Question

How does the degree of dissociation affect ka?

Answer 1

The larger the value of `K_a`, the greater the extent of dissociation.

For any acid, `HA`, we can write the dissociation process as

`HA(aq) harr H^+(aq) + A^(-)(aq)`

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

`K_a={[H^+][A^(-)]}/([HA])`

If `K_a` is large, then the concentration of dissociated ions is larger than the concentration of dissolved acid, `[HA]`

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%