Nernst equation for
a pH electrode

Nernst equation is a mathematical description of an ideal pH electrode behavior. Hermann Walther Nernst (1864 – 1941) was a German chemist that introduced in 1889 a well known equation, correlating chemical energy and the electric potential of a galvanic cell or battery.

The pH electrode potential

As explained on the pH definition page of this site, the pH value is defined as the negative logarithm of the H+ activity in a given solution (pH = log aH+).

Equation of a straight line

The equation E = E0 - kT·pH is the potential or voltage (millivolt; mV) relation of a pH electrode. It is the equation of a straight line. The slope factor is the term "kT" and it provides the amount of change in total potential (mV) for every change in pH unit.


The equation E = E0 - kT·pH may be stated for any temperature. However, the slope or Nernst factor (kT) will change when temperature changes (T is not constant).

If T = 25 °C the equation will be: E = E0 - 0.0592·pH

Let's draw the graph of this equation:

This is the theoretical equation for an ideal pH electrode. And as you will see there is no ideal or perfect pH sensor. However, first let's read more about pH versus temperature.

Is there something on this page you want to comment on? Click here . . .

Alibris: Books, Music, & Movies - Click Here for ALL Your Office Supply Needs!

Favorite pages:

acids and bases
What is an acid? What is a base? If you want to know, read here!

calculating ph
Do you know what pH stand for? If not, click here!

electrode design
The pH electrode consists of the following parts:
. . read here!
offset error
Real-world pH electrodes are not ideal,
read why.

definition of ph
What is the definition of pH? See the answer. . .

nonglass ph electrode
Is it not possible to use a glass electrode for your application? Use a non-glass pH electrode.

ph measurement
Learn how the temperature affects your pH measurement.

When we share, we learn from each other!

Feel free to share your experiences and opinions of pH measurements. Submit your article or see contributions from other visitors!