Question

Calculate degree of dissociation of a weak monobasic acid in $0.01 \text{ M}$ solution if dissociation constant is $1.6 \times 10^{-5}$.

• A. 0.02
• B. 0.03
• C. 0.04
• D. 0.05

Hint:

Shortcut: $\alpha = \sqrt{\frac{K_a}{C}}$

Answer 1

The Correct Option is C

Concept: For weak acid: \[ K_a = C\alpha^2 \Rightarrow \alpha = \sqrt{\frac{K_a}{C}} \]

Step 1: Substitute values. \[ \alpha = \sqrt{\frac{1.6 \times 10^{-5}}{0.01}} \]

Step 2: Simplify. \[ = \sqrt{1.6 \times 10^{-3}} \]

Step 3: Calculate. \[ \alpha \approx \sqrt{1.6} \times 10^{-1.5} \approx 0.04 \]

Step 4: Conclusion.
Degree of dissociation = 0.04 Final Answer: Option (C)