Question

When \[\ce{KMnO4}\] solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because ______.

Options

• \[\ce{CO2}\] is formed as the product.

• Reaction is exothermic.

• \[\ce{MnO^{-}4}\] catalyses the reaction.

• \[\ce{MnO^{2+}}\] acts as autocatalyst.

Answer 1

When \[\ce{KMnO4}\] solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because \[\ce{MnO^{2+}}\] acts as autocatalyst.

Explanation:

When \[\ce{KMnO4}\] solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because \[\ce{Mn^{2+}}\] acts as an autocatalyst.

Reduction half \[\ce{Mno^{-}4 + 8H^+ + 5e^- -> Mn^{2+} + 4H2O] × 2}\]

Oxidation half \[\ce{C2O^{2-}4 -> 2CO2 + 2e] × 5}\]

Overall equation \[\ce{2Mno^{-}4 + 16H^+ + 5C2O^{2-}4 -> 2Min^{2+} + 10CO2 + 8H2O}\]

End point of this reaction Colourless to light pink.