Question 3
- Using a chemical test, distinguish between glucose and sucrose .
-
- Name two solutions that are used in a redox titration in which an indicator is used.
- Name the indicator normally used.
- State the colour of the indicator.
[4 marks]
- before the end point
- at the end point.
[5 marks]
[2 marks]
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:
- Benedict’s solution / Fehling’s solution is added separately to each of the solutions and then heated.
-
- Iodine solution
- Sodium thiosulphate solution / Sodium trioxosulphur-sulphate(IV)
- Starch solution
- blue-black
- Colourless
- Iodine solution
-
- Soda lime is not deliquescent but NaOH is.
- Soda lime does not attack glass but NaOH does.
- Soda lime is not deliquescent but NaOH is.
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.