Question

What are the applications of electrochemical series (or electromotive series)?

Answer 1

The applications of electrochemical series (or electromotive series) are as follows :

(1) Relative strength of oxidising agents in terms of E⁰_red values : 

The E⁰_red value is a measure of the tendency of the species to be reduced i.e., to accept electrons and act as an oxidising agent. The species mentioned on left hand side of the half reactions are oxidising agents.

The substances in the upper positions in the series and hence in the upper left side of the half reactions have large positive E⁰_red values hence are stronger oxidising agents.

For example,

F_2, Ce⁴⁺, Au³⁺, etc. 

As we move down the series, the oxidising power decreases. 

Hence from the position of the elements in the electrochemical series, oxidising agents can be selected.

(2) Relative strength of reducing agents in terms of E⁰_red values : 

The lower E⁰_red value means lower tendency to accept electrons but higher tendency to lose electrons. The tendency for reverse reaction or oxidation increases as E⁰_red becomes more negative and we move towards the lower side of the series. 

For example, 

Li, K, Al, etc. are good reducing agents.

(3) Identifying the spontaneous direction of reaction : From the standard reduction potentials, E⁰_red ,the spontaneity of a redox reaction can be determined. The difference between E⁰_red values for any two electrodes represents cell potential E⁰_cell ,constituted by them.

If E°cell is positive then the reaction is spontaneous while if E⁰_cell is negative the reaction is non-spontaneous. 

For example,

\(E^0_{Mg^{2+}/Mg}\) and \(E^0_{Ag^{+}/Ag}\) have values -2.37 V and 0.8 V respectively. 

Then Mg will be a better reducing agent than Ag. 

Therefore,

Mg can reduce Ag⁺ to Ag.

The corresponding reactions will be :

Therefore above reaction in the forward direction will be spontaneous while in the reverse direction will be non-spontaneous since for it E⁰_cell = -3.17V.

(4) Calculation of standard cell potential E : From the electrochemical series, the standard cell potential, E⁰_cell from the E⁰_red values for the half reactions given can be calculated.

For example,