Social Science
Literature Arabic Islamic Studies C.R.K HistoryMusicVisual Art Clothing/Textile Home Management Shorthand
Chemistry Paper 1 (Practical) ,May/June 2008  
Questions:       1 2 3 4 5 6   Main
General Comments

Question 2

C is a mixture of two salts.  Carry out 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) Put C into a beaker and add about 10 cm3 of distilled water, stir the mixture and filter.  Test the filtrate with litmus papers.  Keep the residue and the filtrate.   [6 marks]

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

(ii) Add excess NH3 solution to the resulting mixture. [5 marks] 

(c) To about half of the residue from 2(a) above, add about 5 cm3 of dilute HNO3  in drops.  Divide the resulting solution into two equal portions. [4 marks]

(d) (i) To the first portion add ammonia solution in drops and then in  excess.

(ii) To the second portion add dilute hydrochloric acid. [6 marks]


This question was attempted by most candidates and their performance in it was fair.

Candidates correctly carried out the various test with correct observations and inferences.   However, some lost marks because they carried out the test on the solid sample instead of the filterate and residue respectively.  Also, some did not carry out the confirmatory test for the gas evolved.  The required tests,observations and inferences were as tabulated below

C + water
Mixture filtered
Filtrate + Litmus
Partially dissolved/ soluble
colourless Fltrate
White residue, no effect on litmus
C contains soluble & insoluble salts

Filtrate is neutral
b (1)
Filtrate + dilute HNO3 + AgNO3 No (visible) reaction, white ppt Cl- present
Mixture in b(i) + excess NH3 Solution Ppt dissolves Cl- Confirmed
  Residue + dil HNO3 Effervescence/bubbles/colourless, odourless gas evolved.Gas turns lime water milky/turns blue litmus red CO2 evolved, CO32- present
First portion + dil NH3 in drops then in excess
White (chalky) ppt (gelatinous is not accepted). ppt insoluble
Pb2+ may be present . Pb2+ is present
Second portion + dil. White (chalky) ppt Pb2+ confirmed
Powered by Sidmach Technologies(Nigeria) Limited .
Copyright © 2012 The West African Examinations Council. All rights reserved.