Electrode Potentials Including Standard Electrode Potential

The electrode potential is the voltage or potential difference between a cell created from a standard hydrogen electrode and the given electrode with the needed potential.

As a result of charged particle transport and polar molecule adsorption, it is the potential difference between a point on the electrode surface and a point in the bulk of the electrolyte.

The voltage across the standard hydrogen electrode is always zero.

Define Standard Electrode Potential 

The standard electrode potential takes place in a specially designed electrochemical cell. For instance, 

Pressure = 1 atm

Temperature = 298K

Concentration = 1M

The ‘E° cell’ symbol represents the standard electrode potential of the given cell. 

Electrode potential application:

Chemical and electrochemical reactions associated with corrosion can be predicted.

Chemicals and equipment for reaction control are chosen using this method.

The study of electrode potential in crevices and pits for controlling reactions aids in crevice corrosion and pitting research.

An electrode’s potential can be utilized to forecast corrosion responses. When the protective mechanism is inside the protective potential range, it is considered effective. The direction of electrons determines the voltage of an electrode.

It depends on:

Electrolyte concentration

Temperature

Pressure

A standard reference electrode is required for measuring electrode potential. The electrode’s absolute electromotive force (EMF) or voltage cannot be determined directly. Other voltage measurements can be done against this standard reference electrode after the potential of the standard electrode has been determined. The EMF detected can be treated as the absolute EMF of the cathode or anode if the reference electrode voltage is set to zero.

Measurement of Electrode Potential

A voltaic cell is formed by connecting a particular electrode to a standard hydrogen electrode (SHE) via a salt bridge to detect the electrode potential of that electrode.

In the hydrogen half-cell, a 1 M solution is utilized, and the temperature is kept at 25oC.

To determine the cell’s EMF, a calibrated potentiometer or a high resistance voltmeter, i.e., a valve voltmeter, is utilized. The voltmeter reading determines the electrode potential of the electrode. The standard electrode potential of a metal is the voltage difference created in a cell consisting of two electrodes: a pure metal in contact with a molar solution of one of its ions and a standard hydrogen electrode.

Application of standard electrode potential:

• It’s a tool for determining the relative strengths of various oxidants and reductants.

• It’s used to figure out how to determine standard cell potential.

• It’s used to foresee possible outcomes.

• Prediction of the reaction’s equilibrium.

Standard Electrode Potential’s importance in Chemistry

• Redox reactions are the base of all designed electrochemical cells. These are the combination of two and a half reactions.
• The oxidation reaction takes place at the given anode, including the loss of an electron.
• A reduction reaction tends to occur at the given cathode, due to which there is electrons gain. Therefore, the electrons move from the given anode and travel towards the cathode.
• Because of the present difference between the respective potential of individual electrodes, we see a rise in the electric potential between the cathode and the anode. 
• To measure the electrochemical cell’s potential, we use a special voltmeter. However, it is not possible to accurately measure a half-cell’s potential. 
• Also, note that this measured potential can vary due to changes in concentration, pressure, and temperature. 
• To find out a half-cell’s reduction potential, the necessity of standard electrode potential gets higher.
• To measure it, we can use a standard hydrogen electrode (SHE) which is a reference electrode. The value of electrode potential is zero volts for SHE. 
• To measure the electrode’s standard electrode potential, we can pair it with the designed SHE and measure the galvanic cell’s potential. 

Standard Electrode Potential Example

The computation of the standard electrode potential of a zinc terminal with the assistance of the common hydrogen electrode is outlined beneath.

It tends to be noticed that the potential is calculated under normal and controlled conditions where we can note:

The temperature = 298K, 

Pressure = 1 atm, 

Concentration of electrolytes = 1M

Electrochemical Series 

Electrochemical series refers to the arrangement of components based on their standard electrode potential values. It’s also known as an activity sequence. Higher standard electrode potential elements are placed over lower standard electrode potential elements. The items at the very top of the series tend to be easily decreased. The elements near the bottom, on the other hand, have the least inclination to be decreased.

Fluorine has the highest standard electrode potential. Hence it has the greatest inclination to be decreased. On the other hand, lithium has the least tendency to degrade because its usual electrode potential is the lowest. As a result, fluorine is a strong oxidising agent, while lithium is a strong reducing agent.

Conclusion 

The standard electrode potential of an electrolyte is defined as the electromotive force which takes place when the two electrodes are completely immersed in it and at equal distances. This potential is measured numerically by applying an external voltage which allows this difference to be measured electrically against a standard potential such as a metallic hydrogen electrode. This method could be related to the equilibrium constant for the electrochemical reaction.