Reference Electrodes of the Second Kind

These reference electrodes can only be used with an interior electrolyte and an appropriate electrolyte bridge.

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Reference Electrodes with Salt Bridge (Reference Electrodes of Second Kind)

In former years, other systems besides the reversible hydrogen electrode have become established as reference electrodes. However, they can only be used with an interior electrolyte and an appropriate electrolyte bridge. These are reference electrodes of the second kind.
These reference electrodes should be chosen according to the measuring solution to avoid contamination and unnecessary diffusion voltages. Moreover, the diaphragm does not need to be as fine-pored, which reduces the transition resistance between the measuring solution and the reference electrode.
For aqueous solutions, the following references have been established:

Silver Silver-chloride Electrode 

Standard reference potential and reference potentials of the silver silver-chloride electrode against NHE @25°C.

(Values adopted from: Küster, Thiel, Rechentafeln für die chemische Analytik, 103. Auflage, 1985; Hamann, Vielstich, Elektrochemie, 3. Auflage, 1998)

 

Electrolyte
Volt
Cl a = 1 mol/kg

0.2224

KCl c = 1 mol/L

0.2368

KCL c = 3 mol/L

0.2070

KCl saturated

0.1976

Temperature dependence of the silver silver-chloride electrode.
Temperature dependence of the silver silver-chloride electrode.

Mercury Mercury-chloride Electrode 

Standard reference potential and reference potentials of the mercury mercury-chloride electrode against NHE @25°C.

(Values adopted from: Hamann, Vielstich: Elektrochemie; Wiley-VCH, 1998)

 

Electrolyte
Volt
KCl c = 0.1 mol/L

0.3337

Cl a = 1 mol/kg

0.2682

KCl c = 1 mol/L

0.2807

KCl saturated

0.2415

Temperature dependence of the mercury mercury-chloride electrode.
Temperature dependence of the mercury mercury-chloride electrode.

Mercury Mercury-sulfate Electrode 

Standard reference potential and reference potentials of the calomel electrode against NHE @25°C.

(Values adopted from: Hamann, Vielstich: Elektrochemie; Wiley-VCH, 1998)

 

Electrolyte
Volt
SO4 a = 1 mol/kg

0.6158

K2SO4 saturated

0.650

H2SO4 c = 0.5 mol/L

0.682

Temperature dependence of the mercury mercury-sulfate electrode.
Temperature dependence of the mercury mercury-sulfate electrode.

Mercury Mercury-oxide Electrode 

Standard reference potential and reference potentials of the mercury mercury-oxide electrode against NHE @25°C.

(Values adopted from: Hamann, Vielstich: Elektrochemie; Wiley-VCH, 1998)

 

Electrolyte
Volt
OH a = 1 mol/kg

0.097

NaOH c = 1 mol/L

0.140

NaOH c = 0.1 mol/L

0.165

Temperature dependence of the mercury mercury-oxide electrode.
Temperature dependence of the mercury mercury-oxide electrode.

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Electrolyte Key – Salt Bridge

An electrolyte bridge, also known as a salt bridge, is used for the contacting of various electrolytes. Commercial reference electrodes rely on salt bridges.

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Electrolytes in wich the hydrogen electrodes can be used.

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