Question

Aqueous solution of borax is ________ in nature:
A.Neutral
B.Acidic
C.Alkaline
D.None

Answer 1

Hint:Aqueous solution of borax yields boric acid and hydroxyl ion. The hydroxyl ion reacts with sodium to give sodium hydroxide which is a strong base in nature. A weak acid and a strong base try to neutralize each other, but due to the high basic strength exerted by sodium hydroxide the solution becomes alkaline.

Complete step by step answer:
Borax is a compound of boron especially present in detergent. The molecular formula of borax is $\text{N}{\text{a}}_{\text{2}}{\text{B}}_{\text{4}}{\text{O}}_{\text{7}}\text{.10}{\text{H}}_{\text{2}}\text{O}$.
During aqueous solution borax undergoing the following reaction:
$N{a}_2{B}_4{O}_7.10H_{2}O+7H_{2}O\to 2NaOH+4H_{3}B{O}_3+10H_{2}O$
In the aqueous solution of borax it gets hydrolyzed and borate ion donate hydroxyl group ($\text{O}{\text{H}}^{\text{-}}$) in the solution. The hydroxyl ion then reacts with sodium (Na) to give sodium hydroxide (NaOH) in the solution. Sodium hydroxide is a very strong base.
On the other hand, borax is also dissociated into boric acid (${\text{H}}_{\text{3}}\text{B}{\text{O}}_{\text{3}}$) which is a weak acid.
So, both sodium hydroxide and boric acid try to neutralize each other. But due to the high basic strength of sodium hydroxide, weak acid boric acid cannot completely neutralize it in the solution and the solution is slightly alkaline in nature.

So, the correct answer is option-C i.e., aqueous solution of Borax is alkaline in nature.

Additional information:
Uses of borax:
-It is used as an insecticide and antifungal agent.
-It helps to get rid of moulds and stains.
-It used to be a buffer solution in a biochemistry laboratory.

Note:
Borax solution is an alkaline solution due to presence of strong base sodium hydroxide which completely masks the acidic effect of weak acid boric acid and makes the property of solution alkaline.