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KMnO4 decomposes on heating at 513 K to form O2 along with

Redox Reactions · Class 11 · JEE Main Previous Year Question

Question

KMnO4\mathrm{KMnO_4} decomposes on heating at 513 K to form O2\mathrm{O_2} along with

Options
  1. a

    MnO2\mathrm{MnO_2} & K2O2\mathrm{K_2O_2}

  2. b

    K2MnO4\mathrm{K_2MnO_4} & Mn\mathrm{Mn}

  3. c

    Mn\mathrm{Mn} & KO2\mathrm{KO_2}

  4. d

    K2MnO4\mathrm{K_2MnO_4} & MnO2\mathrm{MnO_2}

    ✓
Correct Answerd

K2MnO4\mathrm{K_2MnO_4} & MnO2\mathrm{MnO_2}

Detailed Solution

Step 1 — Thermal decomposition of KMnO4\mathrm{KMnO_4}:

2KMnO4→513 KK2MnO4+MnO2+O2\mathrm{2KMnO_4 \xrightarrow{513\ K} K_2MnO_4 + MnO_2 + O_2}

Step 2 — Verify oxidation states:

  • Mn in KMnO4\mathrm{KMnO_4}: +7+7
  • Mn in K2MnO4\mathrm{K_2MnO_4}: +6+6 (reduced by 1)
  • Mn in MnO2\mathrm{MnO_2}: +4+4 (reduced by 3)
  • O in KMnO4\mathrm{KMnO_4}: −2-2; O in O2\mathrm{O_2}: 00 (oxidised)

This is a disproportionation-type decomposition where Mn is reduced and O is oxidised.

Step 3 — Products: K2MnO4\mathrm{K_2MnO_4} (potassium manganate, green) and MnO2\mathrm{MnO_2} (manganese dioxide, black) are formed along with O2\mathrm{O_2}.

Answer: Option (4) — K2MnO4\mathrm{K_2MnO_4} & MnO2\mathrm{MnO_2}

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