Arsenate ion (AsO₄³⁻)

Arsenate is one arsenic atom surrounded by four oxygen atoms, with a 3− charge. It is arsenic acid, H₃AsO₄, with all three of its hydrogen ions removed. Arsenates are toxic; they were once sprayed as pesticides and used to preserve wood, and arsenate is the main form of arsenic in groundwater that contains oxygen.

• Arsenic sits right below phosphorus in group 15, so arsenate imitates phosphate, which is one reason it poisons living cells.
• Arsenite, AsO₃³⁻, has one oxygen fewer and the same 3− charge, following the -ate and -ite pattern.
• Calcium arsenate, Ca₃(AsO₄)₂, was once sprayed on cotton crops to kill insect pests.

Compounds that contain arsenate

Other ions with a −3 charge