AS LEVEL CHEMISTRY

PAPER 2
PRACTICE PAPER 11
(structured questions only)
Answer all questions
Max 80 marks

	
Name		……………………………………………………………..

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

1.        A student carried out an experiment to determine the rate of decomposition of hydrogen peroxide 	into water and oxygen gas.
	The student used 100 cm3 of a 1.0 mol dm–3 solution of hydrogen peroxide at 298 K and measured 	the volume of oxygen collected.
	Curve R, in each of Figures 1, 2 and 3, shows how the total volume of oxygen collected changed 	with time under these conditions.
(a)     Draw a curve on Figure 1 to show how the total volume of oxygen collected will change with time if the experiment is repeated at 298 K using 100 cm3 of a 2.0 mol dm–3 solution of hydrogen peroxide.
Figure 1

(2)
(b)     Draw a curve on Figure 2 to show how the total volume of oxygen collected will change with time if the experiment is repeated at 298 K using 100 cm 3 of a 0.4 mol dm–3 solution of hydrogen peroxide.
Figure 2

(2)

(c)     Draw a curve on Figure 3 to show how the total volume of oxygen collected will change with time if the original experiment is repeated at a temperature higher than 298 K.
You should assume that the gas is collected at a temperature of 298 K.
Figure 3

(2)
(d)     Explain why the slope (gradient) of curve R decreases as time increases.
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(e)     The student discovered that hydrogen peroxide decomposes at a faster rate when a few drops of aqueous hydrogen bromide are added to the solution.
The student found on the Internet that this decomposition is thought to proceed in two steps as shown by the following equations.
Step 1         H2O2    +    HBr         HBrO    +    H2O
Step 2         HBrO    +    H2O2         H2O    +    O2    +    HBr
(i)      Write an equation for the overall reaction.
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(1)
(ii)     Give one reason, other than the increase in rate of reaction, why the student was able to deduce that hydrogen bromide behaves as a catalyst in this two-step reaction.
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(1)
(Total 10 marks)
 2.	Ammonia is manufactured by the Haber process in which the following equilibrium is established.
 
 	N2(g)	+	3H2(g)		2NH3(g)	
 
(a)     Give two features of a reaction at equilibrium.
Feature 1 .......................................................................................................
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Feature 2 .......................................................................................................
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(b)     Explain why a catalyst has no effect on the position of an equilibrium.
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 (2)

(c)     The diagram shows how the equilibrium yield of ammonia varies with changes in pressure and temperature.
 
(i)      Use the diagram to state the effect of an increase in pressure at constant temperature on the yield of ammonia. Use Le Chatelier's principle to explain this effect.
Effect on yield ........................................................................................
Explanation ............................................................................................
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(ii)     Use the diagram to state the effect of an increase in temperature at constant pressure on the yield of ammonia. Use Le Chatelier's principle to explain this effect.
Effect on yield ........................................................................................
Explanation ............................................................................................
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(d)     At equilibrium, with a pressure of 35 MPa and a temperature of 600 K, the yield of ammonia is 65%.
(i)      State why industry uses a temperature higher than 600 K.
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(1)
(ii)     State why industry uses a pressure lower than 35 MPa.
Do not include references to safety.
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(1)
(Total 12 marks)

3.       Glucose, produced during photosynthesis in green plants, is a renewable source from which ethanol can be made. Ethanol is a liquid fuel used as a substitute for petrol.
The processes involved can be summarised as follows.
Process 1                          Photosynthesis in green plants
6CO2 + 6H2O → C6H12O6 + 6O2
Process 2                          Fermentation of glucose to form ethanol
Process 3                          Complete combustion of ethanol
CH3CH2OH + 3O2 → 2CO2 + 3H2O
(a)     State three essential conditions for the fermentation of aqueous glucose in Process 2.
Write an equation for the reaction that takes place during this fermentation.
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(4)

(b)     It has been claimed that there is no net carbon (greenhouse gas) emission to the atmosphere when ethanol made by Process 2 is used as a fuel.
State the term that is used to describe fuels of this type.
Use the equations for Processes 1, 2 and 3 to show why it can be claimed that there is no net emission of carbon-containing greenhouse gases.
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(3)
(c)     Use the information from the equation for Process 3 above and the mean bond enthalpies from the table below to calculate a value for the enthalpy change for this process.
 
 	C–H	C–C	C–O	O–H	C=O	O=O	
Mean bond
enthalpy / kJ mol–1	+412	+348	+360	+463	+743	+496	
Give one reason why the value calculated from mean bond enthalpies is different from the value given in a data book.
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(4)

(d)     A student carried out a simple laboratory experiment to measure the enthalpy change for Process 3. The student showed that the temperature of 200 g of water increased by 8.0 °C when 0.46 g of pure ethanol was burned in air and the heat produced was used to warm the water.
Use these results to calculate the value, in kJ mol–1, obtained by the student for this enthalpy change. (The specific heat capacity of water is 4.18 J K–1 g–1)
Give one reason, other than heat loss, why the value obtained from the student’s results is less exothermic than a data book value.
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(4)
(Total 15 marks)
 4.      Oxygen and ozone (O3) both occur as gases in the upper atmosphere.
Chlorine atoms catalyse the decomposition of ozone and contribute to the formation of a hole in the ozone layer.
These chlorine atoms are formed from chlorofluorocarbons (CFCs) such as CF3Cl
(a)     (i)      Give the IUPAC name of CF3Cl
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(ii)     Complete the following equation that shows the formation of a chlorine atom from a molecule of CF3Cl

(1)
(iii)     State what the • represents in Cl•
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(b)     Write two equations that show how chlorine atoms catalyse the decomposition of ozone into oxygen.
Equation 1 ....................................................................................................
Equation 2 ....................................................................................................
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(c)     An equilibrium is established between oxygen and ozone molecules as shown below.
3O2(g)  2O3(g)                ΔH = +284 kJ mol–1
(i)      State Le Chatelier’s principle.
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(ii)     Use Le Chatelier’s principle to explain how an increase in temperature causes an increase in the equilibrium yield of ozone.
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(d)     Chemists supported the legislation to ban the use of CFCs. Modern refrigerators use pentane rather than CFCs as refrigerants.
With reference to its formula, state why pentane is a more environmentally acceptable refrigerant.
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(1)
(Total 9 marks)
 
5.          When chlorine reacts with trichloromethane, tetrachloromethane, CCl4, is formed.
(a)     (i)      Write the overall equation for this reaction.
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(ii)     State one essential condition for this reaction.
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(b)     The mechanism for the chlorination of trichloromethane is free-radical substitution, which proceeds by a series of steps. Write equations for the steps named below in this chlorination.
Initiation step
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First propagation step
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Second propagation step
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A termination step
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(4)
(Total 6 marks)
  
6.             In the presence of reagent X, the alcohol shown below undergoes a reaction to form two isomeric alkenes.

(i)      Name this alcohol.
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(ii)     Give the name of the type of reaction involved in the formation of the two alkenes.
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(iii)     Suggest the identity of reagent X.
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(iv)    Give the structural formulae of the two isomeric alkenes.
          Alkene 1                                             Alkene 2

 
  
(5)
(Total 5 marks)
 
7.     (a)     The equation below shows the reaction of 2-bromopropane with an excess of ammonia.
CH3CHBrCH3   +   2NH3   →   CH3CH(NH2)CH3   +   NH4Br
Name and outline the mechanism involved.
Name of mechanism ….................................................................................
Mechanism

 

 

(5)
(b)     When 2-bromopropane is heated with ethanolic potassium hydroxide, an elimination reaction occurs. State the role of potassium hydroxide and outline a mechanism for this reaction.
Role of potassium hydroxide ........................................................................
Mechanism

 

 

(5)
(Total 10 marks)

 

8.	Baking powder contains sodium hydrogencarbonate and an acid or a mixture of acids. One acid that may be in baking powder is 2,3-dihydroxybutanedioic acid. This has the molecular formula C4H6O6 and it is often referred to as tartaric acid.
(a)     Draw the structural formula of tartaric acid.

 
  
(1)
(b)     Write an equation for the reaction of tartaric acid (C4H6O6) with sodium hydrogencarbonate to form a salt, carbon dioxide and water.
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(c)     Substances that contain carbonate or hydrogencarbonate ions can be used to confirm the presence of an acid.
Identify one other substance that could be used to confirm the presence of acid groups in tartaric acid.
State the observation you would make when this other substance is added to an aqueous solution of tartaric acid.
Substance ......................................................................................................
Observation ....................................................................................................
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(2)

(d)     It is known that tartaric acid contains alcohol and carboxylic acid functional groups only. 
A test can be used to show that tartaric acid contains secondary alcohol groups, not tertiary alcohol groups.
(i)      Identify a reagent for this test and state the observation you would make for each type of alcohol.
Reagent ................................................................................................
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Observation for secondary alcohol .......................................................
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Observation for tertiary alcohol .............................................................
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(ii)     Suggest why this test cannot be used to distinguish between a primary alcohol and a secondary alcohol.
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(e)     Baking powder usually contains starch. Starch is added to absorb any water vapour that may come into contact with the baking powder when the container is opened.
Deduce a reason why this water vapour needs to be absorbed.
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(f)     Sodium hydrogencarbonate in baking powder forms carbon dioxide during the production of bread and cakes.
Suggest one advantage of having an acid in baking powder.
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(1)

(g)     Safety information indicates that tartaric acid and its salts can act as muscle toxins. 
These can cause paralysis and possible death.
Suggest one reason why the use of tartaric acid in baking powder is not a hazard to health.
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(1)
(Total 11 marks)

9.	In an experiment to determine the rate of a reaction, the volume of gas produced in the reaction was measured at regular intervals for several minutes.
(a)     State one experimental condition that must be kept constant during the experiment.
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(1)
(b)     Describe how the initial rate of this reaction can be determined from a graph of volume of gas produced against time.
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(1)
(Total 2 marks)