PREPARATIONS g s (3) Alkaline Potassium Permanganate. Add similarly to a second jar 1-2 ml. of very dilute aqueous potassium permanganate solution to which an equal volume of sodium carbonate solution has previously been added. On shaking as before, the purple colour of the permanganate is replaced by the green colour of potassium manganate, K 2 MnO 4 ; further reduction ultimately causes the green manganate to be replaced by a brown precipitate of manganese dioxide. Note that a partial vacuum again exists owing to the absorption of ethylene. In this reaction the ethylene is oxidised to ethylene glycol, C 2 H 4 (OH) 1 . C 4 H 4-f H 2 O + O = C 8 H 4 (OH), If a solution of potassium permanganate containing dilute sulphuric acid is used, the purple colour disappears and the solution ultimately becomes 2KMnO 4 H- 3H 2 SO 4 = K 8 SO 4 + 2MnSO 4 + 3H 2 O + sO colourless. The use of the sodium carbonate solution, and the consequent change in colour first to the green manganate and then to the brown manganese
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