Zinc chromate

Zinc chromate, sometimes known by the trade name Zinc Yellow is an inorganic compound with the chemical formula ZnCrO₄. It is a lemon-yellow solid sometimes used as a pigment.

Properties

Chemical

Like other chromates, zinc chromate is an oxidizer and may react with certain organic materials. Upon treatment with hot solutions of sodium hydroxide, the color gradually lightens to white, reflecting conversion to zinc oxide and the formation of sodium chromate in solution.

Physical

Zinc chromate most often appears as a dense, lemon-yellow powder, making it a desirable pigment. Unlike its more toxic counterpart, lead chromate, zinc chromate may degrade in color over time in bright light. Among pigments, however, it is still considered light-stable and is far less toxic than cadmium or lead yellows, making it more desirable than these.

Preparation

Zinc chromate is easily produced by the combination of a solution of sodium or potassium chromate with a solution of zinc nitrate, chloride, or another water-soluble zinc salt. The brightest yellows appear to emerge from slightly acidic solutions at elevated temperature.

Projects

• Homemade yellow paint

Handling

Safety

Zinc chromate, as with all other zinc compounds, is toxic if consumed, and can lead to zinc poisoning in the body. The hexavalent chromium in zinc chromate is also a potent oxidizer, and has been demonstrated to be carcinogenic. It is best to handle this compound with gloves, although given its insoluble nature, it is unlikely that one would incur harm from anything less than inhaling or eating it. Additionally, it is still far less toxic than other yellow pigments, such as lead chromate or cadmium sulfide.

Storage

Zinc chromate is very stable and does not require special storage considerations.

Disposal

As mentioned above, boiling sodium hydroxide solution leaches zinc chromate, producing relatively harmless zinc oxide and a solution of sodium chromate. The chromate solution can be acidified and reduced with sulfite or ascorbic acid and disposed of.