Question 1
(a) This questions concerns the essential features of the electrolytic process by which sodium hydroxide is manufactured in a diaphragm cell.
(i) Identify the electrolyte used.
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(1)
(ii) Give the equation for the reaction at the anode.
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(1)
(iii) Give the equation for the reaction at the cathode.
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(1)
(iv) Give the equation for the overall reaction occurring
in the cell.
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(1)
(b) (i) How would the electrolytic process be modified
in order to manufacture sodium chlorate(I)?
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(1)
(ii) Write an equation to show how sodium chlorate(I)
is formed.
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(1)
(iii) Give one large-scale use of sodium chlorate(I).
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(1)
(c) Chlorate(I) ions are capable of undergoing disproportionation.
(i) What is meant by the term disproportionation?
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(1)
(ii) Write an ionic equation for the disproportionation
of sodium chlorate(I). Indicate the oxidation numbers of chlorine
in the species in which it occurs.
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(2)
(iii) Write two ionic half equations for this process
which illustrate your definition of disproportionation.
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(4)
Total 14 marks
Question 2
(a) At high temperatures phosphorus pentacloride is a gas which dissociates as follows
PCl5(g) <--> PCl3(g) + Cl2(g)
(i) Write an expression for the equilibrium constant Kp
for this equilibrium.
(2)
(ii) At a given temperature 39% of an original sample
of the PCl5(g) is dissociated at equilibrium. If the total
equilibrium pressure is 2atm, calculate the values of the equilibrium partial
pressures of:
PCl5
PCl3
(4)
(iii) Hence calculate the value of Kp and give its units.
(2)
(b) Aluminium chloride occurs in the anhydrous state and in the hydrated state. You may regard the structure of the anhydrous state as having the formula AlCl3. When water is added to solid anhydrous aluminium chloride, steamy acidic fumes are seen.
(i) What the steamy fumes?
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(1)
(ii) Write an equation for the reaction occurring.
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(1)
(iii) Explain by reference to the structures of AlCl3
how the first step of this reaction occurs.
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(2)
(c) (i)When water is added to hydrated aluminium chloride
no steamy fumes are seen. What does this indicate about the bonding
in hydrated aluminium chloride?
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(1)
(ii) Hydrated aluminium chloride dissolves in water to
give a solution which is acidic.
Suggest an explanation for the fact that the solution
is acidic. Give an equation to illustrate your answer.
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(2)
Total 14 marks
Question 3
This question concerns the lead-acid battery.
The following data will be required.
Eo/V
PbO2(s) + 4H+(aq) + SO42-(aq)
+2e- <--> PbSO4(s) + 2H2O(l)
+1.69
PbSO4(s) + 2e- <--> Pb(s)
+ SO42-(aq)
-0.36
(a) The lead-acid battery is one form of storage cell. What substance is used for:
(i) the negative pole;
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(1)
(ii) the positive pole;
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(1)
(iii) the electrolyte.
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(1)
(b) Give the equation for the overall cell reaction during
discharge.
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(2)
(c) Calculate the e.m.f. of the cell.
(2)
(d) A storage cell, as used in the lead-acid battery, is a simple cell in which the reactions are reversible i.e. once the chemicals have been used up they can be reformed.
Write an equation for the chemical reaction which occurs
on charging.
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(1)
(e) Dive one disadvantage of such batteries for use in
cars.
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(1)
(f) (i) State the essential requirement for the rusting
of iron in water.
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(1)
(ii) Explain why corrosion of iron results in deep pitting
of the metal surface.
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(1)
(iii) Explain why sheet iron which has been fabricated
to a particular shape. sometimes under high pressure, is more likely to
corrode than a single strip of pure iron.
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(2)
(iv) An underground iron pipe is less likely to corrode
if bonded at intervals to magnesium stakes. Give a reason for this.
Explain why aluminium would be a poor substitute for magnesium.
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(2)
Total 15 marks
Question 4
(a) (i) Define the term lattice enthalpy illustrating
your answer by reference to the oxide of a Group 2 metal.
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(3)
(ii) What are the factors which affects the magnitude
of lattice enthalpy?
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(2)
(iii) Why is lattice enthalpy for a given compound found
by the use of a Born-Haber cycle rather than being measured by direct experiment?
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(1)
(iv) Lattice enthalpies can be calculated from a formula
based on a purely ionic model. Why do values calculated in the way
often differ from those from a Born-Haber cycle?
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(1)
(b) (i) How does the solubility of hydroxides of the Group
2 metals change with increasing atomic number?
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(1)
(ii) Suggest an explanation for this trend.
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(3)
(c) (i) Explain why there is an increase in metallic character
with increase in atomic number in Group 4.
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(2)
(ii) Explain why compounds of lead in oxidation state
+4 are oxidising.
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(2)
(d) Write an equation to illustrate the oxidising ability
of a lead(IV) compound.
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(2)
Total 17 marks