A challenge!

Question

1. Explain the meaning of pH, both in terms of hydrogen ions and hydronium ions.

2. Why do chemists not usually use pH to describe [H3O+] when the pH value would be a negative number?

Answer 1

1.
pH = -log[H^+(aq)] or pH = -log[H3O^+(aq)]
where [H^+(aq)] is the concentration of hydrogen ions,
and [H3O^+(aq)] is the concentration of hydronium ions,

2.
Chemists usually use the whole range of pH (approximately from -1 to 15). However, pH values less than 0 and greater than 14 are usually not used in layman level, because such pH values would make confusion for people who are not good in Chemistry.