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Chemistry Paper 2,Nov/Dec 2009  
Questions:   1 2 3 4 5 6 7 8   Main
General Comments
Weakness/Remedies
Strength




Question 7

  1. Copy and complete the following table:

Oxide of nitrogen

Oxidation state of nitrogen

Colour of gas

Solubility in water

Action on damp blue litmus paper

N2O

+ 1

 

Insoluble

 

NO

 

Colourless

 

 

NO2

 

 

 

 

                                                                                                                             [8 marks]

  1.  (i)    Mention one compound that makes water

   I.             temporarily hard;
   II.           permanently hard.

  (ii)      State one method that could be used to remove
            I.          only temporary hardness;
            II.        permanent hardness.

    (iii) Write an equation to show the removal of :

  1. temporary hardness;
  2. permanent hardness.
  1. (i) List three sources of water pollution.

(ii) Mention two ways by which water pollution can be controlled.       
                                                                       [5 marks]

  1. state the function of each of the following substances in the purification of water for town supply:    
  2. sodium aluminate (III) (NaAIO2);
  3. lime (calcium hydroxide);
  4. calculated mount of iodine;
  5. sand bed.
_____________________________________________________________________________________________________
OBSERVATION

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
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