Difference Between Orthophosphoric Acid and Phosphoric Acid

The name phosphoric acid is the IUPAC name of orthophosphoric acid. The prefix –ortho is used to distinguish this acid from other phosphorous containing acids (polyphosphoric acids). There is no difference between orthophosphoric acid and phosphoric acid because both these names describe the same compound.

1. Overview and Key Difference
2. What is Orthophosphoric Acid
3. What is Phosphoric Acid
4. Orthophosphoric Acid vs Phosphoric Acid
5. Summary

What is Orthophosphoric Acid?

Orthophosphoric acid is a weak mineral acid having the chemical formula H₃PO₄. It is a non-toxic acid. Furthermore, it is an important phosphorous-containing compound from which the dihydrogen phosphate ion (H₂PO₄^–) derives. Therefore, is a very important ion for plants because it is the major source of phosphorous.

Difference Between Orthophosphoric Acid and Phosphoric Acid

Figure 01: The Chemical Structure of Orthophosphoric Acid

Some chemical facts about this acid are as follows:

Chemical formula = H₃PO₄
Molar mass = 97.99 g/mol
Melting point =35 °C (anhydrous form)
Boiling point = 158 °C
Appearance = a white solid, deliquescent
Odor = odorless

Orthophosphoric acid production has two pathways such as wet process and thermal process. The wet process uses fluoroapetite (phosphate rock) for the production of this acid along with concentrated sulfuric acid. The chemical reaction is as follows:

Ca₅(PO₄)3F + 5H₂SO₄ + 10H₂O →3H₃PO₄ + 5CaSO4.2H2O + HF

In the thermal process, liquid phosphorous (P₄) and air undergo a chemical reaction inside a furnace at 1800-3000 K. Firstly, a machine sprays the phosphorus liquid into the furnace chamber. There the phosphorous burns in the air reacting with oxygen (O₂). The product from this step reacts with water in a hydration tower to produce the acid.

P_4(l)+ 5O_2(g)→2P₂O_5(g)

P₂O_5(g)+ 3H₂O_(l)→2H₃PO_4(aq)

The major application of this acid is in the production of phosphorous-containing fertilizers. There are three forms of phosphate salts which are used as fertilizers.

Triple superphosphate (TSP)
Diamonium hydrogenphosphate (DAP)
Monoammonium dihydrogenphosphate (MAP).

What is Phosphoric Acid?

Phosphoric acid is the IUPAC name of orthophosphoric acid.

There is no difference between orthophosphoric acid and phosphoric acid because both names describe the same chemical compound having the chemical formulaH₃PO₄.

Summary – Orthophosphoric Acid vs Phosphoric Acid

There is no difference between orthophosphoric acid and phosphoric acid because both these names describe the same compound. The term phosphoric acid is the IUPAC name of orthophosphoric acid.

Reference:

1. Lazonby, John. “Phosphoric Acid.” The Essential Chemical Industry Online. Available here
2. “Phosphoric Acid.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine. Available here