pH is mathematically defined as the negative log of the hydronium concentration. Or:
pH = –log[H3O+]So, what is H3O+? Simply put, it is the active ingredient of acid. A more concentrated acid will produce more H3O+.
Water spontaneously reacts with itself to form hydronium (H3O+) and hydroxide (OH-):
2H2O <----> H3O+ + OH-At 25°C, the concentration of hydronium times the concentration of hydroxide is always 1x10-14 moles per liter (M). Mathematically:
[H3O+][OH-]= 1x10-14To make a long story short, [H3O+] cannot be zero and will never be zero. So, any and all aqueous solutions must have a pH value. Besides, the log of 0 is really big. I mean really, really big.
A neutral solution has equal amounts of hydronium and hydroxide:
[H3O+] = [OH-] = 1x10-7 M (at 25°C)The pH of a neutral solution is 7 since -log(1x10-7) = 7.
So, it is inaccurate to say a solution does not have a pH.
A solution can have a negative pH. For example a pH of -1.0 would correlate to a hydronium concentration of 10M.
Every common usage of pH is at 25°C. pH is temperature dependent. For example a neutral solution of pure water at 100°C has a pH of 6.14!!! Even though the pH is <7, this is neutral solution!!!!