Calculate pH of a weak acid HA, if the degree of dissociation of 1M solution being 10%:

Question

Accepted Answer

To calculate the pH of a weak acid HA with a degree of dissociation of 10% in a 1M solution, we need to understand the relationship between dissociation, concentration, and pH.

1. **Understanding Degree of Dissociation:**
   - The degree of dissociation (α) is given as 10%, which means that 10% of the acid dissociates into its ions.
   - For a 1M solution, this means that 0.1M of the acid dissociates into H⁺ ions and A⁻ ions.

2. **Calculating [H⁺]:**
   - Since 10% of the 1M solution dissociates, the concentration of H⁺ ions ([H⁺]) is 0.1M.

3. **Calculating pH:**
   - pH is calculated using the formula: pH = -log[H⁺].
   - Substituting the value of [H⁺] = 0.1M, we get:
     $$
     \text{pH} = -\log(0.1) = 1
     $$

4. **Justification for Option 1:**
   - The calculation shows that the pH of the solution is 1, which matches Option 1. This confirms that Option 1 is the correct answer.

5. **Explanation of Incorrect Options:**
   - **Option 2 (pH = 2):** This would imply that the concentration of H⁺ ions is 0.01M, which is not consistent with a 10% dissociation of a 1M solution.
   - **Option 3 (pH = 3):** This would imply that the concentration of H⁺ ions is 0.001M, which is far less than the 0.1M calculated from the 10% dissociation.
   - **Option 4 (pH = 4):** This would imply that the concentration of H⁺ ions is 0.0001M, which is incorrect given the degree of dissociation.

In conclusion, the correct answer is Option 1, as the pH of the solution, calculated based on the given degree of dissociation, is indeed 1.