sodium chromate
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 446461906
| Name = Sodium chromate
| ImageFile = Sodium-chromate.svg
| ImageName =
| ImageFile1 = Chroman sodný.JPG
| ImageName1 =
| IUPACName = Sodium chromate
| OtherNames = Chromic acid, (Na2CrO4), disodium salt
Chromium disodium oxide
Rachromate
|Section1={{Chembox Identifiers
| CASNo = 7775-11-3
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID = 22896
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 6A49BO6K4M
| PubChem = 24488
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 78671
| EINECS = 231-889-5
| RTECS = GB2955000
| UNNumber = 3288
| InChI = 1S/Cr.2Na.4O/q;2*+1;;;2*-1
| SMILES = [O-][Cr](=O)(=O)[O-].[Na+].[Na+]
}}
|Section2={{Chembox Properties
| Formula = Na2CrO4
| MolarMass = 161.97 g/mol
| Density = 2.698 g/cm3
| MeltingPtC = 792
| MeltingPt_notes = (anhydrous)
20 °C (decahydrate)
| Solubility = 31.8 g/100 mL (0 °C)
84.5 g/100 mL (25 °C)
126.7 g/100 mL (100 °C)
| Solvent1 = methanol
| Solubility1 = 0.344 g/100 mL (25 °C)
| SolubleOther = slightly soluble in ethanol
| Appearance = yellow crystals
| Odor = odorless
| MagSus = +55.0·10−6 cm3/mol
}}
|Section3={{Chembox Structure
| CrystalStruct = orthorhombic (hexagonal above 413 °C)
}}
|Section4={{Chembox Thermochemistry
| DeltaHf = −1329 kJ/mol
| DeltaGf = −1232 kJ/mol
| Entropy = 174.5 J/mol K
| HeatCapacity = 142.1 J/mol K
}}
|Section7={{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics1370.htm ICSC 1370]
| GHSPictograms = {{GHS05}}{{GHS06}}{{GHS07}}{{GHS08}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|301|312|314|317|330|334|340|350|360|372|410}}
| PPhrases = {{P-phrases|201|202|260|261|264|270|271|272|273|280|281|284|285|301+310|301+330+331|302+352|303+361+353|304+340|304+341|305+351+338|308+313|310|312|314|320|321|322|330|333+313|342+311|363|391|403+233|405|501}}
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R =
| NFPA-S = OX
| FlashPt = Non-flammable
}}
|Section8={{Chembox Related
| OtherCations = Potassium chromate
Calcium chromate
Barium chromate
| OtherAnions = Sodium dichromate
Sodium molybdate
Sodium tungstate
}}
}}
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.
Production and reactivity
It is obtained on a vast scale by roasting chromium ores in air in the presence of sodium carbonate:
:2Cr2O3 + 4 Na2CO3 + 3 O2 → 4 Na2CrO4 + 4 CO2
This process converts the chromium into a water-extractable form, leaving behind iron oxides. Typically calcium carbonate is included in the mixture to improve oxygen access and to keep silicon and aluminium impurities in an insoluble form. The process temperature is typically around 1100 °C.{{cite book |url=https://monographs.iarc.fr/ENG/Monographs/vol49/mono49-6B.pdf |title=IARC Monographs 49 Ch. 2 |isbn=9789283212492 }} For lab and small scale preparations a mixture of chromite ore, sodium hydroxide and sodium nitrate reacting at lower temperatures may be used (even 350 C in the corresponding potassium chromate system).{{cite journal |title= A new method of potassium chromate production from chromite and KOH-KNO3-H2O binary submolten salt system|author=Zhi Sun, Yi Zhang, Shi-Li Zheng, Yang Zhang |doi=10.1002/aic.11871 |volume=55 |issue = 10|journal=AIChE Journal |pages=2646–2656|year = 2009}} Subsequent to its formation, the chromate salt is converted to sodium dichromate, the precursor to most chromium compounds and materials. The industrial route to chromium(III) oxide involves reduction of sodium chromate with sulfur.
=Acid-base behavior=
It converts to sodium dichromate when treated with acids:
: 2 Na2CrO4 + 2HCl → Na2Cr2O7 + 2NaCl + H2O
Further acidification affords chromium trioxide:
:Na2CrO4 + H2SO4 → CrO3 + Na2SO4 + H2O
Uses
Aside from its central role in the production of chromium from its ores, sodium chromate is used as a corrosion inhibitor in the petroleum industry.{{Ullmann | author = Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger | title = Chromium Compounds | doi =10.1002/14356007.a07_067}} It is also a dyeing auxiliary in the textile industry. It is a diagnostic pharmaceutical in determining red blood cell volume.{{cite web |url=http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=6525 |title=chromitope sodium (Sodium Chromate, Cr 51) injection, solution |access-date=2008-06-20 |author=Bracco Diagnostics Inc. |publisher=DailyMed}}
In organic chemistry, sodium chromate is used as an oxidant, converting primary alcohols to carboxylic acids and secondary alcohols to ketones.Louis F. Fieser "Δ4-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. {{doi|10.15227/orgsyn.035.0036}} Sodium chromate is a strong oxidizer.
Safety
As with other Cr(VI) compounds, sodium chromate is carcinogenic.{{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
|archive-date = 2020-03-17
|archive-url = https://web.archive.org/web/20200317095517/https://publications.iarc.fr/_publications/media/download/3026/50ed50733f7d1152d91b30a803619022ef098d59.pdf
|url-status = dead
}} The compound is also corrosive and exposure may produce severe eye damage or blindness.{{cite web | publisher = JT Baker| title = Potassium dichromate MSDS | url = http://hazard.com/msds/mf/baker/baker/files/p5719.htm}} Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.
See also
References
{{Reflist}}
Further reading
- {{cite web |url=http://www.inchem.org/documents/icsc/icsc/eics1370.htm |title=Sodium chromate |access-date=2008-06-20 |publisher=inchem}}
- {{GESTIS|ZVG=4030|Name=Sodium chromate}}
{{Sodium compounds}}
{{Chromates and dichromates}}