Potassium Permanganate
Formula: KMnO₄ — Potassium manganate(VII), Condy’s crystals
Appearance: Deep purple-black crystals; dissolves to vivid violet solution
Hazard: Oxidizer · Irritant · Stains skin/surfaces brown
Properties
Strong oxidizing agent. Manganese sits at its highest common oxidation state (+7) in the permanganate ion. Reacts with reducing agents through stepwise reduction: Mn⁷⁺ (purple) → Mn⁶⁺ (green, strong base only) → Mn⁴⁺ (brown MnO₂ precipitate, neutral) → Mn²⁺ (colorless, acid). The endpoint of reduction depends entirely on pH. Stains skin and most surfaces brown from MnO₂; reduces immediately with ascorbic acid solution.
Historical Context
Synthesized in 1659 by Johann Rudolf Glauber, potassium permanganate became widely used as a disinfectant and deodorizer in the 19th century under the trade name “Condy’s crystals.” Its vivid purple color and dramatic reactions with organic matter made it a mainstay of early analytical chemistry, where it was used to titrate reducing agents including oxalic acid, iron(II), and hydrogen peroxide. It remains a standard analytical reagent and is used in water treatment, wound care, and organic synthesis.
Experiments
Colors of Permanganate: Demonstrate all four Mn oxidation states in four test tubes. Acidic conditions with ascorbic acid → colorless Mn²⁺. Neutral conditions → brown MnO₂ precipitate. Alkaline conditions with NaOH + glucose → green manganate then brown. The entire redox chemistry of manganese in one session.
Chameleon Reaction: In a sealed bottle with NaOH and glucose, the solution cycles between purple, green, and brown as glucose reduces the permanganate and shaking reintroduces oxygen. Repeatable many times.
Experiments using this chemical:
- The Many Colors of Permanganate - Four oxidation states, four colors
Safety
Oxidizer — keep away from flammable materials, organic solvents, and concentrated acids.
Irritant to skin, eyes, and mucous membranes. Dilute solutions (≤0.1%) are much safer. Stains skin and surfaces brown (from MnO₂ reduction); remove stains with dilute ascorbic acid or sodium metabisulfite solution. Wash hands thoroughly after handling.
Incompatible with: Glycerin, hydrogen peroxide, and other easily oxidized organics (can ignite or react violently); concentrated sulfuric acid; reducing agents in excess