What is the Difference Between Orthoboric Acid and Metaboric Acid?

Orthoboric acid and metaboric acid are both inorganic boron compounds, but they differ in their molecular structure, forms, and hydration states. The main differences between orthoboric acid and metaboric acid include:

1. Molecular Structure: Orthoboric acid has the molecular formula ${H3}B{O3}$, while metaboric acid has the molecular formula $HB{O_2}$.
2. Forms: Orthoboric acid occurs only in molecular form, whereas metaboric acid can occur in both molecular and polymeric forms.
3. Hydration State: Orthoboric acid is in a hydrated form, while metaboric acid is in a dehydrated form.
4. Melting Point: The melting point of metaboric acid is about 236°C, while the melting point of orthoboric acid is 170.9°C.

In summary, orthoboric acid and metaboric acid differ in their molecular structure, forms, hydration state, and melting points. Orthoboric acid is a hydrated molecular compound, while metaboric acid can exist in both molecular and polymeric forms and is dehydrated.

Comparative Table: Orthoboric Acid vs Metaboric Acid

The main difference between orthoboric acid and metaboric acid lies in their structural forms and hydration states. Here is a comparison between the two:

Orthoboric acid, also known as boric acid or boric powder, is an inorganic acid that usually appears as a white-colored powder. It is a weak acid and has antiviral, antifungal, and antiseptic properties. Metaboric acid, on the other hand, is a derivative of boric acid and forms from the dehydration of boric acid. It can occur in both molecular and polymeric forms.

Heating orthoboric acid above 140°C leads to its dehydration, resulting in the formation of metaboric acid (HBO₂) and the release of one water molecule. Further heating of metaboric acid above 180°C triggers the second dehydration step, leading to the formation of tetraboric acid, also known as pyroboric acid (H2B4O7), with the release of an additional water molecule.