Question

The correct statement(s) for orthoboric acid is/are :
a.) It behaves as a weak acid in water due to self-ionization
b.) Acidity of its aqueous solution increases upon addition of ethylene glycol
c.) It has a three-dimensional structure due to hydrogen bonding
d.) It is a weak electrolyte in water

Answer 1

Hint: The orthoboric acid is a weak monobasic compound. After accepting $O{H^ - }$ ions from water even then it can not complete its octet. It is a weak lewis acid. It has square planar geometry even after hydrogen bonding.

Complete step by step answer:
First, we will see what is orthoboric acid.
It is also called hydrogen borate or boric acid is a lewis acid of boron. It is weak and monobasic in nature.
Let us see the options given to us and analyse them one by one.
The first option says that it behaves as a weak acid in water due to self-ionization.
Now let us see the reaction of boric acid with water.
${H_3}B{O_3} + 2{H_2}O \to {[B{(OH)_4}]^ - } + {H_3}{O^ + }$

From the reaction it is clear that it is accepting $O{H^ - }$ from water molecules and thus it does not self ionize. So, the option a.) is not correct.

Now, the option b.) says that acidity of its aqueous solution increases upon addition of ethylene glycol
For this let us see the reaction of orthoboric acid with ethylene glycol which is as-

The product formed is stable. So, the reaction will occur and thus, the acidity of its aqueous solution will increase upon addition of ethylene glycol.
So, the option b.) is the correct answer.

The option c.) is that it has a three-dimensional structure due to hydrogen bonding.
This statement is wrong because it has planar structure not three-dimensional.
The last option is that it is a weak electrolyte in water.
This statement is true because it is a weak acid. Thus, it will be weak electrolyte.
So, the option d.) is also correct. So, the correct answer is “Option B and D”.

Note: Boric acid is commonly used as antiseptic, insecticide and neutron absorber. As the acidity of boric acid increases in presence of polyols. With the different concentrations of mannitol, the boric acid shows pKa value of five orders of magnitude. This property is used to determine boron content in aqueous solution in analytical chemistry.