Question

Borax when dissolved in water exhibits
A. Alkaline nature
B. Acidic nature
C. Neutral nature
D. Amphoteric nature

Answer 1

Hint: The nature of a solution can be identified by the presence of ions in it. A solution can have an acidic nature, if it has higher concentration of hydronium ion. Similarly if a solution has higher concentration of \[O{{H}^{-~}}\]ions, it will have a basic or alkaline nature. The neutral nature of a solution can be identified if It has equal content of both the ions. And the amphoteric nature of a substance is when the substance can have acidic as well as basic nature.


Complete step by step answer:
If we consider the options which are given in the question. A solution which is alkaline in nature, will have higher concentration of hydroxide ion content in it. This is because the base which is present in the solution will liberate its \[O{{H}^{-~}}\] ion in the water.
The next option is a solution which has acidic nature. Just like an alkaline solution has a characteristic of \[O{{H}^{-~}}\] ion content, similarly an acidic solution has characteristic of \[{{H}^{+}}\] ion content. This is due to the acidic molecule present in the solution, tends to liberate its \[{{H}^{+}}\] ions, and so the solution will have higher concentration of hydronium ions. As we know that proton does not exist in its single proton form, it exists as hydronium ion.
Now if we consider the third option which is the neutral nature of the solution. This is interesting as the \[{{H}^{+}}\] and \[O{{H}^{-~}}\] content in a neutral solution will be equal and so the pH will be exactly$7$. This is because the equal number of both the ions will combine to form oxygen, which will nullify their individual acidic or basic nature.
Now consider the last option given in the question. It says if the solution is amphoteric in nature. Now we all know that amphoteric molecules or substances are those which can have acidic as well as basic nature, depending on the conditions and other reactants.
When borax is dissolved in aqueous solution the formation of sodium borate and boric acid takes place which forms a strong base hence it is alkaline in nature.
The chemical formula of borax is
\[Na\left[ B{{O}_{5}}\left( OH \right) \right]\cdot 8HO\]
Borax has a tendency to dissociate to form \[{{B}_{4}}{{O}_{7}}{{}^{2-~}}\] ions
After dissociation \[{{B}_{4}}{{O}_{7}}{{}^{2-}}\to 2O{{H}^{-}}+4{{H}_{3}}B{{O}_{3}}\]
The formation of \[O{{H}^{-~}}\] ions indicates that the solution is alkaline in nature.

So, the correct answer is Option A.

Note: Water is an amphoteric reagent, as it can act as base when acid is added to it, and will accept the \[{{H}^{+}}\] ions which will be liberate from the acid present in the solution. And it can act as acid when base is added to it, as it will liberate the proton in order to compensate for the hydroxide ion concentration.
Borax has a number of common household applications as it can be used as a fungicide, laundry detergent booster, insecticide preservative, cleaner, disinfectant, herbicide, and desiccant.