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Compounds of Mn and Cr

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Estimated time: 4 minutes
Maharashtra State Board: Class 12

Key Points: Compounds of Mn and Cr

Potassium Permanganate (KMnO₄)

Preparation:

2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O

K₂MnO₄ → KMnO₄ (by oxidation)

Chemical Properties:

Acidic medium:

  • MnO₄⁻ → Mn²⁺

Oxidises:

  • I⁻ → I₂
  • Fe²⁺ → Fe³⁺
  • S²⁻ → S
  • H₂C₂O₄ → CO₂

Neutral / Alkaline medium:

MnO₄⁻ → MnO₂

I⁻ → IO₃⁻

Potassium Dichromate (K₂Cr₂O₇)

Preparation:

  • FeCr₂O₄ → Na₂CrO₄ (fusion)
  • Na₂CrO₄ → Na₂Cr₂O₇ (acidification)
  • Na₂Cr₂O₇ → K₂Cr₂O₇ (with KCl)

Chemical Properties (Acidic medium):

  • Cr₂O₇²⁻ → Cr³⁺

Oxidises:

  • I⁻ → I₂
  • S²⁻ → S
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