Question

# Name the ion(s) when $HCl$ dissociates in aqueous solution.A. ${{H}_{3}}{{O}^{+}}$B. $C{{l}^{-}}$C. Both A and BD. None of the above

Hint: $HCl$, a covalent gas acts as a typical acid when it is dissolved in the aqueous solution. Hydrogen ions (${{H}^{+}}$) in the aqueous solution are called hydronium ions (${{H}_{3}}{{O}^{+}}$).
The other ion formed is a halide ion. Halides are the elements present in the Group-17 of the periodic table. These are fluorine, chlorine, bromine and iodine.

$HCl$ being a covalent gas is a poor conductor of electricity because there are no free electrons or ions.
When dissolved in an aqueous solution, it dissociates into ${{H}_{3}}{{O}^{+}}$ and $C{{l}^{-}}$ ions.
The reaction is as follows:
$HCl(aq)\text{ }+\text{ }{{H}_{2}}O(l)\text{ }\rightleftharpoons \text{ }{{H}_{3}}{{O}^{+}}(aq)+\text{ }C{{l}^{-}}(aq)$
The solution turns blue litmus paper into red because of the presence of ${{H}^{+}}$(aq) ions.
$HCl$ is completely dissociated in water.
So it is a strong acid. It has a higher value of dissociation constant.
Dissociation constant (${{K}_{a}}$) $\text{= }\dfrac{[{{H}_{3}}{{O}^{+}}(aq)]\text{ }[C{{l}^{-}}(aq)]}{[HCl(aq)]}$
Acids are proton donors and bases are proton acceptors.
So, the correct option is C.

$pH$ of a compound is the negative logarithm of the concentration of hydrogen ions in the compound.
Note: The strength of an acid is determined by the stability of the anion being formed when dissolved in an aqueous solution. $HCl$ dissociates into ${{H}_{3}}{{O}^{+}}$ and $C{{l}^{-}}$ ions in the solution. Now, the larger the counter anion the acid will be stronger because a large sphere can balance negative charge better than a small sphere. For this reason, $HCl$ is a strong acid.