And that's because pure water dissociates into H plus and hydroxide. So at any given time, we can measure the concentration of of this guy in terms of molar amount. Now, if you want to learn more about how H plus relates to acids and oh, Myers relates to bases, check out the link below. So what happens when we add some substance to our pure water, our PR substance? Well, for example, suppose we add HDL to our water. What happens?