Introduction of Standard Electrode Potential

The electromotive force of a cell made up of two electrodes is known as the electrode potential in electrochemistry.

The letter E stands for it. It is impossible to directly quantify the absolute value of a single electrode potential. Experimentally, only the difference in potential between two electrodes may be measured. So, in an experiment to measure electrode potential, one electrode is used as a reference electrode with a known potential, while another electrode with an unknown potential is used in a cell. The cell potential, which is equal to the total of the potentials on the two electrodes, is measured experimentally.

EAnode + ECathode = ECell  

The electrode potential of one electrode is already known, hence the electrode potential of another (electrode with unknown electrode potential) can be estimated using a voltmeter.

What does it mean to have a standard electrode potential?

The standard electrode potential for that half-cell or half-reaction is the potential of the half-reaction (half-cell) measured against the standard hydrogen electrode under standard conditions. Standard conditions are a temperature of 298K, a pressure of 1 atm, and an electrolyte concentration of 1M. It is calculated using typical hydrogen electrodes.

A gas – ion electrode is the most common type of hydrogen electrode. It is used to determine the standard electrode potential of elements and other half cells as a reference electrode. It may function as both an anode and a cathode half-cell. At 25°C or 298K, its standard reduction potential and standard oxidation potential are both zero. It is the foundation of the oxidation-reduction potentials thermodynamic scale.

E0 stands for the standard electrode potential. A standard hydrogen electrode can be used to compute either a standard reduction potential or a standard oxidation potential for an electrode. The difference between the standard reduction potentials of two half–cells or half–reactions is the standard cell potential. – is one way to express it.

Ecathode – Eanode = E0cell

Calculating the Zinc Electrode’s Standard Reduction

Potential

• By putting a zinc electrode in a half cell containing zinc sulphate (electrolyte) against a standard hydrogen electrode, we may calculate standard reduction potential. For standard hydrogen potential, the standard reduction and oxidation potentials are always set to 0.00. The following is a description of the experiment:
• To make a typical hydrogen electrode, fill a glass beaker halfway with a hydrogen chloride solution of 1M. A platinum inert electrode with platinum black foil at one end is now immersed in the beaker and covered with a glass jacket to prevent oxygen from entering. Pure hydrogen gas (1 atm) can be injected into the solution through an input. The temperature is kept at 25°C. The Standard Hydrogen Electrode is seen in the diagram below.
• A half cell of conventional hydrogen electrode is coupled to a half cell of zinc electrode in this configuration. In a beaker, zinc sulphate is placed, and a zinc rod is dipped in it. The electrolyte zinc sulphate is administered at a concentration of 1M. The temperature is kept at 25°C. Using a voltmeter to detect the electrode potential of the cell, this zinc electrode is now linked to a typical hydrogen electrode. A salt bridge is also used to avoid intermixing of the solutions and to keep the solutions electrically neutral. The cathode is a zinc half cell, and the anode is a hydrogen half cell.
• As we all know, in standard settings, the standard reduction potential of a standard hydrogen electrode is always set to zero, and we are utilising normal conditions in this experiment. As a result, E0H+/H2 = 0.
• The voltmeter is used to determine the value of the cell’s standard reduction potential. As a result of the experiment, we know the value of E0cell, and we already know the value of E0H+/H2. We may compute the value of E0Zn2+/Zn using equation (1).
• The experiment yields a result of -0.76V for E0cell. As the typical reduction potential for SHE is 0, the value of E0   Zn2+/Zn is -0.76V.
• By utilising a half cell with copper electrode and copper sulphate electrolyte instead of zinc electrode and zinc sulphate electrolyte, we may compute the standard reduction potential of the copper electrode using the same approach. The value of  E0  Cu2+/Cu obtained from the experiment is +0.34V.
• If the Daniel cell representation is Zn(s)/Zn2+(aq)||Cu2+(s)/Cu(aq) and standard conditions are applied, such as 1M electrolyte concentration, 298K temperature, and 1 atm pressure, the result is Zn(s)/Zn2+(aq)||Cu2+(s)/Cu(aq). The standard electrode potential for the cell can therefore be calculated as follows:

 E0 cathode –  E0 anode =  E0 cell

 E0cell = E0Cu2+/Cu –  E0Zn2+/Zn 

(If you use a + instead of a – in the equation, you must write the zinc electrode as an oxidation electrode, which is E0cell = E0Cu2+/Cu + E0Zn2+/Zn)

+0.34 E0cell – (-0.76)

E0cell = 1.1V E0cell = 1.1V

As a result, Daniel’s cell’s EMF, or standard cell potential, is 1.1V.

E0cell has a positive value when the reaction occurs spontaneously, while it has a negative value when the reaction occurs spontaneously in the opposite direction.

• The qualities of the solution to be examined should not impact the standard hydrogen electrode used as a reference electrode, and it must be physically isolated. Many additional electrodes, such as calomel electrodes, quinhydrone electrodes, and others, are employed as reference electrodes in addition to traditional hydrogen electrodes.

Series of electrochemical reactions

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 have a tendency 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. Because lithium has the lowest standard electrode potential, it has the least tendency to be lowered. As a result, fluorine is a strong oxidising agent, while lithium is a strong reducing agent.

Standard Electrode Potentials and Their Applications

The following are some of the applications of standard electrode potentials:

• 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.

Conclusion

Only aqueous equilibrium can be measured using standard electrode potentials. Using typical electrode potentials, we can estimate reaction possibilities, but not the rate of reaction.

This was a quick overview of standard electrode potential and how to calculate it using examples. Concentrate on the notion and how it is calculated.