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Electrochemical series, also commonly referred to as activity series, is a list that explains the arrangement of components in order of their rising electrode potential values. The series has been produced by comparing the potential of several electrodes vs standard hydrogen electrodes (SHE).

In electrochemical series, the electrodes (metals and non-metals) in touch with their ions are organized on the grounds of the values of their standard reduction or oxidation potentials. Standard electrode potential is acquired by measuring the voltage when the half-cell is connected to the standard hydrogen electrode under standard circumstances.

Electropositive and Electronegative Elements

Elements (other than hydrogen) that demonstrate a stronger tendency to lose electrons to their solution are typically classed as electropositive. Similarly, elements that receive electrons are considered to be electronegative. They are frequently below the element hydrogen in the series. In any event, if we look at the electrochemical series, we can figure out the sequence in which metals will replace one another from their salts. So, electropositive metals often replace hydrogen from acids.

Electrochemical Series Chart

The Electrochemical series chart is a simple way of showing comparable vs. dissimilar metals. For roofers, we need to know what compatibility difficulties exist with reference to material. In this chart, common roofing metals (as well as rare) are shown. In most basic words, metals that reside further apart from one other on this scale will react with a higher tendency for corrosion than ones that are near together. (i.e. Zinc and Copper = far apart from each other scale. This implies we would never have a copper pipe draining water onto a zinc-coated roof). 4

Reaction

Standard electrode potential

(E°) in volts at 25 °C

F2(g) + 2e– 2F–(aq)

+2.87

H2O{aq) + 2H+(aq) + 2e– 2H2O(1)

+ 1.77

Au+(aq) + e– Au(s)

+ 1.68

Cl2(g) + 2e– 2c1–(aq)

+ 1.36

O2(g) + 4H+(aq) + 4e– 2H2O(1)

+ 1.23

Bri{I) + 2e– 2Br–(aq)

+ 1.09

Ag+(aq) + e– Ag(s)

+0.80

Fe H(aq) + e– Fe2+(aq)

+0 .77

02(g) + 2H+(aq) + 2e– H202(aq)

+0.68

12(s) + 2e– 21–(aq)

+0 .54

O2(g) + 2H2O(1) + 4e– 4OH–(aq)

+0.40

Cu2+(aq) + 2e– Cu(s)

+0.34

Sn4+(aq) + 2e– Sn2+(aq)

+0.15

S(s) + 2H+(aq) + 2e– H2S(g)

+0.14

2H+(aq) + 2e– H2(g)

0.00

Pb2+(aq) + 2e– Pb(s)

-0. 13

Sn2+(aq) + 2e– Sn(s)

-0.14

Ni2+(aq) + 2e– Ni(s)

-0.23

Co2+(aq) + 2e– Co(s)

-0.28

Fe2+(aq) + 2e– Fe(s)

-0.44

Zn2+(aq) + 2e– Zn(s)

-0.76

2H2O(1) + 2e– H2(g) + 2OH–(aq)

-0.83

Mn2+(aq) + 2e– Mn(s)

–1.03

Al 3+(aq) + 3e– Al(s)

-1.67

Mg2+(aq) + 2e– Mg(s)

-2.34

Na+(aq) + e– Na(s)

-2.71

Ca2+(aq) + 2e– Ca(s)

–2.87

K+(aq) + e– K(s)

–2 .93

Li+(aq) + e– Li(s)

-3.02

Application of Electrochemical Series

  1. Oxidizing and Reducing Strengths

Electrochemical series enables us to find a suitable oxidizing agent or reducing agent. All the item appearing on the top of the electrochemical series are a good oxidizing agent i.e., they have positive Value of standard reduction potential whereas those showing on the bottom of the electrochemical series are a good reducing agent i.e., they have a negative value of standard reduction potential. 

  1. Calculation of Standard emf (E0) of Electrochemical Cell

The normal emf of the cell is the sum of the conventional reduction reaction of the two half cell: reduction half cell and oxidation half cell

Eocell = Eored + Eooxi

By convention, the standard oxidation potential is always represented in terms of reduction potential.

Thus, standard oxidation potential (Eooxi) = – standard reduction potential Eored

Therefore, Eocell = ( standard reduction potential of reduction half cell) – (standard reduction potential of oxidation half cell) (standard reduction potential of oxidation half cell)

As oxidation takes place at anode and reduction takes place at the cathode. Hence, Eocell = Eocathode – Eoanode

  1. Predicting the Feasibility of Redox Reaction

Any redox reaction could happen suddenly if the free energy change (ΔG) is negative. The free energy is connected to cell emf in the following manner:

ΔGo = nFEo

Where n is the number of electrons involved, F is the Faraday constant and Eo is the cell emf.

  • ΔGo can be negative if Eo is positive.
  • When Eo is positive, the cell response is spontaneous and acts as a source of electrical energy.
  • If it ends up negative then the spontaneous reaction cannot take place.
  • The resulting value of Eo for redox reaction is essential in determining the stability of a metal salt solution when kept in another metal container.
  1. Predicting the Product of Electrolysis

In case, two or maybe more types of positive and negative ions are present in solution, during electrolysis some metal ions are discharged or freed at the electrodes in preference to others. In general, in such competition, the ion which is a stronger oxidizing agent (high value of standard reduction potential) is discharged first at the cathode.

Significance of electrochemical series

  • In the electrochemical series, the reduction potential of an element is taken in relation to the hydrogen scale where Eo = zero. As per the definition, the standard reduction potential of a component is stated as the measure of the tendency of a component to undergo reduction.
  • The greater the reduction potential of a component the more readily it will be decreased. Meanwhile, elements that have little reduction potential will get oxidized considerably rapidly and readily.
  • Alternatively, elements who give up electrons without any effort have negative or lower reduction potential. Elements that do not give up electrons readily rather they receive electrons easily have positive or greater reduction potential.
  • Stronger reducing agents that have negative standard reduction potential are frequently located below the hydrogen in the electrochemical series. On the other hand, weaker reducing agents with positive standard reduction potential are located above the hydrogen in the series.

Conclusion:

Activity series or electrochemical series is a list that consists of groupings of components in the terms of increasing electrode potential values. By analysing and evaluating the Standard Hydrogen Electrode (SHE) with regard to the potential electrodes, the series has been created. All the electrodes (metals and non-metals) as per their interaction with their ions are grouped in the electrochemical series on the grounds of their distinct values of standard oxidation and reduction potential.