Potassium dichromate
- Potassium dichromate
- Double Chromate Potassium
- Pyrochromsaures potassium
- Chromkali
- Kaliumpyrochromat
Orange-red, non-hygroscopic, triclinic boards
Fixed
- 2.68 g · cm -3 ( α - modification)
- 2.10 g · cm -3 ( β - modification)
- 397.5 ° C ( α - modification)
- 89 ° C ( β - modification)
Thermal decomposition: ~ 500 ° C
- Well in water (123 g · l-1 at 20 ° C)
- Insoluble in ethanol
Risk
Repealed as carcinogenic
- 25 mg · kg -1 ( LD50, rat, oral)
- 14 mg · kg -1 ( LD50, Rabbit, transdermal)
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Potassium dichromate K2Cr2O7, the potassium salt of dichromic unstable in free form. Other names are: potassium bichromate, potassium bichromate, potassium Pyrochromsaures, Chromkali, English: Potassium dichromate.
Historical
In 1856, the first dye was artificially produced by W. H. Perkin in the oxidation of impure aniline with potassium dichromate Mauvein (also Perkinviolett ) discovered.
Production and representation
The industrial production is performed by melting together chromite, potassium carbonate (potash ), and calcium carbonate, and oxidation by air blown. It initially formed while the yellow potassium chromate K2CrO4, which is leached out and, after addition of acid and recrystallization of potassium dichromate.
On a laboratory scale potassium can be obtained by fusing together potassium nitrate and chromium ( III) oxide.
Properties
Potassium dichromate is bright orange-red crystals without water of crystallization, which have a melting point of 397 ° C and decompose at 500 ° C under oxygen delivery to potassium chromate K2CrO4 and chromium ( III ) oxide Cr2O3.
Potassium is a strong oxidizing agent, particularly in acidic solutions. In an alkaline medium is mainly present CrO42 - the yellow chromate, which acts much less oxidizing. Potassium dichromate is soluble in water. The dichromate anion - Cr2O72 is in aqueous solution in equilibrium with HCrO4, CrO42 -. Therefore, formed with barium, lead and silver ions ( Ba2 , Pb2 , Ag ) yellow sparingly soluble chromates and not Dichromate. Many acid anions react to other anion complexes, for example, hydrochloric acid is produced in CrO3Cl - which can be crystallized as the potassium salt. Similarly react bromide and iodide, because although ( thermodynamically ) should actually take place, the oxidation of the elemental halogens, oxidation by the low reaction rate is inhibited (kinetic inhibition). The chromium in potassium dichromate in the oxidation state VI.
Use
In the laboratory, potassium dichromate is used (detection of hydrogen peroxide by blue color ) and volumetric standard because of the good storability and ponderability as common oxidant reagent. In art, it is used in leather tanning, electroforming and for the production of chromic acid. In photography and the Darkroom method of potassium dichromate is used as the light-sensitive, colloids tanning substance, especially in light print and rubber print. In the neurohistology a method for staining of individual nerves and neurons was developed by Camillo Golgi. Known as "black reaction ", so nerve cells are stained up in the finest structures by means of potassium dichromate and silver nitrate. Disposable tests for the determination of alcohol in the breath contain potassium, which is why they should be disposed of as hazardous waste.
Potassium dichromate was previously included with chemistry sets. The fabric should be brought in the original container for garbage collection problem or a waste disposal company.
Hazards
Although the material was still classified as Xi (irritant) until a few years ago, potassium is classified as very toxic, inflammable, dangerous for the environment, mutagenic, toxic for reproduction and carcinogenic today. It irritates the skin, respiratory system and eyes. Repeated skin contact sensitization occurs, it can even allergies arise.
With organic, combustible compounds, reducing agents, concentrated sulfuric acid, metals in powder form ( especially magnesium, iron) are possible violent reactions to the self- ignition or explosion. Although potassium is not flammable, but oxidizing. Disposing of potassium can be effected with iron sulfate, wherein it is reduced to Cr3 , which chromium hydroxide is precipitated as an insoluble substantially non-hazardous. Commercial Chromatvergiftungen reportable and compensable occupational diseases.