any of the major appearances or aspects in which a thing of varying modes or conditions manifests itself to the eye or mind. 2. a stage in a process of change or development: Each phase of life brings its own joys. 3. a side, aspect, or point of view: This is only one phase of the question.
The pH of a neutral solution is 7. At this pH, the solution has equal concentrations of both the H+ and OH- ions, which is 10^-7 mole/litre. The presence of both the hydrogen and hydroxyl ions in equimolar concentrations makes the solution neutral.
A solution with a pH of 7 is neutral, while a solution with a pH below 7 is an acid and a solution with a pH above 7 is a base. An acid dissociates (breaks apart) and donates protons, or hydrogen ions, in an aqueous solution, while a base donates hydroxide ions in a solution.