AS LEVEL CHEMISTRY

PAPER 1
PRACTICE PAPER 10
(structured questions only)
Answer all questions
Max 80 marks

	
Name		……………………………………………………………..

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

1.      (a)     Sodium carbonate forms a number of hydrates of general formula Na2CO3.xH2O
A 3.01 g sample of one of these hydrates was dissolved in water and the solution made up to 250 cm3.
In a titration, a 25.0 cm3 portion of this solution required 24.3 cm3 of 0.200 mol–1 dm–3 hydrochloric acid for complete reaction.
The equation for this reaction is shown below.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
(i)      Calculate the number of moles of HCl in 24.3 cm3 of 0.200 mol dm–3 hydrochloric acid.
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(ii)     Deduce the number of moles of Na2CO3 in 25.0 cm3 of the Na2CO3 solution.
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(iii)     Hence deduce the number of moles of Na2CO3 in the original 250 cm3 of solution.
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(iv)    Calculate the Mr of the hydrated sodium carbonate.
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(5)
(b)     In an experiment, the Mr of a different hydrated sodium carbonate was found to be 250.
Use this value to calculate the number of molecules of water of crystallisation, x, in this hydrated sodium carbonate, Na2CO3.xH2O
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(3)

(c)     A gas cylinder, of volume 5.00 × 10–3 m3, contains 325 g of argon gas.
(i)      Give the ideal gas equation.
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(ii)     Use the ideal gas equation to calculate the pressure of the argon gas in the cylinder at a temperature of 298 K.
(The gas constant R = 8.31 J K–1 mol–1)
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 (4)
(Total 12 marks)
 
2.	The following equation shows the reaction of a phosphine molecule (PH3) with an H+ ion.
PH3 + H+  PH4+
(a)     Draw the shape of the PH3 molecule. Include any lone pairs of electrons that influence the shape.

(1)
(b)     State the type of bond that is formed between the PH3 molecule and the H+ ion.
Explain how this bond is formed.
Name of bond ................................................................................................
How bond is formed ......................................................................................
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(2)
(c)     Predict the bond angle in the PH4 + ion.
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(1)
(d)     Although phosphine molecules contain hydrogen atoms, there is no hydrogen bonding between phosphine molecules.
Suggest an explanation for this.
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(1)
(Total 5 marks)
 
3.      (a)     Describe the bonding in, and the structure of, sodium chloride and ice. In each case draw a diagram showing how each structure can be represented. Explain, by reference to the types of bonding present, why the melting point of these two compounds is very different.

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(12)

(b)     Explain how the concept of bonding and non-bonding electron pairs can be used to predict the shape of, and bond angles in, a molecule of sulfur tetrafluoride, SF4.
Illustrate your answer with a diagram of the structure.
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(8)
(Total 20 marks)
 
4.	This question is about the gaseous equilibrium between compounds E, F and G as shown in the equation.
E (g)    +    2F(g)     2G(g)         ΔH = –50 kJ mol–1
(a)     A 2.0 mol sample of E was heated in a sealed container with a 1.0 mol sample of F.
Equilibrium was established at a given temperature and the equilibrium mixture formed contained 0.80 mol of G.
Calculate the amount, in moles, of E and of F in this equilibrium mixture.
Moles of E ......................................................................................................
Moles of F ......................................................................................................
(2)

(b)     Write an expression for the equilibrium constant Kc for this equilibrium.
State the units of Kc
Expression .....................................................................................................
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Units ...............................................................................................................
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(2)
(c)     A different mixture of E and F reached equilibrium at temperature T1 in a container ofvolume 1.50 dm3. This equilibrium mixture contained 2.50 mol of E, 1.20 mol of F and 0.85 mol of G.
Calculate a value of Kc for the equilibrium at temperature T1
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(2)
(d)     The mixture in part (c) was allowed to reach equilibrium at temperature T1 in a different container of volume 3.00 dm3.
State whether the amount of G in the equilibrium mixture will increase, decrease or stay the same. Explain your answer.
Effect on the amount of G ..............................................................................
Explanation ....................................................................................................
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(3)

(e)     The mixture in part (c) was allowed to reach equilibrium at temperature T2 in the original container of volume 1.50 dm3.
The value of Kc for the equilibrium was found to have increased.
State and explain which of T1 or T2 is the higher temperature.
Higher temperature ........................................................................................
Explanation ....................................................................................................
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(3)
(Total 12 marks)

5.     (a)     State and explain the trend in electronegativity down Group VII from fluorine to iodine.
Trend ...........................................................................................................
Explanation …...............................................................................................
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(3)
(b)     (i)      Describe what you would observe when an aqueous solution of bromine is added to an aqueous solution containing iodide ions. Write an equation for the reaction occurring.
Observation .........................................................................................
Equation ..............................................................................................
(ii)     Explain why bromine does not react with aqueous chloride ions.
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(3)
(c)     Describe what you would observe when aqueous silver nitrate is added to separate aqueous solutions of potassium fluoride and potassium bromide.
Observation with KF(aq) ..............................................................................
Observation with KBr(aq) .............................................................................
(2)
(d)     Write an equation to show how solid potassium fluoride reacts with concentrated sulphuric acid.
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(1)

(e)     Write an equation for the redox reaction of sodium bromide with concentrated sulphuric acid.
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(2)
(Total 11 marks)
 
6.	Magnesium carbonate, MgCO3, can occur as the anhydrous compound, or as hydrates with 2, 3 or 5 molecules of water of crystallisation. All types of magnesium carbonate can be decomposed to form magnesium oxide, an important starting material for many processes. This decomposition reaction can be used to identify the type of magnesium carbonate present in a mineral.
A chemist was asked to identify the type of magnesium carbonate present in a mineral imported from France. The chemist weighed a clean dry crucible, and transferred 0.25 g of the magnesium carbonate mineral to the crucible. The crucible was then heated for a few minutes. The crucible was then allowed to cool, and the crucible and its contents were reweighed. This process was repeated until the crucible and its contents had reached constant mass. The mass of the crucible and its contents was then recorded.
The experiment was repeated using different masses of the magnesium carbonate mineral.
For each experiment the chemist recorded the original mass of the mineral and the mass of magnesium oxide left after heating to constant mass. The chemist’s results are shown in the table below.
 
 	Experiment	1	2	3	4	5	6	
 	Mass of mineral / g	1.60	1.17	0.74	1.31	1.80	1.34	
 	Mass of magnesium oxide / g	0.54	0.39	0.24	0.44	0.61	0.49	

(a)     Plot a graph of the mass of the mineral (x-axis) against the mass of magnesium oxide on the grid below.
Draw a straight line of best fit on your graph.
 
(4)
(b)     Use the graph to determine the mass of the mineral which would have formed 0.50 g of magnesium oxide.
Mass of the mineral .......................................................................................
(1)

(c)     Calculate the amount, in moles, of MgO present in 0.50 g of magnesium oxide.
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(1)
(d)     Use your answers from part (b) and from part (c) to calculate the Mr of the magnesium carbonate present in the mineral.
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(1)
(e)     Use your answer from part (d) to confirm that this mineral is MgCO3.2H2O
(If you could not complete the calculation in part (d), you should assume that the experimental Mr value is 122.0 This is not the correct answer.)
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(1)
(f)     Explain why it was not necessary to use a more precise balance in this experiment.
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(1)
(g)     Consider your graph and comment on the results obtained by the chemist. Identify any anomalous results.
Comment .......................................................................................................
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Anomalous results .........................................................................................
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(2)
(h)     Explain why it was necessary for the chemist to heat the crucible and its contents to constant mass.
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(1)

(i)      Suggest one reason in each case why
(i)      small amounts of the mineral, such as 0.10 g, should not be used in this experiment.
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(1)
(ii)     large amounts of the mineral, such as 50 g, should not be used in this experiment.
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(1)
(j)      Analysis of a different hydrated magnesium carbonate showed that it contained 39.05% by mass of water. Determine the formula of this hydrated magnesium carbonate.
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(2)
(k)     Magnesium oxide is produced by the thermal decomposition of magnesium carbonate and by the thermal decomposition of magnesium hydroxide. The equations for the reactions taking place are shown below.
 
 	Reaction 1
Reaction 2	MgCO3
Mg(OH)2	→
→	MgO + CO2
MgO + H2O	

Show that Reaction 2 has the greater atom economy for the production of magnesium oxide.
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(2)
(l)      Apart from cost, suggest one advantage of using magnesium hydroxide rather than magnesium carbonate to reduce acidity in the stomach.
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(1)
(Total 19 marks)

7.	The table below shows some information about three hydrochloric acid solutions used to clean bricks and concrete.
 
 	Cleaner	Acid content by mass / %	Price per 25dm3 / £	
 	Plattern Concrete Acid	24.0	14.39	
 	Dub-Lit Brick Cleaner	28.9	16.99	
 	Conpat Brick Acid	35.9	24.99	

Use the data in the table above to determine the cleaner that offers the best value for money, based on acid content. Show your working.
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(Total 1 mark)