Equilibrium - Result Question 61
####63. A weak acid, HA, has a $K_a$ of $1.00 \times 10^{-5}$. If $0.100 mol$ of this acid is dissolved in one litre of water, the percentage of acid dissociated at equilbrium is closest to
(a) $1.00 %$
(b) $99.9 %$
(c) $0.100 %$
(d) $99.0 %$
[2007]
Show Answer
Solution:
- (a) Given $K_a=1.00 \times 10^{-5}, C=0.100 mol$ for a weak electrolyte, degree of dissociation
$\alpha=\sqrt{\frac{K_a}{C}} \sqrt{\frac{1 \times 10^{-5}}{0.100}}=10^{-2}=1 %$
