AS LEVEL CHEMISTRY

PAPER 2
PRACTICE PAPER 20
(structured questions only)
Answer all questions
Max 80 marks

	
Name		……………………………………………………………..

	
Mark		……../80	……....%	Grade ………
		
Note – this paper only contains structured questions

1.	When boric acid (H3BO3) is applied as a coating on wood, it acts as a fire retardant by decreasing the rate of combustion.
Thermal decomposition of boric acid takes place in two stages.
In an experiment a sample of boric acid was heated in a crucible at 170 °C. The results of this experiment are given in the table.
 
 	Time of heating / minutes	Mass of crucible and contents / g	
 	0	35.85	
 	5	35.10	
 	10	34.41	
 	15	34.00	
 	20	33.70	
 	25	33.56	
 	30	33.50	
 	35	33.50	

(a)	Plot a graph of the results from the table above to show the mass of the crucible and boric acid 	(y-axis) against time of heating on the grid.

(Total 4 marks)

	

	

(Total 16 marks)
2.	

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(Total 15 marks)

3.          Pent-1-ene is a member of the alkene homologous series.
(a)     Pent-1-ene can be separated from other alkenes.
State the physical property of alkenes that allows them to be separated from a mixture by fractional distillation.
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(1)
(b)     (i)      State the meaning of the term structural isomerism.
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(2)
(ii)     Name the branched chain isomer of pent-1-ene shown below.
		 	
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(1)
(iii)     Draw the structure of a functional group isomer of pent-1-ene.

(1)
(c)     The cracking of one molecule of compound X produces pent-1-ene, ethene and butane in a 1:2:1 mol ratio.
Deduce the molecular formula of X and state a use for the ethene formed.
Molecular formula of X .................................................................................
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Use of ethene ...............................................................................................
(2)
(Total 7 marks)
 
4.          Cetane (C16H34) is a major component of diesel fuel.
(a)     Write an equation to show the complete combustion of cetane.
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(1)
(b)     Cetane has a melting point of 18 °C and a boiling point of 287 °C.
In polar regions vehicles that use diesel fuel may have ignition problems.
Suggest one possible cause of this problem with the diesel fuel.
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(1)
(c)     The pollutant gases NO and NO2 are sometimes present in the exhaust gases of vehicles that use petrol fuel.
(i)      Write an equation to show how NO is formed and give a condition needed for its formation.
Equation .............................................................................................
Condition .............................................................................................
(2)
(ii)     Write an equation to show how NO is removed from the exhaust gases in a catalytic converter. Identify a catalyst used in the converter.
Equation ..............................................................................................
Catalyst ...............................................................................................
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(iii)     Deduce an equation to show how NO2 reacts with water and oxygen to form nitric acid (HNO3).
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(d)     Cetane (C16H34) can be cracked to produce hexane, butene and ethene.
(i)      State one condition that is used in this cracking reaction.
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(1)
(ii)     Write an equation to show how one molecule of cetane can be cracked to form hexane, butene and ethene.
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(1)
(iii)     State one type of useful solid material that could be formed from alkenes.
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(Total 10 marks)
 
5.          Many hydrocarbon compounds burn readily in air.
(i)      Write an equation to show the complete combustion of C15H32
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(ii)      One of the gaseous products of the incomplete combustion of methane in gas fires is known to be poisonous. Identify this product and write an equation for the reaction in which it is formed from methane.
Identity of product ........................................................................................
Equation .......................................................................................................
(Total 4 marks)
	6.

	

	
(Total 13 marks)

7.

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(Total 15 marks)