Question

Boric acid is an acid because its molecule

• A. contains replaceable $H^{+}$ ion
• B. gives up a proton
• C. accepts $OH^{-}$ 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 $OH ^{-}$ ion i.e., behaves as Lewis acid.

$H _{3} PO _{3}+ H _{2} O \rightarrow B ( OH )_{4}^{-}+ H ^{+}$

or $B ( OH )_{3}+2 H _{2} O \rightarrow\left[ B ( OH )_{4}\right]^{-}+ H _{3} O ^{+}$

The structure of $H _{3} BO _{3}$ is as shown below, where the octet of boron in $H _{3} BO _{3}$ is incomplete.