The hydrogen ion concentration of 0.1 M solution of acetic acid, which is 20% dissociated, is

Options

A. 0.02 M
B. 2 M
C. 0.2 M
D. 0.002 M

Answer

To find the hydrogen ion concentration of a 0.1 M solution of acetic acid that is 20% dissociated, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the given values**:
- Concentration of acetic acid (C) = 0.1 M
- Degree of dissociation (α) = 20% = 0.20 (as a fraction)

2. **Write the dissociation equation**:
Acetic acid (CH₃COOH) dissociates in water as follows:
\[ \text{CH}_3\text{COOH} \rightleftharpoons \text{CH}_3\text{COO}^- + \text{H}^+ \]

3. **Determine the change in concentration**:
- Initial concentration of acetic acid = C = 0.1 M
- At equilibrium, the concentration of dissociated acetic acid will be:
\[ \text{Concentration of dissociated acetic acid} = C \cdot \alpha = 0.1 \cdot 0.20 = 0.02 \, \text{M} \]

4. **Calculate the hydrogen ion concentration**:
- Since each molecule of acetic acid that dissociates produces one hydrogen ion (H⁺), the concentration of hydrogen ions [H⁺] will be equal to the concentration of dissociated acetic acid:
\[ [\text{H}^+] = C \cdot \alpha = 0.1 \cdot 0.20 = 0.02 \, \text{M} \]

5. **Final answer**:
- The hydrogen ion concentration of the 0.1 M solution of acetic acid that is 20% dissociated is **0.02 M**.