What is pH?  pH is the measure of the hydronium ion concentration in a solution.  The scale runs from 0-14, with the lower numbers indicating higher concentration of the hydronium ion and therefore an increase in acidity.

A similar scale exists for the hydroxide ion.  The pOH scale runs 0-14 with the lower numbers indicating higher concentration of the hydroxide ion and therefore greater basicity.

The pH scale can be used to determine the hydronium ion and hydroxide ion concentrations.  As I have already mentioned, the lower numbers indicate higher acidity.  On the pH scale, the higher numbers indicate higher basicity and higher concentration of the hydroxide ion.  Its quite easy to convert between pH and pOH.  The equation relating the two is simply:

\(pH + pOH = 14\)

But perhaps you would like to convert between pH and the hydronium ion concentration \([H_3O^+]\)? To do this, you can utilize the following equation:

\(pH = – log [H_3O^+]\)

Similarly pOH can be converted to \([OH^-]\) by using the following equation:

\(pOH=-log[OH^-]\)

One might want to convert between \([H_3O^+]\) and \([OH^-]\).  To do this, you need the autoionization constant of water, or \(K_w\), which is \(1×10^{-14}\):

\(K_w=[H^+]X[OH^-]\)

Converting between pH and \([H_3O^+]\) is simple by using your logarithmic functions:

\([H_3O^+]=10^{-pH}\)

These equations can be combined into a handy chart as follows: