Potassium Permanganate (KMnO₄) — Properties, Uses & Safety

Overview

Potassium permanganate (KMnO4) is a powerful inorganic oxidizing agent with a molar mass of 158.03 g/mol. It appears as a striking dark purple to almost black crystalline solid that dissolves in water to produce an intensely purple solution — so deeply colored that even a few crystals can tint a large volume of water. This vivid color arises from charge transfer transitions in the permanganate ion (MnO4-), where manganese is in its +7 oxidation state, the highest common oxidation state for manganese. KMnO4 carries extensive GHS hazard codes: H272 (may intensify fire as an oxidizer), H290 (corrosive to metals), H302 (harmful if swallowed), H311 (toxic in contact with skin), H314 (causes severe skin burns), H332 (harmful if inhaled), H400 and H410 (very toxic to aquatic life). It must be handled with care, as it can ignite combustible materials on contact and stains skin brown due to the deposition of manganese dioxide (MnO2). Potassium permanganate is used in water treatment to remove iron, manganese, and hydrogen sulfide; in organic chemistry as an oxidizing agent for alkenes where Baeyer's test produces a brown color change from purple; as a disinfectant and antiseptic for skin conditions; and in survival kits for water purification and fire starting. For chemistry students, KMnO4 is an extraordinarily valuable teaching compound. Its dramatic color changes during redox reactions make oxidation state changes visible — in acidic solution, purple MnO4- (Mn7+) is reduced to nearly colorless Mn2+, while in neutral or basic solution it forms brown MnO2 (Mn4+). This makes it ideal for redox titrations, where the endpoint is self-indicating as the first persistent pink color signals excess permanganate. KMnO4 connects to lessons on oxidation states, half-reactions, balancing redox equations, titration techniques, and transition metal chemistry.

IUPAC Name

potassium permanganate

CAS Number

7722-64-7

PubChem CID

516875

Molecular Formula

KMnO₄

Molar Mass

158.034 g/mol

State at STP

solid

Appearance

Purple to black crystalline solid