Sodium chromate

Sodium chromate
Names
	IUPAC name Sodium chromate
	Other names Chromic acid, (Na2CrO4), disodium salt; Chromium disodium oxide; Rachromate
Identifiers
CAS Number	7775-11-3 ;
3D model (JSmol)	Interactive image ;
ChEBI	CHEBI:78671 ;
ChemSpider	22896 ;
ECHA InfoCard	100.028.990
EC Number	231-889-5;
PubChem CID	24488 ;
RTECS number	GB2955000;
UNII	6A49BO6K4M ;
UN number	3288
CompTox Dashboard (EPA)	DTXSID7032056 ;
	InChI InChI=1S/Cr.2Na.4O/q;2+1;;;2-1;
	SMILES [O-][Cr](=O)(=O)[O-].[Na+].[Na+];
Properties
Chemical formula	Na2CrO4
Molar mass	161.97 g/mol
Appearance	yellow crystals
Odor	odorless
Density	2.698 g/cm3
Melting point	792 °C (1,458 °F; 1,065 K) (anhydrous) ; 20 °C (decahydrate)
Solubility in water	31.8 g/100 mL (0 °C) ; 84.5 g/100 mL (25 °C) ; 126.7 g/100 mL (100 °C)
Solubility	slightly soluble in ethanol
Solubility in methanol	0.344 g/100 mL (25 °C)
Magnetic susceptibility (χ)	+55.0·10−6 cm3/mol
Structure
Crystal structure	orthorhombic (hexagonal above 413 °C)
Thermochemistry
Heat capacity (C)	142.1 J/mol K
Std molar; entropy (S⦵298)	174.5 J/mol K
Std enthalpy of; formation (ΔfH⦵298)	−1329 kJ/mol
Gibbs free energy (ΔfG⦵)	-1232 kJ/mol
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H312, H314, H317, H330, H334, H340, H350, H360, H372, H410
Precautionary statements	P201, P202, P260, P261, P264, P270, P271, P272, P273, P280, P281, P284, P285, P301+P310, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P304+P341, P305+P351+P338, P308+P313, P310, P312, P314, P320, P321, P322, P330, P333+P313, P342+P311, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 OX
Flash point	Non-flammable
Safety data sheet (SDS)	ICSC 1370
Related compounds
Other anions	Sodium dichromate ; Sodium molybdate ; Sodium tungstate
Other cations	Potassium chromate ; Calcium chromate ; Barium chromate
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Last updated June 13, 2023

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.^[1] 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).^[2] Subsequent to its formation, the chromate salt is converted to sodium dichromate, the precursor to most chromium compounds and materials.^[3] 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.^[3] It is also a dyeing auxiliary in the textile industry.^[3] It is a diagnostic pharmaceutical in determining red blood cell volume.^[4]

In organic chemistry, sodium chromate is used as an oxidant, converting primary alcohols to carboxylic acids and secondary alcohols to ketones.^[5] Sodium chromate is a strong oxidizer.

Safety

As with other Cr(VI) compounds, sodium chromate is carcinogenic.^[6] The compound is also corrosive and exposure may produce severe eye damage or blindness.^[7] Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.

Related Research Articles

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.

<span class="mw-page-title-main">Oxidizing agent</span> Chemical compound used to oxidize another substance in a chemical reaction

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.

Chromic acid is an inorganic acid composed of the elements chromium, oxygen, and hydrogen. It is a dark, purplish red, odorless, sand-like solid powder. When dissolved in water, it is a strong acid. There are 2 types of chromic acid, they are: molecular chromic acid with the formula H^₂CrO^₄ and dichromic acid with the formula H^₂Cr^₂O^₇.

<span class="mw-page-title-main">Chromate and dichromate</span> Chromium(VI) anions

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.

<span class="mw-page-title-main">Chromite</span> Crystalline mineral

Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr₂O₄. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr₂O₄). A substitution of the element aluminium can also occur, leading to hercynite (FeAl₂O₄). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy.

<span class="mw-page-title-main">Potassium dichromate</span> Chemical compound

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 laboratories because it is not deliquescent, in contrast to the more industrially relevant salt sodium dichromate.

<span class="mw-page-title-main">Chromium trioxide</span> Chemical compound

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 and bright orange when wet. The substance dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating. Chromium trioxide is a powerful oxidiser, a mutagen, and a carcinogen.

Chromium(III) oxide is an inorganic compound with the formula Cr^₂O^₃. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.

<span class="mw-page-title-main">Potassium chromate</span> Chemical compound

Potassium chromate is the inorganic compound with the formula K₂CrO₄. This yellow solid is the potassium salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially.

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.

Chromyl chloride is an inorganic compound with the formula CrO₂Cl₂. It is a reddish brown compound that is a volatile liquid at room temperature, which is unusual for transition metal compounds.

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.

Chromium is a member of group 6, of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.

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.

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.

<span class="mw-page-title-main">Chromium(VI) oxide peroxide</span> Chemical compound

Chromium(VI) peroxide or chromium oxide peroxide is an unstable compound with the formula CrO₅. This compound contains one oxo ligand and two peroxo ligands, making a total of five oxygen atoms per chromium atom.

The Jones oxidation is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones. The reaction was an early method for the oxidation of alcohols. Its use has subsided because milder, more selective reagents have been developed, e.g. Collins reagent.

References

↑ IARC Monographs 49 Ch. 2 (PDF). ISBN 9789283212492.
↑ Zhi Sun, Yi Zhang, Shi-Li Zheng, Yang Zhang (2009). "A new method of potassium chromate production from chromite and KOH-KNO3-H2O binary submolten salt system". AIChE Journal. 55 (10): 2646–2656. doi:10.1002/aic.11871.{{cite journal}}: CS1 maint: multiple names: authors list (link)
1 2 3 Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger. "Chromium Compounds". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_067.{{cite encyclopedia}}: CS1 maint: multiple names: authors list (link)
↑ Bracco Diagnostics Inc. "chromitope sodium (Sodium Chromate, Cr 51) injection, solution". DailyMed. Retrieved 2008-06-20.
↑ Louis F. Fieser "Δ⁴-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. doi : 10.15227/orgsyn.035.0036
↑ IARC (2012) [17-24 March 2009]. Volume 100C: Arsenic, Metals, Fibres, and Dusts (PDF). Lyon: International Agency for Research on Cancer. ISBN 978-92-832-0135-9 . Retrieved 2020-01-05. 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).
↑ "Potassium dichromate MSDS". JT Baker.