To determine which aqueous solution of salts has the lowest pH value, we need to analyze the nature of each salt provided. The pH of a solution depends on whether the salt is derived from a strong acid and a strong base, a weak acid and a strong base, a strong acid and a weak base, or a weak acid and a weak base.
### Step-by-Step Solution:
1. **Identify the salts and their components**:
- **CH3COONa** (Sodium acetate): Derived from a weak acid (acetic acid, CH3COOH) and a strong base (sodium hydroxide, NaOH).
- **NaCl** (Sodium chloride): Derived from a strong acid (hydrochloric acid, HCl) and a strong base (sodium hydroxide, NaOH).
- **CH3COONH4** (Ammonium acetate): Derived from a weak acid (acetic acid, CH3COOH) and a weak base (ammonium hydroxide, NH4OH).
- **NH4Cl** (Ammonium chloride): Derived from a weak base (ammonium hydroxide, NH4OH) and a strong acid (hydrochloric acid, HCl).
2. **Analyze the pH contributions of each salt**:
- **CH3COONa**: The acetate ion (CH3COO-) will undergo hydrolysis to form CH3COOH and OH-. This makes the solution basic, resulting in a pH greater than 7.
- **NaCl**: Neither Na+ nor Cl- ions will hydrolyze in water since they come from a strong acid and a strong base. Thus, the solution remains neutral with a pH of 7.
- **CH3COONH4**: The acetate ion will produce OH- (making it basic), while the ammonium ion (NH4+) will produce H+ (making it acidic). The overall effect will depend on the relative strengths of these ions, but it generally results in a near-neutral pH.
- **NH4Cl**: The ammonium ion (NH4+) will hydrolyze to produce H+, making the solution acidic. Therefore, the pH will be less than 7.
3. **Conclusion**:
Among the given salts, **NH4Cl** produces the most H+ ions due to the hydrolysis of NH4+, leading to the lowest pH value. Thus, the aqueous solution of **NH4Cl** has the lowest pH.
### Final Answer:
The aqueous solution of **NH4Cl** has the lowest pH value.
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