What is the Nernst Equation?

The glass electrode response is governed by the Nernst Equation.

E = E0  + 2.3 (RT/nF) log H+

E = mV output from the electrode

E0  = Zero offset for the electrode

R = Ideal gas constant

F = Faraday constant

T = Temperature (ºK)

N = Ionic Charge (+1 for hydrogen)

By using Nernst, you can calculate that for each 1 unit change in pH, the measured mV value will change by 59.16mV at 25C.

The equation is a fundamental to pH measurement.

E = E0 – 2.3(RT/nF)log (Activity)

but pH = -log ( H+ ), the Sorenson equation so at 25°C, by substituting constant values.

The mV on meter µ  59.16.pH

So for every 1 unit change in pH, the mV reading on the meter will change by 59.16.

The graph for the Nernst equation is straight.

At ideal conditions, it should pass through 0mV, the iso potential point.

Posted in: E-chem