AS LEVEL CHEMISTRY

PAPER 1
PRACTICE PAPER 13
(structured questions only)
Answer all questions
Max 80 marks

	
Name		……………………………………………………………..

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

1.      (a)    Graphene is a new material made from carbon atoms. It is the thinnest and strongest material known. Graphene has a very high melting point and is an excellent conductor of electricity.
Part of the structure of graphene is illustrated in the diagram.
		
(i)      Deduce the type of crystal structure shown by graphene.
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(1)
(ii)     Suggest why graphene is an excellent conductor of electricity.
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(2)
(iii)    Explain, in terms of its structure and bonding, why graphene has a high melting point.
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(2)

(b)    Titanium is also a strong material that has a high melting point. It has a structure similar to that of magnesium.
(i)      State the type of crystal structure shown by titanium.
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(1)
(ii)     Explain, in terms of its structure and bonding, why titanium has a high melting point.
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(2)
(c)     Titanium can be hammered into objects with different shapes that have similar strengths.
(i)      Suggest why titanium can be hammered into different shapes.
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(ii)     Suggest why these objects with different shapes have similar strengths.
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(1)
(d)     Magnesium oxide (MgO) has a melting point of 3125 K.
Predict the type of crystal structure in magnesium oxide and suggest why its melting point is high.
Type of crystal structure ................................................................................
Explanation ....................................................................................................
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(3)
(Total 13 marks)

 

2.	At high temperatures and in the presence of a catalyst, sulfur trioxide decomposes according to the following equation.
2SO3(g)		2SO2(g)	+	O2(g)	∆Hϴ = +196 kJ mol–1	

(a)     In an experiment, 8.0mol of sulfur trioxide were placed in a container of volume 12.0 dm3 and allowed to come to equilibrium.
At temperature T1 there were 1.4 mol of oxygen in the equilibrium mixture.
(i)      Calculate the amount, in moles, of sulfur trioxide and of sulfur dioxide in the equilibrium mixture.
Amount of sulfur trioxide .......................................................................
Amount of sulfur dioxide ........................................................................
(2)
(ii)     Write an expression for the equilibrium constant, Kc, for this equilibrium.
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(1)
(iii)    Deduce the units of Kc for this equilibrium.
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(1)
(iv)     Calculate a value of Kc for this equilibrium at temperature T1
(If you were unable to complete the calculations in part (a)(i) you should assume that the amount of sulfur trioxide in the equilibrium mixture was 5.8 mol and the amount of sulfur dioxide was 2.1 mol. These are not the correct values.)
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 (3)

(b)     The experiment was repeated at the same temperature using the same amount of sulfur trioxide but in a larger container.
State the effect, if any, of this change on:
(i)      the amount, in moles, of oxygen in the new equilibrium mixture
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(1)
(ii)     the value of Kc
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(1)
(c)     The experiment was repeated in the original container but at temperature T2
The value of Kc was smaller than the value at temperature T1
State which is the higher temperature, T1 or T2
Explain your answer.
Higher temperature ........................................................................................
Explanation ....................................................................................................
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 (3)
(Total 12 marks)
 
3.       State the trends in solubility of the hydroxides and of the sulphates of the Group II elements Mg–Ba.
Describe a chemical test you could perform to distinguish between separate aqueous solutions of sodium sulphate and sodium nitrate. State the observation you would make with each solution. Write an equation for any reaction which occurs.
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(Total 6 marks)
 4.      (a)     In terms of electrons, what happens to an oxidising agent during a redox reaction?
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(1)
(b)     Consider the following redox reaction.
SO2(aq) + 2H2O(l) + 2Ag+(aq) → 2Ag(s) + SO42-(aq) + 4H+(aq)
(i)      Identify the oxidising agent and the reducing agent in this reaction.
Oxidising agent ...................................................................................
Reducing agent ...................................................................................
(ii)     Write a half-equation to show how sulphur dioxide is converted into sulphate ions in aqueous solution.
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(3)
(c)     Fe2+ ions are oxidised to Fe3+ ions by ClO3- ions in acidic conditions. The ClO3- ions are reduced to Cl– ions.
(i)      Write a half-equation for the oxidation of Fe2+ ions in this reaction.
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(ii)     Deduce the oxidation state of chlorine in ClO3- ions.
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(iii)     Write a half-equation for the reduction of ClO3- ions to Cl– ions in acidic conditions.
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(iv)    Hence, write an overall equation for the reaction.
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(4)
(d)     Sulphur is removed from impure iron by reacting it with magnesium. Write an equation for this reaction and identify the oxidising agent.
Equation ......................................................................................................
Oxidising agent ............................................................................................
(2)
(Total 10 marks)

5.      (a)     In Peru, chlorine was removed from the water supply due to concerns about it reacting with organic chemicals in the water to produce toxic substances. This resulted in the death of ten thousand people due to cholera. The cholera epidemic ceased when chlorination of the water supply was restarted.
State why chlorine is added to the water supply and give a reason why the amount of chlorine must be carefully monitored. Write an equation for the reaction of chlorine with water.
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(3)
(b)     How can the addition of an aqueous solution of chlorine be used to distinguish between aqueous solutions of sodium bromide and sodium iodide?
State any observations you would make and write equations for the reactions occurring.
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(4)

(c)     How can reactions with concentrated sulphuric acid be used to distinguish between solid samples of sodium bromide and sodium iodide?
State the observations you would make and give all the oxidation and reduction products formed in both reactions. Using half-equations, construct an overall equation for one of these redox reactions.
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(11)
(Total 18 marks)
 
6.	Ammonium salts such as ammonium nitrate are used in fertilisers. The ammonium nitrate content of a fertiliser can be determined by heating a sample of the fertiliser with an excess of sodium hydroxide solution. An equation for this reaction is shown below.
NH4NO3  +  NaOH   NH3  +  NaNO3  +  H2O
Heating ensures that all of the ammonia produced is given off as a gas. The unreacted sodium hydroxide remaining in the solution can be determined by a titration with standard hydrochloric acid.
(a)     Explain why it is necessary to remove all of the ammonia before titrating the unreacted sodium hydroxide.
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(1)

(b)     Suggest why it is important to test samples from more than one batch of the fertiliser.
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(c)     Ammonium nitrate decomposes when heated to form water and one other product. 
Write an equation for this reaction.
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(d)    The table below shows some information about three salts that could be used in fertilisers.
 
 	Salt	Nitrogen content 
by mass / %	Price per 
tonne / £	
 	Ammonium chloride	26.2	134	
 	Ammonium nitrate	35.0	175	
 	Ammonium sulfate	21.2	111	
 
(i)      Use the data in the table to determine the salt that offers the best value for money, based on nitrogen content. Show your working.
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(2)
(ii)     Ammonium nitrate is very soluble in water. Suggest one disadvantage of its high solubility when ammonium nitrate is used in a fertiliser.
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(1)
(e)     A saturated solution of ammonia contains 300 g of ammonia in 1.00 dm3 of solution. 
Calculate the concentration, in mol dm–3, of ammonia in this solution.
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(1)
(Total 7 marks)

7.	Sodium carbonate is manufactured by the Solvay Process.
The separate stages involved in this process are shown in this diagram.
 
(a)     In Reactor 1, calcium carbonate is decomposed into calcium oxide and carbon dioxide. Despite no significant leakage of carbon dioxide from this decomposition, this part of the process results in an increase in carbon dioxide in the atmosphere.
State why this increase in carbon dioxide occurs.
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(1)
(b)     In Reactor 2, sodium chloride solution, carbon dioxide and ammonia react to form sodium hydrogencarbonate and ammonium chloride.
Write an equation for this reaction.
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(c)     Use information from the diagram to deduce an equation for the reaction taking place in Reactor 3.
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(1)

(d)     An equation for the overall reaction in the Solvay Process is
2NaCl(aq)    +    CaCO3(s)   Na2CO3(s)    +    CaCl2(aq)
(i)      Calculate the percentage atom economy of this reaction to produce sodium carbonate. Show your working.
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(2)
(ii)     State what could be done to improve the percentage atom economy of the Solvay Process.
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(1)
(e)     Use information from the diagram to suggest why ammonia is not regarded as a raw material in the Solvay Process.
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(1)
(Total 7 marks)

8.   (a)     Potassium carbonate can also be prepared by the decomposition of potassium hydrogencarbonate. The equation for the reaction is shown below with a diagram of the apparatus used.
2KHCO3   K2CO3  +  CO2  +  H2O
 
A student was asked to check the purity of a sample of potassium hydrogencarbonate. 
The student weighed a clean, dry crucible, and transferred 1.00 g of the potassium hydrogencarbonate to the crucible. A lid was placed on the crucible and the crucible was then heated for a few minutes. After cooling, the mass of the crucible and its contents was recorded.
(i)      Explain why the use of a wet crucible would give an inaccurate result.
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(1)
(ii)     Give one reason why the use of a lid improves the accuracy of the experiment.
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(1)
(iii)    State one reason why the use of a very small amount of potassium hydrogencarbonate could lead to a less accurate result.
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(1)

(b)     In another experiment, the decomposition of a 1.00 g sample of pure potassium hydrogencarbonate gave 0.81 g of solid in the crucible.
(i)      Calculate the mass of potassium carbonate that can be formed from 1.00 g of potassium hydrogencarbonate. 
Show your working.
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(3)
(ii)     In this experiment the mass of solid remaining in the crucible was greater than expected. Suggest one reason for this result.
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(1)
(Total 7 marks)