Question

$H_{3}B{O}_3$ is

• A. Monobasic and weak Lewis acid
• B. Monobasic and weak Bronsted acid
• C. Monobasic and strong Lewis acid
• D. Tribasic and weak Bronsted acid

Answer 1

The correct option is A

Monobasic and weak Lewis acid

Boric acid - $B(OH{)}_3$ - is a hydroxide acceptor. When it accepts a hydroxide ion from water, the split $H_{2}O$ produces a proton and hence the monoacid nature. This is a bit controversial though. Because the boron atom is attached to three oxygen atoms, the lone pair from the oxygen atoms involve in back bonding (with the pure p empty orbital of boron) and thus the Lewis acidity is reduced.

$H_{3}B{O}_3+2H_{2}O\rightleftharpoons \left[B\right(OH{)}_4{]}^{\ominus }+H_3{O}^{\oplus }$