Now, the middle column describes that acid based reaction that takes place. On the left side, we have the acid. On the right side, we have the conjugate base that is formed when an H plus ion is actually lost. And the final column describes the PKA value. Now, what is the PKA value? Well, if the PH of our solution, in which that molecule is in, is equal to the PKA value, then what that means is exactly 50% of the molecules will exist in the acid form, and the other 50% will exist in the conjugate base form.