Chemistry Paper 3B Nov/Dec 2015

Question 3

 

3(a)   Copper (II) oxide was reacted with a dry hydrogen gas as shown in the                  following diagram.

 


Study the diagram and answer the questions that follow.

  1. Identify Q, R, X and Y.
  2. What will be the colour change of the copper (II) oxide?
  3. What is the role of X?                                                     [ 7 marks]

           (b) State one gas which:
(i) smells like rotten egg;
(ii) has an irritating smell like that of burning sulphur;
(iii) has yellowish green colour;
(iv) fumes with HCl gas;
(v)  has reddish brown colour.                                          [5 marks]
(c)   Give one use each of the following laboratory apparatus:
( i )       volumetric flask;
(ii)        wash bottle;
(iii)       glass rod;
(iv)       dessicator                                                          { 4 marks}    

Observation

 

In part (a), majority of the candidates could not identify the colour change of copper (II) oxide in the diagram. They could not explain the role of X in the diagram.
In part (b), majority of the candidates could not state a gas that has reddish brown colour.
In part (c), candidates could not identify the functions of the  laboratory apparatus.          
The expected answers include:          
QUESTION 3

  1. (i)         Q – Copper (II) oxide

            R- Water
            X- Ice cube
            Y- Flame of burning hydrogen

(ii)       Black to reddish brown
 OR changes to reddish brown
(iii)     X cools / condenses water vapour formed
        OR X acts as a coolant
                                                                                           

  1. (i)        Hydrogen sulphide / H2S
  2. Sulphur (IV) oxide / SO2
  3. Chlorine / Cl2
  4. Ammonia / NH3
  5. Nitrogen (IV)oxide / NO2

                                                                                   

  1. (i) Volumetric flask: for preparing standard solutions

(ii)Wash bottle: (contains distilled water) for rinsing containers /for topping volumes 
up to the mark.  
(iii) Glass rod: for stirring mixtures/to transfer liquid from one container/ testing for
ammonia gas
(iv) Desiccator: for keeping substances dry