Introduction to electro chemical series and corrosion of metals.
The potential difference between an anode and a cathode can be measured by a voltage measuring device but since the absolute potential of an anode or cathode cannot be measured directly - all potential measurements are made against a standard electrode. The standard electrode potential is set to zero and the measured potential difference can be considered as absolute.
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 a metal M and the Standard Hydrogen Electrode - SHE
The electro-chemical series (electro-motive series) is a list of metals arranged in order of their standard potentials to the hydrogen electrode:
Elements - Electrode Potential
Electrode Potential (volts)
Note! - metals higher up in the electro-chemical series displaces metals lower in the series - which means that when connecting two metals with different potentials the metal with the lowest potential corrodes.
Corrosion Problem when Connecting Copper and Iron/Steel
A very common connection in piping systems are copper and iron/steel. with this connection iron/steel corrodes many times faster than iron/steel alone.