Which one of the following mixtures is suitable for making a buffer solution will an optimum pH of 9.2 - 9.3 ?

Options

A. `CH_3CO_2Na//CH_3CO_2H (K_a = 1.8 xx10^(-5))`
B. `NH_3//NH_4Cl (K_a(NH_4^(+))=5.6 xx10^(-10)) `
C. `NaNO_2//HOCl(K_a = 4.5 xx10^(-8))`
D. `NaNO_2//HNO_2(K_a = 4.5xx10^(-4))`

Answer

To determine which mixture is suitable for making a buffer solution with an optimum pH of 9.2 - 9.3, we need to understand the components of a basic buffer solution. A basic buffer is typically made from a weak base and its conjugate acid (which is usually a salt formed from a strong acid).

### Step-by-step Solution:

1. **Identify the pH Range**: The question specifies that we need a buffer solution with a pH of 9.2 - 9.3. This indicates that we are looking for a basic buffer since this pH is above 7.

2. **Components of a Basic Buffer**: A basic buffer is generally composed of:
- A weak base (e.g., NH3)
- A salt of that weak base with a strong acid (e.g., NH4Cl, where NH4+ is the conjugate acid of NH3)

3. **Examine the Given Options**:
- **Option 1**: CSTCO2Na and CSTCO2H (Acetic Acid and its salt) - This is an acidic buffer.
- **Option 2**: NH3 and NH4Cl - This is a weak base (NH3) and its salt (NH4Cl), making it a basic buffer.
- **Option 3**: NaNO2 and HOCl - This is also an acidic buffer.
- **Option 4**: NaNO2 and HNO2 - This is another acidic buffer.

4. **Determine the Correct Option**: Among the options provided, only **Option 2 (NH3 and NH4Cl)** is suitable for creating a basic buffer that can maintain a pH of 9.2 - 9.3.

5. **Conclusion**: Therefore, the correct answer is **Option 2**.