Potassium permanganate (KMnO4 )Potassium permanganate (CAS 7722-64-7) reacts with most reducing organic compounds. It is more reactive (less selective) in acidic solution.
Acidic solutionA 0.1M solution of potassium permanganate (1.6g in 100mL water) is acidified by the addition of sulphuric acid (1-2M, 5mL).
Many compounds appear as yellow spots against a purple background.
Basic solutionTo 50mL of a 1% solution of potassium permanganate is added 50mL of a 2% sodium carbonate solution.
At first yellow spots appear against a purple background but soon they become brown and difficult to discern. Rinsing with water removes unreacted permanganate but leaves brown spots of manganese dioxide (MnO2 ) on a white background.