Observation

Majority of the candidates responded to this question.

In part (a), majority of the candidates were not familiar with the basic concepts of    the collision theory.

In part (b), majority of the candidates did not label the axes of the graphical representation of Charles’ law correctly.
However, majority of the candidates calculated the volume of oxygen that would be required for the complete combustion of 2.5 moles of ethanol at s.t.p.

In part (c), majority of the candidates were able to define esterification and give two uses of alkanoates. However, only one product of the alkaline hydrolysis of ethyl ethanoate was given.

In part (d), this question was not satisfactorily answered by the candidates. They could not explain the plate that corrodes faster when a tin coated plate and a galvanized plate were exposed for the same length of time.

The expected answers include:

(a)        (i)         States that atoms, molecules/ions / particles / reactants involved in a chemical  
reaction must collide before reaction can take place.
(ii)        When temperature is increased/decreased the reacting molecules gain / lose
kinetic energy and move faster / slower.       
Frequency of collision and effective collision increases/decreases therefore rate of reaction increases/decreases.    

(The explanation must correspond to score)

(ii)        C2H5OH(aq) + 3O2(g) → 3H2O(l) + 2CO2(g)                     
From the equation 1 mole of ethanol requires 3 x 22.4 dm3 of oxygen

(c) (i)  Esterification is the reaction between an alkanol and alkanoic acid to produce
an alkanoate / ester (and water in the presence of a mineral acid.)    
(ii)  - used as solvents (e.g. for paints, nail, varnishes, lacquer, adhesives and  
cellulose nitrates)
-  used in perfumes/cosmetics
-  used in (artificial) flavouring for foods
-  production of soap
-   plasticizers

(iii) ethanol / C2H5OH and sodium ethanoate (CH3COONa) / potassium ethanoate(CH3COOK)                                                         
                                                                                                                          
(d)(i)  Tin – coated plate      
(ii) Zinc is more reactive than tin / higher in the electrochemical series than tin. When the tin coated plate is exposed, the plate goes into solution / corrodes. In zinc coated (galvanized) plate, it is the zinc that dissolves / corrodes hence protecting the plate better and zinc coated plate does not corrode.