Boric Acid

What is boric acid powder?

Boric acid or Boric Powder, also called hydrogen borate or orthoboric acid is a white crystalline solid with the chemical formula of H₃BO₃. Boric powder is commonly prepared by acidifying and heating borax solution in chemistry.

It is found in minerals and volcanic water or the end product of hydrolysis of boron halides or hydrides. It is commonly used as an antiseptic, insecticide, and neutron absorber in the nuclear power generation process

Boric acid structure

The shining white polymeric crystal structure of boric acid contains B(OH)₃ units linked with infinite hexagonal layers due to hydrogen bonding.

Each acid molecule contains a boron-hydrogen chemical bond. The boron atom is the central atom (sp² hybridized) liked with three hydroxyl groups. The overall molecular geometry of H₃BO₃ is the trigonal planner.

Acidity of boric acid

The water solution of the boric acid molecule shows weak acid properties (pH scale = 9.2). It does not use hydrogen ions to show an acidic character. It is a Lewis acid that accepts electron pairs from the hydroxyl ion.

The conductance in an aqueous solution of H₃BO₃ is very weak. It can be enhanced by the addition of alcohol like ethanol, mannitol, glycerol, etc.

For acid base titration, we added alcohol to increase acidity and then titrated with a base solution using phenolphthalein as an indicator. This reaction is the basis of the borax phenolphthalein test of glycerol in learning chemistry.

Boric acid preparation

It is commonly obtained by boiling borax with acids and then crystallizing it. The acid is also produced during the hydrolysis reaction of boron halides.

Na₂B₄O₇(OH)₄ + 2 HCl + 3 H₂O → 4 H₃BO₃ + 2 NaCl
BCl₃ + 3 H₂O → H₃BO₃ + 3 HCl

Chemical properties of H₃BO₃

Dilute aqueous boric acid solution contains mononuclear compounds but various polymeric ions formed in concentrated chemical solution depending on the pH, concentration, and temperature

1. At 100°C, the acid changed to metaboric acid (HBO₂).
2. At 140°C to pyroboric acid.
3. Finally, at a higher temperature, it is converted to boron trioxide (B₂O₃).

Chemical reactions

H₃BO₃ reacts with ethyl alcohol or ethanol in the presence of sulfuric acid to form alkyl or ethyl borate. It is used for quantitative chemical analysis of borates.

On fusion with metal oxides colored borate glasses are formed. On fusion with NH₄HF₂ ultimately BF₃ is obtained. It acts as a strong acid in anhydrous sulfuric or nitric acid solution.

The reaction of H₃BO₃ with sodium peroxide or hydrogen peroxide gives sodium or mono peroxo-borates. The structure of the peroxoborate ion, [B₂(O₂)₂(OH)₄]⁻² contains sp³ hybridized boron atoms. The tetrahedral sp³ hybridized orbitals of boron are linked by bridging μ-peroxo groups.

Boric acid powder uses

• Boron and boric acid are extensively used in the modern age as reinforcement materials in space shuttles, aircraft, and the textile industry. It is also used for making borosilicate glasses.
• For the preparation of enamels of our teeth, we use shining H₃BO₃ and borax powder.
• Over a hundred years, boric acid has been used for the treatment of vaginal suppositories or infections.
• It is commonly used by physicians and patients as an antiseptic, antibacterial in medicine, or treatment of candidiasis and BV.
• Sodium perborate which is prepared from H₃BO₃ used for detergent preparation in the chemical industry.
• Boron carbides and metal borides are extensively used as neutron shielding chemicals and control rods in nuclear power plants.
• We used boric acid widely in the carrom board.
• Boric acid is uses in the preservation of food grains like wheat and rice from insecticides mainly cockroaches.