- Take about 3 mL of ethanol in a test tube and warm it gently in a water bath.
- Add a 5% solution of alkaline potassium permanganate drop by drop to this solution.
- Does the colour of potassium permanganate persist when it is added initially?
- Why does the colour of potassium permanganate not disappear when excess is added?
The solution is as follows:
1. When we add potassium permanganate in alkaline medium to ethanol, it oxidises ethanol to ethanoic acid.
2. The potassium permanganate initially is of violet colour which fades away and black manganese oxide precipitates are formed.
3. The reaction is as follows:
3 CH3CH2OH (aq) + 4 KMnO4(aq) 3 CH3COOH (aq) + 4 MnO2(s) + 5 H2O (l)
(violet solution) (black)
Once all the ethanol is converted to acetic acid there is no more ethanol left for conversion and the purple colour persist due to the excess of Potassium permanganate in the solution .
1. When we add potassium permanganate in alkaline medium to ethanol, it oxidises ethanol to ethanoic acid.
2. The potassium permanganate initially is of violet colour which fades away and black manganese oxide precipitates are formed.
3. The reaction is as follows:
3 CH3CH2OH (aq) + 4 KMnO4(aq) 3 CH3COOH (aq) + 4 MnO2(s) + 5 H2O (l)
(violet solution) (black)
Once all the ethanol is converted to acetic acid there is no more ethanol left for conversion and the purple colour persist due to the excess of Potassium permanganate in the solution .