Question

3 mL of ethanol is taken in a test tube and warmed gently in a water bath. A 5% solution of alkaline potassium permanganate is added to the first drop by drop to this solution, then in excess.

1. How is a 5% solution of KMnO₄ prepared?
2. State the role of alkaline potassium permanganate in this reaction. What happens on adding it in excess?
3. Write the chemical equation of this reaction.

Answer 1

1. 5 g potassium permanganate is dissolved in 100 ml of water for preparing a 5% solution of KMnO₄.
2. Alkaline potassium permanganate is adding oxygen to alcohol and converting that to an acid. Hence, it is acting as an oxidising agent. When KMnO₄ is added, initially colour disappears because coloured permanganate ions of potassium permanganate are consumed to oxidise ethanol. When an excess of KMnO₄ is added, colour does not change because there is no more alcohol left for the reaction.
3. \[\ce{\underset{\text{Ethanol}}{C2H5OH} ->[Alkaline KMnO4 + Heat]\underset{\text{Acetic acid}}{CH3COOH}}\]