AS Chemistry
Unit 2 Practice Exam Questions – Test 6

Name………………………………………………………..

1.	Crude oil is first separated by fractional distillation. The fractions can then be refined further by cracking, reforming and isomerisation.
The reaction sequence below shows the production of heptane, C7H16, from fractional distillation of crude oil, followed by cracking, reforming and isomerisation.

(a)	What is meant by the term fractional distillation?
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[1]
(b)	The cracking of heptane produces propene and A.
Write a balanced equation for this cracking of heptane.
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[1]
(c)	The reforming of heptane produces methylcyclohexane and B.
(i)	Show the structural formula of methylcyclohexane.
[1]
 
(ii)	Write a balanced equation for this reforming.
[1]

(d)	The isomerisation of heptane produces seven branched alkanes, five of which are shown below.

		

	

	

(i)	Name compound C.
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[1]
(ii)	In the boxes above, draw skeletal formulae for the other two branched alkanes formed by isomerisation of heptane.
[2]
(iii)	Predict which of 2-methylhexane, 2,3-dimethylpentane and
2,2,3-trimethylbutane has the lowest boiling point.
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[1]
 
(iv)	Explain why 2-methylhexane, 2,3-dimethylpentane and
2,2,3-trimethylbutane have different boiling points.
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[2]
[Total 10 marks]
 
2.	Ethanol can be formed by fermentation of glucose, C6H12O6.
(i)	Write a balanced equation, including state symbols, for the formation of ethanol by fermentation.
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[2]
 
(ii)	Fermentation only occurs in the presence of yeast. State two other essential conditions.
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[2]
(iii)	How would you know when fermentation of glucose is complete?
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[1]
[Total 5 marks]
3.	(a)	Propan-2-ol can be formed by the hydration of an alkene in the presence of a catalyst.
(i)	Suggest a suitable catalyst for this reaction.
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[1]
(ii)	This is an electrophilic addition reaction. What is meant by the term electrophile?
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[1]
 
(b)	A mechanism for the reaction in (a) is shown below.

(i)	Add ‘curly arrows’ to the mechanism to show the movement of electron pairs in steps 1, 2 and 3.
[3]
(ii)	Suggest, with a reason, the role of the H+.
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[1]
[Total 6 marks]
4.	Propan-2-ol is flammable and readily burns.
Write a balanced equation for the complete combustion of propan-2-ol.
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[Total 2 marks]

5.	Methyl allyl chloride, MAC, is an important industrial chemical. It is used as an intermediate in the production of synthetic fibres, pharmaceuticals and epoxy resins. The structural formula of MAC is shown below.

	(a)	Give the systematic chemical name of MAC.
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[1]
(b)	MAC contains the alkene group and can undergo polymerisation. Draw a section of the polymer, poly(MAC), showing two repeat units.
[2]
[Total 3 marks]
6.	Butane, C4H10, under certain conditions, reacts with Cl2 to form a mixture of chlorinated products. One possible product is C4H9Cl.
C4H10 + Cl2 ® C4H9Cl + HCl
	(a)	(i)	State the conditions.
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[1]
 
(ii)	Write equations to show the mechanism of this reaction.
initiation ..................................................................................................
propagation ............................................................................................
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[3]
(iii)	Write one equation for a reaction that would terminate this mechanism.
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[1]
(iv)	State the type of bond fission involved in the initiation step. ..................
[1]
 
(b)	One other possible product of the reaction between butane and chlorine is compound J, C4H8Cll2, shown below.
	
(i)	Name compound J.
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[1]
(ii)	Draw the skeletal formula of compound J.
[1]
(iii)	In addition to compound J, suggest one other possible structural isomer of C4H8Cl2 that could have been formed in this reaction.
[1]
[Total 9 marks]
7.	In this question, one mark is available for the quality of use and organisation of scientific terms.
·	Describe, with the aid of a suitable diagram, the formation of the p-bond in propene.
·	State the shape, and an approximate value for the bond angles, around each carbon atom in propene.
·	Describe, with the aid of a suitable example, why some alkenes show
cis-trans isomerism.
[9]
Quality of Written Communication [1]
[Total 10 marks]

8.	A group of students investigated the effect of concentration on the rate of a reaction. They used the reaction between magnesium carbonate and dilute hydrochloric acid and measured the rate at which the gas was collected.
(a)	(i)	An incomplete equation for this reaction is given below. Complete the equation by balancing it and inserting state symbols.
MgCO3(.....) + HCl(.....)MgCl2(.....) + CO2(.....) + H2O(.....)
[1]
(ii)	Write the ionic equation for this reaction.
[1]

(b)	The students added dilute hydrochloric acid to some magnesium carbonate. The students collected the gas and measured the volume, at regular intervals, until after the reaction was complete. They then plotted a graph of their results.

	Use collision theory to explain the changes in the rate of the reaction as it proceeds.
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[3]
 
(c)	The students repeated the experiment using a weak acid instead of hydrochloric acid.
Assume the concentration of both acids and all other conditions are the same.
(i)	On the axes in (b), sketch the graph the students obtained from this experiment.
[2]
(ii)	State and explain what effect changing the acid has on the rate of the reaction.
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[2]
[Total 9 marks]

9.	Propane, C3H8, is a gas at room temperature and pressure. It is used in blow torches to melt the bitumen needed to apply the felt to flat roofs.
Write the equation for the complete combustion of propane.
[Total 2 marks]

 
10.	Define the term standard enthalpy change of combustion.
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[Total 3 marks]

11.	Esters are used as flavourings. They are made by a reversible reaction between a carboxylic acid and an alcohol.
carboxylic acid + alcohol  ester + water
(a)	Give two features of a reversible reaction, when a dynamic equilibrium has been set up.
1 ......................................................................................................................
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2 ......................................................................................................................
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[2]
 
(b)	The production of esters is catalysed homogeneously by the presence of acids.
(i)	What is meant by a catalyst?
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[1]
 (ii)	What is meant by homogeneous?
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[1]
(iii)	Using the fact that acids are needed to catalyse this reaction, deduce the formula of the ion that acts as the catalyst.
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[1]

(iv)	Catalysts do not affect the position of an equilibrium. Explain why not.
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[1]
[Total 6 marks]

12.	(i)	On the axes below, draw and label the Boltzmann distribution to show the energies of molecules in a gas at a fixed temperature.

[2]
(ii)	Use the graph to explain the effect of a catalyst on the rate of a reaction.
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[2]
[Total 4 marks]
 
13.	Ammonia, NH3, is made industrially by the Haber process. This is an equilibrium reaction.
N2(g) + 3H2(g)  2NH3(g) DH = –92 kJ mol–1
(a)	State the pressure and temperature that are used in the Haber process.
pressure ..........................................................................................................
temperature .....................................................................................................
[2]

b)	Describe and explain why these conditions are a compromise between rate and equilibrium.
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[9]
[Total 11 marks]