Untitled - Kelly Walsh High School

268 CHEMISTRY FOR THE UTTERLY CONFUSED
Quick Tip
In using either of these methods, you must follow the rules in the order listed.
Check with your instructor to see which method is preferred.
18-2 Galvanic (Voltaic) Cells
Galvanic (voltaic) cells produce electricity by using a redox reaction. Let’s take that
zinc/copper redox reaction that we studied before (the direct electron transfer one)
and make it a galvanic cell by separating the oxidation and reduction half-reactions.
V
Zn Cu
Zn 2+ Cu 2+
Instead of one container, we will use two. We place a piece of zinc metal in one,
a piece of copper metal in another. We add a solution of aqueous zinc sulfate
to the beaker containing the zinc electrode and an aqueous solution of copper(II)
sulfate to the beaker containing the copper metal. The zinc and copper
metals will form the electrodes of the cell, the solid portion of the cell that conducts
the electrons that are involved in the redox reaction. The solutions in
which we immerse the electrodes are the electrode compartments. We connect
the electrodes by a wire and complete the circuit with a salt bridge. A salt
bridge is often an inverted U-tube containing a concentrated electrolyte solution,
such as KNO 3. The anions in the salt bridge will migrate through the gel
into the beaker containing the zinc metal and the salt-bridge cations will
migrate in the opposite direction. In this way, both electrode compartments
maintain electrical neutrality. The zinc electrode is being oxidized in one beaker
and the copper(II) ions in the other beaker are being reduced to copper metal.
The same redox reaction is happening in this indirect electron transfer as happened
in the direct one:
Zn(s) Cu 2 (aq) l Zn 2 (aq) Cu(s)