Does pKa affect pH?

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Answer 1 · 2016-12-06T19:07:19

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 · 2016-12-06T19:35:02

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

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.