Potassium chromate: Difference between revisions

{{chembox

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 448301546

| ImageFile = Potassium-chromate-sample.jpg

| ImageFile2 = Potassium_chromate.svg

| ImageSize2 =

| IUPACName = Potassium chromate

| OtherNames = Potassium dichromate, Chromic acid, (K2CrO4), dipotassium salt

|Section1={{Chembox Identifiers

| CASNo = 7789-00-6

| CASNo_Ref = {{cascite|correct|CAS}}

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = 5P0R38CN2X

| PubChem = 24597

| ChEBI_Ref = {{ebicite|changed|EBI}}

| ChEBI = 75249

| RTECS = GB2940000

| EINECS = 232-140-5

| SMILES = [O-][Cr](=O)(=O)[O-].[K+].[K+]

| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}

| ChemSpiderID = 22999

| InChI = K2CrO4

| InChIKey = XMXNVYPJWBTAHN-QALQIXLOAU

| StdInChI_Ref = {{stdinchicite|changed|chemspider}}

| StdInChI = 1S/Cr.2K.4O/q;2*+1;;;2*-1

| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}

| StdInChIKey = XMXNVYPJWBTAHN-UHFFFAOYSA-N

| UNNumber = 3077

|Section2={{Chembox Properties

| Cr=1 | K=2 | O=4

| Formula = {{Chem|K|2|CrO|4}}

| Appearance = Yellow powder

| Odor = odorless

| Density = 2.7320 g/cm³

| Solubility = 63.7 g/100 mL (20 °C) <br> 75.1 g/100 mL (80 °C) <br> 79.2 g/100 mL (100 °C)

| SolubleOther = insoluble in [[ethanol|alcohol]]

| MeltingPtC = 968

| BoilingPtC = 1000

| RefractIndex = 1.74

| MagSus = &minus;3.9·10⁻⁶ cm³/mol

|Section3={{Chembox Structure

| CrystalStruct = rhombic

|Section7={{Chembox Hazards

| ExternalSDS = [https://www.fishersci.com/msds?productName=AC202345000 Fisher Scientific]

| GHSPictograms = {{GHS07}}{{GHS08}}{{GHS09}}

| NFPA-H = 2

| NFPA-F = 0

| NFPA-R = 0

| NFPA-S = OX

| HPhrases = {{H-phrases|H315|H317|H319|H335|H340|H350i|H410}}

}}

|Section8={{Chembox Related

| OtherAnions = [[Potassium dichromate]]<br/>[[Potassium molybdate]]<br/>[[Potassium tungstate]]

| OtherCations = [[Sodium chromate]]<br/>[[Calcium chromate]]<br/>[[Barium chromate]]

| OtherFunction = [[Potassium hypochromate]]<br/>[[Potassium perchromate]]

| OtherFunction_label = chromates

'''Potassium chromate''' is the inorganic compound with the formula [[Potassium|K]]₂[[Chromate ion|CrO₄]]. This yellow solid is the potassium salt of the [[Chromate ion|chromate]] anion. It is a common laboratory chemical, whereas [[sodium chromate]] is important industrially.

==Structure==

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&nbsp;°C.<ref name=Ullmann>Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger, "Chromium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. {{doi|10.1002/14356007.a07_067}}</ref> These structures are complex, although the chromate ion adopts the typical tetrahedral geometry.<ref>Gaultier, M.; Pannetier, G. "Structure cristalline de la forme 'basse temperature' du sulfate de potassium K₂SO₄-beta" (Crystal structure of the "low temperature" β-form of potassium sulfate) Bulletin de la Société Chimique de France 1968, vol. 1, pp. 105-12.</ref>

<gallery mode=packed>

File:Structure of K2SO4, K2CrO4 and some related compounds.tif|Structure of β-K₂CrO₄.

File:TopView10cnK.tif|Coordination sphere of one of two types of K⁺ site.

File:SO4sphere.tif|The environment about the tetrahedral CrO₄²⁻ center in β-K₂CrO₄.

</gallery>

==Production and reactions==

It is prepared by treating [[potassium dichromate]] with [[potassium hydroxide]]:

:<chem>K2Cr2O7(aq) + 2KOH -> 2K2CrO4 + H2O</chem>

Or, the fusion of [[potassium hydroxide]] and [[chromium trioxide]]:

:<chem>2KOH + CrO3 -> K2CrO4 + H2O</chem>

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.

==Applications==

Unlike the less expensive sodium salt, potassium salt is mainly used for laboratory work in situations where an anhydrous salt is required.<ref name=Ullmann/> 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 titration]]s 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|date=November 2008}}

As with other [[Cr(VI)]] compounds, potassium chromate is [[carcinogen]]ic.<ref name="book100C">{{cite book

|author = IARC

|author-link = International Agency for Research on Cancer

|title = Volume 100C: Arsenic, Metals, Fibres, and Dusts

|orig-year = 17–24 March 2009

|url = https://publications.iarc.fr/_publications/media/download/3026/50ed50733f7d1152d91b30a803619022ef098d59.pdf

|access-date = 2020-01-05

|date = 2012

|isbn = 978-92-832-0135-9

|quote = 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)''.

|publisher = International Agency for Research on Cancer

|location = Lyon

}}</ref> The compound is also [[corrosive]] and exposure may produce severe eye damage or blindness.<ref name="MSDS">{{cite web | publisher = JT Baker| title = Potassium dichromate MSDS | url = http://hazard.com/msds/mf/baker/baker/files/p5719.htm}}</ref> Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.

{{Chromates and dichromates}}