Chapter 18, Problem 40A

Interpretation Introduction

Interpretation: The reaction that occurs during the recharging of an automobile battery needs to be explained.

Concept Introduction: Electrolysis is the breakdown of compound’s chemical bonds to create elemental substances. The method involves passing of electrical current through the electrolyte to be degraded at different voltage between two electrodes. The electrolytes consist of cations and anions.

Answer to Problem 40A

In lead storage battery, reducing agent is Pb metal, and the oxidizing agent is Pb(IV) oxide, ${\text{PbO}}_{\text{2}}$ . The reaction is as follows:

${\text{PbO}}_{\text{2}}\left(\text{s}\right)\text{+Pb}\left(\text{s}\right){\text{ + 2H}}_{\text{2}}{\text{SO}}_{\text{4}}\left(\text{aq}\right)\to {\text{2PbSO}}_{\text{4}}\left(\text{s}\right){\text{+2H}}_{\text{2}}\text{O}\left(\text{l}\right)$

Explanation of Solution

The lead storage battery can be recharged, it is the most important characteristic of this battery. The half -cell reaction that occurs at the two electrodes is listed below:

In anode:

${\text{Pb + H}}_{\text{2}}{\text{SO}}_{\text{4}}\to {\text{PbSO}}_{\text{4}}{\text{+2H}}^{+}+2{\text{e}}^{-}$

In cathode:

${\text{PbO}}_2{\text{ + H}}_{\text{2}}{\text{SO}}_{\text{4}}+2{\text{e}}^{-}+2{\text{H}}^{+}\to {\text{PbSO}}_{\text{4}}{\text{+H}}_2\text{O}$

As the battery runs, ${\text{PbO}}_{\text{2}}$ and $\text{Pb}$ are consumed and ${\text{PbSO}}_4$ is produced. The overall reaction is as follows:

${\text{PbO}}_{\text{2}}\left(\text{s}\right)\text{+Pb}\left(\text{s}\right){\text{ + 2H}}_{\text{2}}{\text{SO}}_{\text{4}}\left(\text{aq}\right)\to {\text{2PbSO}}_{\text{4}}\left(\text{s}\right){\text{+2H}}_{\text{2}}\text{O}\left(\text{l}\right)$

Conclusion

Electrolysis is the process in which a chemical change produces on applying current in cell.