Potassium Manganate & Potassium Permanganate?

2020-07-22 4:54 pm

I have a solution of potassium manganate in water. At first it was a dark blue colour, but over time has turned to a dark purple colour. My question is, has it slowly oxidised in solution to form potassium permanganate?

回答 (1)

micatkie

2020-07-22 5:32 pm

✔ 最佳答案

The color change is due to the disproportionation (self-redox reaction) of potassium manganate in water to form deep purple potassium permanganate, but is not due to the oxidation of potassium manganite by atmospheric oxygen. The equation for the disproportionation is:
3K₂MnO₄ → KMnO₄ + 2MnO₂ + 4KOH

The colour of potassium manganate is deep green. The initial dark blue colour observed may be due to that a small amount of potassium permanganate is formed in the above disproportionation.

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