
[Total 4 marks]

2.	(a)	Hex-3-ene reacts with Br2 to produce 3,4-dibromohexane.
	Describe, with the aid of curly arrows, the movement of the electrons in the mechanism.
	Show the intermediate, any relevant dipoles and lone pairs of electrons.

intermediate	3,4-dibromohexane
[4]
(b)	The mechanism in (a) shows cis-hex-3-ene reacting with Br2. Trans-hex-3-ene also reacts with Br2 to produce 3,4-dibromohexane.
(i)	How does the structure of trans-hex-3-ene differ from that of cis-hex-3-ene?
...............................................................................................................
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[1]
(ii)	Explain why both cis and trans hex-3-ene react with Br2 to produce the same structural isomer.
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[1]
[Total 6 marks]
3.	Four possible structural isomers of C4H10O are alcohols. Two are shown below.
		
butan-1-ol	butan-2-ol	
(i)	Draw the other two structural isomers of C4H10O that are alcohols
		
isomer 1	isomer 2	
[2]
 
(ii)	Name isomer 1. ...............................................................................................
[1]
[Total 3 marks]
4.	Butan-2-ol can be dehydrated to produce a mixture of three alkenes each with a molecular formula C4H8.
	Draw the displayed formula for each of the three alkenes.
			
[Total 3 marks]

5.	(a)	Butan-1-ol can be oxidised to form butanal.
(i)	State a suitable oxidising mixture for this reaction.
................................................................................................................
[2]
(ii)	State the colour change you would see during this oxidation.
from ................................................. to ..................................................
[1]
(b)	A sample of the butanal from (a) was analysed using infra-red spectroscopy. The infra-red spectrum contained an absorption in the region 1680–1750 cm–1 but did not contain a broad absorption in the region 2500–3300 cm–1.
	Refer to the Data Sheet for Chemistry provided.
(i)	What does the absorption in the region 1680–1750 cm–1 indicate?
................................................................................................................
[1]
(ii)	What does the absence of a broad absorption in the region 2500–3300 cm–1 indicate?
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[1]
(iii)	The reaction in (a) was carried out using distillation and not reflux.
	Explain why.
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[2]
[Total 7 marks]

6.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
	The fractions from crude oil can be processed by cracking, reforming and isomerisation.
•	Outline these processes with the aid of suitable equations.
•	State clearly the industrial importance of the products formed in each process.
[8]
Quality of Written Communication [1]
[Total 9 marks]

7.	Cylcohexane and cyclohexene are both cyclic hydrocarbons.

cyclohexane	 cyclohexene
(i)	What is the molecular formula of cyclohexene? .............................................
[1]

(ii)	What is the empirical formula of cyclohexene? ..............................................
[1]
(iii)	Calculate the percentage, by mass, of carbon in cyclohexene. Give your answer to two significant figures.

answer ...............................................
[2]
[Total 4 marks]
 
8.	Cyclohexene can be converted into cyclohexane.

cyclohexene	cyclohexane
	Suggest suitable reagents and conditions for this reaction.
reagents ...................................................................................................................
conditions .................................................................................................................
[Total 2 marks]
9.	(a)	Cyclohexane can be converted into cyclohexene via a three-stage synthesis.

cyclohexane	cyclohexanol	cyclohexene
 
(i)	In stage 1, cyclohexane reacts with chlorine to form the organic product, compound A.
	Show the structure of compound A.

[1]
 
(ii)	Stage 3 involves the dehydration of an alcohol.
	State a suitable reagent for dehydrating an alcohol.
................................................................................................................
[1]
 
(iii)	Write a balanced equation for the dehydration of cyclohexanol, C6H11OH.

[1]

(b)	The reaction in stage 1 is difficult to control. One other possible chlorinated product is 1,4-dichlorocyclohexane.This is shown below.

cyclohexane	1,4-dichlorocyclohexane
	1,4-Dichlorocyclohexane reacts in the same way as compound A in stages
2 and 3.
 
(i)	Suggest the structure of compound B.

[1]
 
(ii)	Two cyclic alkenes, C and D are formed in stage 3. C and D are structural isomers. Suggest the structures of C and D.
		
[2]
[Total 6 marks]

10.	Alkanes are important hydrocarbons since they are used as fuels in homes and in industry. It is important that the enthalpy changes involved in alkane reactions are known.
(i)	Define the term enthalpy change of formation of a compound.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
[2]
(ii)	Write the equation, including state symbols, that accompanies the enthalpy change of formation of hexane, C6H14(l).
[2]
(iii)	What conditions of temperature and pressure are used when measuring the standard enthalpy change of formation?
temperature ...............................................................
pressure .........................................................
[1]
[Total 5 marks]

11.	The standard enthalpy change of formation of hexane is –199 kJ mol–1.
Using the axes below, show the enthalpy profile diagram for the formation of hexane.
	On your diagram label the enthalpy change of reaction, DH, and the activation energy, Ea.

[Total 3 marks]
12.	Enthalpy changes can be calculated using enthalpy changes of combustion. The table below shows some values for standard enthalpy changes of combustion.
substance	DHcӨ/ kJ mol−1	
C(s)	−394	
H2(g)	−286	
CH4(g)	−890	
Use these values to calculate the standard enthalpy change of the reaction below.
	C(s) + 2H2(g) ® CH4(g)
standard enthalpy change = ........................................... kJ mol−1
[Total 3 marks]
13.	The equations for the combination of gaseous atoms of carbon and hydrogen to form methane, CH4, and ethane, C2H6, are shown below.
C(g) + 4H(g) ® CH4(g)	DH = −1652 kJ mol−1
2C(g) + 6H(g) ® C2H6(g)	DH = −2825 kJ mol−1
Use these data to calculate:
(i)	the bond enthalpy of a C−H bond,
bond enthalpy = ........................................... kJ mol−1
[1]
(ii)	the bond enthalpy of a C−C bond.
bond enthalpy = ........................................... kJ mol−1
[2]
[Total 3 marks]
14.	Many industrial processes, used to manufacture important chemicals, involve equilibrium reactions. Chemists use their understanding of rates of reaction and of yields at equilibrium to find the most economic conditions for the reactions.
Chemists were investigating the production of a chemical, X2Y, that could be formed from X2 and Y2 as shown in equilibrium 3.1 below.
	2X2(g) + Y2(g)  2X2Y(g)	equilibrium 3.1
(a)	State le Chatelier’s principle.
.........................................................................................................................
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[2]

(b)	State and explain the effect on equilibrium 3.1 of a decrease in pressure on:
(i)	the equilibrium position of the reaction,
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[2]
(ii)	the rate of the reaction.
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[2]
(c)	The chemists measured the percentage conversion of X2 at various temperatures. The results are shown in the graph below.

(i)	Use the graph to predict the percentage conversion at 350 °C.
answer = .....................................................%
[1]

(ii)	The forward reaction in equilibrium 3.1 is exothermic. Explain how the graph supports this statement.
................................................................................................................
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[2]
 
(d)	The chemists decided to use a catalyst in the process.
State, and explain, the effect of using a catalyst on:
(i)	the rate of conversion of X2 and Y2 into X2Y,
................................................................................................................
................................................................................................................
[2]
 
(ii)	the percentage conversion at equilibrium of X2 and Y2 into X2Y.
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[2]
[Total 13 marks]