The key difference between isopoly and heteropoly acids is that isopoly acids form from the combination of similar acids or anions, whereas heteropoly acids form from the combination of different acids or anions.
A poly acid is an acidic compound that forms from the combination of two acids via elimination of a water molecule. If the acids that combine are similar, then the resulting acid is an isopoly acid. But if the final product is a combination of two or more types of acids, then we call it a heteropoly acid.
CONTENTS
1. Overview and Key Difference
2. What are Isopoly Acids
3. What are Heteropoly Acids
4. Side by Side Comparison – Isopoly vs Heteropoly Acids in Tabular Form
5. Summary
What are Isopoly Acids?
Isopoly acids are inorganic acidic compounds that form from the combination of acids or anions of the same type. In this formation process, a water molecule is eliminated during the combination of two acids or anions. Some examples of isopoly acids include isopolychromate, isopolymolybdate, isopolytungstate, isopolyvanadate, isopolyniobates, etc.
For example, isopoly acids of molybdenum forms when molybdenum trioxide is dissolved in aqueous sodium hydroxide. It can form dimolybdate, trimolybdate, tetramolybdate, etc. These acids form from the combination of the basic unit MoO6. Since this basic unit has an octahedral geometry, the isopoly acidic compounds form via the combination of either the corners or edges of these octahedral units. However, this combination that occurs through the corners causes repulsion between the Mo metal atoms. And, this repulsion can be reduced using another metal, other than molybdenum.
What are Heteropoly Acids?
Heteropoly acids are inorganic acidic compounds which form from the combination of acids or anions of different types. Usually, these acids are combinations of oxygen and hydrogen atoms with particular metals and nonmetals. These acids are very important as re-usable catalysts in chemical reactions. They have applications as both homogeneous and heterogeneous catalysts.
Figure 01: Heteropoly Acids are Complicated Structures
There are a few requirements we have to check before categorizing an acid as a heteropoly acid. It should have a metal (e.g. tungsten, molybdenum, etc), oxygen atom(s), an element from the p-block of the periodic table, and hydrogen atoms that are acidic. The metal atoms are called addenda atoms. There are four types of heteropoly acids.
- 1:12 tetrahedral
- 2:18 tetrahedral
- 1:6 tetrahedral
- 1:9 tetrahedral
Furthermore, some examples of heteropoly acids include H3PW12O40, H6P2Mo18O62, etc.
What is the Difference Between Isopoly and Heteropoly Acids?
A poly acid is an acidic compound which forms from the combination of two acids via elimination of water molecules. The key difference between isopoly and heteropoly acids is that isopoly acids form from the combination of similar acids or anions whereas heteropoly acids form from the combination of different acids or anions. Therefore, isopoly acids have the same repeating unit but heteropoly acids have different repeating units.
Examples of isopoly acids include isopolychromate, isopolymolybdate, isopolytungstate, isopolyvanadate, isopolyniobates, etc. Examples of heteropoly acids include H3PW12O40, H6P2Mo18O62, etc.
The following table summarizes the difference between isopoly and heteropoly acids.
Summary – Isopoly vs Heteropoly Acids
A poly acid is an acidic compound which forms from the combination of two acids via elimination of a water molecule. In summary, the key difference between isopoly and heteropoly acids is that isopoly acids form from the combination of similar acids or anions whereas heteropoly acids form from the combination of different acids or anions.
Reference:
1. “Heteropoly Acid.” Wikipedia, Wikimedia Foundation, 19 Apr. 2018, Available here.
2. Halpern, Jack, and George B. Kauffman. “Isopoly and Heteropoly Anions.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 3 Aug. 2018, Available here.
Image Courtesy:
1. “Phosphotungstate-3D-polyhedra” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia