Question

0.01 moles of a weak acid HA($K_a=2.0\times {10}^{-6}$) is dissolved in $1.0L$ of $0.1MHCl$ solution. The degree of dissociation of HA is _______$\times {10}^{-5}$ (Round off to the Nearest Integer). Assume degree of dissociation << 1.

Answer 1

Concentration $H^{+}=0.1+0.01\alpha \approx 0.1$

$K_a=\frac{\left[H^{+}\right]\left[A^{-}\right]}{\left[HA\right]}$
$\Rightarrow 2\times {10}^{-6}=\frac{\left[0.1\right]\left[0.01\alpha \right]}{\left[0.01\right]}$
$\alpha =2\times {10}^{-5}$