The Foundations of Chemistry

THE COPPER–SILVER CELL

Now consider a similar standard voltaic cell consisting of a strip of Cu immersed in 1 M

CuSO 4 solution and a strip of Ag immersed in 1 MAgNO 3 solution. A wire and a salt

bridge complete the circuit. The following observations have been made.

1.The initial voltage of the cell is 0.462 volt.

2.The mass of the copper electrode decreases. The Cu^2 ion concentration increases

in the solution around the copper electrode.

3.The mass of the silver electrode increases. The Agion concentration decreases in

the solution around the silver electrode.

In this cell the Cu electrode is the anode because Cu metal is oxidized to Cu^2 ions.

The Ag electrode is the cathode because Agions are reduced to metallic Ag (Figure

21-7).

Cu88nCu^2  2 e (oxidation, anode)

2(Age88nAg) (reduction, cathode)

Cu2Ag88nCu^2 2Ag (overall cell reaction)

As before, ions from the salt bridge migrate to maintain electroneutrality. Some NO 3 

ions (from the cathode vessel) and some Cu^2 ions (from the anode vessel) also migrate

into the salt bridge.

Recall that in the zinc–copper cell the copper electrode is the cathode;now in the

copper–silver cell the copper electrode is the anode.

21-10

862 CHAPTER 21: Electrochemistry

e– e–

Salt bridge

Cu(s) → Cu2+ +2e–

Oxidation, anode

Voltmeter

1 M CuSO 4

Ag+ + e– → Ag(s)

Reduction, cathode

1 M AgNO 3

Cu^2 +

NO 3 –

Ag(s)

K+

K+ NO 3 –

–+

(5% agar)

Ag+

Cu(s)

Figure 21-7 The copper–silver voltaic cell utilizes the reaction

Cu(s)2Ag(aq)88nCu^2 (aq)2Ag(s)

The standard potential of this cell is 0.462 volt. This standard cell can be represented as

Cu
Cu^2 (1 M)

Ag(1 M)
Ag.