Chemical chameleon

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Chemical chameleon reaction

The chemical chameleon is a redox reaction, well known from classroom demonstrations, that exploits the dramatic color changes associated with the various oxidation states of manganese. [1] [2]

Glauber reported the first description of the production of potassium permanganate when he noted that manganese dioxide (as the mineral pyrolusite) could be reacted at high temperatures with alkali to obtain a material that dissolved in water to give a green solution which slowly shifted to a violet-red. [3] This process, similar to that still used in the production of potassium permanganate, [4] oxidized manganese dioxide to potassium manganate which, acidified by carbon dioxide 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: [1] [2] [5]

KMnO4 (violet) → K2MnO4 (green) → MnO2 (brown/yellow suspension)

Blue potassium hypomanganate may also form as an intermediate. [6]

Oxidation states of manganese [7]
+7 KMnO
4 (violet)
+6 K
2MnO
4 (green)
+5 K
3MnO
4 (blue)
+4 MnO
2 (yellow)

The reaction proceeds in alkaline conditions under the influence of a reducing agent. Sodium hydroxide, potassium hydroxide, and ammonium hydroxide can be used to alkalize the permanganate solution, while a variety of reducing agents can be used, sugars being common. [1] [5] [8]

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. [9]

Related Research Articles

<span class="mw-page-title-main">Oxidizing agent</span> Chemical compound used to oxidize another substance in a chemical reaction

An oxidizing agent is a substance in a redox chemical reaction that gains or "accepts"/"receives" an electron from a reducing agent. In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide, and the halogens.

<span class="mw-page-title-main">Manganese dioxide</span> Chemical compound

Manganese dioxide is the inorganic compound with the formula MnO
2. 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 MnO
2 is for dry-cell batteries, such as the alkaline battery and the zinc–carbon battery. MnO
2 is also used as a pigment and as a precursor to other manganese compounds, such as KMnO
4. It is used as a reagent in organic synthesis, for example, for the oxidation of allylic alcohols. MnO
2 has an α-polymorph that can incorporate a variety of atoms in the "tunnels" or "channels" between the manganese oxide octahedra. There is considerable interest in α-MnO
2 as a possible cathode for lithium-ion batteries.

<span class="mw-page-title-main">Potassium permanganate</span> Chemical compound

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 MnO−
4, an intensely pink to purple solution.

<span class="mw-page-title-main">Potassium ferrate</span> Chemical compound

Potassium ferrate is the chemical compound with the formula K2FeO4. This purple salt is paramagnetic, and is a rare example of an iron(VI) compound. In most of its compounds, iron has the oxidation state +2 or +3 (Fe2+ or Fe3+). Reflecting its high oxidation state, FeO2−4 is a powerful oxidizing agent.

<span class="mw-page-title-main">Permanganate</span> Chemical compound

A permanganate is a chemical compound with the manganate(VII) ion, MnO−
4, the conjugate base of permanganic acid. 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. 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 present and the oxidant used. For example, trichloroethane (C2H3Cl3) is oxidised by permanganate ions to form carbon dioxide (CO2), manganese dioxide (MnO2), hydrogen ions (H+), and chloride ions (Cl−).

<span class="mw-page-title-main">Manganate</span> Chemical compound

In inorganic nomenclature, a manganate is any negatively charged molecular entity with manganese as the central atom. However, the name is usually used to refer to the tetraoxidomanganate(2−) anion, MnO2−
4, also known as manganate(VI) because it contains manganese in the +6 oxidation state. Manganates are the only known manganese(VI) compounds.

<span class="mw-page-title-main">Sodium manganate</span> Chemical compound

Sodium manganate is the inorganic compound with the formula Na2MnO4. This deep green solid is a rarely encountered analogue of the related salt K2MnO4. Sodium manganate is rare because it cannot be readily prepared from the oxidation of manganese dioxide and sodium hydroxide. Instead this oxidation reaction tends to stop at producing sodium hypomanganate, Na3MnO4, and even this Mn(V) salt is unstable in solution. Sodium manganate can be produced by reduction of sodium permanganate under basic conditions:

Permanganic acid (or manganic(VII) acid) is the inorganic compound with the formula HMnO4. This strong oxoacid has been isolated as its dihydrate. It is the conjugate acid of permanganate salts. It is the subject of few publications and its characterization as well as its uses are very limited.

<span class="mw-page-title-main">Potassium manganate</span> Chemical compound

Potassium manganate is the inorganic compound with the formula K2MnO4. This green-colored salt is an intermediate in the industrial synthesis of potassium permanganate, a common chemical. Occasionally, potassium manganate and potassium permanganate are confused, but each compound's properties are distinct.

Potassium hypomanganate is the inorganic compound with the formula K3MnO4. 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 oxidation state. It is an intermediate in the production of potassium permanganate and the industrially most important Mn(V) compound.

<span class="mw-page-title-main">Sodium permanganate</span> Chemical compound

Sodium permanganate is the inorganic compound with the formula NaMnO4. 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. Being about 15 times more soluble than KMnO4, sodium permanganate finds some applications where very high concentrations of MnO4− are sought.

Permanganometry is one of the techniques used in chemical quantitative analysis. It is a redox titration that involves the use of permanganates to measure the amount of analyte present in unknown chemical samples. It involves two steps, namely the titration of the analyte with potassium permanganate solution and then the standardization of potassium permanganate solution with standard sodium oxalate solution. The titration involves volumetric manipulations to prepare the analyte solutions.

<span class="mw-page-title-main">Ammonium permanganate</span> Chemical compound

Ammonium permanganate is the chemical compound NH4MnO4, or NH3·HMnO4. It is a water soluble, violet-brown or dark purple salt.

<span class="mw-page-title-main">Calcium permanganate</span> Chemical compound

Calcium permanganate is an oxidizing agent and chemical compound with the chemical formula Ca(MnO4)2. This salt consists of the metal calcium and two permanganate ions.

<span class="mw-page-title-main">Sodium bismuthate</span> Chemical compound

Sodium bismuthate is an inorganic compound, and a strong oxidiser with chemical formula NaBiO3. It is somewhat hygroscopic, but not soluble in cold water, which can be convenient since the reagent can be easily removed after the reaction. It is one of the few water insoluble sodium salts. Commercial samples may be a mixture of bismuth(V) oxide, sodium carbonate and sodium peroxide.

<span class="mw-page-title-main">Barium manganate</span> Chemical compound

Barium manganate is an inorganic compound with the formula BaMnO4. It is used as an oxidant in organic chemistry. It belongs to a class of compounds known as manganates in which the manganese resides in a +6 oxidation state. Manganate should not be confused with permanganate which contains manganese(VII). Barium manganate is a powerful oxidant, popular in organic synthesis and can be used in a wide variety of oxidation reactions.

Barium permanganate is a chemical compound, with the formula Ba(MnO4)2. It forms violet to brown crystals that are sparingly soluble in water.

<span class="mw-page-title-main">Glycerol and potassium permanganate</span>

The chemical redox reaction between potassium permanganate and glycerol is often used to demonstrate the powerful oxidizing property of potassium permanganate, especially in the presence of organic compounds such as glycerol. The exothermic (heat producing) reaction between potassium permanganate (KMnO4), a strong oxidizing agent, and glycerol (C3H5(OH)3), a readily oxidised organic substance, is an example of an experiment sometimes referred to as a "chemical volcano".

<span class="mw-page-title-main">Rubidium permanganate</span> Chemical compound

Rubidium permanganate is the permanganate salt of rubidium, with the chemical formula RbMnO
4.

<span class="mw-page-title-main">Caesium permanganate</span> Chemical compound

Caesium permanganate is the permanganate salt of caesium, with the chemical formula CsMnO4.

References

  1. 1 2 3 "Science Brothers: The Chemical Chameleon". Archived from the original on 2015-07-06. Retrieved 2014-03-20.
  2. 1 2 Oxidation states and the Chemical Chameleon Catholic High School, Petaling Jaya Science and Maths Society
  3. ↑ Weeks, M. E. and Leicester, H. M.; Discovery of the Elements, Journal of Chemical Education 1968
  4. ↑ Reidies, Arno H. (2002) "Manganese Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi : 10.1002/14356007.a16_123
  5. 1 2 "The Chemical Chameleon". Ontario Institute for Studies in Education. Archived from the original (docx) on 20 March 2014. Retrieved 20 March 2014.
  6. ↑ "Faculty of Science Perth University: Chemistry experiment – KMnO4 + NaOH + sugar". Archived from the original on 2015-03-16. Retrieved 2014-03-20.
  7. ↑ Schmidt, Max (1968). "VII. Nebengruppe". Anorganische Chemie II (in German). Wissenschaftsverlag. pp. 100–109.
  8. ↑ Chem C3000 Experiment Manual (PDF). Thames & Kosmos. p. 53. Archived from the original (PDF) on 2013-04-07. Retrieved 2014-03-20.
  9. ↑ Thompson, Robert Bruce (17 February 2012). "Lab 10.2: Oxidation States of Manganese". Illustrated Guide to Home Chemistry Experiments. ISBN   9781449331429.
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