Chapter 20.1, Problem 14SSC

Interpretation Introduction

Interpretation:

A concept map including all the new vocabulary terms for section 20.1 is to be prepared.

Concept introduction:

Redox reaction is a reaction in which one substance loses electrons, that is undergoes oxidation whereas another substance gains electrons, that is undergoes reduction. An example of such reaction is as follows:

$\text{Zn}\left(s\right)+{\text{CuSO}}_{\text{4}}\left(aq\right)\to {\text{ZnSO}}_{\text{4}}\left(aq\right)+\text{Cu}\left(s\right)$

$\text{Zn}$ is oxidized to ${\text{Zn}}^{2+}$ and ${\text{Cu}}^{2+}$ ions is reduced to $\text{Cu}$.

These reactions are accompanied by release of some energy called chemical energy which can be transformed to electrical energy by a device known as galvanic cell or electrochemical cell.

Electrochemistry is study of relation between electrical energy and chemical changes that takes place in redox reaction. It involves utilization of two types of cells:

1. Electrochemical cell
2. Electrolytic cell

Answer to Problem 14SSC

• Electrochemical cell is an instrument used to transform chemical energy produced in redox reaction into electrical energy.
• Voltaic cell is an electrochemical cell used to convert chemical energy produced in a spontaneous redox reaction into electrical energy.
• Anode: is an electrode at which oxidation reaction that is loss of electron occurs.
• Cathode: is an electrode at which reduction reaction that is gain of electron occurs.
• Salt bridge: which has two major roles to play, those are:
• To complete the electrical circuit by allowing the ions to flow from one solution to the other without mixing the two solutions.
• To maintain the electrical neutrality of the solutions in the two half cells.
• Electrode potential or cell potential is capacity of electrode to gain or lose electron when it is dipped in solution of its own ions.
• Standard hydrogen electrode (S. H. E) is reference electrode used to measure standard reduction potential of any reaction at $\text{289K}$ .
• Half cells are electrodes in electrochemical cell in which separate oxidation and reduction reaction occurs.

Explanation of Solution

Electrochemical cell is an instrument used to transform chemical energy produced in redox reaction into electrical energy. It is based on spontaneous redox reaction.

Voltaic cell is an electrochemical cell used to convert chemical energy produced in a spontaneous redox reaction into electrical energy. Its major components are as follows:

• Anode: is an electrode at which oxidation reaction that is loss of electron occurs.
• Cathode: is an electrode at which reduction reaction that is gain of electron occurs.
• Salt bridge: which has two major roles to play, those are:
• To complete the electrical circuit by allowing the ions to flow from one solution to the other without mixing the two solutions.
• To maintain the electrical neutrality of the solutions in the two half cells.
• External circuit: To conduct the flow of electron between two electrodes.

Electrode potential or cell potential is capacity of electrode to gain or lose electron when it is dipped in solution of its own ions. The absolute magnitude of cell potential of an electrode cannot be determined as oxidation half reaction or reduction half reaction cannot occur alone. It can be measured by taking a reference electrode. The reference electrode used is standard hydrogen electrode (S. H. E). In SHE, hydrogen gas at $\text{1bar}$ pressure is passed into unit molar $\text{HCl}$ at $\text{289K}$ in which a foil of platinum coated with platinum black remains immersed. It acts as an inert electrode with standard potential $\text{0}\text{V}$.

Oxidation potential is specific term used for cell potential if oxidation occurs at electrode and reduction potential is the term used if reduction occurs at electrode, with respect to standard hydrogen electrode. As per the latest convention of sign, the electrode at which reduction occurs with respect to standard hydrogen electrode is assigned positive sign or has higher reduction potential and the electrode at which oxidation occurs with respect to standard hydrogen electrode is assigned negative sign or has lower reduction potential.

An electrochemical cell is formed of two electrodes that is two half cells in which separate oxidation and reduction reaction occurs. One of these electrodes has higher electrode potential than the other due to which potential difference is created and current flows.

The formula for cell potential is as follows:

$E_{\text{cell}}^{\text{0}}=E_{\text{Reduction}}^{\text{0}}-E_{\text{oxidation}}^{\text{0}}$

Where,

$E_{\text{cell}}^{\text{0}}$ is standard cell potential.

$E_{\text{Reduction}}^{\text{0}}$ is half cell potential for reduction.

$E_{\text{oxidation}}^{\text{0}}$ is half cell potential for oxidation.

Conclusion

• Electrochemical cell is an instrument used to transform chemical energy produced in redox reaction into electrical energy.
• Voltaic cell is an electrochemical cell used to convert chemical energy produced in a spontaneous redox reaction into electrical energy.
• Anode: is an electrode at which oxidation reaction that is loss of electron occurs.
• Cathode: is an electrode at which reduction reaction that is gain of electron occurs.
• Salt bridge: which has two major roles to play, those are:
• To complete the electrical circuit by allowing the ions to flow from one solution to the other without mixing the two solutions.
• To maintain the electrical neutrality of the solutions in the two half cells.
• Electrode potential or cell potential is capacity of electrode to gain or lose electron when it is dipped in solution of its own ions.
• Standard hydrogen electrode (S. H. E) is reference electrode used to measure standard reduction potential of any reaction at $\text{289K}$ .
• Half cells are electrodes in electrochemical cell in which separate oxidation and reduction reaction occurs.