Chromate

Chromate is an ion that contains one chromium atom (in its +6 oxidation state) and four oxide atoms. Its formula is CrO₄. Its overall charge is -2. Dichromate is similar, but it contains two chromium atoms and seven oxide atoms (therefore, Cr₂O₇).

Chromate

Names
Systematic IUPAC name Chromate and Dichromate
Identifiers
Properties
Chemical formula	CrO2− 4 and Cr 2O2− 7
Molar mass	115.994 g mol-1 and 215.988 g mol-1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chromate and dichromate are strongly oxidizing in acidic conditions, but weakly oxidizing in basic conditions. Chromates are generally bright yellow, while dichromates are generally orange or red. They can be made by reaction of chromium(III) oxide and a metal oxide in a basic environment. They can be destroyed by reaction with reducing agents. The oxygen in the air boosts the chromium atom's oxidation state from +3 to +6.

Chromates and dichromates are harmful when powdered because the dust is carcinogenic (it can cause cancer). This can be avoided by reducing chromate with something like iron(II) sulfate.

Examples

Chromates

• Sodium chromate
• Potassium chromate

Dichromates

• Potassium dichromate
• Ammonium dichromate

Related pages

• Chromium
• Chromium(III) oxide