Question

When a strong base (NaOH) is added to a weak acid (acetic acid,$C{{H}_{3}}COOH$) then dissociation of acetic acid increases. This effect is known as:
[A] Common ion effect
[B] Reverse ion effect
[C] Saltation effect
[D] Solubility effect.

Answer 1

Hint: To solve this, firstly write down the dissociation of the weak acid given to you. Check the ions furnished by the acid and the base and see if they have any common ions. Use this to answer the question.

Complete step by step answer:
Here, a strong acid and a strong base are given to us. To answer this question, let us discuss the effects mentioned in the options.
Firstly we have a common ion effect. It refers to the decrease in solubility of the precipitate of an ionic compound upon addition of a solution of a soluble compound with an ion common with the precipitate. This effect is commonly seen as an effect on solubility of salts and weak electrolytes. It is based upon the fact that the original salt and the solution will contain an ion in common.
Then we have a reverse ion effect. It is basically the opposite of the common ion effect. Dissociation of opposite ions in a solution will
Next we have salt effect. Rate of a reaction can be altered by addition of an inert or non-reacting species in a solution. The effect upon the rate of the reaction on addition of the inert salt is known as the saltation effect.
Lastly, we have a solubility effect. Interaction of the solute with the solution particles leads to the stabilization of the solute. The solute is surrounded by the solution particles and thus affects the rate of the reaction.
Now to answer the question, let us write down the dissociation reaction of acetic acid.
     \[C{{H}_{3}}COOH\rightleftharpoons C{{H}_{3}}CO{{O}^{-}}+{{H}^{+}}\]
We can see that it furnishes hydrogen ions in solution. When we add a strong base like NaOH, the concentration of the hydrogen ion decreases as it combines with the hydroxyl ions furnished by NaOH and the reaction moves in the forward direction.
     \[\begin{align}
  & C{{H}_{3}}CO{{O}^{-}}+N{{a}^{+}}\to C{{H}_{3}}COONa \\
 & {{H}^{+}}+O{{H}^{-}}\to {{H}_{2}}O \\
\end{align}\]
Presence of the reverse ions increases the dissociation of the weak acid and as neutralization progresses, ionization of acetic acid increases. This is the reverse ion effect.
Therefore, the correct answer is option [B] reverse ion effect.

Note: Acetic acid is a weak acid. When NaOH is added (that is a strong base), the concentration of the hydrogen ions furnished by the weak acid decreases and thus the pH of the solution increases and the solution becomes basic. The equilibrium for dissociation of acetic acid shifts towards right and the concentration of $C{{H}_{3}}CO{{O}^{-}}$ increases in the solution.