Difference Between Orthoboric Acid and Metaboric Acid

The key difference between orthoboric acid and metaboric acid is that orthoboric acid occurs only in the molecular form, whereas metaboric acid can occur in both molecular and polymeric forms.

Orthoboric acid is another name for boric acid or boric powder in common terms. Metaboric acid is a derivative of boric acid.

CONTENTS

1. Overview and Key Difference
2. What is Orthoboric Acid 
3. What is Metaboric Acid
4. Side by Side Comparison – Orthoboric Acid vs Metaboric Acid in Tabular Form
5. Summary

What is Orthoboric Acid?

Orthoboric acid is an inorganic acid that usually appears as a white coloured powder. This compound has some other names, including hydrogen borate, boracic acid, and boric powder. It is a weak and monobasic Lewis acid of the chemical element boron. Monobasic means this substance can release only one proton per molecule in an acidic medium; however, some of its behaviours suggest that it can be tribasic as well. The chemical formula of this compound is H3BO3. In its mineral form from which it is derived, orthoboric acid is named as sassolite.

We can prepare orthoboric acid from the reaction between borax and mineral acids such as HCl acid. It is also formed as a byproduct of the hydrolysis process of boron trihalide and diborane. Usually, orthoboric acid is water-soluble, specifically in boiling water. However, above 170 Celsius degrees, this substance tends to dehydrate, forming metaboric acid or HBO2.

There are many different uses of orthoboric acid, including the manufacture of monofilament fibreglass or textile fibreglass, reduction of the surface oxidation in the jewellery industry, as an ingredient in the electroplating process, as an antiseptic substance, as an ingredient in insecticides, in flame retardants, as a neutron absorber, and as a precursor to other chemical compounds.

What is Metaboric Acid?

Metaboric acid is an inorganic compound formed from the dehydration of boric acid. This acid occurs as a colourless solid having the chemical formula HBO2. There are two major types of metaboric acid: molecular form and polymer form.

We can prepare metaboric acid via heating boric acid at a high temperature (around 100 Celsius temperature). This is the boiling temperature for water which leads to the release of water molecules, giving orthorhombic metaboric acid. This molecule is the molecular form of metaboric acid that contains discrete trimers. The molecule has a sheet-like structure that is similar to boric acid. Moreover, upon heating of this product (orthorhombic metaboric acid) at an even higher temperature in a sealed ampoule, the compound converts into the monoclinic form. This form is the polymeric form of metaboric acid.

What is the Difference Between Orthoboric Acid and Metaboric Acid?

Orthoboric acid is an inorganic acid which usually appears as a white coloured powder. Metaboric acid is an inorganic compound that forms from the dehydration of boric acid. The key difference between orthoboric acid and metaboric acid is that orthoboric acid occurs only in the molecular form, whereas metaboric acid can occur in both molecular and polymeric forms. Moreover, orthoboric acid is in hydrated form whereas metaboric acid is in dehydrated form.

The below infographic summarizes the differences between orthoboric acid and metaboric acid in tabular form.

Summary – Orthoboric Acid vs Metaboric Acid

Orthoboric acid is an inorganic acid which usually appears as a white coloured powder. Metaboric acid is an inorganic compound that forms from the dehydration of boric acid. The key difference between orthoboric acid and metaboric acid is that orthoboric acid occurs only in the molecular form, whereas metaboric acid can occur in both molecular and polymeric forms.

Reference:

1. “Metaboric Acid. ” Science Direct, Available here.

Image Courtesy:

1. “Boric-acid-2D” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
2. “Metaboronic acid molecule” By Smokefoot – Own work (CC BY-SA 3.0) via Commons Wikimedia