 Okay, so what is the Ka expression for the following reaction? So Ka is just like K, okay? It's just Ka means that it's an acid. So it's just an equilibrium constant, okay? So for the equilibrium constant, all you got to do is take the concentration of the products and put them over the concentration of the reactions. But you got to remember that you want to only do it for the aqueous stuff, okay? So, concentration of BRO minus divided by the concentration of pychogroma acid, which should be, and the Ka for this one is actually, oh, three. So if we wanted to find the pKa of this, what's the pKa of that? You just take, so the pKa equals what? The negative log of the KaK, so the negative log.