Phosphoric Acid

Products

Phosphoric acid is available in pharmacies and drugstores in various concentrations.

Structure and properties

Phosphoric acid or orthophosphoric acid (H3PO4, Mr = 97.995 g/mol) exists as an aqueous to viscous, syrupy, clear, colorless, and odorless liquid that is miscible with water, depending on the concentration. Concentrated phosphoric acid can solidify to a colorless crystalline mass at a low temperature. The pharmacopoeia distinguishes between the following two concentrations:

The salts and esters of phosphoric acid are called phosphates. Phosphoric acid is a three-proton acid that dissociates as follows. The pKa1 is 2.14:

  • H3PO4 H2PO4 + H+ HPO42- + H+ PO43- + H+

The conjugated bases are called dihydrogen phosphate, hydrogen phosphate and phosphate.

Effects

Phosphoric acid has irritant, corrosive and antimicrobial properties. It plays an enormously important role in all living things, for example as a component of nucleic acids RNA and DNA, bones, for the energy carrier ATP and for signal transmission. It often exists as an ester or as a salt.

Areas of application

Phosphoric acid is used in the form of suitable preparations for the following areas of application, among others:

  • As a pharmaceutical excipient, e.g. for acidification or pH adjustment (phosphate buffer, acidity regulator).
  • For the preparation of active ingredient salts, e.g., codeine phosphate.
  • As a cleaning and decalcifying agent.
  • For chemical syntheses, as a reagent.
  • As a food additive (E 338), for example, in the Coca-Cola.

Adverse effects

Concentrated phosphoric acid is corrosive and may cause severe burns to the skin, mucous membranes and eyes. The appropriate precautions in the safety data sheet must be observed.