Chemistry Paper 3,May/June 2014  
Questions:   1 2 3   Main
General Comments

Question 2

C contains two cations and two anions.  Perform the following exercises
            on C.  Record your observations and identify any gas(es) evolved.  State the
            conclusion you draw from the result of each test.

            (a)        Dissolve all of C in about 10 cm3 of distilled water:
                        Stir the resulting solution thoroughly.

                        (i)         To about 2cm3 of the solution, add few drops of
                                    AgNO3 solution, followed by HNO3(aq).

                        (ii)        To another 2cm3 portion of the solution, add dil. HC1
                                    followed by BaC12 solution.

                        (iii)       To another 2 cm3 portion of the solution, add NaOH(aq)
                                    dropwise and then in excess.  Warm the mixture.

                        (iv)       To another 2cm3 portion of the solution, add NH3(aq)
                                    dropwise and then in excess. 
                                                                                                                                    [20 marks]


This question is based on qualitative analysis.  It involved the identification of cations and onions.

The question was attempted by majority of the candidates and their performance was fair.

Majority of the candidates carried out the required text, made their observation and inferences logically.

Some candidates lost marks due to wrong test, observation, inference or the used of wrong charges on ions.


            The expected answers include:






C(aq) + AgNO3(aq)  
+ HNO3(aq)            
Mixture + NH3(aq) exces

White precipitate formed   Precipitate insoluble.
 Precipitate soluble / dissolved  

Cl-, S2-, CO32-
Cl- present    


C(aq) + HCl(aq)

 + BaCl2(aq)

No visible reaction / no gas evolved   
White (chalky) precipitate


SO42- present   


C(aq) + NaOH(aq) in drops
 in excess


Mixture warmed

White gelatinous precipitate   
White precipitate dissolved / soluble  

Colourless gas evolved  
 pungent / choking / irritating smell evolved   
Gas turns red litmus paper blue/forms dense white  fumes with concentrated HCl.  

Zn2+ , Al3+ indicated   
Zn2+, Al3+   indicated




NH3    gas evolved
 NH4+     present


C(aq) + NH3(aq) in drops


then excess

White gelatinous precipitate   


Precipitate dissolved / soluble  

Zn2+ , Al3+ indicated    








Powered by Sidmach Technologies(Nigeria) Limited .
Copyright © 2015 The West African Examinations Council. All rights reserved.