The chemical chameleon is a

redox reaction Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

, well known from classroom demonstrations, that exploits the dramatic color changes associated with the various oxidation states of

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

. Oxidation states and the Chemical Chameleon

Catholic High School Catholic schools are pre-primary, primary and secondary educational institutions administered under the aegis or in association with the Catholic Church. , the Catholic Church operates the world's largest religious, non-governmental school syste ...

Science and Maths Society Glauber reported the first description of the production of

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

when he noted that

manganese dioxide Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-cell ...

(as the mineral

pyrolusite Pyrolusite is a mineral consisting essentially of manganese dioxide ( Mn O2) and is important as an ore of manganese.. It is a black, amorphous appearing mineral, often with a granular, fibrous, or columnar structure, sometimes forming reniform ...

) could be reacted at high temperatures with

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

to obtain a material that dissolved in water to give a green solution which slowly shifted to a violet-red. This process, similar to that still used in the production of potassium permanganate,Reidies, Arno H. (2002) "Manganese Compounds" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim. oxidized

potassium manganate Potassium manganate is the inorganic compound with the formula . This green-colored salt is an intermediate in the industrial synthesis of potassium permanganate (), a common chemical. Occasionally, potassium manganate and potassium ''per''manga ...

which, acidified by

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

absorbed from the air, oxidized further to purple potassium permanganate. 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: : KMnO₄ (violet) → K₂MnO₄ (green) → MnO₂ (brown/yellow suspension) Blue

potassium hypomanganate Potassium hypomanganate is the inorganic compound with the formula . Also known as potassium manganate(V), this bright blue solid is a rare example of a salt with the hypomanganate or manganate(V) anion, where the manganese atom is in the +5 oxida ...

may also form as an intermediate. The reaction proceeds in alkaline conditions under the influence of a reducing agent.

Sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...

, and

ammonium hydroxide Ammonia solution, also known as ammonia water, ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or (inaccurately) ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although ...

can be used to alkalize the permanganate solution, while a variety of reducing agents can be used,

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...

s being common. A similar demonstration involves soaking paper in alkalized permanganate solution, which produces the same color changes as the paper is oxidized and the permanganate reduced.

References

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