So initially, when we haven't added those H plus ions yet, we are at a PH of seven. And that's because we're dealing with pure water. Now, notice what happens along the curve. As soon as we add even a tiny amount of those H plus ions as soon as even a tiny number of those H plus ions are mixed into our solution. Notice what happens to the curve. The curve drops from seven all the way to two very drastically immediately following the addition of H plus ions.