Question

Acetic acid is a weak acid whereas $\text{HCl}$ is a strong acid. Give reasons.

Answer 1

Hint: The stronger electrolyte is the one which virtually undergoes the $100{\scriptstyle{}^{0}/{}_{0}}$ ionization into its corresponding ions. The equilibrium for strong electrolyte always lies to the left. The weak electrolyte is those which do not undergo $100{\scriptstyle{}^{0}/{}_{0}}$ ionisation. The equilibrium for weak electrolyte lies to the right. The hydrochloric acid is a strong electrolyte thus easily loses a proton and therefore it is a strong acid. However, the acetic acid cannot easily donate the proton as it is a weak electrolyte.

Complete step by step solution:
The strength of an acid depends on the proportion in which the acid reacts in water to generate ions.
We will use the Bronsted-Lowry definition of acid. The acid is the species that donates the proton. When the acid dissolves in the water, the proton ${{\text{H}}^{\text{+}}}$ is produced. Hydrogen chloride is a strong electrolyte. It completely dissociates into its corresponding ions in water.
The $\text{HCl}$ dissociate into the ${{\text{H}}^{\text{+}}}$and $\text{C}{{\text{l}}^{\text{-}}}$ ions. The equation for the ionization of hydrogen chloride is as follows:
$\text{HCl }\to \text{ H}_{\text{(aq)}}^{\text{+}}\text{ + Cl}_{\text{(aq)}}^{\text{-}}$
According to Bronsted –Lowry concept we can write it as:
$\text{HCl+}{{\text{H}}_{\text{2}}}\text{O}\rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{+}}}\text{+C}{{\text{l}}^{\text{-}}}$
Where ${{\text{H}}_{\text{2}}}\text{O}$ acts as a base. The ${{\text{H}}_{\text{3}}}{{\text{O}}^{\text{+}}}$ is the conjugate acid and $\text{C}{{\text{l}}^{\text{-}}}$ is the conjugate base.
The equilibrium for the reaction lies very much to the right (in forwarding direction) and the reverse reaction, representing the gain of protons by the chloride ion leading to the reformation of $\text{HCl}$, will take place to a very small extent. Thus, the chloride ion is a weak base.
If acid is a weak acid such as acetic acid, then it would have the only weak tendency to lose protons.
$\text{C}{{\text{H}}_{\text{3}}}\text{COOH+}{{\text{H}}_{\text{2}}}\text{O}\rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{+}}}\text{+C}{{\text{H}}_{\text{3}}}\text{CO}{{\text{O}}^{\text{-}}}$
Thus, the equilibrium lies mostly towards the left, and the reverse reaction representing the gain of protons by the $\text{C}{{\text{H}}_{\text{3}}}\text{CO}{{\text{O}}^{\text{-}}}$ion leading to the formation of $\text{C}{{\text{H}}_{\text{3}}}\text{COOH}$will take place to a very large extent .thus $\text{C}{{\text{H}}_{\text{3}}}\text{CO}{{\text{O}}^{\text{-}}}$ion is a strong base.

Note: The strong acids like $\text{ HCl , HN}{{\text{O}}_{\text{3}}}\text{ , }{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{ , etc}$ being the covalent compounds easily dissociate only in the solvent like water which can take up the proton, strong bases such as $\text{ NaOH , KOH , Ba(OH}{{\text{)}}_{\text{2}}},\text{ etc}$ being electrovalent compounds exist as an ion in the solid-state.