Phosphoric acid (or orthophosphoric acid) is a colorless, odorless,solid substance. It is a water soluble, hygroscopic compound and an acid of medium strength; that is, in an aqueous solution, it contains fewer hydronium ions than an aqueous solution of sulfuric acid of the same concentration. It reacts with alkalis; the salts formed during the reaction are called phosphates. It forms esters with organic compounds and is a constituent of nucleic acids.
Occurrence and production
It most commonly occurs naturally in the form of phosphorite and apatite. It is formed with the reaction of water and diphosphorus pentoxide produced by burning phosphorus.
In industry, it is used to flavor drinks and treat metals. Domestic uses include limescale and rust removal.