Question

Calculate dissociation constant of 0.001M weak monobasic base undergoing 2% dissociation.

• A. $4 \times 10^{-7}$
• B. $2 \times 10^{-6}$
• C. $2 \times 10^{-7}$
• D. $1 \times 10^{-7}$

Hint:

Chemistry Tip: For weak electrolytes, $K=C\alpha^2$ when $\alpha$ is small.

Answer 1

The Correct Option is A

Step 1: Given concentration $C=0.001$ M and degree of dissociation $$ \alpha = 2\% = \frac{2}{100}=0.02 $$

Step 2: For weak monobasic base, $$ K_b=C\alpha^2 $$

Step 3: Substitute values: $$ K_b=0.001(0.02)^2 $$

Step 4: Calculate: $$ =10^{-3}\times4\times10^{-4}=4\times10^{-7} $$ $$ \therefore \text{Correct option is (A).} $$