NationMaster - Encyclopedia: Potassium dichromate

Potassium dichromate, K₂Cr₂O₇, is a common inorganic chemical reagent, most commonly used as an oxidising agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is potentially harmful to health and must be handled and disposed of appropriately. It is a crystalline ionic solid with a bright, red-orange colour. Solubility is a chemical property referring to the ability for a given substance, the solute, to dissolve in a solvent. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, the triclinic crystal system is one of the 7 lattice point groups. ... The coordination geometry of an atom is the geometrical pattern formed by its neighbors in a molecule or a crystal. ... A tetrahedron (plural: tetrahedra) is a polyhedron composed of four triangular faces, three of which meet at each vertex. ... The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 atmosphere... In chemistry, the standard molar entropy is the entropy content of one mole of substance, under conditions of standard temperature and pressure. ... The examples and perspective in this article or section may not represent a worldwide view. ... R-phrases are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations. ... S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. ... For other uses, see Flash point (disambiguation). ... This article is about the electrically charged particle. ... Potassium Chromate is a yellow chemical indicator used for Identifying concentrations of Chloride ions in a salt solution with Silver nitrate. ... This article is about the electrically charged particle. ... Ammonium dichromate, (NH4)2Cr2O7, sometimes known as Vesuvian Fire, is a chemical compound that was used as an oxidizer in early photography and pyrotechnics, and in the formation of tabletop volcanoes. Ammonium dichromate forms orange crystals, and is toxic and corrosive. ... Sodium dichromate is a chemical, formula Na2Cr2O7. ... Potassium permanganate is the chemical compound KMnO4. ... The plimsoll symbol as used in shipping In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals exactly). ... Traditionally, inorganic compounds are considered to be of mineral, not biological, origin. ... An oxidizing agent is a substance that oxidizes another substance in electrochemistry or redox chemical reactions in general. ... A Hexavalent chromium compound: Chromium(VI)-oxide Hexavalent chromium or Cr(VI) compounds are those which contain the element chromium in the +6 oxidation state. ...

Chemistry

In organic chemistry, potassium dichromate is a mild oxidizer compared with potassium permanganate. It is used to oxidise alcohols. It converts primary alcohols into aldehydes, or into carboxylic acids if heated under reflux. In contrast, with permanganate, carboxylic acids are the sole products. Secondary alcohols are converted into ketones — no further oxidation possible. For example, menthone may be prepared by oxidation of menthol with acidified dichromate.^[1] Potassium permanganate is the chemical compound KMnO4. ... Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. ... This article does not cite any references or sources. ... Diagram of typical reflux apparatus. ... l-Menthone Menthone is a naturally occurring organic compound with a molecular formula C10H18O. l-Menthone (or (5R, 2S)-trans-5-methyl-2-(l-methylethyl)cyclohexanone), shown at right, is the most abundant in nature of the four possible stereoisomers. ... Menthol is a covalent organic compound made synthetically or obtained from peppermint or other mint oils. ...

Tertiary alcohols are not able to be oxidized to give a carbonyl group. In chemistry, a carbonyl group is a functional group composed of an atom of carbon double-bonded to an atom of oxygen. ...

In an aqueous solution the colour change exhibited can be used to test whether an aldehyde or ketone is present. When an aldehyde is present the chromium ions will be reduced from the +6 to the +3 oxidation state, changing colour from orange to green. This is because the aldehyde can be further oxidised to the corresponding carboxylic acid. A ketone will show no such change because it cannot be oxidised further, and so the solution will remain orange. In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. ...

Uses

Cleaning

Like other chromium(VI) compounds (chromium trioxide, sodium dichromate), potassium dichromate may be used to prepare "chromic acid", which can be used for cleaning glassware and etching materials. In chemistry, chromic acid (or Jones reagent) is a chromium (Cr) compound, yet to be isolated, that would have the formula H2CrO4. ... Sodium dichromate is a chemical, formula Na2Cr2O7. ... In chemistry, chromic acid is a chromium (Cr) compound, yet to be isolated, with the formula H2CrO4. ...

Construction

It is used as an ingredient in cement in which it retards the setting of the mixture and improves its density and texture. This usage commonly causes contact dermatitis in construction workers.^[2] For other uses, see Cement (disambiguation). ... Contact dermatitis is a term for a skin reaction resulting from exposure to allergens or irritants. ... Two construction workers at work. ...

Ethanol determination

The concentration of ethanol in a sample can be determined by back titration with acidified potassium dichromate. Reacting the sample with an excess of potassium dichromate, all ethanol is oxidized to acetic acid: Back titration is an analytical chemistry technique which allows the user to find the concentration of a reactant of unknown concentration by reacting it with an excess volume of another reactant of known concentration. ... R-phrases , S-phrases , , , Flash point 43 Â°C Related Compounds Related carboxylic; acids Formic acid; Propionic acid; Butyric acid Related compounds acetamide; ethyl acetate; acetyl chloride; acetic anhydride; acetonitrile; acetaldehyde; ethanol; thioacetic acid; acetylcholine; acetylcholinesterase Supplementary data page Structure and properties n, Îµr, etc. ...

The excess dichromate is determined by titration against sodium thiosulfate. Subtracting the amount of excess dichromate from the initial amount, gives the amount of ethanol present. Accuracy can be improved by calibrating the dichromate solution against a blank. R-phrases R35 S-phrases Flash point Non flammable Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Sodium thiosulfate (Na2S2O3) (sometimes spelled thiosulphate) is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3... Chromates and Dichromates are salts of chromic acid. ...

One major application for this reaction is in old police breathalyzer tests. When alcohol vapor makes contact with the yellow dichromate-coated crystals, the color changes from yellow to green.The degree of the color change is directly related to the level of alcohol in the suspect's breath. A reaction is the following: In physics, a reaction (physics) is defined by Newtons third law: For every action there is an equal and opposite reaction. The idea that any given force has a pair or opposite force. ... Kevin is the best person in the world [Image:Breathalyzer. ... Color is an important part of the visual arts. ...

Homeopathic uses

Potassium dichromate is used in the homeopathic preparation of Kali (or Kalium) bichromicum, although little may remain in the final dilution.^[3] One notable homeopathic product that contains it as the active ingredient is HeadOn,^[4] in which the potassium dichromate is diluted to one part per million. Homeopathic remedy Rhus toxicodendron, derived from poison ivy. ... Head On TV commercial screenshot HeadOn is a topical product intended for headache relief, produced by Miralus Healthcare, which claims it is a homeopathic remedy. ... The parts-per notations are used to denote low concentrations of chemical elements. ...

Leather

It is used to tan leather which is used for footwear.^[5] This article is about making hides into leather. ... High-heeled shoe Footwear consists of garments worn on the feet. ...

Photography

Potassium dichromate has important uses in photography and in photographic screen printing, where it is used as an oxidizing agent together with a strong mineral acid. Photography [fÓ™tÉ‘grÓ™fi:],[foÊŠtÉ‘grÓ™fi:] is the process of recording pictures by means of capturing light on a light-sensitive medium, such as a film or electronic sensor. ... Silkscreen redirects here. ...

Gum bichromate printing was one of the very first stable photographic printing processes, dating back to about 1850. A solution of gum arabic and potassium dichromate, once applied to paper and dried, will harden when exposed to ultraviolet light. Gum bichromate is a 19th century photographic printing process based on the light sensitivity of dichromates. ... Acacia senegal plant from Koehlers Medicinal-Plants 1887 Gum arabic, a natural gum also called gum acacia, is a substance that is taken from two sub-Saharan species of the acacia tree, Acacia senegal and Acacia seyal. ...

Chromium intensification uses potassium dichromate together with equal parts of concentrated hydrochloric acid diluted down to approximately 10% v/v to treat weak and thin negatives of black and white photograph roll. This solution reconverts the elemental silver particles in the film to silver chloride. After thorough washing and exposure to actinic light, the film can be redeveloped to its end-point yielding a stronger negative which is able to produce a more satisfactory print. Hydrochloric acid is the aqueous solution of hydrogen chloride gas (HCl). ... Related Compounds Other anions silver(I) fluoride, silver bromide, silver iodide Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Silver chloride is a chemical compound with the chemical formula AgCl. ... Actinism is a property of radiation (particularly solar radiation) that leads to the production of photochemical effects. ...

A potassium dichromate solution in sulfuric acid can be used to produce a reversal negative (i.e,. a positive transparency from a negative film). This is effected by developing a black and white film but allowing the development to proceed more or less to the end point. The development is then stopped by copious washing and the film then treated in the acid dichromate solution. This converts the silver metal to silver sulfate, a compound that is insensitive to light. After thorough washing and exposure to actinic light, the film is developed again allowing the previously unexposed silver halide to be reduced to silver metal. Sulfuric acid, (also known as sulphuric acid) H2SO4, is a strong mineral acid. ... This article is about the chemical element. ... Silver sulfate (Ag2SO4) is an ionic compound used in anions experiments, silver plating and as a non-staining substitute to silver nitrate. ...

The results obtained can be unpredictable, but sometimes excellent results are obtained producing images that would otherwise be unobtainable. This process can be coupled with solarisation so that the end product resembles a negative and is suitable for printing in the normal way. Solarisation is a phenomenon in photography in which the image recorded on a negative or on a photographic print is wholly or partially reversed in tone. ...

Cr^VI compounds have the property of tanning animal proteins when exposed to strong light. This quality is used in photographic screen printing. In screen printing a fine screen of bolting silk of similar material that is required to be printed is then taped securely onto the surface of the screen and the whole thing exposed to strong light for a period - typically about half an hour in bright sunlight. When the design is removed, the gelatine on the screen is washed off with hot water. All the gelatine exposed to sun-light will have been hardened by the dichromate and will be retained on the screen leaving a precise mask of the required design which can be printed in the usual way. This article is about making hides into leather. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Silkscreen redirects here. ...

Wood treatment

Potassium dichromate is used to finish certain types of wood. It brings out the color and grain to a very deep, rich appearance. This is particularly effective on mahogany.^[6] This article is about the timber. ...

Safety

Potassium dichromate is one of the most common causes of chromium dermatitis^[7]; chromium is highly likely to induce sensitization leading to dermatitis, especially of the hand and fore-arms, which is chronic and difficult to treat. It is also toxic, with doses of approximately 100 mg/kg being fatal in rabbits and rodents.^[8] Dermatitis is a blanket term literally meaning inflammation of the skin. It is usually used to refer to eczema, which is also known as Dermatitis eczema. ...

As with other Cr^VI compounds, potassium dichromate is carcinogenic and should be handled with gloves and appropriate health and safety protection. The compound is also corrosive and exposure may produce severe eye damage or blindness.^[9] Look up carcinogen in Wiktionary, the free dictionary. ... Corrosion is the destructive reaction of a metal with another material, e. ...

Sulphur dioxide

Potassium dichromate(VI) paper can be used to test for sulphur dioxide, as it turns distinctively from orange to green. Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ...

References

^ L. T. Sandborn. "l-Menthone". Org. Synth.; Coll. Vol. 1: 340.
^ Pekka Roto, Hannele Sainio, Timo Reunala, Pekka Laippala (January 1996), "Addition of ferrous sulfate to cement and risk of chromium dermatitis among construction workers", Contact Dermatitis, <http://www.blackwell-synergy.com/doi/abs/10.1111/j.1600-0536.1996.tb02111.x>
^ Constantine Hering. The Guiding Symptoms of Our Materia Medica. B.Jain, 312. ISBN 8170214378.
^ Jamie Sotonoff (21 Dec 2006), Intriguing infomercials beg the question: Does it work?, Daily Herald, <http://goliath.ecnext.com/coms2/summary_0199-6100693_ITM>
^ M. Saha, C. R. Srinivas, S. D. Shenoy, C. Balachandran (May 1993), "Footwear dermatitis", Contact Dermatitis, <http://www.blackwell-synergy.com/doi/abs/10.1111/j.1600-0536.1993.tb03428.x>
^ Woodworking: Contemporary Headboard. DIY Network. Retrieved on 2008-01-28.
^ Farokh J. Master (2003). Diseases of Skin, 223. ISBN 8170211360.
^ Safety data for potassium dichromate HSci project
^ Potassium dichromate MSDS. ScienceLab.com. Retrieved on 2008-01-28.

Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 28th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 28th day of the year in the Gregorian calendar. ...

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