AS Chemistry
Unit 2 Practice Exam Questions – Test 2

Name………………………………………………………..

1.	(a)	Compound A is a chloroalkene with the percentage composition by mass:
C, 24.7%; H, 2.1%; Cl, 73.2%.
(i)	Calculate the empirical formula of compound A. Show your working.
[2]
(ii)	The relative molecular mass of compound A is 145.5. Show that the molecular formula is C3H3Cl3.
[2]
 
(b)	Compound A is one of six possible structural isomers of C3H3Cl3 that are chloroalkenes. Two of these isomers are shown below as isomer 1 and isomer 2.

(i)	Draw two other structural isomers of C3H3Cl3 that are chloroalkenes.

			
[2]
(ii)	Name isomer 1. ......................................................................................
[2]
 
(c)	All of the isomers in (b) readily polymerise.
(i)	Draw a section of the polymer P that could be formed when isomer 2 polymerises.
	Show two repeat units.

polymer P	
[2]
 (ii)	Addition polymers can be difficult to dispose of.
	State two general problems in the disposal of polymers and identify an extra problem when disposing of polymer P.
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[3]
[Total 13 marks]
2.	Leaf alcohol reacts with bromine as shown in the equation below.

(i)	State what you would see when bromine reacts with leaf alcohol.
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[1]
 
(ii)	Complete, with the aid of curly arrows, the mechanism involved in the reaction between leaf alcohol and bromine. Show any relevant dipoles, charges and lone pairs of electrons.

[4]
[Total 5 marks]
3.	Trifluorochloromethane, CF3Cl, is an example of a chlorofluorocarbon, CFC, that was commonly used as a propellant in aerosols. Nowadays, CFCs have limited use because of the damage caused to the ozone layer.
(i)	Draw a diagram to show the shape of a molecule of CF3Cl.
[1]
(ii)	Predict an approximate value for the bond angles in a molecule of CF3Cl.
bond angle ....................
[1]
(iii)	Suggest a property that made CF3Cl suitable as a propellant in an aerosol.
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[1]
(iv)	When CFCs are exposed to strong ultraviolet radiation in the upper atmosphere, homolytic fission takes place to produce free radicals.
Explain what is meant by the term homolytic fission.
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[2]
(v)	Suggest which bond is most likely to be broken when CF3Cl is exposed to ultraviolet radiation. Explain your answer.
bond ................................................................................................................
reason .............................................................................................................
[1]
 
(vi)	Identify the two free radicals most likely to be formed when CF3Cl is exposed to ultraviolet radiation.
...................................................... and ...........................................................
[2]
[Total 8 marks]

4.	Ethanol, C2H5OH, can be produced by the fermentation of glucose, C6H12O6.
Write a balanced equation for the fermentation of glucose.
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[Total 2 marks]

5.	Ethanol has a relatively high boiling point. This can be explained in terms of intermolecular hydrogen bonds.
Draw a second molecule of ethanol alongside the one drawn below and show how a hydrogen bond could be formed. Clearly show any relevant dipoles and lone pairs of electrons.

[Total 3 marks]

6.	(a)	When ethanol is heated with acidified potassium dichromate(VI) solution, it can be oxidised to form either ethanal, CH3CHO (Fig. 1), or ethanoic acid, CH3COOH (Fig. 2).

Fig. 1	Fig. 2

	The boiling points of ethanol, ethanal and ethanoic acid are given in the table below.
	CH3CH2OH	CH3CHO	CH3COOH	
boiling point/ °C	78	21	118	
	Use this table of boiling points to explain
(i)	why the organic product is likely to be ethanal if the apparatus shown in Fig. 1 is used,
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[2]
 
(ii)	why the organic product is likely to be ethanoic acid if the apparatus shown in Fig. 2 is used.
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[2]
(b)	Write a balanced equation for the oxidation of ethanol to ethanoic acid. Use (O) to represent the oxidising agent.
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[2]
(c)	The ethanal collected using the apparatus shown in Fig. 1 was analysed by infra-red spectroscopy. Use your Data Sheet to justify which of the three spectra shown below is most likely to be that of ethanal.

	The organic product collected when using the apparatus shown in Fig. 1 is most
	likely to be that shown by spectrum .......... because.......................................
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[3]
[Total 9 marks]
 
7.	In this question, one mark is available for the quality of use and organisation of scientific terms.
Different cars require different grades of petrol. The first stage in the production of petrol in an oil refinery is to fractionate the crude oil. After that, refineries carry out further processes.
·	Outline, with the aid of equations, three of these processes in the production of
	petrol.
·	Explain why, in the long term, ethanol could replace oil-based fuels.
·	Write an equation for the combustion of ethanol.
[10]
Quality of Written Communication [1]
[Total 11 marks]

8.	The combustion of butane is shown in the equation below.
C4H10(g) + 6 O2(g) ® 4CO2(g) + 5H2O(l)
(i)	The standard enthalpy change of combustion of butane is –2877 kJ mol–1. What does standard mean in this context?
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[1]
(ii)	Define the term enthalpy change of combustion.
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[2]
(iii)	Complete the enthalpy profile diagram for the combustion of butane. Label the activation energy, Ea, and the enthalpy change, DH.

[3]
[Total 6 marks]
9.	Enthalpy changes of combustion can be used to determine enthalpy changes of formation.
(i)	Write the equation for the standard enthalpy change of formation of butane, C4H10. Include state symbols in your answer.
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[2]

(ii)	Use the following data to calculate the standard enthalpy change of formation of butane.
	standard enthalpy change of combustion / kJ mol–1	
carbon	–394	
hydrogen	–286	
butane	–2877	
answer .............................. kJ mol–1
[3]
[Total 5 marks]
10.	Part of the manufacture of ammonia involves the equilibrium below.
	N2(g) + 3H2(g)  2NH3(g)	DH = − 92 kJ mol–1
State le Chatelier’s principle.
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[Total 2 marks]
11.	A mixture of N2 and H2 was made and left to reach equilibrium.
	Explain how the following changes would affect the time taken to reach equilibrium.
(i)	use of a catalyst
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 [2]
(ii)	a higher temperature
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 [2]
(iii)	a lower pressure
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 [2]
[Total 6 marks]
12.	A mixture of N2 and H2 was left until it had reached equilibrium as shown below.
	N2(g) + 3H2(g)  2NH3(g)	DH = − 92 kJ mol–1
	At that stage, N2, H2 and NH3 were present in the equilibrium mixture.
Explain how the following changes would affect the amounts of N2, H2 and NH3 present in the equilibrium mixture.
(i)	use of a catalyst
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[1]
(ii)	a higher temperature
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[2]
(iii)	a lower pressure
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[2]
[Total 5 marks]
 13.	The table below lists the boiling points of some alkanes.
alkane	number of carbon atoms	molecular formula	boiling point / °C	
butane	4	C4H10	0	
pentane	5	C5H12	36	
hexane	6		69	
heptane	7	C7H16	99	
octane	8	C8H18		
nonane	9	C9H20	152	
decane	10	C10H22	175	
(a)	What is the molecular formula of hexane?......................................................
[1]

(b)	(i)	State the trend in the boiling points of the alkanes.
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[1]
(ii)	Explain the trend in the boiling points of the alkanes.
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[1]
(iii)	Predict the boiling point of octane.	.................. °C
[1]
[Total 4 marks]

14.	Long chain alkanes, such as nonane, can be cracked into shorter chain alkanes and alkenes.
(i)	Write a balanced equation for the cracking of nonane into heptane and ethene.
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[1]
(ii)	Much of the ethene is then converted into ethanol.
Write a balanced equation for the conversion of ethene into ethanol. State the essential conditions.
equation ..........................................................................................................
[1]
conditions ........................................................................................................
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[2]
[Total 4 marks]

15.	(a)	Heptane can be isomerised to produce branched chain alkanes such as
2-methylhexane or 2,3-dimethylpentane.
	The equation below shows the isomerisation of heptane into 2-methylhexane.

(i)	Using skeletal formulae, complete the balanced equation for the isomerisation of heptane into 2,3-dimethylpentane.

[1]
 
(ii)	The boiling point of 2,3-dimethylpentane is 84 °C.
	Predict the boiling point of 2-methylhexane.	................. °C
[1]
 
(b)	Heptane can be reformed to produce methylcyclohexane which is a cycloalkane. Write a balanced equation to show the reforming of heptane to obtain methylcyclohexane

[2]
 
(c)	State why branched chain alkanes and cycloalkanes are more useful than straight chain alkanes.
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[1]
[Total 5 marks]