59pH Definition and Measurement
Technical Definition of pH
In technical terms, pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion
activity, aH+, in a solution.
Ion-selective electrodes are often used to measure pH, respond to activity.
In this calculation of electrode potential, E, follows the Nernst equation, which, for the hydrogen
ion can be written as
where E is a measured potential, E^0 is the standard electrode potential, R is the gas constant, T is
the temperature in kelvin, F is the Faraday constant. For H+ number of electrons transferred is one.
It follows that electrode potential is proportional to pH when pH is defined in terms of activity.