Question

Boric acid is an acid because its molecule

• A. contains replaceable $H^{+}$ ion
• B. gives up a proton
• C. accepts $O{H}^{-}$ from water releasing proton
• D. combines with proton from water molecule

Answer 1

Answer: (C)

Lewis acids are substances whose octet is incomplete and accepts electrons.

Boric acid is a monobasic weak acid. It does not liberate $H^{+}$ ion but accepts electrons from $O{H}^{-}$ ion i.e., behaves as Lewis acid.

$H_{3}P{O}_3+H_{2}O\to B(OH{)}_4^{-}+H^{+}$

or $B(OH{)}_3+2H_{2}O\to {\left[B(OH{)}_4\right]}^{-}+H_3{O}^{+}$

The structure of $H_{3}B{O}_3$ is as shown below, where the octet of boron in $H_{3}B{O}_3$ is incomplete.