Observation

The performance of majority of the candidates in this question was below average.

In part (a), majority of the candidates were able to distinguish between glucose and sucrose using a chemical test.

In part (b), majority of the candidates did not understand the chemistry of redox titration.

In part (c), majority of the candidates could not state the reasons why soda lime is preferred to sodium hydroxide in the laboratory preparation of methane.

The expected answers include:

1. Benedict’s solution / Fehling’s solution is added separately to each of the solutions and
then heated.



Orange precipitate with Benedict’s solution or brick-red precipitate with Fehlings solution indicates that the substance in glucose.

Sucrose solution forms no precipitate




OR




Add Tollene’s reagent to each of the solutions separately and warm silver mirror or black precipitate indicates the presence of glucose while no precipitate indicates sucrose.



2. 1. Iodine solution
      
      

   2. Sodium thiosulphate solution / Sodium trioxosulphur-sulphate(IV)
   
   
   3. Starch solution
   
   
   4. blue-black
   
   
   5. Colourless
   
   
3. 1. Soda lime is not deliquescent but NaOH is.
      
      

   2. Soda lime does not attack glass but NaOH does.