Chemistry Paper 1 (Practical) ,May/June 2011  
Questions:       1 2 3 4 5 6   Main
General Comments

Question 5

F is a mixture of two compounds.  Carry out the following exercises on F.  Record your observations and identify any gas(es) evolved.  State the conclusion drawn from the results of each test.

  1. Put all of F into a beaker or a boiling tube and add about 10 cm3 of distilled water.  Stir the mixture thoroughly and filter.  Keep both the filtrate and the residue.
  2. (i) Divide the filtrate into two portions.
      I.To the first portion, add dilute HNO3  followed byAgNO3(aq).
      II. Add excess NH3(aq) to the resulting mixture.
    (ii) To the second portion, add NH3(aq) in drops and then in excess.
  3. Add about 5 cm3  of distilled water to the residue in a test tube.  Boil and allow to cool.  Add few drops of iodine solution.


Majority of the responding candidates carried out the required tests, made their observations and drew inferences in the prescribed format.  However, some candidates lost marks for not reporting that no visible reaction was observed on adding HNO3 to the filtrate and for including pb2+ as ions present when the filtrate was treated with NH3(aq)

Observation of jelly-like paste was also not recorded by many candidates when water was added to residyue and then heated. 

On addition of iodine to the cooled mixture, most candidates recorded black ppt instead of blue-black colouration.  General performance was fair.

The expected answers are:






F + water, stirred mixture
and filtered

Partly dissoves/soluble Colourless filtrate
White residue

F contains soluble and insoluble salts

b) (i)  I



Filtrate + dil HNO3

+ Ag NO3(aq)

Mixture in (b)(i)  +
excess NH3 solution  

No visible reaction

White precipitate formed


Precipitate dissovles


Cl- present


Cl- confirmed


Filtrate + HN3(aq) in drops


then in excess

White gelatinous precipitate


Precipitate dissovles

Zn+2 or A13+
may be present

Zn2+ confirmed


Residue + water + heat

allow to cool + iodine solution

Jelly-like paste is formed

Dark/deep blue/blue black colouration is obtained


Starch is confirmed

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