What is the correct order of electrode potential series?
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Electrochemical Series
Electrochemical Series
Table of Content
Characteristics of Electrochemical Series
Applications of Electrochemical Series
Reactivity of Metals
Electropositive Character of Metals
Displacement Reactions
Reducing Power of Metals
Oxidising Nature of Nonmetals
Thermal Stability of Metallic Oxides
Products of Electrolysis
Increasing Order of Deposition
Increasing Order of Discharge
Corrosion of Metals
Extraction of Metals
Related Resources
By measuring the potentials of various electrodes versus standard hydrogen electrode (SHE), a series of standard electrode potentials has been established.
When the electrodes (metals and non-metals) in contact with their ions are arranged on the basis of the values of their standard reduction potentials or standard oxidation potentials, the resulting series is called the electrochemical or electromotive or activity series of the elements.
By international convention, the standard potentials of electrodes are tabulated for reduction half reactions, indicating the tendencies of the electrodes to behave as cathodes towards SHE.
Electrodes with positive E° values for reduction half reactions do in fact act as cathodes versus SHE, while those with negative E° values of reduction half reactions behave instead as anodes versus SHE. The electrochemical series is shown in the following table.
Standard Aqueous Electrode Potentials at 25°C 'The Electrochemical Series'
Element
Electrode Reaction (Reduction)
Standard Electrode Reduction potential Eo, volt
Li
Li+ + e- → Li
-3.05
K
K+ + e- → K
-2.925
Ca
Ca2+ + 2e- → Ca
-2.87
Na
Na+ + e- → Na
-2.714
Mg
Mg2+ + 2e- → Mg
-2.37
Al
Al3+ + 3e- → Al
-1.66
Zn
Zn2+ + 2e- → Zn
-0.7628
Cr
Cr3+ + 3e- → Cr
-0.74
Fe
Fe2+ + 2e- → Fe
-0.44
Cd
Cd2+ + 2e- → Cd
-0.403
Ni
Ni2+ + 2e- → Ni
-0.25
Sn
Sn2+ + 2e- → Sn
-0.14
H2
2H+ + 2e- → H2
0.00
Cu
Cu2+ + 2e- → Cu
+0.337
I2
I2 + 2e- → 2I-
+0.535
Ag
Ag+ + e- → Ag
+0.799
Hg
Hg2+ + 2e- → Hg
+0.885
Br2
Br2 + 2e- → 2Br-
+1.08
Cl2
Cl2 + 2e- → 2Cl-
+1.36
Au
Au3+ + 3e- → Au
+1.50
F2
F2 + 2e- → 2F-
+2.87
The negative sign of standard reduction potential indicates that an electrode when joined with SHE acts as anode and oxidation occurs on this electrode.
For example, standard reduction potential of zinc is -0.76 volt.
When zinc electrode is joined with SHE, it acts as anode (-ve electrode) i.e., oxidation occurs on this electrode. Similarly, the +ve sign of standard reduction potential indicates that the electrode when joined with SHE acts as cathode and reduction occurs on this electrode.

Characteristics of Electrochemical Series
The substances which are stronger reducing agents than hydrogen are placed above hydrogen in the series and have negative values of standard reduction potentials.
All those substances which have positive values of reduction potentials and placed below hydrogen in the series are weaker reducing agents than hydrogen.
The substances which are stronger oxidising agents than H+ion are placed below hydrogen in the series.
The metals on the top (having high negative values of standard reduction potentials) have the tendency to lose electrons readily. These are active metals.
The activity of metals decreases from top to bottom.
The non-metals on the bottom (having high positive values of standard reduction potentials)
have the tendency to accept electrons readily. These are active non-metals.
The activity of non-metals increases from top to bottom.
Applications of Electrochemical Series
Reactivity of Metals
The activity of the metal depends on its tendency to lose electron or electrons, i.e., tendency to form cation (M"+). This tendency depends on the magnitude of standard reduction potential.
The metal which has high negative value (or smaller positive value) of standard reduction potential readily loses the electron or electrons and is converted into cation. Such a metal is said to be chemically active.
The chemical reactivity of metals decreases from top to bottom in the series. The metal higher in the series is more active than the metal lower in the series. For example,
Alkali metals and alkaline earth metals having high negative values of standard reduction potentials are chemically active. These react with cold water and evolve hydrogen. These readily dissolve in acids forming corresponding salts and combine with those substances which accept electrons.
Metals like Fe, Pb, Sn, Ni, Co, etc., which lie a little down in the series do not react with cold water but react with steam to evolve hydrogen.
Metals like Cu, Ag and Au which lie below hydrogen are less reactive and do not evolve hydrogen from water.
Electropositive Character of Metals
The electropositive character also depends on the tendency to lose electron or electrons. Like reactivity, the electropositive character of metals decreases from top to bottom in the electrochemical series. On the basis of standard reduction potential values, metals are divided into three groups: