Areas of Use :
Phosphoric acid is produced industrially by a wet method in which 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 contains about 32-46% H, 3 PO 4 , so it is then concentrated (by water evaporation) to produce higher concentrations of phosphoric acid, commercial grade.
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 phosphoric acid 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 NaH 2 PO 4 , Na 2 HPO 4 , and Na 3 PO 4 , respectively.
At high temperatures, phosphoric acid molecules can react and combine (with loss of a 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)