Observation

This is a compulsory question. The performance of candidates in this question was fair.

In part (a), majority of the candidates arranged the three states of matter in order of decreasing kinetic energy and force of cohesion.

 

In part (b), majority of the candidates could not state how electrolysis affects the pH of electrolysis using each of the following substances as electrode:

(i)   copper;
(ii)  carbon.

 

In part (c), only few candidates could state the change in oxidation number of magnesium and hydrogen.

 

In part (d), majority of the candidates stated the differences between boiling and evaporation.

 

In part (e), majority of the candidates could not state the significance of the equilibrium constant K.

 

In part (f), majority of the candidates could not give the IUPAC name of the compounds.

 

In part (g), majority of the candidates could not give the reason why organic compounds are classified on the basis of functional groups.

 

In part (h), majority of the candidates could not state the differences between the solubility of solids in liquids and gases in liquids.

 

In part (i), a good number of the candidates could write a balanced chemical equation for the reaction between fluorine and water.

 

In part (j), majority of the candidates defined the term basicity of an acid.

 

The expected answers include:

(a)

(i)  gas > liquid > solid  / gas, liquid, solid

(ii)  solid > liquid > gas  / solid, liquid, gas                                                               

(b) Cancelled

                                                                                                                       
(c) (i) (I)        0 to +2             
(II)       +1 to 0

             

(ii)(I)   Magnesium / Mg          
(II)   Hydrogen / H⁺ / HCl

 

(iii)  Hydrochloric acid / HCl
                                                                                                           
(d) (i)        

Evaporation	Boiling
-   occurs on the surface of   Liquid	-  occurs at the entire length of Liquid
-  occurs slowly	-  occurs rapidly
-  occurs at any temperature	-  occurs at specific temperature
-  produces cooling	-  does not produce cooling
-  occurs using internal energy/is    Spontaneous	-  requires an external source of Heat / not spontaneous
- bubbles are not seen	- bubbles are seen

                                                                       
(ii) The temperature required to boil the water decreases / boils at temperature lower than 100⁰ C    
                                                                                                                       
(e) The equilibrium constant k,  indicates the extent to which a reaction will proceed / it gives an idea of where the equilibrium lies / when k is large, more of the products are formed / when k is small, less of the products are formed.

(f)  C₃H₇COOH: butanoic acid                  
(CH₃)₃COH:   2 – methyl propan-2-ol   
                                                                                                           
(g) Functional groups are atoms or groups of atoms that are responsible for particular chemical properties and reactions of organic compounds.
                                                                                                           
(h)       

Solids in liquids	Gases in liquid
-  solubility increases with temperature	-   solubility decreases as temperature increases
- it is not affected by change in pressure / does not have any significant effect	-   is greatly affected by pressure, increases with increase in pressure
-  increasing and decreasing of pH affects the solubility	-  pH does not affect them
-  depends on the nature of solute and solvent	-  depends on nature of gas and solvent

                                   

(i)         2F_{2 (g)} + 2H₂O _(l) → 4HF _(aq) + O_{2 (g)}

 

(j) is the number of replaceable hydrogen ions in a molecule of an acid / number of ionisable hydrogen atoms in one molecule of acid.