So if we have a beaker of pure water, even in that beaker of pure water, water molecules will also dissociate by this same equation. So even though water is a weak acid, water molecules will still dissociate into these two ions, an H plus ion and a hydroxide ion. Now, by using basic chemistry, we can set up the equation for the equilibrium constant K. So the equilibrium constant K for this reaction is equal to the product of the concentration or the product of the concentrations of these two molecules divided by the concentration of the reactant, in this case, pure water. Now, at room temperature, this cave value is measured to be 1.8 times ten to negative 16. And the concentration of water in pure water is always a constant value. It's always equal to 55.5.