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The d & f Block Elements — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe d & f Block Elements1 Mark
MCQ
When KMnO4 solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because
  • A
    $\text{CO}_2$is formed as the product.
  • B
    Reaction is exothermic.
  • C
    $\text{MnO}_4^-$ catalyses the reaction.
  • D
    $\text{Mn}^{2+}$acts as autocatalyst.
✓

Answer

  1. Mn2+ acts as autocatalyst.

Explanation:

When KMnO4 solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because Mn2+ acts as an autocatalyst.

Reduction half $\text{MnO}^-_4+8\text{H}^++5\text{e}^-\rightarrow\text{Mn}^{2+}+4\text{H}_2\text{O]}\times2$

Oxidation half $\text{C}_2\text{O}_4^{2-}\rightarrow2\text{CO}_2+2\text{e}^-]\times5$

Overall equation $2\text{MnO}_4^-+16\text{H}^++5\text{C}_2\text{O}_4^{2-}\rightarrow2\text{Mn}^{2+}+10\text{CO}_2+8\text{H}_2\text{O}$

End point of this reaction Colourless to light pink

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