Question

The chemical reaction between two substances is characterised by a change in colour from orange to green. These two substances are most likely to be
(a) potassium dichromate solution and sulphur dioxide
(b) potassium permanganate solution and sulphur dioxide
(c) potassium permanganate solution and lemon juice
(d) potassium dichromate solution and carbon dioxide.

Answer 1

Answer

1.a. should be the answer.....

Answer 2

Change in colour chemical reaction:

These two substances are most likely to be (a) potassium dichromate solution and sulphur dioxide.

Explanation:

• The acidified potassium dichromate reacts with sulphur dioxide to form potassium sulphate and chromium (II) sulphate. The acid is added to initiate the reaction.

        $K_{2} C r_{2} O_{7}+H_{2} S O_{4}+3 S O_{2} \rightarrow K_{2} S O_{4}+C r_{2}\left(S O_{4}\right)_{3}+H_{2} O.$

• In potassium dichromate, the potassium ion is colourless and dichromate ion is orange in colour. This reacts with sulphur dioxide (colourless) to form chromium ion in green colour.

         $\begin{array}{c}{C r_{2} O_{7}^{2-}} \\ {(\text {orange})}\end{array} \rightarrow \begin{array}{c}{C r^{3+}} \\ {(\text {green})}\end{array}$

• In this reaction, reduction takes place with the help of sulphur dioxide (reducing agent) and oxidation takes place with help of potassium dichromate (oxidising agent). Since, both oxidation reaction and reduction reaction takes place, it is a redox reaction.