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 ...

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

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 ...

: :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 ...

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. Fieser "Δ⁴-cholesten-3,6-dione" Org. Synth. 1955, 35, 36.

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

corrosive

and exposure may produce severe eye damage or blindness. Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.

Production and reactivity

Acid-base behavior

Uses

See also

Safety

References

Further reading