Question

The colour of $KMnO_4$ disappears when oxalic acid is added to its solution in acidic medium. This can be explained as

• A. the $pH$ of the solution changes on adding oxalic acid, hence $KMnO_4$ is decolourised
• B. $KMnO_4$ oxidises oxalic acid to $CO_2$ and itself changes to $Mn^{2+}$ ions which are colourless
• C. $KMnO_4$ is oxidised to potassium sulphate which is colourless
• D. on exposure to air the acidic solution of $KMnO_4$ becomes colourless.

Answer 1

Answer: (D)

$5 C _{2} O _{4}^{2-}+\underset{\text { (coloured) }}{2 MnO _{4}^{-}}+16 H ^{+} \longrightarrow \underset{\text { (colourless) }}{2 Mn ^{2+}}+8 H _{2} O +10 CO _{2}$