The overall reaction is slow and is an oxidation reaction of sucrose (white sugar) with KMnO4, in alkaline conditions. Because of the slow rate, you
see the Mn going from oxidation state VII (purple, permanganate), to VI (green, manganate) to IV (brownish, manganese dioxide). It's a nice
demonstration of the gradual nature of such an oxidation and the colours of three of the main oxidation states of Mn. In acid conditions the whole
thing would go down to Mn II (and much faster, I believe).
The oxidation product of the sucrose could be various things. With concentrated nitric acid sucrose can be oxidised to oxalic acid. With dry
permanganate it can quite violently be oxidised to CO2. So it depends rather on conditions of temperature, pH and concentration what it is that you
obtain as an oxidation product.
Pyrolusite (the mineral form of MnO2) was once also known as 'chameleon stone' because when you heat it with KOH and KNO3 it oxidises to green K2MnO4
(potassium manganate)
[Edited on 14-4-2013 by blogfast25] |