kromaattien

Kromaattien, or chromates, are a family of inorganic compounds containing the chromate anion CrO4^2-, in which chromium is in the +6 oxidation state. They are related to dichromates (Cr2O7^2-) and, depending on the pH, chromate can convert to dichromate in equilibrium. Chromates form salts with many metal cations and exhibit a characteristic yellow color in many cases.

Chromates occur in nature as minerals, such as crocoite (lead chromate, PbCrO4), and are produced industrially by precipitation from soluble chromate salts or by oxidation of chromium-containing precursors in alkaline media. Common soluble chromates include sodium chromate and potassium chromate, which are used in various chemical processes and analyses.

In terms of properties, chromates are typically colored yellow and can range from highly soluble to highly insoluble depending on the counter-cation. They are generally oxidizing agents, with Cr(VI) compounds known for their strong oxidizing power. The chromate/dichromate equilibrium is pH-dependent: under acidic conditions, chromate converts to dichromate.

Uses of chromates have included pigments, such as lead chromate in historical chrome-yellow pigments, and strontium chromate in modern pigments. They also serve in corrosion protection as components of primers and coatings, and in analytical chemistry, where chromates participate in qualitative tests (for example, forming characteristic precipitates with certain cations such as barium).

Safety and regulation are important considerations. Hexavalent chromium compounds are toxic and carcinogenic, prompting stringent controls and restrictions in many jurisdictions. Environmental concerns focus on contamination of water and soil, necessitating proper handling, containment, and disposal, along with the development of safer alternatives where possible.