Question

The $pH$ of a $0.1M$ aqueous solution of a weak acid (HA) is 3. What is its degree of dissociation?

• A. $1$%
• B. $10$%
• C. $5$%
• D. $25$%

Answer 1

Answer: (A)

$1$%

Given:-

$pH=3$

Concentration $⟶0.1M$

Weak acid $⟶HA$

$HA\rightleftharpoons H^{\oplus }+A^{⊝}$

$C$ $0$ $0$

$C(1-\alpha )$ $C\alpha$ $C\alpha$

$\left[H^{+}\right]=C\alpha$

$\Rightarrow -\log \left[H^{+}\right]=3$

$\Rightarrow \left[H^{+}\right]={10}^{-3}$

$\Rightarrow {10}^{-3}=0.1\times \alpha$

$\Rightarrow \alpha ={10}^{-2}$

$\Rightarrow \alpha =1$%