Animated Solution for Chemistry - Ionic Equilibrium: Which of the following salts is the most basic in aqueous solution?

Why Some Are Acidic and Others Are Basic

When we think of "salt," we often picture the neutral table salt ($\text{NaCl}$) we sprinkle on our food. But in chemistry, salts are a diverse family, and they don't always play neutral! When dissolved in water, some salts can make the solution acidic, while others make it basic. This phenomenon is known as salt hydrolysis. Let's dive into a classic JEE problem to understand how this works.

Every salt is the "child" of an acid and a base reacting together in a neutralization reaction. The personality of the salt solution depends entirely on the strength of its parents.

- Strong Acid + Strong Base = Neutral Salt (e.g., $\text{NaCl}$) - Strong Acid + Weak Base = Acidic Salt (e.g., ${\text{NH}}_4\text{Cl}$) - Weak Acid + Strong Base = Basic Salt (e.g., ${\text{CH}}_3\text{COONa}$) - Weak Acid + Weak Base = It's complicated! (Depends on $K_a$ and $K_b$)

Let's interrogate the four salts given in our problem:

1. ${\text{FeCl}}_3$: This salt comes from ${\text{Fe(OH)}}_3$ (a weak base) and $\text{HCl}$ (a strong acid). The strong acid dominates, meaning the ${\text{Fe}}^{3+}$ ions will undergo cationic hydrolysis to release ${\text{H}}^{+}$ ions. Result? Acidic.

2. ${\text{Al(CN)}}_3$: Born from ${\text{Al(OH)}}_3$ (weak base) and $\text{HCN}$ (weak acid). Both parents are weak, so they fight it out. The solution will be close to neutral, perhaps slightly acidic or basic depending on the exact dissociation constants, but definitely not the most basic.

3. ${\text{Pb(CH}}_3{\text{COO)}}_2$: Similar story here. It's derived from ${\text{Pb(OH)}}_2$ (weak base) and ${\text{CH}}_3\text{COOH}$ (weak acid). Again, a weak-weak combination leading to a roughly neutral solution.

4. ${\text{CH}}_3\text{COOK}$: Ah, here we go! This salt is the product of $\text{KOH}$ (a very strong base) and ${\text{CH}}_3\text{COOH}$ (a weak acid). The strong base leaves its mark.

Why exactly does ${\text{CH}}_3\text{COOK}$ make the water basic? When it dissolves, it completely dissociates into ${\text{K}}^{+}$ and ${\text{CH}}_3{\text{COO}}^{-}$ ions.

The ${\text{K}}^{+}$ ion is the conjugate acid of a strong base ($\text{KOH}$). It's so weak that it just floats around as a spectator.

But the acetate ion (${\text{CH}}_3{\text{COO}}^{-}$) is the conjugate base of a weak acid. It's strong enough to react with water in a process called anionic hydrolysis:

Look at the products! The reaction generates hydroxide ions (${\text{OH}}^{-}$), which directly increases the pH of the solution, making it basic.

By simply identifying the parent acid and base of each salt, we can easily predict the nature of the resulting aqueous solution. Potassium acetate, with its strong base lineage, takes the crown as the most basic salt in this lineup.