Question

Compound ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ is named as ______.
A) Boric acid.
B) Monobasic and weak Bronsted acid.
C) Dibasic and strong Lewis acid.
D) Tribasic and weak Bronsted acid.

Answer 1

Any acid is defined as monobasic or dibasic or tribasic based on the capacity of the acid to donate hydrogen i.e. ${{\text{H}}^ + }$ ions. A species that accepts a pair of electrons to form a covalent bond is known as Lewis acid. A species that has very little tendency to donate a proton is known as a Bronsted acid.

Complete answer:
${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ is named as boric acid. Boric acid is also known as hydrogen borate or boracic acid or orthoboric acid.
Thus, ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ is named as boric acid. Thus, option (A) is correct
We are given a compound having molecular formula ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$. ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ dissociates in its solution as follows:
${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}} + {{\text{H}}_{\text{2}}}{\text{O}} \to {\text{B}}\left( {{\text{OH}}} \right)_4^ - + {{\text{H}}^ + }$
Water splits into hydrogen $\left( {{{\text{H}}^ + }} \right)$ ions and hydroxyl $\left( {{\text{O}}{{\text{H}}^ - }} \right)$ ions. The hydroxyl ions coming from water form bonds with ${\text{B}}{\left( {{\text{OH}}} \right)_3}$ and the hydrogen ions are released in water.
Thus, as ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ releases only one hydrogen ion it is known as monobasic acid.

A species that accepts a pair of electrons to form a covalent bond is known as Lewis acid.
Thus, as ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ accepts a pair of electrons i.e. ${\text{O}}{{\text{H}}^ - }$ to form a covalent bond it is a Lewis acid.
Also, incomplete dissociation of ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ occurs and thus, ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ is a weak acid.
Thus, ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ is a monobasic and weak Lewis acid. Thus, option (B), (C) and (D) are not correct.
Thus, ${{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}$ is named as boric acid.

Thus, the correct option is (A) boric acid.

Note: Boric acid is used as an antiseptic, insecticide, flame retarder, neutron absorber, etc. boric acid exists as a colourless crystal or white powder that is soluble in water. It is less toxic to the human body. On coming in contact with skin, boric acid causes skin irritation. If swallowed it leads to nausea, vomiting, stomach pain and diarrhoea.