Usage areas of Phosphoric acid

Phosphoric acid is produced industrially by a wet method where sulfuric acid reacts with apatite (tricalcium phosphate rock).

Ca 5 (PO 4) 3 CI + 5H 2 SO 4 + 10H 2 O → 3H 3 PO 4 + 5 CaSO 4 2H 2 O + HCI

The resulting phosphoric acid solution is about 32-46% H3PO4, so it is then concentrated (by water evaporation) to produce a commercial grade of higher concentration of phosphoric acid.

Pure phosphoric acid is a white crystalline solid with a melting point of 42.35 °C. When less concentrated, it is a colorless, odorless, viscous liquid with a density of 1.885 g/mL. It is non-toxic and non-volatile. The most common concentration of H₃PO₄ is 85% in water.

Phosphoric acid has three acidic and replaceable H atoms. Thus, it reacts differently from other mineral acids. It can react with bases to form three classes of salts by replacing one, two, or three H atoms, such as NaH2PO4, Na2HPO4 and Na3PO4, respectively.

At high temperatures, H ₃PO₄ molecules can react and combine (with loss of water molecule) to form dimers, trimers, and even long polymeric chains such as polyphosphoric acids and metaphosphoric acids.

2H 3 PO 4 → lH 4 P 2 O 7 (- H 2 O)

Usage areas