AS Chemistry
Unit 2 Practice Exam Questions – Test 5

Name………………………………………………………..

1.	Crude oil is a complex mixture of hydrocarbons. Initial separation is achieved by fractional distillation. The separate fractions are then further refined to produce hydrocarbons such as decane.
(a)	(i)	State what is meant by the term hydrocarbon.
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[1]
(ii)	A molecule of decane contains ten carbon atoms. State the molecular formula of decane.
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[1]
(iii)	Deduce the empirical formula of decane. ...............................................
[1]
(b)	Dodecane, C12H26, is a straight chain alkane that reacts with chlorine to produce a compound with molecular formula C12H25Cl.
	C12H26 + Cl2 ® C12H25Cl + HCl
The reaction is initiated by the formation of chlorine free radicals from chlorine.
(i)	What is meant by the term free radical?
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[1]
(ii)	State the conditions necessary to bring about the formation of the chlorine free radicals from Cl2.
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[1]
(iii)	State the type of bond fission involved in the formation of the chlorine free radicals.
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[1]
(iv)	The chlorine free radicals react with dodecane to produce C12H25Cl. Write equations for the two propagation steps involved.
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[2]

(v)	How many different structural isomers can be formed when chlorine reacts with dodecane to form C12H25Cl?
answer ........................................................
[1]

(c)	Dodecane, C12H26, can be cracked into ethene and a straight chain alkane such that the molar ratio ethene: straight chain alkane is 2 : 1.
(i)	Write a balanced equation for this reaction.
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[2]
(ii)	Name the straight chain alkane formed.
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[1]
 
(d)	Straight chain alkanes such as heptane, C7H16, can be isomerised into branched chain alkanes and reformed into cyclic compounds.
(i)	Using skeletal formulae, write an equation to show the isomerisation of heptane into 2,2,3-trimethylbutane.
[2]
(ii)	Write a balanced equation to show the reforming of heptane into methylcyclohexane.
[2]
[Total 16 marks]

2.	Ethanol and glycerol (propane-1,2,3-triol) are both produced industrially on a large scale.
Ethanol is manufactured by both fermentation and the hydration of ethene.
Glycerol is produced as a by-product of soap manufacture.

	The relatively low volatility of alcohols such as ethanol can be explained by the existence of intermolecular bonds.
 
(i)	Explain what is meant by the terms:
low volatility, ....................................................................................................
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intermolecular bonds ......................................................................................
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[2]
 
(ii)	On the ethanol molecules below, label any relevant dipoles, show the intermolecular bond formed and state the type of intermolecular bond.

type of intermolecular bond ...............................................
[3]
 
(iii)	Glycerol forms the same type of intermolecular bonds as ethanol. Predict, with a reason, whether the boiling point of glycerol will be higher or lower than that of ethanol.
	The boiling point of glycerol will be ................... than that of ethanol because
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[1]
[Total 6 marks]

3.	This question is about the halogenoalkane 2-chlorobutane.
	2-Chlorobutane reacts with NaOH, but the products are dependent on the solvent used.
	
2-Chlorobutane reacts with OH– in aqueous conditions to produce alcohol A.
 
(i)	Identify alcohol A.
[1]
(ii)	Describe, with the aid of curly arrows, the movement of the electrons in the mechanism. Show any relevant dipoles, lone pairs of electrons and the products.
[4]
[Total 5 marks]

4.	Compound E can be oxidised to form a carboxylic acid.
(i)	State a suitable oxidising mixture for this reaction.
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[2]
 
(ii)	Write a balanced equation for this oxidation of compound E.
	Use [O] to represent the oxidising mixture.
	
[3]
 
(iii)	Explain how compound E and the carboxylic acid could be distinguished by
infra-red spectroscopy.
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[1]
[Total 6 marks]

5.	Methane reacts with oxygen to produce carbon dioxide and water. The equation for this reaction is given below.
		CH4(g) + 2O2(g) ® CO2(g) + 2H2O(g)
Gas cookers use methane as a fuel because this reaction is exothermic and takes place at a fairly fast rate.
Activation energy is important in considering the conditions needed to change the rate of a reaction.
(a)	What is meant by the term exothermic?
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[1]

(b)	The figure below is an incomplete enthalpy profile diagram for the reaction between methane and oxygen.

(i)	Complete the figure to show the complete enthalpy profile for the reaction.
[2]
(ii)	Label the activation energy, Ea, on the figure above.
[1]
[Total 4 marks]

6.	The Boltzmann distribution can be used to show the effect of a change in temperature on the rate of a reaction.
·	Draw a labelled Boltzmann distribution diagram.
·	Explain the essential features of your diagram.
·	Using your diagram, explain how an increase in temperature affects the rate of a reaction.
[Total 9 marks]

7.	Methane can be reacted with steam to produce carbon monoxide and hydrogen. The equation for this process is given below.
	CH4(g) + H2O(g) ® CO(g) + 3H2(g)
	The table below shows the enthalpy changes of formation for methane, steam and carbon monoxide.
compound	DHf / kJ mol–1	
CH4	–75	
H2O	–242	
CO	–110	
 
(a)	Define the term enthalpy change of formation.
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[2]
 
(b)	Write the equation, including state symbols, representing the enthalpy change of formation for methane, CH4.
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[2]
 
(c)	Use the DHf values in the table to calculate the enthalpy change for the reaction shown in the equation shown above.
.................. kJ mol–1
[3]

(d)	State one important manufacturing process in which hydrogen is used.
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[1]
[Total 8 marks]

8.	Limestone contains calcium carbonate, CaCO3.
	Limestone is an important source of commercially important chemicals such as lime, calcium oxide, CaO.
(a)	If calcium carbonate is heated strongly in an open container, it decomposes according to the equation below.
	CaCO3(s) ® CaO(s) + CO2(g)	DH = +180 kJ mol–1
	Suggest two reasons why it is necessary to heat the calcium carbonate strongly to achieve decomposition.
1 ......................................................................................................................
2 ......................................................................................................................
2]
(b)	Another sample of calcium carbonate was placed in a closed container before being heated strongly. This allows an equilibrium to be set up. This equilibrium is shown below.
		CaCO3(s)  CaO(s) + CO2(g)
(i)	What can you say about the rates of the forward and reverse reactions when the calcium carbonate starts to decompose?
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[1]
(ii)	What can you say about the rates of the forward and reverse reactions when the equilibrium has been established?
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[1]
 
(iii)	A valve allowed some of the carbon dioxide to escape.
	State and explain what happens to the composition of the mixture in the container.
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[3]
[Total 7 marks]
9.	A chemical C is made by reacting chemical A with chemical B in a reversible reaction. A, B and C are all gases under the reaction conditions.
Research chemists wanted to know the optimum conditions to use in the manufacture of C. They carried out a series of reactions under different conditions of temperature and pressure. The percentage conversion of A at equilibrium is shown in the table below.
pressure / MPa	temperature / °C	% A converted	
	350	8	
10	450	12	
	550	16	
	350	11	
20	450	21	
	550	29	
	350	18	
40	450		
	550	49	
(a)	Suggest the percentage of A that is converted at 450 °C and 40MPa.
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[1]
 
(b)	(i)	Use the data in the table above to state the effect of increasing pressure on the percentage of A converted.
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[1]
(ii)	What can be deduced, from this change, about the total number of moles of reactants A and B compared with the number of moles of product C in the equation for the reaction? Explain how you reached your conclusion.
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[2]

(c)	Use the data in the table to deduce whether the reaction between A and B is exothermic or endothermic. Explain how you reached your conclusion.
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[2]
 
(d)	It was found necessary to use a catalyst in the production of C.
(i)	What is meant by a catalyst?
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[2]
 
(ii)	Suggest and explain two reasons why catalysts are used in industrial processes.
1 .............................................................................................................
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2 .............................................................................................................
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[2]
 
(e)	Conditions were used that should have given a conversion of A of 39%. In the manufacture, using these conditions, it was found that only 20% conversion was achieved.
Suggest why the conversion was much less than theory suggested.
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[1]

(f)	Give two economically important processes that use catalysts.
process 1 ........................................................................................................
catalyst used in process 1 ..............................................................................
process 2 ........................................................................................................
catalyst used in process 2 ..............................................................................
[2]
[Total 13 marks]
 
10.	The graph below shows the boiling points of some alkanes.

(a)	Draw a smooth curve through the points on the graph and estimate the boiling points of
	octane C8H18, ………………	hexadecane, C16H34 .………………
[2]
(b)	State how decane, C10H22, can be separated from a mixture of the alkanes.
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[1]

(c)	Isomerisation of hexane, C6H14, produces a mixture of structural isomers, three of which are shown in the boxes below.
(i)	Draw, using skeletal formulae, two other structural isomers of hexane.

[2]
 
(ii)	Name isomer B. ....................................................................................
[1]
(iii)	Isomers A, B and C have different boiling points. In the boxes below, list the isomers A, B and C in order of their boiling points.
lowest boiling point				highest boiling point	
[1]
(iv)	Explain the order given in (c) (iii).
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[2]
(d)	Hexane can be reformed to produce cyclohexane as one of the products.
(i)	Draw the structural formula of cyclohexane.
[1]
(ii)	Write a balanced equation for the reforming of hexane into cyclohexane.
[1]
(iii)	Suggest one reason why oil companies reform alkanes such as hexane.
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[1]

(e)	Oxygen-containing compounds can be added to improve the efficiency and performance of fuels.
	In Formula One racing cars, it is common practice to add oxygen-containing compounds, such as 2-methylpropan-2-ol, (CH3)3COH. The amount of oxygen-containing compounds added is strictly controlled by the Federation Internationale de l’Automobile, FIA.
(i)	Calculate the percentage by mass of oxygen in (CH3)3COH. Give your answer to three significant figures.
answer ……………………
[2]
(ii)	Write a balanced equation for the complete combustion of (CH3)3COH.
[2]
[Total 16 marks]