Definition of pH:

What is of interest in this reading, however, is the acid-base
nature of a substance like water. Water actually behaves both like
an acid and a base. The acidity or basicity of a substance is defined
most typically by the pH value, defined as below:



At equilibrium, the concentration of is 1.00 × 10-7,
so we can calculate the pH of water at equilibrium as:

= -log[1.00 × 10-7] = 7.00

Solutions with a pH of seven (7) are said to be neutral,
while those with pH values below seven (7) are defined as acidic
and those above pH of seven (7) as being basic.

pOH gives us another way to measure the acidity of a solution.
It is just the opposite of pH. A high pOH means the solution is acidic
while a low pOH means the solution is basic.