What is the Difference Between Ortho Pyro and Meta Phosphoric Acid

The key difference between ortho pyro and meta phosphoric acid is that ortho phosphoric acid contains one phosphoric acid unit, and pyro phosphoric acid contains two phosphoric acid units, whereas phosphoric acid contains more than two phosphoric acid units.

There are different forms of phosphoric acid compounds we can distinguish from each other according to the number of phosphoric acid units that they contain.

CONTENTS

1. Overview and Key Difference
2. What is Ortho Phosphoric Acid
3. What is Pyro Phosphoric Acid
4. What is Meta Phosphoric Acid
5. Ortho vs Pyro vs Meta Phosphoric Acid in Tabular Form
6. Summary – Ortho vs Pyro vs Meta Phosphoric Acid

What is Ortho Phosphoric Acid?

Orthophosphoric acid can be defined as 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–) is derived. Therefore, it is a very important ion for plants because it is the major source of phosphorous.

When considering the chemical properties of this substance, its molar mass is 97.99 g/mol, and the melting point of the anhydrous orthophosphoric acid is 35 degrees Celsius. It appears as a white solid that is deliquescent at room temperature. This compound is odorless.

Orthophosphoric acid production has two pathways as wet process and thermal process. The wet process uses fluorapatite (phosphate rock) for the production of this acid, along with concentrated sulfuric acid. In the thermal process, liquid phosphorous (P₄) and air undergo a chemical reaction inside a furnace at 1800-3000 K. First, 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.

The major application of this acid is in the production of phosphorous-containing fertilizers. There are three forms of phosphate salts that are used as fertilizers: triple phosphate, diammonium hydrogenphosphate, and monoammonium dihydrogenphosphate.

What is Pyro Phosphoric Acid?

Pyro phosphoric acid is an inorganic compound having the chemical formula H4P2O7. It is also known as diphosphoric acid because it is formed from the combination of two phosphoric acid units. This compound is colorless and odorless. Moreover, it is soluble in water and in some organic solvents such as diethyl ether and ethyl alcohol.

The anhydrous form of pyrophosphoric acid can crystalize in two polymorphic forms. The ester, anions, and salts of this substance are collectively named pyrophosphates. Moreover, the conjugate base of this compound is pyrophosphate. This compound is considered a corrosive compound.

We can prepare pyrophosphate through an ion exchange technique using sodium pyrophosphate. We can also prepare it from an alternative method which includes treating lead pyrophosphate with hydrogen sulfide. Usually, it is not produced through the dehydration of phosphoric acid.

What is Meta Phosphoric Acid?

Meta phosphoric acid is an inorganic compound having the chemical formula HPO3. It is also known as hydrogen-phosphate. It occurs as a solid compound at room temperature. Usually, this compound occurs as a cyclic structure where phosphoric acid units are bonded to each other in a ring structure. Here, the simplest metaphosphoric acid compound is trimetaphosphoric acid, which contains three phosphoric acid units are bonded in a ring structure. It has the chemical formula H3P3O9.

The conjugate bases of these metaphosphoric acid compounds are the metaphosphates. A common example of such a compound is sodium hexametaphosphate. It is useful as a sequestrant and as a food additive.

What is the Difference Between Ortho Pyro and Meta Phosphoric Acid?

Orthophosphoric acid can be defined as a weak mineral acid having the chemical formula H3PO4. Pyro phosphoric acid is an inorganic compound having the chemical formula H4P2O7. Meta phosphoric acid is an inorganic compound having the chemical formula HPO3. The key difference between ortho pyro and meta phosphoric acid is that orthophosphoric acid contains one phosphoric acid unit, and pyrophosphoric acid contains two phosphoric acid units, whereas phosphoric acid contains more than two phosphoric acid units.

The following infographic lists more differences between ortho pyro and meta phosphoric acid in tabular form for side by side comparison.

Summary – Ortho vs Pyro vs Meta Phosphoric Acid

There are different forms of phosphoric acid compounds. We can distinguish them from each other according to the number of phosphoric acid units that they contain. The key difference between ortho pyro and meta phosphoric acid is that ortho phosphoric acid contains one phosphoric acid unit, and pyro phosphoric acid contains two phosphoric acid units, whereas phosphoric acid contains more than two phosphoric acid units.

Reference:

1.“Metaphosphoric Acid.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine.

Image Courtesy:

1. “Pyrophosphoric-acid-2D” (Public Domain) via Commons Wikimedia
2. “Trimetaphosphoric-acid-3D-vdW” (Public Domain) via Commons Wikimedia