The question was attempted by most candidates and the performance was good.
In part (a) candidates correctly copied and completed the table as follows:
Oxide of nitrogen |
Oxidation state of nitrogen |
Colour of gas |
Solubility in water |
Action on damp blue litmus paper |
N2O |
|
Colourless |
|
No effect |
NO |
+2 |
|
Insoluble |
No effect |
NO2 |
+4 |
Reddish brown |
Soluble |
Turns damp blue litmus red |
In part (b) (i) I and II, candidates knew that Ca(HCO3)2/Mg(HCO3)2 and CaCl2 / CaSO4/MgSO4 /FeSO4 makes water to be temporarily and permanently hard respectively.
In (b)(ii), candidates correctly wrote an equation for the removal of each of the hardness as follows:
I. Ca(HCO3)2(aq) + Ca(OH)2(s) 2CaCO3(s) + 2H2O (1)
OR
boil
Ca(HCO3)2(aq) CaCO3(s) + H2O (1) + CO2(g)
II. Na2CO3(aq) + CaSO4(aq) → CaCO3(s) + Na2SO4(aq)
OR
Na2Y (aq) + CaSO4 (aq) → CaY + Na2SO4(aq)
In part (c), candidates listed three sources of water pollution and mentioned two ways by which water pollution can be controlled in (i) and (ii) from among the following:
(i) - domestic sewage
- industrial waste/sewage/effluent
- agricultural waste
- oil spillage
- volcanic eruptions
(ii) - sewage should be treated
- measures should be implemented to prevent oil spillage
- education and enlightenment on the environment should be intensified
- enactment of strict laws to control the environment
In part (d)(i) – (iv), candidates correctly stated the function of each of the substances in the purification of water for town supply