Observation

This question was popular among the candidates as most of the responded to it.

In part (a), majority of the candidates  named two gases that can be used to perform the fountain experiment, but could not state the aim of the experiment.

In part (b), some candidates wrote brand names instead of chemical industries.

In part (c), majority of the candidates named three products of the destructive distillation of coal, but could not give one use of any of the products named.

In part (d), majority of the candidates named substances responsible for hardness in water and stated advantages of hard water.

The expected answers include:

(a)        (i)         -           ammonia
                        -           hydrogen chloride
                        -           sulphur (IV) oxide
                                                                                               
            (ii)        To demonstrate high / extreme solubility of gases HCl / SO2 /NH3 in water.
                                                                                                           
            (iii)       A flask, fitted with a glass jet is filled with dry ammonia or any soluble gas 
                        Inject water through the inlet into the flask this dissolves the ammonia /                                                     soluble gas and causes a fountain through the jet.  
                                                                                                                       
                                                OR

• A round bottomed flask is filled with gas and fitted with two delivery tubes and closed by use of clips A and B
• Invert the flask into a beaker of water
• Open a clip A to allow small volume of water to enter the flask, then close it
• The gas dissolves in water causing sudden reduction of pressure in the flask
• Open clip B reduced gas pressure causes water from the beaker through delivery tube    into the flask forming fountain

(b)        (i)

            (ii)       

-           improvement in the standard of living of people
-           employment opportunities
-           development in the community
-           pollution (air, land, water, etc)
                                                                                   
(c)       

(i)        

-           coke
-           coal tar
-           coal gas
-           ammoniacal liquor                                                       

(ii)       

Coke    -           (solid) fuel / production of water gas / extraction of metals
Coal tar -          synthesis of chemicals / perfumes / dyes / paints / drugs / plastics /
Explosives / tarring of roads                                                                 

                        Coal gas -         as fuel (in homes and industries)

                        Ammoniacal liquor -     production of fertilizer  

                                                                                                    
(d)       

(i)        

-           calcium hydrogen trioxocarbonate (IV)
-           calciumtetraoxosulphate (VI)
-           magnesiumtetraoxosulphate (VI)
-           magnesium hydrogen trioxocarbonate  (IV)
-           iron (III) chloride

(ii)       

-           heating the water to boiling / distillation
-           addition of calculated amount of calcium hydroxide
-           addition of washing soda crystals
-           ion exchange resin / permutit method    

(iii)      

-           calcium ions in the water are good for children’s teeth and bones
-           it helps to reduce heart diseases  
-           does not dissolve lead pipes
-           tastes better than soft water
-           provides calcium salts used in manufacturing of food in plants
-           production of exoskeleton of animals / shells