Chemistry Paper 3 WASSCE (PC), 2022

Question 2

 

C is a mixture of two salts containing two cations and two anions.
                       

The following tests were carried out on C. Complete the table.

                       

 

TEST

OBSERVATION

INFERENCE

(a)

C + conc. H2SO4

 

Resulting solution warmed

Colourless gas evolved which forms dense white fumes with NH3(g)

brown fumes produced

 

………………

………………

(b)(i)

Solution of C + NaOH(aq) in drops + excess

 

+ heat

White gelatinous precipitate formed
………………….

A colourless pungent smelling gas evolved which formed white dense fumes with conc. HCl

 

 

………………

 

 

 

………………

   (ii)

Solution of C + NH3(aq) in drops
+ excess

 

White precipitate formed.
Precipitate soluble

 

……………..

  (iii)

Solution of C + HNO3(aq)
+ AgNO3
+………………………..

No precipitate, no gas evolved
White precipitate formed
Precipitate soluble

……………..
……………..
Cl- confirmed

(iv)

Solution of  C + FeSO4(aq) +………………………….

Brown ring formed at the junction of the two layers

 

NO3- confirmed

           
(c)        State the possible salts
[14 marks]


Observation

This question tested the knowledge of qualitative analysis. Majority of the candidates responded to this question and their performance was average.

In part (a), majority of the candidates could not write correct inferences to the test.


In part (b), majority of the candidates majority of the candidates did not write correct charges on ions when writing the inferences.


In part (c), majority of the candidates could not state the possible salt.

 

The expected answers include:

 

 

TEST

OBSERVATION

INFERENCE

(a)

C + conc H2SO4

 

 

Resulting solution warmed

Colourless gas evolved which forms dense
white fumes with
NH3(g)

Brown fumes produced

 

HCl gas 

 

NO2 gas  

 

(b)(i)

 

Solution of C +
NaOH(aq) in drops
+ excess

+ heat

White gelatinous
precipitate formed
precipitate soluble 

a colourless pungent smelling gas evolved
which formed white
dense fumes with
Conc. HCl

Zn2+(l), Al3+    

 

NH3 gas 
from NH4+  

 (ii)

Solution of C +
NH3(aq) in drops
+ excess

White precipitate formed

precipitate soluble

 

Zn2+   

(iii)

Solution of C +
HNO3(aq)

 

 

+ AgNO3
+ NH3(aq) in (excess) 

No precipitate, no
gas evolved

 

 

White precipitate formed
precipitate soluble

CO32- , SO32-, S2-   absent (Any 2 for 2 marks /
Cl-, Br-, I-, SO42- present (Any 2 for 2 marks)

Cl- present 
Cl- confirmed

(iv)

Solution of C +
FeSO4(aq) +
(Conc.) H2SO4 
(dil H2SO4, no score)

Brown ring formed
at the junction of
the two layers

 

NO3- confirmed

           
(c)        Zn(NO3)2 and NH4Cl / ZnCl2 and NH4NO3