Sodium chromate is a common inorganic salt formed by the ionic bonding of a metal and a chromium-containing ion. Chromates are chemical compounds that contain the chromate anion (\(\text{CrO}_4\)), a polyatomic ion composed of one chromium atom and four oxygen atoms. This yellow, crystalline substance is widely used in industrial processes, but its chemistry and handling require a clear understanding of its components and hazardous nature.
Determining the Formula for Sodium Chromate
The chemical formula for sodium chromate is \(\text{Na}_2\text{CrO}_4\). This formula is determined by the need for the compound to be electrically neutral, balancing the positive and negative charges of its constituent ions. Sodium (Na) forms a cation with a single positive charge (\(\text{Na}^+\)).
The chromate ion (\(\text{CrO}_4\)) is a polyatomic ion that carries a negative two charge (\(\text{CrO}_4^{2-}\)). To balance the \(-2\) charge, two sodium ions, each with a \(+1\) charge, are required.
This combination yields the electrically neutral formula \(\text{Na}_2\text{CrO}_4\). In this compound, the chromium atom is in the hexavalent state, meaning it has an oxidation state of \(+6\).
Characteristics and Industrial Applications
Sodium chromate typically appears as an odorless, bright yellow crystalline solid in its anhydrous form. It is highly soluble in water and can also exist in various hydrated forms, such as the decahydrate, which absorbs water from the air. The solid material possesses an orthorhombic crystalline structure.
Sodium chromate is widely used across several industries. Its primary commercial application is as a corrosion inhibitor, particularly in oil-well drilling muds and sealed water cooling systems. It forms a passive, protective layer on metal surfaces that prevents rust and degradation.
It is also used in the manufacturing of pigments for inks and paints. In the textile industry, it serves as a dyeing auxiliary, helping to fix certain dyes to wool and other fabrics. It is an important intermediate in the production of other chromium compounds, such as sodium dichromate.
Essential Safety Information
Sodium chromate must be handled with caution because it contains hexavalent chromium, or Cr(VI), which is highly toxic. The Cr(VI) form is classified as a human carcinogen, with evidence linking it to lung cancer in exposed individuals. It is also a strong irritant that can cause severe burns to the skin and eyes upon contact.
Inhalation can irritate the nose and throat, potentially leading to respiratory complications. Ingestion is toxic, causing damage to organs like the liver and kidneys. Proper handling requires the use of personal protective equipment, including gloves and eye protection, to prevent direct contact.
Due to its toxicity, strict disposal procedures are mandated to prevent environmental contamination, as it is toxic to aquatic life.