What is the Difference Between Orthophosphate and Polyphosphate

The key difference between orthophosphate and polyphosphate is that orthophosphate contains only one phosphate unit, whereas polyphosphate contains several phosphate units.

Orthophosphate and polyphosphate are inorganic salt compounds. We can distinguish these two compounds from their chemical structure: depending on the number of phosphate units in the chemical structure.

CONTENTS

1. Overview and Key Difference
2. What is Orthophosphate 
3. What is Polyphosphate
4. Orthophosphate vs Polyphosphate Acid in Tabular Form
5. Summary – Orthophosphate vs Polyphosphate 

What is Orthophosphate?

The term orthophosphate can be defined as any salt or ester of orthophosphoric acid. When H+ ions are lost from orthophosphoric acid, an orthophosphate anion is formed. The chemical formula of orthophosphate anion is –PO₄^-3 , and its molar mass is 94.97 g/mol.

We generally name this anion as phosphate anion because orthophosphate is the simplest among the members of the phosphate series. Moreover, we can call it monophosphate because it consists of one phosphate unit. Other members of the phosphate series have two or more phosphate units.

When considering the applications of orthophosphate, it is a common corrosion inhibitor that is useful for water suppliers in order to prevent the lead pipes from leaching.

What is Polyphosphate?

The term polyphosphate is used for salts or esters of polymeric oxyanions that are formed from tetrahedral phosphate structural units. These structural units are linked together via sharing oxygen atoms. Usually, these salt compounds tend to adopt a linear or a cyclic ring structure.

Two common polyphosphate compounds include ADP and ATP. These compounds are important in energy storage. There are various different polyphosphates that have different applications in mineral sequestration in municipal waters. Moreover, polyphosphates are useful in the food industry as food additives under the E number E452.

When considering the formation and synthesis of polyphosphate salts, we can produce them through the polymerization of phosphoric acid derivatives. Typically, this polymerization begins with two phosphate units that come together in a condensation reaction. This condensation reaction is usually an equilibrium.

Further, polyphosphate compounds are weak bases. There is a lone electron pair on an oxygen atom. This lone electron pair can be donated to a hydrogen ion or a metal ion through a Lewis acid-Lewis base interaction.

What is the Difference Between Orthophosphate and Polyphosphate?

The term orthophosphate can be defined as any salt or ester of orthophosphoric acid while the term polyphosphate is used for salts or esters of polymeric oxyanions that are formed from tetrahedral phosphate structural units. We can distinguish orthophosphate compounds from polyphosphate compounds from their chemical structure. The key difference between orthophosphate and polyphosphate is that orthophosphate contains only one phosphate unit, whereas polyphosphate contains several phosphate units.

Usually, orthophosphates are small molecules because there is one phosphate unit per molecule. But polyphosphates are larger molecules than orthophosphates because there is more than one phosphate unit per molecule. Moreover, orthophosphate is a common corrosion inhibitor that is used by water suppliers to prevent the lead pipes from leaching, whereas polyphosphate has multiple uses, including its role as a thickening agent in food industry, use in water treatment systems, etc.

The following table summarizes the difference between orthophosphate and polyphosphate in tabular form for side by side comparison.

Summary – Orthophosphate vs Polyphosphate

Orthophosphate and polyphosphate are inorganic salt compounds. We can distinguish these two compounds from their chemical structure, depending on the number of phosphate units in the chemical structure. The key difference between orthophosphate and polyphosphate is that orthophosphate contains only one phosphate unit, whereas polyphosphate contains several phosphate units.

Reference:

1. “Polyphosphate.” An Overview | ScienceDirect Topics.
2. “Polyphosphate.” Quality Water Treatment – SPER Chemical Corporation.

Image Courtesy:

1. “Phosphat-Ion” By NEUROtiker ⇌ – Own work (Public Domain) via Commons Wikimedia
2. “Polyphosphoric acid” By Diphosphorsäure_-_Diphosphoric_acid.svg: NEUROtikerderivative work: Daniele Pugliesi (talk) – Diphosphorsäure_-_Diphosphoric_acid.svg (Public Domain) via Commons Wikimedia