Why is KMnO4 colored

Chemical encyclopedia K

Potassium permanganate

Sum formula:

KMnO* Mr / F.W. 158.04 g / mol Other names: Potassium manganate (VII); "Over-Manganese Potash (um)"; Latin: Kalium permanganicum, Kalium hypermanganicum; Kalii permanganas (Ph.Eur.), Potassii permanganas, Permanganas kalicus; engl .: Potassium permanganate; French: Permanganate de potassium; Italian: Permanganato di Potassio
CAS no .:[7722-64-7]
EG / EINECS-No .:231-760-3
EC index no .:025-002-00-9
RID / ADR:UN 1490 5.1 / 17b
HS-No .:2841 60 10

description

The substance is a deep, dark purple, almost black, metallic-steel-blue shimmering rhombic prism, which dissolves in approx. 16 parts of water with a blue-red color. They are even more soluble in boiling water (in approx. 3.5 parts). The color of aqueous solutions is very intense; In a 20 cm thick layer, the red tint of a potassium permanganate solution diluted 1: 500,000 can still be recognized. Above 240 ° C, potassium permanganate decomposes with the release of oxygen. The density is r20 = 2.703 g / cm3. presentation

The technical extraction is based on the oxidation von Braunstein, MnO2, with atmospheric oxygen in the presence of potassium hydroxide, which initially leads to the green colored potassium manganate (VI) (liquid phase process):

MnO2 + 2 KOH + 1/2 O2   K2MnO4 + H2O

This connection is allowed by anodic oxidation (anode material: nickel or Monell metal) Potassium permanganate continue to react (this causes oxidation of the manganese+ VI to manganese+ VII):

2 K2MnO4 + 2 H.2O 2 KMnO4 + 2 KOH + H2

A laboratory-appropriate preparation method is also based on the above formulated oxidation of manganese dioxide with the formation of the intermediate product potassium manganate (VI), only in this case potassium chlorate is used as the oxygen supplier for the manganese dioxide oxidation:

3 MnO2 + 6 KOH + KClO3   3 K2MnO4 + KCl + 3H2O

And further:

3 K2MnO4 + 2 CO2 + H2O 2 KMnO4 + MnO2 x H2O + 2 K2CO3

The conversion of the components manganese dioxide, potassium hydroxide and potassium chlorate takes place by heating the mixture for a long time in a fire-proof clay or iron crucible to red heat.

To the work specification. The reverse reaction (formation of potassium manganate from potassium permanganate) can be found below.

The manufacture by oxidizing melt with chlorine or ozone as oxidizing agents is hardly of any practical importance.

The formation of permanganate through the oxidation of manganese (II) salts in acidic solution is used for analysis. The following can be used as oxidizing agents: Potassium periodate (KIO4), Lead dioxide in the presence of nitric acid and ammonium peroxodisulfate in the presence of silver nitrate as a catalyst. The variant with lead dioxide is formulated:

2 mn2+ + 5 PbO2 + 4 H.+  2 MnO4- + 5 Pb2+ + 2 H.2O

The permanganate anion can be recognized by its purple color.

Application / historyPotassium permanganate is a substance with a high oxidizing power. This property is widely used in chemistry and technology, for example in dimensional analysis (oxidimetry-permanganometry), in analysis in general (reagent) or in organic synthesis; continues to be used as a bleaching agent, disinfectant, deodorant and algicide.

If potassium permanganate is used in the form of very dilute solutions (approx. 0.02 to 0.05%) for disinfection, the compound splits off oxygen. Manganese dioxide (brownstone) is created through reduction, which, if protein (skin, mucous membrane) is present, provides a desired astringent effect. The treated areas turn brown. Such brown spots also form when they come into contact with other organic material (wood, paper, textiles, etc.).

Brownstone stains and deposits on glass utensils that have come into contact with permanganate solution can be cleaned by treating with sodium hydrogen sulfite solution to which a little dilute hydrochloric acid has been added. Manganese dioxide forms colorless and water-soluble manganese dithionate with the sulfur dioxide formed from hydrogen sulfite and hydrochloric acid:

MnO2 + 2 SUN2  MnS2O6

Sodium thiosulphate solution can also be used for this purpose, which when decomposed with hydrochloric acid also yields sulfur dioxide, but at the same time separates sulfur. This sulfur deposition is undesirable in stain removal. Formula scheme:

N / A2S.2O3 + 2 HCl 2 NaCl + S + 3 SO2+ H2O

Potassium permanganate can also develop its oxidizing effect when it is added to gastric lavage (used for poisoning with morphine and related toxins); it also destroys snake venom when injected into the bite site in a more concentrated solution (1-5%). After removing the sting, bee stings are treated by rubbing them with the solution. Another medical use is to use it as an antidote for hydrocyanic acid and cyanide poisoning (formation of potassium cyanate).1)

In photography, potassium permanganate is also used as a bleaching agent, as well as a reducer, haze remover and fixing salt destroyer. Earlier photographers used the substance as an ingredient in flash powder.2)

1)Special legal regulations and purity regulations apply to the use of chemicals as medicinal products.2)IMPORTANT NOTE:
We would like to point out that such mixtures are explosive and the regulations governing explosives apply to their production (Law on Explosive Substances, SprengG, and related ordinances in their current version).

In technology for cleaning metal surfaces (wires, profiles) and for water treatment (removal of Mn, Fe, action against algae infestation).

Reactions

a) If hydrochloric acid with a higher concentration is allowed to act on potassium permanganate, green chlorine gas is formed (caution, stinging and cough-irritating, very toxic gas). Here, too, the permanganate acts as an oxidizing agent:

2 KMnO4 + 16 HCl 2 KCl + 2 MnCl2 + 5 cl2 + 8 H.2O
Fig. Right: Production of chlorine gas from hydrochloric acid with potassium permanganate

The reaction must be carried out in a well-drawing hood or outdoors. The individual parts of the apparatus should be within easy reach. Avoid inhaling chlorine vapors.

Experimental setup: Put a good knife point of potassium permanganate into an Erlenmeyer flask (100 ml content is sufficient) and pour approx. 10 ml hydrochloric acid (25%) over the substance. Immediately close with the well-fitting pierced stopper, which carries a glass tube bent twice at right angles. Under the action of the acid, the permanganate crystals crackle and break down, releasing chlorine gas. Chlorine is heavier than air, so the glass cylinder (right) is filled with the greenish gas from bottom to top. After filling, it is closed with the glass plate; the content is available for further investigation. Excess chlorine is introduced into a test tube filled with water. This solution can also be used for the investigation.

b) Potassium permanganate = potassium manganate (VII) can be used as follows in Potassium manganate (VI) to be convicted:

In a suitable Erlenmeyer flask, carefully mix 5 g of potassium permanganate, 15 g of potassium hydroxide pellets and 25 ml of water. The batch is boiled until the solution shows a pure green color. Evaporated water is refilled in the process. After the reaction, it is cooled with ice and allowed to crystallize. The crystals formed are filtered off with suction, washed with a little 1 molar potassium hydroxide solution and finally dried over phosphorus pentoxide in a desiccator.

c) The oxidizing effect is illustrated by the following small experiment: Something is boiled Onion juice with a potassium permanganate solution. The onion odor disappears as the odorous substances have been destroyed.

Identity reactions

1. Dissolve about 50 mg of the test substance in 5 ml of water and add 1 ml of 96% ethyl alcohol. After a further addition of 0.3 ml of dilute sodium hydroxide solution (8.5% m / V), a green color appears. If the solution is heated to the boil, a dark brown precipitate forms.

2. The solution of 10 mg of the test substance in 5 ml of water and 1.5 ml of sulfuric acid (3 N) is immediately decolorized with 1 ml of dilute hydrogen peroxide solution (3%). Oxygen is formed in the process:

2 KMnO4 + 5 H.2O2 + 3 H.2SO4   2 MnSO4 + 5 O2 + 8 H.2O + K2SO4

3. Permanganates oxidize iodide to elemental iodine in acidic (e.g. sulfuric acid) solution:

MnO4- + 5 I.- + 8 H.+  

Mn2+ + 2.5 I.2 + 4 H.2O

This reaction is also used when determining the content of potassium permanganate, since the iodine which has separated out can be titrated with sodium thiosulphate standard solution.

4. The very dilute solution (1: 1000) mixed with dilute sulfuric acid is immediately discolored by a few grains of sodium sulfite or iron (II) sulfate, by oxalic acid or sodium oxalate solution when heated.

5. A sample of potassium permanganate is heated in a refractory test tube. With a crackling noise, a gas develops that ignites a smoldering wood chip: oxygen.

Determination of salaryPotassium permanganate standard solutionhazards

Labeling according to EC directives / GefStoffV:

Danger sign: O, Xn
R-phrasesR 8Fire in contact with combustible material
(Hazard warnings)R 22Harmful if swallowed
S-phrasesS 2Keep out of the reach of children
(Safety advice)
The strenght Oxidizing power of permanganates is also largely responsible for their dangers. The substance under-reacts with polyhydric alcohols such as ethylene glycol, glycerine, mannitol and the like, as well as with liquids such as triethanolamine, acetaldehyde and benzaldehyde (the list is not complete!) spontaneous inflammation. When the dry, especially the finely powdered salt is rubbed together with flammable substances (such as charcoal, sulfur, sugar, metal powder) and organic substances dangerous explosions occur. Potassium permanganate is harmful if swallowed. Symptoms of poisoning include stomach pain and vomiting. If larger amounts are ingested, this leads to severe burns which can be fatal. Potassium permanganate may not be given to minors (according to the Chemicals Prohibition Ordinance).

Reference to: Handling instructions for oxidizing substances

The substance may only be used in a permitted manner, in particular for scientific or artistic research, analysis, demonstration or training purposes. Reference is made to the legal regulations applicable to the handling of chemicals.

Water hazard class / WGK 2. Swiss poison list: Poison class 3.

References / List of sources Potassium permanganate

[1] Birett K., dealing with hazardous substances 3rd edition 1990 (ecomed Verlagsges. MbH, Landsberg) - dealing with fire-promoting solid substances

[2] British Pharmacopoeia - BP 1988 Vol. 1, p. 455f (Her Majesty's Stationery Office, London) - Monograph "Potassium Permanganate"

[3] German Pharmacopoeia 6th edition 1926, reprint 1951, p. 371 (Dt. Apotheker-Verlag, Stuttgart) - monograph "Kalium permanganicum"

[4] German Pharmacopoeia 7th edition 1968, commentary by Böhme / Hartke, list of reagents R 231, P. 220, monograph p. 931ff (WVG mbH Stuttgart, GOVI-Verlag Frankfurt)

[5] Ellmer R./Weil H., Instructions for qualitative analysis 6th edition 1973, p. 49 (Umschau Verlag, Frankfurt / M.)

[6] European Pharmacopoeia 3rd Edition 1997 - Pharmacopoea Europaea, Official German Edition, p. 1159 (DAV, Stuttgart / Govi-Verlag, Eschborn) and Supplement 1999 (reagent section)

[7] Ewald C.A./Heffter A., ​​Drug Ordinance Doctrine, 14th ed. 1911, p. 439f (Aug. Hirschwald, Berlin)

[8] Food Chemicals Codex Third edition (Fourth Printing) 1989, p. 563, 566 (National Academy Press, Washington): Reagents "Potassium Permanganate 0.1 N", "Potassium Permanganate TS"

[9] HAGER's Handbook of Pharmaceutical Practice 5th Edition Volume 8 Substances E-O, p. 657f (Springer-Verlag 1993) - monograph "Kaliumpermanganat"

[10] Hörath H., Poisonous Substances - Hazardous Substances Ordinance 3rd edition 1991, p. 204 (Wiss. Verlagsges. MbH, Stuttgart)

[11] HUNNIUS Pharmaceutical Dictionary 7th edition (Walter de Gruyter, Berlin and New York 1993)

[12] Jander G./Blasius E., textbook on analytical and preparative inorganic chemistry, 13th edition (S. Hirzel Verlag, Stuttgart 1989)

[13] Jander / Jahr / Knoll, Maßanalyse 13th edition, p. 48ff (Göschen Collection, Walter de Gruyter, Berlin 1973)

[14] Kempter G. et. al., study library: practical course on general and inorganic chemistry 2nd edition 1975, pp. 254, 255 (VEB Deutscher Verlag der Wissenschaften, Berlin)

[15] Latscha / Klein, Inorganic Chemistry - Basic Knowledge I, p. 395 (Springer-Verlag, Berlin Heidelberg New York 1978)

[16] Merck Index 11, 7643

[17] Raaf Hermann, Chemistry of Everyday Life - A Lexicon of Practical Chemistry, 28th edition, p. 144 (Herder, Freiburg i. Brsg. 1990)

[18] Ridder K./Katholing F., Hazardous Goods Ordinance Railway with RID (ecomed Verlagsges. MbH)

[19] Rojahn C.A., Regulations for the Representation of Chemical-Pharmaceutical and Phytochemical Preparations, Volume 1: Inorganic-Chemical Preparations, p. 44f (Deutscher Apotheker-Verlag, Berlin W 15, 1936)

[20] Römpp 8, 2022

[21] RÖMPP Chemielexikon Ed. Falbe / Regitz 9. Edition 1995 Volume 3 H-L, p. 2134f (G. Thieme Verlag, Stuttgart)

[22] Römpp H./Raaf H., Chemical experiments that succeed 16th ed., P. 45f, 124 (Franckh, Stuttgart 1971)

[23] Römpp H./Raaf H., Chemie des Alltags, 21st edition, pp. 11, 120, 143, 212 (Franckh, Stuttgart 1971)

[24] Willmes A., Textbook Chemical Substances, 1st edition 1990 (self-published by Dr. Willmes GmbH)

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It is expressly pointed out that numerous legal regulations and restrictions apply to the handling of hazardous substances. Chemicals may only be stored and used by persons with the required theoretical and practical expertise in compliance with all locally and nationally applicable regulations. The safety precautions, accident prevention guidelines and occupational hygiene measures that correspond to the current state of chemical science and technology must also be observed.

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