The Foundations of Chemistry

Whether a particular electrode acts as an anode or a cathode in a voltaic cell depends

on what the other electrode of the cell is.

The two cells we have described show that the Cu^2 ion is more easily reduced (is a
stronger oxidizing agent) than Zn^2 , so Cu^2 oxidizes metallic zinc to Zn^2 . By contrast,
Agion is more easily reduced (is a stronger oxidizing agent) than Cu^2 ion, so Ag
oxidizes Cu atoms to Cu^2 . Conversely, metallic Zn is a stronger reducing agent than
metallic Cu, and metallic Cu is a stronger reducing agent than metallic Ag. We can now
arrange the species we have studied in order of increasing strength as oxidizing agents
and as reducing agents.

Zn^2 Cu^2 Ag AgCuZn

8888888888888888888888n88888888888888888n

Increasing strength Increasing strength

as oxidizing agents as reducing agents

21-10 The Copper–Silver Cell 863

The standard

Cu
Cu^2 (1 M)

Ag(1 M)
Ag cell.

(Left) A spiral of copper wire was

placed in a colorless solution of

silver nitrate, AgNO 3. The silver has

been displaced from solution and

adheres to the wire. The resulting

copper nitrate solution is blue. The

same reaction occurs when the two

half-reactions are separated in the

copper–silver cell (see Figure 21-7).

(Right) No reaction occurs when

silver wire is placed in a blue copper

sulfate solution. The reaction

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

is the reverseof the spontaneous

reaction in Figure 21-7; it has a

negative E^0 celland is nonspontaneous.

e–

Silver atom,

Ag

Silver

ion, Ag+

e–

Copper

atom, Cu

Copper

ion, Cu2+