The dissociation constant Kw is 1. H2O varies with temperature, but at 25℃, KW = 10- 14, that is, only at this temperature, the pH=7 of neutral solution is 7. If at 62℃, KW = 10- 13, pure water = 6.5. Similarly, at 20℃, the pH of pure water is 7. 1. In other words, the criterion of acidity and alkalinity has lost its strictness;

2. According to the standard of pH value, the stronger the acidity of the solution, the lower the pH value; The weaker the acidity, the higher the pH value. Alkaline solution, pH >；; 7。 For a very strong acid, the pH becomes negative instead, which is contrary to the general thinking logic.

3. From a mathematical point of view, -lg[H+] should have a unit, because [H+] has a unit (mol/L), but in fact pH is used as an unitless scalar, which is not strict in mathematics. Based on this, a new concept of acidity, AG, was recently proposed to replace pH ... Ag is defined as: