An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called an anion) typically found in aqueous solution and written with the chemical formula C₂H₃O⁻². The neutral molecules formed by the combination of the acetate ion and a positive ion (called a cation) are also commonly called "acetates" (hence, acetate of lead, acetate of aluminium, etc.). The simplest of these is hydrogen acetate (called acetic acid) with corresponding salts, esters, and the polyatomic anion CH₃CO⁻², or CH₃COO⁻.