Question 4
- (i) State the law of conservation of matter.
(ii) State three postulates of the kinetic theory of gases. [5 marks]
- (b) Name the fuel produced when:
(i) air is passed over heated carbon;
(ii) steam is passed over heated carbon;
(iii) write a balanced chemical equation for the reaction in 4(b)(ii). [4 marks] - (i) Name a suitable solvent for each of the following substances:
I. sulphur;
II. carbon(II) oxide;
III. paint.
(ii) I. State what would be observed when dry hydrogen gas is passed over heated copper (II) oxide.
II Write a chemical equation for the reaction in 4(c)(ii)I. [7 marks] [6 marks] - (i) Define air pollution.
(iii) State two methods of reducing carbon (II) oxide in the atmosphere. [4 marks] - (i) State three applications of electrolysis.
(iii) State two materials used in the extraction of iron from its ore.
Observation
The question was popular among the candidates
In part (a), few candidates failed to give a concise and acceptable definition of the law of conservation of matter. The key words required to score were missing. Majority of the candidates stated the postulates of the kinetic theory of gases.
In part (b), majority of the candidates named the fuel produced when air is passed over heated carbon; steam is passed over heated carbon. However, they could not write a balanced chemical equation for the reaction in 4(b)(ii).
In part (c), majority of the candidates could not name suitable solvent for sulphur, carbon (II) oxide and paint.
In part (d), majority of the candidates defined air pollution correctly. However, only two of them could state two method of reducing carbon (II) oxide in the atmosphere.
In part (e), majority of the candidates stated three applications of electrolysis and raw materials used in the extraction of iron from its ore.
The expected answer include
- (i)Law of conservation of matter states that matter is neither created nor destroyed during a chemical reaction.
(ii)- the forces of attraction and repulsion between gas molecules are negligible
- gas molecules move randomly, colliding with one another and with the walls of the container
- the collisions of the molecules are perfectly elastic
- the volume occupied by the gas molecule is negligible as compared to the volume of the container
- temperature of the gas is a measure of the average kinetic energy of the gas molecules - (i) Producer gas
(ii) Water gas
(iii) C(s) + H2O(g) → CO(g) + H2(g) - (i) I - Carbon (IV) Sulphide / methyl benzene
II - ammoniacal copper (I) chloride
III - turpentine
(ii) I - black colour (1) changes to brown / reddish brown
II - CuO(s) + H2(g) → H2O(g) + Cu(s) -
(i) Air pollution is the release of poisonous substances into the atmosphere(in such concentration) that is harmful to the environment.
(ii) - Laws should be passed and enforced to make factories and users of motor-vehicles keep air pollution down.
- Machinery should be improved for more efficient fuel combustion
- People should be educated to make them aware of the causes and dangers of pollution
- Users of combustion engines must ensure engines are used in areas of plenty of air / complete combustion of fuel - (i) - extraction of metals
- purification of metals / refining of metals
- electroplating
- preparation of compounds
(ii) - haematite ( Fe2O3 ) / magnetite ( Fe3O4) / siderite ( FeCO3) /iron pyrites ( FeS2) / Limonite (Fe2O3. H2O)
- Limestone / CaCO3 Coke / C