A buffer solution cannot be prepared from a mixture of

Options

A. sodium acetate and acetic acid in water
B. Sodium acetate and hydrochloric acid in water
C. ammonia and ammonium chloride in water
D. ammonia and sodium hydroxide in water.

Answer

To determine which mixture cannot form a buffer solution, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Buffer Solutions**:
- A buffer solution is an aqueous solution that can resist changes in pH upon the addition of small amounts of acid or base. It is typically made from a weak acid and its conjugate base or a weak base and its conjugate acid.

2. **Analyzing the Options**:
- **Option A: Sodium Acetate (CH₃COONa) and Acetic Acid (CH₃COOH)**:
- Sodium acetate is the salt of acetic acid (a weak acid). When mixed, they can create a buffer solution because:
- CH₃COOH ⇌ CH₃COO⁻ + H⁺
- This mixture can resist pH changes, so it **can** form a buffer.

- **Option B: Sodium Acetate and Hydrochloric Acid (HCl)**:
- Hydrochloric acid is a strong acid. In the presence of a strong acid, the weak acid (acetic acid) will not be able to maintain the buffer capacity effectively.
- The reaction would lead to the formation of sodium chloride and acetic acid, which does not maintain the buffer system effectively due to the dominance of the strong acid.
- Thus, this mixture **cannot** form a buffer solution.

- **Option C: Ammonia (NH₃) and Ammonium Chloride (NH₄Cl)**:
- Ammonia is a weak base, and ammonium chloride is its conjugate acid. This combination can create a basic buffer solution:
- NH₃ + H⁺ ⇌ NH₄⁺
- Therefore, this mixture **can** form a buffer.

- **Option D: Ammonia and Sodium Hydroxide (NaOH)**:
- Sodium hydroxide is a strong base. Mixing ammonia (a weak base) with a strong base does not produce a conjugate acid-base pair that can maintain a buffer system.
- There is no salt formed in this case, so it **cannot** form a buffer solution.

3. **Conclusion**:
- The mixtures that cannot form a buffer solution are:
- **Option B: Sodium Acetate and Hydrochloric Acid**
- **Option D: Ammonia and Sodium Hydroxide**

### Final Answer:
A buffer solution cannot be prepared from a mixture of **Sodium Acetate and Hydrochloric Acid (Option B)** and **Ammonia and Sodium Hydroxide (Option D)**.

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