Question

Boric acid is considered a weak acid. Why?

Answer 1

Hint: As we know that boric acid is also known as hydrogen borate, boracic acid and orthoboric acid and its chemical formula is ${{H}_{3}}B{{O}_{3}}$. It is a weak, monobasic Lewis acid of boron element. It is mostly used as an antiseptic, flame retardant, insecticide, neutron absorber and also as precursor to other chemical compounds. So here we have to tell the reason behind boric acid being a weak acid by nature.

Complete answer:
Let us discuss about Boric acid as follows:-
-Boric acid: Its chemical formula is ${{H}_{3}}B{{O}_{3}}$ and it is also known as hydrogen borate, boracic acid and orthoboric acid. It exists in the form of colorless crystals or sometimes in the form of white powder that dissolves in water.
-Weak acid: These are the acidic compounds that can donate hydrogen ions but not completely as they do not dissociate well in aqueous solution. They only release a few ions and the rest remains intact. It is a weak, monobasic Lewis acid of boron element.
-Boric acid is a weak acid because it does not completely ionize in water or other aqueous solution. It is not able to release ${{H}^{+}}$ ions on its own because firstly it receives hydroxide ions ($O{{H}^{-}}$) from water molecule in order to complete its octet and then it releases ${{H}^{+}}$ ions.
-This reaction is shown below:-
$~B{{\left( OH \right)}_{3}}+2{{H}_{2}}O\to {{\left[ B{{\left( OH \right)}_{4}} \right]}^{-}}+{{H}_{3}}{{O}^{+}}$
-It has a pKa value of 9.2 as it is a weak acid. Boric acid is present in its non-dissociated form at lower pH values but at a pH greater than 10.5, it changes to dissociated borate form.

Note:
-Remember that Lewis acids are those compounds which accept electron pairs from Lewis base and form an adduct as we saw in the above chemical equation where boric acid acts as weak Lewis acid and water acts as Lewis base.