Strength of an acid/base

[Chisomaga Azu]

How do we tell the strength of an acid/base based off the opposite pKa/pKb. Is there a way to tell the strength of an acid based off the pKb or would we need to find the pKa and vice versa for the strength of a base.

[Pranaya Vijay 1E]

You could convert pKa to pKb and then use that as an indicator of the strength of the base/acid.

[306020260]

The stronger the acid is (interchangeable with base), the weaker it's conjugate. If the acid is weak, its conjugate base is strong. High pKb indicates weak base and low pKb indicates a strong base (interchangeable with pKa). Therefore:
If the opposite pKa is high, it means it is a weak conjugate acid, and since we know that strong bases produce weak acids, we know the base is strong.
If the opposite pKa is low, we can assume it is a strong conjugate acid. Since we know that only weak bases make strong conjugate acids, we know the base is strong.
Hope this helps!

[Miyown Meeks 2F]

Hi, so yes you can find the strength of an acid based off of pKb. To explain, strong acids have weak conjugate bases, and a high pKb indicates a weak base. So if you have a high pKb you have a weak base, telling you that you have a strong acid! This same logic can be applied to bases as strong bases have weak conjugate acids.