Question

Boric Acid is:
A) monobasic and weak lewis acid.
B) monobasic and weak bronsted acid.
C) monobasic and strong lewis acid.
D) tribasic and strong bronsted acid.

Answer 1

Hint: We know that an acid is called monobasic when it contains only one hydrogen ion that is available for donation to a base. In other words, it contains only one hydrogen ion that is replaceable. Similarly, an acid is tribasic if it contains three hydrogen ions for donation.

Complete answer:
Now, let’s discuss Lewis acid in detail.
> Lewis acids are the class of acids that can easily accept nonbonding pairs of electrons. They are also called electron pair acceptors. Depending upon the tendency to accept the electrons acids further classified as strong and weak Lewis acids. Similarly, Bronsted acids are the species that can easily donate a proton.
> We know that Boron is a typical non-metal, belonging to group 13. Orthoboric acid, ${H_3}B{O_3}$ is a white crystalline solid, with soapy touch. It is slightly soluble in water but highly soluble in hot water. Orthoboric acid is prepared by acidifying an aqueous solution of borax. It is a planar in structure in which there are various layers of $B{O_3}$ . Boric acid is a weak monobasic acid. Because it is not able to release \[{H^ + }\] ions on its own. It receives \[O{H^ - }\] ions from water molecules to complete its octet and in turn releases \[{H^ + }\] ions. It does not contain hydrogen ions so not a protonic acid but they can accept electrons from \[O{H^ - }\]so it is a Lewis acid.
${\rm{B(OH}}{{\rm{)}}_3}{\rm{ + 2HOH }} \to {\rm{ B(OH)}}_4^ - \, + \,{H_3}{O^ + }$

Hence option A is correct.

Note: Orthoboric acid on heating above 370K forms metaboric acid, \[HB{O_{2\,}}\] which on further heating yields boric oxide,\[{B_2}{O_3}\].