Pyrophosphoric acid, also known under the name diphosphoric acid, is a syrupy liquid or a needle-like crystaline solid. Pyrophosphoric acid is colorless, odorless, hygroscopic and is soluble in water, diethyl ether, and ethyl alcohol. It is the anhydride of phosphoric acid and is produced from phosphoric acid by dehydration. Pyrophosphoric acid is a medium strong inorganic acid. The anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. Pyrophosphoric acid slowly hydrolyzes in the presence of water into phosphoric acid.
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