Chapter 21: Sulphuric acid and Sulphur dioxide

All the following "answers" are for your reference only!

The "best" answers are based on your actual experimental results!

 

Experiment 21.1: To prepare a small amount of sulphur dioxide by burning sulphur

3.   Blue.

5.   The paper changed from orange to green (then white).

6.   It changes to red then white.

 

Experiment 21.2: The bleaching action of sulphur dioxide

1.   The colour on the petals fades.

The petals become colourless.

A white precipitate is formed.

Sulphate ion. Aqueous sulphur dioxide / sulphite solution is oxidized to sulphate ion.

2.   The colour becomes red then fades.

The pH paper becomes colourless.

A white precipitate is formed.

Sulphate ion. Aqueous sulphur dioxide / sulphite solution is oxidized to sulphate ion.

3.   SO₂(g) + H₂O(l) ¾® H₂SO₃(aq)

H₂SO₃(aq) D 2H⁺(aq) + SO₃^2-(aq)

4.   SO₃^2-(aq) + dye with O ¾® SO₄^2-(aq) + dye without O

 

Experiment 21.3: Reducing properties of sulphur dioxide and sulphite ions

1.   Orange.

Colourless.

Bromine is reduced to bromide which is colourless.

2Br^-(aq) ¾® Br₂(g) + 2e^-

2.   Orange.

Green.

The orange dichromate ion is reduced to chromium(III) ion which is green.

14H⁺(aq) + Cr₂O₇^2-(aq) + 6e^- ¾® 2Cr³⁺(aq) + 7H₂O(l)