What is the Difference Between Chromate and Dichromate?

The main difference between chromate and dichromate lies in their chemical structure and appearance. Chromate and dichromate are oxyanions of chromium, with chromate having the chemical formula CrO4²⁻ and dichromate having the chemical formula Cr2O7²⁻.

Key differences between chromate and dichromate include:

• Appearance: Chromate usually appears as a bright yellow substance, while dichromate appears as a bright orange color.
• Chemical Structure: Chromate has one chromate anion, whereas dichromate has two chromate anions in combination with each other.
• pH Dependence: In an aqueous solution, there is an equilibrium between chromate and dichromate. Chromate is more prevalent at high pH values (> 6.5 pH), while dichromate is more prevalent at low pH values (< 6.5 pH).

In the context of plating, chromate and dichromate often refer to the same hexavalent chromium conversion coating, and the choice between yellow chromate or yellow dichromate is more related to the color preference rather than any significant differences in their properties.

Comparative Table: Chromate vs Dichromate

Here is a table comparing the differences between chromate and dichromate:

Both chromate and dichromate are oxyanions of chromium, which means they contain chromium and oxygen atoms. They have similar chemical structures but different appearances, with chromate appearing as a bright yellow color and dichromate appearing as a bright orange color.