Which of the following mixtures forms an acid buffer ?

Options

A. `NaOH + HCl`
B. `CH_(3)COOH + CH_(3)COONa`
C. `NH_(4)Cl + NH_(4)OH`
D. `H_(2)CO_(3) + (NH_(4))_(2)CO_(3)`

Answer

To determine which of the given mixtures forms an acid buffer, we need to understand the components that make up an acidic buffer solution. An acidic buffer consists of a weak acid and its conjugate base (which is typically a salt formed from the weak acid and a strong base).

Let's analyze the options step by step:

### Step 1: Identify the components of each mixture

1. **NaOH + HCl**
- NaOH is a strong base.
- HCl is a strong acid.
- This mixture forms a neutral salt (NaCl) and water.
- **Conclusion**: This does not form an acidic buffer.

2. **Acetic Acid (CH₃COOH) + Sodium Acetate (CH₃COONa)**
- Acetic acid is a weak acid.
- Sodium acetate is the salt formed from acetic acid and a strong base (NaOH).
- **Conclusion**: This mixture forms an acidic buffer.

3. **Ammonium Chloride (NH₄Cl) + Ammonium Hydroxide (NH₄OH)**
- Ammonium hydroxide is a weak base.
- Ammonium chloride is the salt formed from a weak base (NH₄OH) and a strong acid (HCl).
- **Conclusion**: This forms a basic buffer, not an acidic buffer.

4. **Carbonic Acid (H₂CO₃) + Ammonium Carbonate (NH₄CO₃)**
- Carbonic acid is a weak acid.
- Ammonium carbonate is formed from a weak base (NH₄OH) and a weak acid (H₂CO₃).
- **Conclusion**: This does not form an acidic buffer since it does not have a strong base.

### Step 2: Determine the correct option

From the analysis above, the only mixture that forms an acidic buffer is:

- **Acetic Acid (CH₃COOH) + Sodium Acetate (CH₃COONa)**

### Final Answer:
The correct option that forms an acidic buffer is **Acetic Acid + Sodium Acetate**.

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