The classical first year chemistry definition of “pH” refers back to Danish biochemist Søren Sørenson, who originated the term, alluding to the “potential of hydrogen ion.” Specifically, pH is the negative logarithm of the molar concentration of the hydrogen ion (H+) in the particular solution.
This is usually expressed as a formula…
pH = -log[H+]
where [H+] is that molar concentration, and
log refers to the common logarithm—or log to the base 10—as will be applied in the formula.
Often, though, more detail is required on this concept, since the above definition oversimplifies the chemistry involved. Thus, we link to two excellent discussions of pH. The first provides a good basic understanding, while the second expands the concept quite a bit.