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