Colours change from purple to blue, green and orange
name: Potassium permanganate is slowly reduced by glucose and comes through several oxidation states that have different colors
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The chemical chameleon experiment represents a number of red-ox reactions, which cause the solution to change color. The different colors of the solution are associated with various oxidation states of manganese.
Manganate is reduced by glucose in a few steps. Alkali acts as catalyst - the substance which does not take part in the reaction itself but speeds it up. The first step is the reduction of permanganate ion (MnO4)(Mn oxidation state +7) - to manganate ion (MnO4)2- (Mn oxidation state +6).
MnO4- + e- → (MnO4)-2
The color turns from the violet (MnO4)- to green (MnO4)-2.
Next the manganate (Mn oxidation state +6) is reduced again to manganese dioxide (Mn oxidation state +4):
(MnO4)-2 + 2H2O + 2e- → MnO2 + 4OH-
MnO2 is a brown solid substance. When it is formed its particles are small and give a yellow color to the solution.
In parallel with the reduction of potassium permanganate the oxidation of glucose takes place. In the presence of NaOH glucose (C5H11O5(CH)=O) goes to its enol form (C5H11O5(C)-OH) which is a very active redacting agent. When it is oxidized by permanganate and manganite ions it turns to gluconic acid, which is colorless. The overall equation of considered chemical reaction looks as follows:
MnO4- + 2C6H12O6 → MnO2 + 2C6H12O7