pH of `10^(-5) M HA` is :-

Options

A. less than 6
B. exactly equal to 6
C. just greater than 6
D. equal to 7

Explanation

To find the pH of a `10^(-5) M HA` solution, we can follow these steps:

### Step 1: Understand the dissociation of the weak acid (HA)
The weak acid HA dissociates in water as follows:
\[ HA \rightleftharpoons H^+ + A^- \]

Initially, we have a concentration of `10^(-5) M` for HA, and at equilibrium, we will have:
- Concentration of HA = `10^(-5) M - x`
- Concentration of \( H^+ \) = \( x \)
- Concentration of \( A^- \) = \( x \)

Since HA is a weak acid, we can assume that \( x \) is very small compared to `10^(-5) M`, so we can approximate:
\[ [HA] \approx 10^{-5} \]

### Step 2: Set up the equilibrium expression
At equilibrium, the concentration of \( H^+ \) ions will be approximately equal to \( x \). Therefore, we can say:
\[ [H^+] \approx 10^{-5} + x \approx 10^{-5} \]
Thus, we can assume:
\[ [H^+] \approx 10^{-5} \]

### Step 3: Calculate the pH
The pH is calculated using the formula:
\[ \text{pH} = -\log[H^+] \]
Substituting the value of \( [H^+] \):
\[ \text{pH} = -\log(10^{-5}) \]

### Step 4: Simplify the logarithm
Using the properties of logarithms:
\[ \text{pH} = -(-5) \cdot \log(10) \]
Since \( \log(10) = 1 \):
\[ \text{pH} = 5 \]

### Step 5: Conclusion
The pH of `10^(-5) M HA` is 5.