June 1995  Module 1 Exam

Return to AS and A2 Chemistry
 

1. (a) Define the term isotope.
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(b) Identify x, y, and z in the following nuclear processes:

94Be + 42He -----> 126C + x
           3215P -----> 3216S + y
23592U + 10n -----> 9438Sr + z + 210n

x: .................................................................................
y: .................................................................................
z: ................................................................................. (4)

(c) The third of these reactions is the basis for the nuclear power industry.
What feature makes this possible?
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(d) The diagram shows part of the mass spectrum for chloroethane, C2H5Cl.
What ions are responsible for the peaks at m/e 66 and 64, and 29 and 28?

66: .....................................................................................................................
64: ......................................................................................................................
29: .....................................................................................................................
28: ....................................................................................................................(4)

(e) Define the term first ionisation energy.
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(f) The graph shows a plot of lg(ionisation energy) vs number of the electron removed for sodium.  Explain the form of this graph in terms of the electron structure of sodium.

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                                                                                        TOTAL 15 marks


2. (a) Define oxidation in terms of electron transfer.
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(b) State three properties which distinguish transition metals from main group metals.
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(c) Give the electronic configuration for Fe and for Fe3+ in the table below.

Suggest why Fe3+ is a more stable ion than Fe2+ under normal conditions.
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(d) (i) Name the types of reaction involved in the following changes:

                          aqueous NH3                          aqueous NH3
[Cu(H2O)6]2+    ----->   blue precipitate  ----->  deep blue solution
     A                             B                            C
A to B  ............................................................................
B to C .............................................................................

(ii) Give the formula of compound B.
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(iii) Draw the structure of the ion responsible for the colour in solution C and show its shape.
 
 
 
 
 
 
 
 
 
 

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(e) Addition of aqueous copper(II) ions to aqueous iodide ions gives a precipitate of copper(I) iodide and liberates iodine; the iodine can be titrated with aqueous sodium thiosulphate, so these reactions form the basis for a volumetric analysis of copper, for example in metal alloys.

(i) Write an ionic equation for the reaction of copper(II) ions with iodide ions.
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(ii) Given that the reaction of iodine with sodium thiosulphate is
I2(aq) + 2S2O32-(aq) -----> 2I-(aq) + S4O62-(aq)
find the volume of sodium thiosulphate solution of concentration 1.00 mol dm-3 needed to react with the iodine liberated by copper ions from a brass screw of mass 2.00g, containing 60% of copper by mass.
 
 
 
 
 
 
 
 
 
 
 

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                                                                                            TOTAL 16 marks


3. (a) The graph shows the boiling temperatures of the hydrides of Group 6.

Why is the boiling temperature of water higher than would be expected from the group trend?
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(b) Why is solid water less dense than liquid water?
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(c) Silicon tetrachloride, SiCl4, is a colourless liquid; its bonds are polar, but the molecule is not.  Explain.
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(d) Silicon tetrachloride, SiCl4, reacts with water to give silicon dioxide, SiO2, and HCl; it will react with atmospheric moisture unless kept in a sealed tube.  1.00g of a poorly-kept sample of SiCl4 was added cautiously to water.  When reaction was complete the solution was made up to 250cm3 with pure water. 25.0cm3 portions of this required on average 21.6cm3 of 0.100 mol dm-3 sodium hydroxide solution for neutralisation.  What percentage of the sample analysed was SiCl4?
 
 
 
 
 
 
 
 
 
 
 
 

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(e) Single crystals of metals conduct electricity equally well in all directions, but a single crystal of graphite will conduct in only one direction.  Suggest an explanation in terms of the structures of these materials.
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                                                                                                            TOTAL 14 marks


4. (a) Enter the formulae of the oxides for the elements shown in the empty boxes in the top two rows of the table.  Indicate in the borrom row of boxes the acid-base nature of these oxides.
 
Na Mg Al Si P S Cl
             
             
             

(b) Group 4 elements show a trend from non-metallic to metallic behaviour with increasing atomic number.  How is this shown by the acid base properties of carbon dioxide, CO2, silicon dioxide, SiO2, and lead(II) oxide, PbO?  Write equations to illustrate this behaviour.
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(c) PbO and PbO2 differ strikingly in their properties.  illustrate this by giving the reactions between these two oxides and concentrated HCl, stating the nature of each reaction.

For PbO:
equation: .............................................................................................................
nature of reaction: ..............................................................................................

For PbO2:
equation:
nature of reaction: ...............................................................................................
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(d) The +2 oxidation state of tin is reducing.  Give a reaction illustrate this property.
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                                                                                                TOTAL 15 marks