Chemistry Paper 3 WASSCE (PC 2ND), 2022

Question 2

 

  1. Sample C is a sample organic compound that contains one or more of the following

functional group(s): alkene, alkanoic acid, alkanol or reducing sugar. The following tests were carried out on C.

 

Complete the table below.

 

Test

Observation

Inference

(i)

C + …………….

Reddish-brown
colour not discharged

 

………………………

(ii)

C + Na2CO3(aq)

………………………
……………………….

Gas is CO2

(iii)

C + ZnCl2(aq)
=
+
+

 

no two layers

formed

 

 

 

……………………

(iv)

C + ………………

+heat

no brick-red

precipitate formed  

 

……………………….

                                                                                                                                    [10 marks]

 

 


(b)        D is a solution of a double salt. The following tests were carried out on D.
Complete the table below.

 

[12 marks]

Observation

 

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

 

In part (a), majority of the candidates could not write not write the correct reactants under test. Also, they could not write the observation and inference.

 

In part (b), majority of the candidates could not write not write the correct reactants under test. Also, they could not write the observation and inference.

 

The expected answers include:


(a)


a

Test

Observation

Inference

(i)

C + Br2 / CCl4  
(bromine water)

Reddish-brown colour not discharged.

Alkene group absent

(ii)

C + NaHCO3(aq)

(Effervescence), colourless, odourless gas evolved gas turned lime water milky

Gas is CO2
alkanoic acid  group present

(iii)

C + ZnCl2(aq)
+ HCl
+ Heat / swirl

 

No two layers formed

 

Alkanol group absent

(iv)

C + Fehlings soln 
+ Heat
Accept Benedict’s soln

No brick – red precipitate formed

Reducing sugar absent

           
(b)


b

Test

Observation

Inference

(i)

D(aq) + litmus paper

Turned blue litmus paper to red

D is
acidic

(ii)

D(aq) + BaCl2(aq)

        + dilHCl

White precipitate formed

Precipitate insoluble

, ,

 present

(iii)

D(aq) + NaOH(aq) in drops (Accept NH3(aq))
then in excess

Reddish brown gelatinous precipitate is formed
Precipitate insoluble

 

Fe3+ present
Fe3+

(iv)

Resulting mixture from (iii) + heat

Pungent/choking/irritating  colourless gas evolved/produce dense white fumes with HCl
Gas turned red litmus paper blue

 evolved

 present

(v)

D(aq) + [K4Fe(CN)6](aq) (1)  (Accept IUPAC name)

Deep blue solution formed

Fe3+ confirmed

NB: No mark for (iv) when NH3(aq) is accepted in (iii)