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Phosphoric Acid

Other Names:

Orthophosphoric acid

General Information:


CAS Number: 7664-38-2

Molecular Weight: 97.99 g/mol

Appearance: Colorless, viscous liquid (85% aq)

Boiling Point: 158 C (85% aq)

Density: 1.685 g/mL (85% aq)

The most common form of phosphoric acid (H3PO4) is the 85% aqueous form. Pure anhydrous phosphoric acid is a white solid with a melting point of 42 C. Phosphoric acid has three pKa values covering a wide range (pKa's: 2.15, 7.20, 12.32). This is the reason why phosphoric acid solutions make a great choice as a buffer.


Phosphoric is a relatively weak acid, but still corrosive. It is relatively non-toxic, especially in its dilute form. Phosphoric acid is afterall used in food products such as soft drinks.


1) Wikipedia: Phosphoric acid (link)

2) Phosphoric acid solution (link)