Hydration degree of acids. Acid nomenclature

It can happen that there are acids of the same element, and this element has the same oxidation number (NOX), but the difference is in the degrees of hydration.

For example, below, we have three acids formed by the element phosphorus (P):

H₃DUST₄  H₄P₂O₇ HPO₃

Note that in all three acids the oxidation number of phosphorus is +5; the difference is in the degree of hydration.

Based on this, these acids are differentiated in the nomenclature through the prefixes ortho, pyro and meta.

The most hydrated acid is called ortho. In the example given, the first (H₃DUST₄) is called acid orthophosphoric, because it is the most hydrated of the three. The ortho prefix is ​​expendable, so most of the time this acid will just be called phosphoric acid.

The prefixes pyro and meta are used with ortho acid as the reference point:

• Pyrus: 2 molecules of ortho minus 1 molecule of H₂O

Example: The H₄P₂O₇ is called acid pirophosphoric because it is equal to two molecules of orthophosphoric acid (H₃DUST₄) minus one water molecule.

2. H₃DUST₄ =H₆P₂O₈

H₆P₂O₈ - H₂O = H₄P₂O₇

This process is a intermolecular dehydration:

• Goal: 1 molecule of ortho minus 1 molecule of H₂O

Example: The HPO₃ is called acid goalphosphoric because it is equal to a molecule of orthophosphoric acid (H₃DUST₄) minus one water molecule.

H₃DUST₄ - H₂O = HPO₃

This process is a intramolecular dehydration:

By Jennifer Fogaça
Graduated in Chemistry

Source: Brazil School - https://brasilescola.uol.com.br/quimica/grau-hidratacao-dos-acidos.htm