why the colour of potassium permaganate not disappear when it is added in excess in a warm solution of ethanol?
When potassium permanganate reacts with ethanol, it releases nascent oxygen. ie, an atom of oxygen thus converting the ethanol to acetic acid. Initially colour disappears because coloured permanganate ions of potassium permanganate are consumed to oxidise ethanol.
C2H5OH (WITH ALKALINE KMnO4) CH3COOH+H2O