Question

When add 0.01M HCl in aqueous solution of acetic acid:
A) $C{{H}_{3}}CO{{O}^{-}}$ molar conc. is decrease
B) $C{{H}_{3}}COO{{H}^{{}}}$ molar conc. is decrease
C) $C{{H}_{3}}CO{{O}^{-}}$ molar conc. is increase
D) None of these

Answer 1

Hint:. HCl is a strong acid whereas $C{{H}_{3}}COO{{H}^{{}}}$ is a weak acid.
The dissociation of weak acid is very slow as compared to the strong acid.

Complete step by step answer:
The requirement of the question is the effect that will cause when 0.01M HCl is added to aqueous solution of acetic acid.
- We know that HCl is the one of the strongest acids we know. And strong acid means it can easily dissociate in aqueous solution and can donate ${{H}^{+}}$ ions easily.
So in aqueous solution HCl ionizes as,
$HCl\to {{H}^{+}}+C{{l}^{-}}$
And the rate of ionization will be higher than the weak acids.
- Now let’s see the ionization tendency of acetic acid.
$C{{H}_{3}}COOH$ is a very weak acid, it ionizes rather than dissociation. Dissociation means the acid will get completely ionized or dissociated into its constituent ions.
In acetic acid, they do not undergo complete dissociation, only they are partially ionized.
- In aqueous solution, $C{{H}_{3}}COOH$ ionizes as,
$C{{H}_{3}}COOH\to C{{H}_{3}}CO{{O}^{-}}+{{H}^{+}}$
Only a few molecules of acetic acid undergo ionization and others stay as $C{{H}_{3}}COOH$ itself.
When we add a strong acid into an aqueous solution of weak acid then, the ionization of the weak acid is suppressed.
- Let’s write the reaction involved while 0.01M HCl is mixed with $C{{H}_{3}}COOH$
In aqueous solution, $C{{H}_{3}}COOH$exists as $C{{H}_{3}}CO{{O}^{-}}$
$C{{H}_{3}}CO{{O}^{-}}+{{H}^{+}}C{{l}^{-}}\to C{{H}_{3}}COOH+C{{l}^{-}}$
So from the reaction we came to know that the acetic acid is formed more and more. In the aqueous solution there is already some amount of acetic which has not gone dissociation. While adding HCl the concentration of $C{{H}_{3}}CO{{O}^{-}}$ is decreasing and concentration of $C{{H}_{3}}COOH$ is increasing. So, the correct answer is “Option A”.

Note: Acetic acid is weak acid and some have the concept that as acetic acid is a weak acid it easily ionizes than the strong acid. But the strong acid always suppresses the dissociation of weak acid, as the rate of dissociation of strong acid is far greater than that of the weak acid. The strong acid dissociates at a fast rate and produces ${{H}^{+}}$ ions which combines with weaker acid ions and yields the same acid which increases the concentration of weak acid in the solution.
- Always write the equations of the reactions and we can easily interpret the concentration of ions from the products formed.