CBSE Class 12 · 2002 · Delhi · d and f Block ElementsShort Answer

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With the help of ionic equations describe what happens when:
i) the pH of a solution of dichromate ions is raised
ii) potassium manganate is electrolytically oxidised

Solution

(i) Raising the pH converts orange dichromate into yellow chromate:

C r_{2} O_{7}^{2 -} + 2O H^{-} \to 2Cr O_{4}^{2 -} + H_{2} O

(ii) In the electrolytic oxidation of K

_{2}

MnO

_{4}

, the manganate ion loses an electron at the anode and becomes permanganate:

Mn O_{4}^{2 -} anode Mn O_{4}^{-} + e^{-}

(green → purple; this is the final step of KMnO

_{4}

manufacture).

CBSE Class 12 Board · 2002 · Delhi · Subjective

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