Question

 Write the chemical equation for the preparation of 4 KMnO from 2. MnO Why does purple colour of acidified permanganate solution decolourise when it oxidises Fe^2- to Fe³⁺ ? 

Answer 1

Chemical equations for the preparation of KMnO₄ from MnO₂ 
2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O
`3MnO_4^2+4H -> 2MnO_4^-  + 2 MnO_4^- + MnO_2 + 2H_2O `

\[\ce{ MnO_2 ->[Fused with oxidised][with air or KNO3]}MnO_4^{2-}\] maganate ion 

\[\ce{ \underset{Manganate}{MnO_4^{2-}} ->[Electrolytic oxidation][in alkaline solution] MnO_4^- }\] permanganateion

Purple colour of acidified permanganate solution decolourise when it oxidises Fe2- + Fe³⁺ 
In acidic medium, Reduction

KMnO₄ is behaving as oxidising Agent.
So, purple colour of acidified 4 KMnO solutions decolourises.