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

1. industrial waste/sewage/effluent
2. agricultural waste
3. oil spillage
4. 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