# How does the degree of dissociation affect ka?

Sep 7, 2014

The larger the value of ${K}_{a}$, the greater the extent of dissociation.

For any acid, $H A$, we can write the dissociation process as

$H A \left(a q\right) \leftrightarrow {H}^{+} \left(a q\right) + {A}^{-} \left(a q\right)$

The equilibrium constant for this process is defined as the ratio of equilibrium products and reactants:

${K}_{a} = \frac{\left[{H}^{+}\right] \left[{A}^{-}\right]}{\left[H A\right]}$

If ${K}_{a}$ is large, then the concentration of dissociated ions is larger than the concentration of dissolved acid, $\left[H A\right]$

Examples (assumes the total concentration of acid is 1 M):

If ${K}_{a} = 0.03$ then the degree of dissociation is 15.9%, but if
${K}_{a} = 0.05$ then the degree of dissociation is 20.0%, and if
${K}_{a} = 3.8$ then the degree of dissociation is 82.2%