Ka is the acid dissociation constant while Kpa is simply the negative logarithm of Ka.

The dissociation constant for a strong acid can be as high as 10^7 while for a weak acid it can be as low as 10^-12.

pKa is expressed as a common logarithm (base 10) and not as a natural logarithm (base e).

**Formula to calculate Ka from pKa.**

**Example:**

Suppose the pKa is 7. Calculate the Ka.

Therefore, the Ka is 10^ -7. This means that this is a strong acid.