Question

What do the brackets around $[{{H}^{+}}]$ and $[O{{H}^{-}}]$ represent and what does it do? (this is in context to acid and bases)

Answer 1

Hint: An acid is said to be that compound that has the tendency to liberate hydrogen ions in any solution. While a base is that compound that has the ability to liberate hydroxide ions in any solution. The concentration of these ions decides acidity and basicity. They also change the pH.

Complete answer:
Acids are a substance that has the ability to dissociate and liberate hydrogen, ${{H}^{+}}$ ions in any solution. On the other hand, bases are said to liberate hydroxide, $O{{H}^{-}}$ ions in any solution. The example may be, $2{{H}_{2}}O\rightleftharpoons {{H}_{3}}{{O}^{+}}+O{{H}^{-}}$ where water self ionizes to liberate hydrogen ion that bonds with water to form hydronium ion.
The concentration of these ions may be unknown, therefore to denote the concentrations of the acidic and basic ions, square brackets are used, as $[{{H}^{+}}]$ and $[O{{H}^{-}}]$ or $[{{H}_{3}}{{O}^{+}}]$ and $[O{{H}^{-}}]$.
So, the hydrogen and hydroxide ions in brackets are the concentrations of them. The concentration of $[{{H}^{+}}]$ tells that if the concentration of hydrogen ion in a solution is more than the acid has more strength, which makes the pH of the solution below 7.
The concentration of $[O{{H}^{-}}]$ denotes the liberated ion from base, that tells if more $[O{{H}^{-}}]$are present in a solution, means the solution is more basic. This makes the pH of that solution to be more than 7.
Hence, the brackets around $[{{H}^{+}}]$ and $[O{{H}^{-}}]$ represent the concentration of hydrogen and hydroxide ions respectively. Hydrogen ions are said to make a solution acidic, while hydroxide ions makes a solution basic.

Note:
The strength of an acid and a base id dependent on the liberation of $[{{H}^{+}}]$and$[O{{H}^{-}}]$respectively. If an acid dissociates more hydrogen ions than it is a strong acid which makes the pH between 1 – 2, while if a base dissociates into more hydroxide ions, then it is a strong base that has a pH between 11 to 14. Acids and bases have dissociation constants that tell their extent of dissociation.