After 8-10 students have tried, the color of the solution will suddenly change. Two colorless solutions are mixed. After a few seconds the mixture turns yellow, then green, and then finally a deep blue. Two clear solutions are mixed in a darkened room. A luminescent blue color is produced that last for several seconds.
Potassium permanganate is added dropwise to each.
The purple color persists in the alkane but fades in the alkene.