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Because the manganese atom has a +7 oxidation state, the permanganate(VII) ion is a strong oxidising agent. The ion is a transition metal ion with a tetrahedral structure. [2] Permanganate solutions are purple in colour and are stable in neutral or slightly alkaline media. The exact chemical reaction depends on the carbon-containing reactants ...
For example, addition of potassium permanganate to an aqueous solution of sugar and sodium hydroxide produces the chemical chameleon reaction, which involves dramatic color changes associated with the various oxidation states of manganese. A related vigorous reaction is exploited as a fire starter in survival kits.
The chemical chameleon reaction shows the process in reverse, by reducing violet potassium permanganate first to green potassium manganate and eventually to brown manganese dioxide: [1] [2] [5] KMnO 4 (violet) → K 2 MnO 4 (green) → MnO 2 (brown/yellow suspension) Blue potassium hypomanganate may also form as an intermediate. [6]
Potassium permanganate will decompose into potassium manganate, manganese dioxide and oxygen gas: 2 KMnO 4 → K 2 MnO 4 + MnO 2 + O 2. This reaction is a laboratory method to prepare oxygen, but produces samples of potassium manganate contaminated with MnO 2. The former is soluble and the latter is not.
Permanganic acid has also been prepared through the reaction of hydrofluorosilicic acid with potassium permanganate, [4] through electrolysis, and through hydrolysis of manganese heptoxide, though the last route often results in explosions. [5] Crystalline permanganic acid has been prepared at low temperatures as the dihydrate, HMnO 4 ·2H 2 O. [3]
Dry ammonium permanganate can detonate by heat, shock, or friction, and it may explode at temperatures above 140 °F (60 °C). [1] Ammonium permanganate decomposes explosively to manganese dioxide, nitrogen, and water: [2] 2 NH 4 MnO 4 → 2 MnO 2 + N 2 + 4 H 2 O. Ammonium permanganate decomposes slowly in storage even at normal temperatures.
Sodium permanganate is the inorganic compound with the formula Na MnO 4. It is closely related to the more commonly encountered potassium permanganate, but it is generally less desirable, because it is more expensive to produce. It is mainly available as the monohydrate. This salt absorbs water from the atmosphere and has a low melting point.
Depending on the conditions in which the titration is performed, the manganese is reduced from an oxidation of +7 to +2, +4, or +6. In most cases, permanganometry is performed in a very acidic solution in which the following electrochemical reaction occurs: [3] MnO − 4 + 8 H + + 5 e − → Mn 2+ + 4 H 2 O; E° = +1.51 V [4]