Chapter 20.1, Problem 10SSC

Interpretation Introduction

Interpretation:

The condition under which redox reaction can cause an electric current to flow through a wire is to be described.

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 the study of relation between electrical energy and chemical changes that take place in redox reaction.

Answer to Problem 10SSC

There are two conditions under which redox reaction can cause an electric current to flow through a wire which are as follows:

• The oxidation and reduction reaction must take place in separate containers containing electrolyte, connected by a wire for current to flow.
• Presence of salt bridge between the two electrolytic solutions for completion of circuit by flow of ions between solutions.

Explanation of Solution

A redox reaction can be employed to produce electrical energy or current from chemical energy. An example of such reaction is as follows:

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

Above reaction can also be represented as follows:

$\text{Zn}\left(s\right)+{\text{Cu}}^{2+}\left(aq\right)\to {\text{Zn}}^{2+}\left(aq\right)+\text{Cu}\left(s\right)$

This reaction can also be split into two half reactions as follow:

$\text{Zn}\left(s\right)\to {\text{Zn}}^{2+}\left(aq\right)+2{\text{e}}^{-}$ (Oxidation half reaction)

${\text{Cu}}^{2+}\left(aq\right)+2{\text{e}}^{-}\to \text{Cu}\left(s\right)$ (Reduction half reaction)

If oxidation half reaction and reduction half reaction occurs in separate beakers then, For redox reaction to cause current flow it is necessary that electron given out by zinc metal in one beaker to be gained by copper ions in other beaker. For this to happen Zinc metal rod is placed in zinc sulfate solution in one beaker and copper metal rod is placed in copper sulfate solution. Then the two solutions are connected by a wire and a salt bridge.

Salt bridge helps in mainly two things:

• 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.

Therefore, there are two conditions under which redox reaction can cause an electric current to flow through a wire which are as follows:

• The oxidation and reduction reaction must take place in separate containers containing electrolyte, connected by a wire for current to flow.
• Presence of salt bridge between the two electrolytic solutions for completion of circuit by flow of ions between solutions.

Conclusion

There are two conditions under which redox reaction can cause an electric current to flow through a wire which are as follows:

• The oxidation and reduction reaction must take place in separate containers containing electrolyte, connected by a wire for current to flow.
• Presence of salt bridge between the two electrolytic solutions for completion of circuit by flow of ions between solutions.