Question 5
(a) Describe how iron and aluminium reacts with each of the following substances:
(i) dilute H2SO4;
(ii) dilute HNO3
[8 marks]
(b) (i) Write an equation for the burning of sulphur in air
(ii) Name the catalyst used in the contact process.
(iii) In the contact process, why is an excess of air used?
(iv) Why is it necessary to cool the catalyst used 5(b)(ii)?
(v) Give a reason why the air used in the contact process needs to be as clean as
possible
(vi) State two reasons why SO2 should not be discharged into the atmosphere.
[7 marks]
(c) (i) State the reagents and condition used in the laboratory preparation of chlorine.
(ii) State two uses of chlorine
[5 marks]
(d) (i) Name the drying agents for each of the following gases:
(I) hydrogen;
(II) Sulphur (IV) oxide;
(III) ammonia.
(ii) State the components of the following alloys;
(I) Bronze;
(II) Brass.
[5 marks]
Observation
This question was popular among the candidates as most of them responded to it.
In part (a), majority of the candidates could not describe the reaction of aluminium and iron with dilute H2SO4 and dilute HNO3.
In part (b), majority of the candidates were able to write an equation for the burning of sulphur in air, named the catalyst in the contact process and gave a reason why excess air is used in the contact process.
In part (c), majority of the candidates stated the reagents and condition used in the laboratory preparation of chlorine. Also, they stated the uses of chlorine.
In part (d), majority of the candidates wrote the names of the drying agents instead of the formulae.
The expected answers include:
(a) (i) Iron dissolves readily in dilute H2SO4 liberating hydrogen and forming
FeSO4 while with Aluminium there is no reaction
(ii) With aluminium there is no reaction while iron dissolves in dilute HNO3 liberating
Hydrogen and forming Fe(NO3)2
(b) (i) S + O2 → SO2
(ii) Vanadium (V) oxide / platinized asbestos
(iii) To favour the formation of more product / SO3
(iv) The reaction is exothermic / high temperature favours the formation of more reactants/
backward reaction
(v) Catalysts are easily poisoned / easily damaged by dirt
(vi) - SO2 damages buildings
- damages living things
- causes acid rain
- causes irritation to eyes, nose and throat
- causes lungs and respiratory diseases eg coughing, bronchitis etc
(c) (i) reagents - manganese (IV) oxide / MnO2
- concentrated HCl
condition - heating
OR
Concentrated HCl
Bleaching powder / CaOCl2/ KMnO4 crystals
Room temperature