pKa/pKb

[Nysa Lilani 1J]

In a lot of practice problems from workshops, we are given the pKa value and are asked to order compounds in order of increasing acidity. How does pKa affect acidity, is it such that a lower pKa means a stronger acid and thus a lower pH?

[Chem_Mod]

Hi Nysa,

Your observation is correct! The lower the pKa of an acid, the stronger it is! The way to prove this mathematically is by doing 10^-pka .This gives you a Ka value that corresponds to the pKa of the acid of interest. We know that looking at Ka can give us an indication of whether it's strong or not and from here you can easily understand strengths. The quick method is like you said, the smaller the pKa, the stronger that acid is.

Hope this helps!

-Jaden