0.02 M monobasic acid dissociates 2% hence, pH of the solution is

Options

A. 0.3979
B. 1.3979
C. 1.699
D. 3.3979

Explanation

To find the pH of a 0.02 M monobasic acid that dissociates 2%, we can follow these steps:

### Step 1: Determine the concentration of the acid
The concentration of the monobasic acid (HA) is given as 0.02 M.

### Step 2: Calculate the degree of dissociation
Since the acid dissociates 2%, we can calculate the concentration of the dissociated ions (H⁺) as follows:

\[ \text{Dissociated concentration} = \text{Initial concentration} \times \text{Degree of dissociation} \]
\[ \text{Dissociated concentration} = 0.02 \, \text{M} \times \frac{2}{100} = 0.02 \, \text{M} \times 0.02 = 0.0004 \, \text{M} = 4 \times 10^{-4} \, \text{M} \]

### Step 3: Calculate the pH
The pH is calculated using the formula:

\[ \text{pH} = -\log[H^+] \]
Substituting the value of [H⁺]:

\[ \text{pH} = -\log(4 \times 10^{-4}) \]

Using the logarithmic property:

\[ \text{pH} = -\log(4) - \log(10^{-4}) = -\log(4) + 4 \]

### Step 4: Calculate \(-\log(4)\)
The value of \(-\log(4)\) is approximately \(-0.6\) (since \( \log(4) \approx 0.6\)).

### Step 5: Final calculation of pH
Substituting this value back into the pH equation:

\[ \text{pH} = 4 - 0.6 = 3.4 \]

Thus, the pH of the solution is approximately **3.4**.

### Summary of Steps:
1. Determine the concentration of the acid.
2. Calculate the concentration of dissociated ions using the degree of dissociation.
3. Use the concentration of H⁺ ions to calculate the pH.
4. Use logarithmic properties to simplify the calculation.