How to use a pH meter?

What is a pH meter?

In order to measure pH, we need a measuring instrument with a sensitivity to hydronium ions that determines the pH. It’s a voltmeter.
The basis of the measurement consists in taking a sensor with a glass membrane sensitive to hydronium ions (pH electrode) and in observing the reaction between the membrane and the sample: potential measurement.
This potential is compared to a reference potential delivered by a non-pH-sensitive electrode, by diffusion of an electrolyte towards the sample through a diaphragm: reference electrode (Ag/AgCl).

A solution’s pH is thus the potential difference between both electrodes according to Nernst’s equation :

  E = E0 + 2.3RT / nF * log [H3O+]

  E = measured potential
  E0 = constant
  R = gas constant
  T = temperature in Kelvin degrees
  n = ionic charge
  F = Faraday’s constant

For simpler use, both electrodes are combined in one single electrode.

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