The potential difference between an anode and a cathode can be measured by a voltage measuring device. The absolute potential of the anode and cathode cannot be measured directly. Defining a standard electrode, all other potential measurements can be made against this standard electrode. If the standard electrode potential is set to zero, the potential difference measured can be considered as the absolute potential.

Metals which are higher in the electrochemical series displace metals which are lower in the sequence, which means when connecting two metals, the metal with lowest potential will corrode. A very common connection in piping systems is copper and iron or steel. In a connection like this iron or steel will corrode many times faster than iron or steel alone.

The electrochemical series consists of a list of metals which have been arranged in order of their standard electrode potentials.

• Element---Electrode Potential (Volts)
• Lithium   -3.04
• Rubidium  -2.92
• Potassium -2.92
• Calcium   -2.87
• Barium    -2.80
• Sodium    -2.71
• Magnesium -2.37
• Aluminum  -1.67
• Magnesium -2.34
• Zinc      -0.76
• Chromium  -0.74
• Iron      -0.44
• Nickel    -0.24
• Tin       -0.14
• Lead      -0.13
• Hydrogen  +0.00
• Copper    +0.34
• Iodine    +0.54
• Silver    +0.80
• Gold      +0.80
• Mercury   +0.80
• Iodide    +0.54
• Bromine   +1.07
• Chlorine  +1.36
• Fluorine  +2.87

Standard Hydrogen Electrode
The half-cell in which the hydrogen reaction takes place is called the Standard Hydrogen Electrode - SHE

Standard Electrode Potential
The potential difference measured between metal M, and the Standard Hydrogen Electrode