Which of the following mixture can act as a buffer?

Options

A. NaOH+HCOONa (1:1 molar ratio)
B. HCOOH+NaOH (2:1 molar ratio)
C. `NH_(4)Cl+NaOH` (2:1 molar ratio)
D. HCOOH+NaOH (1:1 molar ratio

Answer

To determine which of the following mixtures can act as a buffer, we need to understand what constitutes a buffer solution. A buffer solution is typically made from a weak acid and its conjugate base or a weak base and its conjugate acid.

Let’s analyze the given mixtures step by step:

1. **Identify the Components of Each Mixture**:
- **Mixture 1**: HCO⁻ (conjugate base) and NaOH (strong base)
- **Mixture 2**: HCOOH (weak acid) and NaOH (strong base)
- **Mixture 3**: NH₄Cl (weak acid) and NaOH (strong base)
- **Mixture 4**: HCOOH (weak acid) and NaOH (strong base)

2. **Analyze Mixture 1 (HCO⁻ and NaOH)**:
- Both components are bases. Since there is no weak acid present, this mixture cannot act as a buffer.

3. **Analyze Mixture 2 (HCOOH and NaOH)**:
- HCOOH is a weak acid, and when it reacts with NaOH, it forms HCO⁻ (the conjugate base) and water. This mixture has both a weak acid (HCOOH) and its conjugate base (HCO⁻), so it can act as a buffer.

4. **Analyze Mixture 3 (NH₄Cl and NaOH)**:
- NH₄Cl can dissociate to give NH₄⁺ (weak acid) and Cl⁻ (conjugate base). When it reacts with NaOH, it forms NH₄OH (weak base) and NaCl. This mixture contains a weak acid (NH₄⁺) and its conjugate base (NH₄OH), so it can also act as a buffer.

5. **Analyze Mixture 4 (HCOOH and NaOH)**:
- Similar to Mixture 2, HCOOH is a weak acid and reacts with NaOH to form HCO⁻ (the conjugate base) and water. This mixture also contains both a weak acid and its conjugate base, so it can act as a buffer.

6. **Conclusion**:
- Mixtures that can act as buffers: Mixture 2 (HCOOH and NaOH), Mixture 3 (NH₄Cl and NaOH), and Mixture 4 (HCOOH and NaOH).
- Mixture 1 (HCO⁻ and NaOH) cannot act as a buffer.

### Summary of Buffer Solutions:
- **Buffer Mixtures**:
- Mixture 2: HCOOH + NaOH (Weak Acid + Strong Base)
- Mixture 3: NH₄Cl + NaOH (Weak Acid + Strong Base)
- Mixture 4: HCOOH + NaOH (Weak Acid + Strong Base)
- **Non-Buffer Mixture**:
- Mixture 1: HCO⁻ + NaOH (Both are Bases)