Question

Does pKa affect pH?

Answer 1

pKa is a measure of how much of the acid will ionize in water creating hydrogen ions. The more hydrogen ions in the water the lower the pH.

Answer 2

The lower (more negative) the `pK_a`, the lower (more negative) the `pH`. `pK_a` quantifies aqueous acidity.

Explanation:

For the generalized acid base reaction in water, we write:

`HA(aq) + H_2O(l) rightleftharpoonsH_3O^+ + A^-`

`K_a=([H_3O^+][A^-])/([HA(aq)])`

`log_10K_a=log_10[H_3O^+]+log_10{[[A^-]]/[[HA]}}`

On rearrangement,

`-log_10[H_3O^+]=-log_10K_a+log_10{[[A^-]]/[[HA]}}`

`pH=pK_a+log_10{[[A^-]]/[[HA]}}`

And thus acids with large `K_a` values, and negative `pK_a` values gives rise to low `pH` solutions.