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Chemistry Paper 3,Nov/Dec 2008  
Questions:         1 2 3       Main
General Comments
Weakness/Remedies
Strength







































Question 2

D is a mixture of a soluble lead salt and an insoluble white powder.  The mixture was added to 15 cm3 of distilled water, stirred and filtered.

The tests indicated in the table below were carried out on the filtrate and the residue.

Copy and complete the table as appropriate.
Do not complete the inference column in 2(a)(i) and 2 (a)(ii).

           Test

      P

       Q

         R

Portion of filtrate + NaOH(aq)  in drops ;then in excess                            

 

 

  8.0  -  9.6

Portion of filtrate + NH3(aq) in drops, then in  excess   

     

Portion of the filtrate+FeSO2(aq) NOpresent  + Conc. H2SO4          

 

  NO-3present 

 
Residue + dil.HNO3                                        

    CO2-3present

 

Portion of solution from White precipitate           
(b)(i) + NaOH(aq) in insoluble in excess   drops, then in  excess                                                                                        

White precipitate  (b)(i) + NaOH(aq) in insoluble in excess

   

 Portion of solution from (b)(i) + NH3(aq)  in drops,  then in excess   

     

Select the indicator(s) that would be suitable for titrating:
(i)    strong acid with strong base;
(ii)  strong acid with weak base;
(iii) weak acid with strong base.                                      

_____________________________________________________________________________________________________
OBSERVATION

This question was attempted by majority of the candidates and the performance was fair.  Candidates correctly copied and completed the table as required but some of them lost marks for wrong observations and inferences.  The expected table from candidates was as follows:                         

           Test

      P

       Q

         R

Portion of filtrate + NaOH(aq)  in drops ;then in excess 

  1. White precipitate Soluble in exces  then in excess                                      

 

 

  8.0  -  9.6

Portion of filtrate + NH3(aq) in drops, then in  excess   

White precipitate  insoluble in excess

   

Portion of the filtrate+FeSO2(aq) NOpresent  + Conc. H2SO4          

Brown ring                         

  NO-3present 

 
Residue + dil.HNO3  ;

 Effervescence  Gas turned lime water milky.
Colourless solution/ ppt
dissolves

    CO2-3present

 

Portion of solution from White precipitate           
(b)(i) + NaOH(aq) in insoluble in excess   drops, then in  excess                                                                                        

White precipitate  (b)(i) + NaOH(aq) in insoluble in excess

   

 Portion of solution from (b)(i) + NH3(aq)  in drops,  then in excess   

No ppt/no visible  

   
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