## Chemistry (4th Edition)

pH is the negative logarithm of the hydronium ion concentration: $pH = -log[H_3O^+]$ We choose to discuss the acidity by pH representation because, it is easier to represent, if compared to the concentration of hydronium ion, which is, most of the time, a very small number.
You can find this information in every textbook that talks about acids and bases, or in the internet. Example of pH representation: $[H_3O^+] = 10^{-7}$ is represented by: $pH = 7$, which is a very simple way to describe the same information.