Names | |
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IUPAC name Potassium chromate | |
Other names Chromic acid, (K2CrO4), dipotassium salt | |
Identifiers | |
3D model (JSmol) | |
ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.029.218 |
EC Number |
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PubChem CID | |
RTECS number |
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UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
K 2CrO 4 | |
Molar mass | 194.189 g·mol−1 |
Appearance | Yellow powder |
Odor | odorless |
Density | 2.7320 g/cm3 |
Melting point | 968 °C (1,774 °F; 1,241 K) |
Boiling point | 1,000 °C (1,830 °F; 1,270 K) |
62.9 g/100 mL (20 °C) 75.1 g/100 mL (80 °C) 79.2 g/100 mL (100 °C) | |
Solubility | insoluble in alcohol |
−3.9·10−6 cm3/mol | |
Refractive index (nD) | 1.74 |
Structure | |
rhombic | |
Hazards | |
GHS labelling: | |
H315, H317, H319, H335, H340, H350i, H410 | |
NFPA 704 (fire diamond) | |
Safety data sheet (SDS) | Chemical Safety Data |
Related compounds | |
Other anions | Potassium dichromate Potassium molybdate Potassium tungstate |
Other cations | Sodium chromate Calcium chromate Barium chromate |
Related chromates | Potassium hypochromate Potassium perchromate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Potassium chromate is the inorganic compound with the formula K 2 CrO4. This yellow solid is the potassium salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially.
Two crystalline forms are known, both being very similar to the corresponding potassium sulfate. Orthorhombic β-K2CrO4 is the common form, but it converts to an α-form above 66 °C. [1] These structures are complex, although the chromate ion adopts the typical tetrahedral geometry. [2]
It is prepared by treating potassium dichromate with potassium hydroxide:
Or, the fusion of potassium hydroxide and chromium trioxide:
In solution, the behavior of potassium and sodium dichromates are very similar. When treated with lead(II) nitrate, it gives an orange-yellow precipitate, lead(II) chromate.
Unlike the less expensive sodium salt, potassium salt is mainly used for laboratory work in situations where an anhydrous salt is required. [1] It is as an oxidizing agent in organic synthesis. It is used in qualitative inorganic analysis, e.g. as a colorimetric test for silver ion. It is also used as an indicator in precipitation titrations with silver nitrate and sodium chloride (they can be used as standard as well as titrant for each other) as potassium chromate turns red in the presence of excess of silver ions.
Tarapacaite is the natural, mineral form of potassium chromate. It occurs very rarely and until now is known from only few localities on Atacama Desert.[ citation needed ]
As with other Cr(VI) compounds, potassium chromate is carcinogenic. [3] The compound is also corrosive and exposure may produce severe eye damage or blindness. [4] Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively charged sodium ions and negatively charged chloride ions.
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.
Chromate salts contain the chromate anion, CrO2−
4. Dichromate salts contain the dichromate anion, Cr
2O2−
7. They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.
Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health. It is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in the laboratory because it is not deliquescent, in contrast to the more industrially relevant salt sodium dichromate.
Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid under anhydrous conditions, bright orange when wet and which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating. Chromium trioxide is a powerful oxidiser and a carcinogen.
Sodium dichromate is the inorganic compound with the formula Na2Cr2O7. However, the salt is usually handled as its dihydrate Na2Cr2O7·2H2O. Virtually all chromium ore is processed via conversion to sodium dichromate and virtually all compounds and materials based on chromium are prepared from this salt. In terms of reactivity and appearance, sodium dichromate and potassium dichromate are very similar. The sodium salt is, however, around twenty times more soluble in water than the potassium salt (49 g/L at 0 °C) and its equivalent weight is also lower, which is often desirable.
Chromate conversion coating or alodine coating is a type of conversion coating used to passivate steel, aluminium, zinc, cadmium, copper, silver, titanium, magnesium, and tin alloys. The coating serves as a corrosion inhibitor, as a primer to improve the adherence of paints and adhesives, as a decorative finish, or to preserve electrical conductivity. It also provides some resistance to abrasion and light chemical attack on soft metals.
Silver chromate is an inorganic compound with formula Ag2CrO4 which appears as distinctively coloured brown-red crystals. The compound is insoluble and its precipitation is indicative of the reaction between soluble chromate and silver precursor salts (commonly potassium/sodium chromate with silver nitrate). This reaction is important for two uses in the laboratory: in analytical chemistry it constitutes the basis for the Mohr method of argentometry, whereas in neuroscience it is used in the Golgi method of staining neurons for microscopy.
Caesium chromate or cesium chromate is an inorganic compound with the formula Cs2CrO4. It is a yellow crystalline solid that is the caesium salt of chromic acid, and it crystallises in the orthorhombic system.
Lead(II) chromate is the inorganic compound with the formula (PbCrO4). It has a vivid yellow color and is generally insoluble. Two polymorphs of lead chromate are known, orthorhombic and the more stable monoclinic form. Monoclinic lead chromate is used in paints under the name chrome yellow. It occurs also as the mineral crocoite.
Ammonium dichromate is an inorganic compound with the formula (NH4)2Cr2O7. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium. It is a salt consisting of ammonium ions and dichromate ions.
Barium chromate, named barium tetraoxochromate(VI) by the IUPAC, is a yellow sand like powder with the formula BaCrO4. It is a known oxidizing agent and produces a green flame when heated, a result of the barium ions.
Potassium chlorochromate is an inorganic compound with the formula KCrO3Cl. It is the potassium salt of chlorochromate, [CrO3Cl]−. It is a water-soluble orange compound is used occasionally for oxidation of organic compounds. It is sometimes called Péligot's salt, in recognition of its discoverer Eugène-Melchior Péligot.
Chromium(III) sulfate usually refers to the inorganic compounds with the formula Cr2(SO4)3.x(H2O), where x can range from 0 to 18. Additionally, ill-defined but commercially important "basic chromium sulfates" are known. These salts are usually either violet or green solids that are soluble in water. It is commonly used in tanning leather.
Barium ferrate is the chemical compound of formula BaFeO4. This is a rare compound containing iron in the +6 oxidation state. The ferrate(VI) ion has two unpaired electrons, making it paramagnetic. It is isostructural with BaSO4, and contains the tetrahedral [FeO4]2− anion.
Calcium chromate is an inorganic compound with the formula CaCrO4, i.e. the chromate salt of calcium. It is a bright yellow solid which is normally found in the dihydrate form CaCrO4·2H2O. A very rare anhydrous mineral form exists in nature, which is known as chromatite.
Sodium chromate is the inorganic compound with the formula Na2CrO4. It exists as a yellow hygroscopic solid, which can form tetra-, hexa-, and decahydrates. It is an intermediate in the extraction of chromium from its ores.
Potassium hypochromate is a chemical compound with the formula K3CrO4 with the unusual Cr5+ ion. This compound is unstable in water but stable in alkaline solution and was found to have a similar crystal structure to potassium hypomanganate.
There is sufficient evidence in humans for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds cause cancer of the lung. Also positive associations have been observed between exposure to Chromium (VI) compounds and cancer of the nose and nasal sinuses. There is sufficient evidence in experimental animals for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds are carcinogenic to humans (Group 1).