Chemistry > p Block Elements > 3.0 Compounds of boron
p Block Elements
1.0 Group $13$ – The Boron Family
2.0 Boron
3.0 Compounds of boron
4.0 Compounds of Aluminium
5.0 Group $14$ – The Carbon family
6.0 Allotropes of Carbon
7.0 Compounds of Carbon
8.0 Properties of Silicon
9.0 Group $15$-The Nitrogen Family
10.0 Oxides of nitrogen
10.1 Nitrogen Oxide $N_2O$ or Laughing gas (Neutral)
10.2 Nitric Oxide $NO$ (Neutral)
10.3 Nitrogen trioxide $N_2O_3$
10.4 Nitrogen dioxide or Di-nitrogen tetroxide $NO_2$ or $N_2O$
10.5 Nitrogen pentaoxide $N_2O_5$
11.0 Oxyacids of Nitrogen
11.1 Nitric acid $HNO_3$
11.2 Oxidation of Metalloid and Inorganic compounds by Nitric acid
11.3 Action of Metals & Proteins
12.0 Phosphorus
13.0 Oxygen
14.0 Sulphur
3.2 Orthoboric acid ($H_3BO_3$)
10.2 Nitric Oxide $NO$ (Neutral)
10.3 Nitrogen trioxide $N_2O_3$
10.4 Nitrogen dioxide or Di-nitrogen tetroxide $NO_2$ or $N_2O$
10.5 Nitrogen pentaoxide $N_2O_5$
11.2 Oxidation of Metalloid and Inorganic compounds by Nitric acid
11.3 Action of Metals & Proteins
It is a white crystalline solid, with soapy touch. It is sparingly soluble in water but highly soluble in hot water. It can be prepared by acidifying an aqueous solution of borax.
$$N{a_2}{B_4}{O_7} + 2HCl + 5{H_2}O \to 2NaCl + 4B{(OH)_3}$$
It is also formed by the hydrolysis (reaction with water or dilute acid) of most boron compounds (halides, hydrides, etc.). It has a layer structure in which planar $BO_3$ units are joined by hydrogen bonds as shown in Figure.
Properties:
1. Boric acid is a weak monobasic acid. It is not a protonic acid but acts as a Lewis acid by accepting electrons from a hydroxyl ion. $$B{(OH)_3} + 2HOH \to {[B{(OH)_4}]^ - } + {H_3}{O^ + }$$
2. On heating, orthoboric acid above $370\ K$ forms metaboric acid, $HBO_2$ which on further heating yields boric oxide, $B_2O_3$. $${H_3}B{O_3}\mathop \to \limits^\Delta HB{O_2}\mathop \to \limits^\Delta {B_2}{O_3}$$
