高锰酸钾Potassium permanganate

酸性溶液：MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O，E° = +1.51 V，紫色褪去。中性或弱碱性溶液：MnO₄⁻ 被还原为棕黑色的 MnO₂ 沉淀。强碱性溶液：被还原为绿色的锰酸根 MnO₄²⁻。酸化时用稀硫酸，不能用盐酸，因为 KMnO₄ 会把 Cl⁻ 氧化为 Cl₂。

In acid: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O, E° = +1.51 V, and the purple colour disappears. In neutral or weakly alkaline solution MnO₄⁻ is reduced to a brown-black precipitate of MnO₂. In strongly alkaline solution it is reduced to green manganate(VI), MnO₄²⁻. Dilute sulfuric acid is used to acidify it, not hydrochloric acid, which it would oxidise to Cl₂.

用 KMnO₄ 标准溶液滴定 Fe²⁺、H₂O₂、草酸等还原性物质时，到达终点后稍过量的一滴使溶液呈持久的浅粉红色，不需另加指示剂。例如 MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O，计量比为 1 : 5。KMnO₄ 不易得到纯品且溶液会缓慢分解，需用草酸钠等基准物标定。

When KMnO₄ is titrated against reducing agents such as Fe²⁺, H₂O₂ or ethanedioate, the first slight excess gives a permanent pale pink colour, so no indicator is needed. For example MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O, a 1 : 5 ratio. KMnO₄ is hard to obtain pure and its solutions slowly decompose, so it is standardised against a primary standard such as sodium ethanedioate.

冷的稀酸性（或碱性）KMnO₄ 使烯烃生成邻二醇，紫色褪去，可用于检验不饱和键。热的浓酸性 KMnO₄ 使碳碳双键断裂，生成酮、羧酸或 CO₂。烷基苯的侧链可被氧化为苯甲酸。

Cold dilute acidified (or alkaline) KMnO₄ converts alkenes into diols and loses its purple colour, a test for unsaturation. Hot concentrated acidified KMnO₄ cleaves C=C bonds, giving ketones, carboxylic acids or CO₂. The side chains of alkylbenzenes are oxidised to benzoic acid.

稀溶液（约 0.01%–0.1%）用于皮肤、水果和器具的消毒，以及饮用水处理中除铁、锰和异味。实验室中加热 KMnO₄ 可制取氧气：2KMnO₄ → K₂MnO₄ + MnO₂ + O₂↑。高锰酸钾是强氧化剂，与浓硫酸、甘油等有机物接触可能剧烈反应甚至起火，固体和浓溶液对皮肤有腐蚀性。

Dilute solutions (about 0.01–0.1%) are used to disinfect skin, fruit and equipment, and in drinking-water treatment to remove iron, manganese and odours. In the laboratory, heating KMnO₄ gives oxygen: 2KMnO₄ → K₂MnO₄ + MnO₂ + O₂↑. It is a strong oxidiser that can react violently or ignite with concentrated sulfuric acid or organic substances such as glycerol, and the solid and strong solutions are corrosive to skin.