The buffering action of an acidic buffer is maximum when its pH equals to

Options

A. 5
B. 7
C. 1
D. `pK_(a)`

Explanation

To determine the pH at which the buffering action of an acidic buffer is maximum, we can follow these steps:

### Step 1: Understand the concept of an acidic buffer
An acidic buffer is a solution that can resist changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid (HA) and its conjugate base (A⁻).

### Step 2: Use the Henderson-Hasselbalch equation
The Henderson-Hasselbalch equation for an acidic buffer is given by:
\[ \text{pH} = \text{pKa} + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right) \]
where:
- pH is the acidity of the solution,
- pKa is the negative logarithm of the acid dissociation constant (Ka) of the weak acid,
- [A⁻] is the concentration of the conjugate base,
- [HA] is the concentration of the weak acid.

### Step 3: Identify the condition for maximum buffering capacity
The buffering capacity of an acidic buffer is maximum when the concentrations of the weak acid (HA) and its conjugate base (A⁻) are equal. This means:
\[ [\text{A}^-] = [\text{HA}] \]

### Step 4: Substitute the condition into the Henderson-Hasselbalch equation
When [A⁻] = [HA], we can substitute this into the Henderson-Hasselbalch equation:
\[ \text{pH} = \text{pKa} + \log\left(\frac{[\text{HA}]}{[\text{HA}]}\right) \]
This simplifies to:
\[ \text{pH} = \text{pKa} + \log(1) \]

### Step 5: Evaluate the logarithm
Since the logarithm of 1 is 0:
\[ \log(1) = 0 \]

### Step 6: Finalize the pH value
Thus, the equation simplifies to:
\[ \text{pH} = \text{pKa} + 0 \]
or simply:
\[ \text{pH} = \text{pKa} \]

### Conclusion
The buffering action of an acidic buffer is maximum when its pH equals the pKa of the weak acid.

### Answer
The correct answer is: **pH = pKa**

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