Chapter 25, Problem 25.1P

Interpretation Introduction

Interpretation:

A cell diagram for zinc-silver electrochemical cell indicating flow of electrons has to be sketched.  The chemical equation for reaction occurs at each electrode and cell diagram have to be written.

Concept Introduction:

An electrode is any solid on the surface of which oxidation-reduction reactions occur. The two solutions in the cell are connected electrically through a salt bridge that consists of a saturated potassium chloride solution mixed with agar.  The electrode at which the reduction half reaction occurs is called the cathode; the electrode at which the oxidation half reaction occurs is called the anode.

In a cell diagram, the single vertical bars in the cell diagram indicate boundaries of phases that are in contact, and the double vertical bars indicate a salt bridge.

Explanation of Solution

The cell diagram of a zinc-silver electrochemical cell is sketched as,

Figure 1

The half-cell reactions and net cell reaction at each electrode is given by

    $\begin{array}{l}{\text{Zn}}_{\text{(s)}}\stackrel{}{\to }{\text{Zn}}^{\text{2+}}{}_{\text{(aq)}}\text{+}{\text{2e}}^{\text{-}}\text{(oxidation of Zn at anode)}\\ \\ {\text{2Ag}}^{\text{+}}{}_{\text{(aq)}}\text{+}{\text{2e}}^{\text{-}}\stackrel{}{\to }{\text{2Ag}}_{\text{(s)}}{\text{(reduction of Ag}}^{\text{+}}\text{ at cathode)}\\ \\ \text{Net}\text{reaction}\text{:}{\text{Zn}}_{\text{(s)}}\text{+}{\text{2Ag}}^{\text{+}}{}_{\text{(aq)}}\stackrel{}{\to }{\text{Zn}}^{\text{2+}}{}_{\text{(aq)}}\text{+}{\text{2Ag}}_{\text{(s)}}\end{array}$

The cell diagram of zinc-silver electrochemical cell is given by

    ${\text{Zn}}_{\text{(s)}}{\text{|ZnCl}}_{\text{2}}{}_{\text{(aq)}}{\text{||AgNO}}_{\text{3}}{}_{\text{(aq)}}{\text{|Ag}}_{\text{(s)}}$