0.01 moles of a weak acid HA(K_a=2.0x10^-6) is dissolved in 1.0 L of 0.1M  HCl solution. The degree dissociation of HA is________x10^-5(Round off to the nearest integer). [Neglect volume change on adding HA. Assume degree of dissociation<<1].

$HA\stackrel{ }{\rightleftarrows }{H}^{+}+A^{-}$

Initial               0.01         0         0
Dissociated      X           ___     ___ 
Produced        ___           x         x
Equilitrium      0.01-x      x        x
$HCL\to H^{+}+C{l}^{-}$

0.1          0.1       0.1

$\begin{array}{l}Total\left[H^{+}\right]=0.1+x\cong 0.1;x<<<0.1\\ K_a=\frac{\left[H^{+}\right]\left[A^{-}\right]}{\left[HA\right]},2\\ 2\times {10}^{-6}=\frac{0.1\times C\alpha }{0.01}\\ \alpha =\frac{2\times {10}^{-6}\times {10}^{-2}}{{10}^{-1}\times {10}^{-2}}=2\times {10}^5=2\end{array}$