Samples of NaF(s) and NH4Cl(s) are dissolved in separate beakers that each contain 100 mL of water. — Acids and Bases Chemistry Question

### STEPS:

1. Identify the species present in each solution:
When soluble salts are placed in water, they dissociate completely into their constituent ions:
* $\text{NaF}(s)$ dissociates to release $\text{Na}^+(aq)$ and $\text{F}^-(aq)$.
* $\text{NH}_4\text{Cl}(s)$ dissociates to release $\text{NH}_4^+(aq)$ and $\text{Cl}^-(aq)$.

2. Evaluate the acid-base properties of each ion (Salt Hydrolysis):
To determine which of these ions reacts with water to form an acidic solution, analyze their strengths as conjugate acids or bases:
* $\text{Na}^+(aq)$ is the conjugate partner of the strong base $\text{NaOH}$. It has negligible acid strength and does not react with water.
* $\text{Cl}^-(aq)$ is the conjugate partner of the strong acid $\text{HCl}$. It has negligible base strength and does not react with water.
* $\text{F}^-(aq)$ is the conjugate base of the weak acid $\text{HF}$. Because $\text{HF}$ is a weak acid, its conjugate partner $\text{F}^-$ acts as a weak base, hydrolyzing water to form $\text{OH}^-$ ions and making the solution slightly basic.
* $\text{NH}_4^+(aq)$ is the conjugate acid of the weak base $\text{NH}_3$. Because $\text{NH}_3$ is a weak base, its conjugate partner $\text{NH}_4^+$ acts as a weak acid, hydrolyzing water to produce hydronium ($\text{H}_3\text{O}^+$) ions and making the solution slightly acidic.

3. Select the corresponding reaction equation:
Since the ammonium ion ($\text{NH}_4^+$) is the species responsible for generating hydronium ions in solution, the hydrolysis reaction is represented as:
$$\text{NH}_4^+(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{NH}_3(aq) + \text{H}_3\text{O}^+(aq)$$
This matches Option C.

*

### WHY_OTHERS_WRONG:

• Option A is wrong because $\text{Na}^+$ is a spectator ion that does not react with water. Additionally, $\text{NaOH}$ is a strong base that exists fully dissociated into $\text{Na}^+$ and $\text{OH}^-$ ions in water, meaning it would not reform as intact neutral molecules.
• Option B is wrong because the hydrolysis of fluoride ($\text{F}^-$) produces hydroxide ions ($\text{OH}^-$), which results in a slightly basic solution, not an acidic one.
• Option D is wrong because chloride ($\text{Cl}^-$) is too weak a base to hydrolyze water. Additionally, $\text{HCl}$ is a strong acid that remains completely ionized in aqueous solutions rather than existing in molecular form.