So let's begin by recalling what Ka and PKA is with respect to some hypothetical acid. So let's suppose we have the following acid and we know that the acid dissociates into the H plus ion and its conjugate base. Now from basic chemistry we know that the equilibrium constant expression for this particular reaction is given by this equation. So the ka, the acid dissociation constant ka is equal to the product of the concentration of these two products divided by the concentration of this acid. Now what exactly does the Ka tell us about the acid? Well, the ka is nothing but a ratio between the concentration of the products and the concentration of the reactants.