Question

Is boric acid a protic acid? Explain.

Answer 1

**: To answer this question, you must recall the Arrhenuis concept of defining acids and bases. A protic acid is the acid that can donate a proton. In simpler terms, a protic acid releases hydrogen ions $\left( {{H^ + }} \right)$ in water.

Complete step by step solution:
According to the Arrhenius concept, a substance which causes an increase in the hydrogen ion concentration and the decrease in hydroxide concentration when added to water is defined as an acid. Similarly a base is defined as the substance which in addition to water causes an increase in the hydroxide ion concentration and a decrease in the hydrogen ion concentration.
Boron is a non-metal and is present in the group 13 of the periodic table. Boric acid or orthoboric acid, that is ${H_3}B{O_3}$, is a crystalline solid. It is prepared by the acidification of aqueous solution of borax. It has three hydrogen atoms attached to three oxygen atoms which in turn are attached to the central boron atom. At first thought, it might seem that boron may lose the hydrogen atoms as protons.
But boron in boric acid is an electron deficient atom. It has only six electrons in its valence shell and has an empty orbital. Thus instead of losing a proton, it accepts a hydronium ion which donates an electron pair to the boron atom thus completing its octet.

Hence, we can say that boric acid is not a protic acid but rather is a Lewis acid.

Note:
Lewis acids are defined as those substances which can accept a pair of electrons forming a bond with the donor. Similarly, the substances that can donate a pair of electrons forming a bond are known as Lewis bases.