Potassium permanganate is a strong oxidizing agent and when it is added to water, it dissociates into potassium ions (K+) and permanganate ions (MnO4-). The permanganate ions are responsible for the colour of the solution. The colour of the solution depends on the concentration of the potassium permanganate. When the concentration is low, the solution will be a light pink colour. As the concentration increases, the colour of the solution will change to a darker purple.

The permanganate ions are reduced by the water molecules to form manganese dioxide (MnO2) and oxygen (O2). The manganese dioxide is a brown solid that precipitates out of the solution. The oxygen gas bubbles out of the solution. The following chemical equation shows the reaction that takes place:

2KMnO4 + H2O → MnO2 + O2 + 2KOH

The reaction between potassium permanganate and water is an example of a redox reaction. A redox reaction is a chemical reaction in which there is a transfer of electrons between two or more species. In the case of the reaction between potassium permanganate and water, the potassium permanganate is reduced and the water is oxidized.