Question

Boric Acid Preparation.

Answer 1

1. From borax

Na₂B₄O₇ + 2HCl + 5H₂O → 2NaCl + 4H₃BO₃

2. From colemanite

Ca₂B₆O₁₁ + 2 SO₂ + 9H₂O → 2CaSO₃ + 6H₃BO₃

Boric acid (H₃BO₃) contains triangular BO₃^3- ions in which boron is sp² –hybridized. In solid state,  B(OH)₃ molecules are H–bonded to form a two–dimensional sheet. It is a weak monobasic acid. 3 It does not act as a protonic acid but acts as a Lewis acid by accepting a pair of electrons from OH^– ion of water thereby releasing a proton.

Reaction with ethyl alcohol. Orthoboric acid reacts with ethyl alcohol in presence of conc. H₂SO₄ to form triethylborate.

The vapours of triethylborate when ignited burn with a green–edged flame. This forms the basis for detecting borates and boric acid in qualitative analysis

Heating