Question

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

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

Answer 1

The correct option is B

Monobasic and weak Lewis acid

$H_{3}B{O}_3$ is better written as $B(OH{)}_3$ where the central Boron atom is electron deficient with only 6 valence electrons. In its reaction with water, it accepts an $O{H}^{-}$ thus releasing $H^{+}$ from water.

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

Each of the three oxygen atoms in the structure has 2 lone pairs (each). These lone pairs try and reduce the electron deficiency in Boron atom via back bonding. The oxygen – boron bonds tend to have a slight double bond character. Hence, the acid – boric acid – is monobasic and a weak Lewis acid.