This question was attempted by majority of the candidates and their performance
was good.
Majority of the candidates demonstrated good understanding of almost all aspect
of question 3. However, only a few candidates were able to attempt correctly
3(c)(ii) on the suitability of Na2CO3 or NaOH for the preparation of standard alkaline solution.
The expected answers include:
(a)(i) - aeration / exposure to sunlight
- add alum / coagulation / flocculation
- sedimentation
- filtration
- add chlorine / disinfect
- add fluoride / iodide
- add Ca (OH)2 / pH control
(ii) Mg, Ca, Fe
(iii) - it wastes soap
- forms stain on white clothing and material
- forms boiler scale and kettle fur / damage
- it is unsuitable for industrial processes e.g.
dyeing and tanning
(iv) - wastes from industries e.g. brewery
- agricultural activities e.g. fertilizer
- waste from quarry activities
- refuse from plant and animal origin
- sewage (industrial and domestic)
- oil spillage
(b) (i) Water is a polar solvent and can therefore easily
dissolve sodium chloride which is ionic / polar salt.
Oil on the other hand is non-polar and hence cannot
dissolve in water which is polar.
(ii) (i) H2SO4 - as a dehydrating agent.
(ii) H2SO4 - as an acid
(iii) H2SO4 - as an oxidizing agent
(c) (i) HCl and O2
(ii) I. Na2CO3
II. Na2CO3 is stable in air and can be weighed accurately
OR
NaOH absorbs water/deliquescent and cannot be weighed accurately