2019 Redox ReactionsTypes of Redox Reactions – Disproportionation Medium Question 13 of 30 in Redox Reactions

Which of the following reactions are disproportionation reaction? (a) $2Cu^+\rightarrow Cu^{2+}+Cu^0$ (b) $3MnO_4^{2-}+4H^+\rightarrow2MnO_4^-+MnO_2+2H_2O$ (c) $2KMnO_4\xrightarrow{\Delta}K_2MnO_4+MnO_2+O_2$ (d) $2MnO_4^-+3Mn^{2+}+2H_2O\rightarrow5MnO_2+4H^+$ Select the correct option from the following:

A (a) and (b) only
B (a), (b) and (c)
C (a), (c) and (d)
D (a) and (d) only

The answer is A.

Solution

(a) $2Cu^+\rightarrow Cu^{2+}+Cu^0$: Cu goes from +1 to +2 and 0 → disproportionation (b) $3MnO_4^{2-}+4H^+\rightarrow2MnO_4^-+MnO_2+2H_2O$: Mn goes from +6 to +7 and +4 → disproportionation (c) $2KMnO_4\rightarrow K_2MnO_4+MnO_2+O_2$: Mn is reduced (+7 → +6, +4) while O is oxidised → not disproportionation (d) $2MnO_4^-+3Mn^{2+}+2H_2O\rightarrow5MnO_2+4H^+$: Mn from +7 and +2 goes to +4 → comproportionation, not disproportionation So only (a) and (b) are disproportionation reactions.

Concept disproportionation reactions

Redox Reactions in past papers

30 questions from this chapter have appeared across 19 exam years.