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Sodium chromate is the
inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a ...
with the formula Na2CrO4. It exists as a yellow hygroscopic solid, which can form tetra-, hexa-, and deca
hydrate In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...
s. 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 Calcium carbonate is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togethe ...

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. 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). Subsequent to its formation, the chromate salt is converted to
sodium dichromate Sodium dichromate is the inorganic compound with the formula Na2Cr2 O7. Usually, however, the salt is handled as its dihydrate Na2Cr2O7·2 H2O. Virtually all chromium ore is processed via conversion to sodium dichromate and virtually all compoun ...
, the precursor to most chromium compounds and materials. The industrial route to
chromium(III) oxide Chromium(III) oxide (or chromia) is an inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition ...
involves reduction of sodium chromate with
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
.


Acid-base behavior

It converts to
sodium dichromate Sodium dichromate is the inorganic compound with the formula Na2Cr2 O7. Usually, however, the salt is handled as its dihydrate Na2Cr2O7·2 H2O. Virtually all chromium ore is processed via conversion to sodium dichromate and virtually all compoun ...
when treated with acids: : 2 Na2CrO4 + 2HCl → Na2Cr2O7 + 2NaCl + H2O Further acidification affords
chromium trioxide Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the chemical formula, formula CrO3. It is the acidic oxide, acidic anhydride of chromic acid, and is sometimes marketed under the same name. Th ...

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. It is also a dyeing auxiliary in the textile industry. It is a diagnostic pharmaceutical in determining
red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...

red blood cell
volume. In organic chemistry, sodium chromate is used as an oxidant, converting primary alcohols to
carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...
s and secondary alcohols to
ketones In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo duri ...

ketones
. Louis F. Fieser4-cholesten-3,6-dione" Org. Synth. 1955, 35, 36.


See also

*
Chromate and dichromate Chromate salts contain the chromate anion, . Dichromate salts contain the dichromate anion, . They are oxyanions of chromium in the 6+ oxidation state and are moderately strong oxidizing agents. In an aqueous Solution (chemistry), solution, chr ...


Safety

As with other
Cr(VI) Hexavalent chromium (chromium(VI), Cr(VI), chromium 6) is chromium in any chemical compound that contains the element in the +6 oxidation state (thus valence (chemistry)#Common valences, hexavalent). Virtually all chromium ore is processed via hexa ...
compounds, sodium chromate is
carcinogen A carcinogen is any substance, radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide A nuclide (or nucleide, from atomic nucleus, nucleus, also known as nuclear species) is a class of atoms characte ...
ic. The compound is also and exposure may produce severe eye damage or blindness. Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.


References


Further reading

* * {{Chromates and dichromates Chromates Sodium compounds Oxidizing agents