Question

Calculate dissociation constant for an acid $\text{HA}$ having $\left[\right.H^{+}\left]\right.$ equals to $\text{0} \text{.1} \, \text{M}$ (Given: degree of dissociation of $\text{HA}$ is $\text{1\%}$ )

• A. $\text{1}\text{0}^{\text{-8}}$
• B. $\text{1}\text{0}^{\text{-6}}$
• C. $\text{1}\text{0}^{\text{-3}}$
• D. $\text{1}\text{0}^{\text{-7}}$

Answer 1

Answer: (C)

$k_{a}=\frac{\alpha ^{2} C}{1 - \alpha }$ , $\alpha $ is very small ;

$\therefore 1-\alpha \approx 1$

$\text{Cα} \, \text{=} \, \text{0} \text{.1}$

$k_{a} \, \text{=} \, \text{(Cα)α}$

$= 0.01 \times 0.1 = 10^{- 3}$