Oxidation-Reduction Reactions Chemistry Worksheet Page 23
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6.4 Voltaic Cells
Table 6.3
Common Voltaic Cells (Batteries)
Voltaic
Anode Reaction
Cathode Reaction
Pros
Cons
Cell
+
2+
‒
‒
Zn(s) → Zn
(aq) + 2e
(s) + 2NH
(aq) + 2e
Dry cell
2MnO
Inexpensive;
Short shelf‑life;
2
4
→ Mn
(s) + 2NH
(aq) + H 2 O(l )
O
reliable
large and heavy;
2
3
3
not rechargeable
‒
‒
Zn(s) + 2OH
(s) + H
O(l ) + 2e
Alkaline
(aq)
2MnO
Longer lasting
More expensive
2
2
‒
‒
→ ZnO(s) + H
O(l ) + 2e
→ Mn
(s) + 2OH
battery
O
(aq)
and slightly
than dry cells;
2
2
3
higher energy
not rechargeable
density than dry
cells
‒
‒
Cd(s) + 2OH
NiO(OH)(s) + H
O(l ) + e
Nickel‑
(aq)
Rechargeable;
Relatively low
2
‒
‒
→ Cd(OH)
(s) + 2e
→ Ni(OH)
(s) + OH
cadmium
(aq)
lower price
energy density;
2
2
battery
than other
less efficient
rechargeable
with repeated
batteries; long life
use
+
‒
‒
‒
Pb(s) + HSO
(aq) + H
(s) + HSO
(aq) + 3H
(aq) + 2e
Lead‑Acid
O(l )
PbO
O
Rechargeable;
Very heavy,
4
2
2
4
3
+
‒
→ PbSO
(s) + H
(aq) + 2e
→ PbSO
(s) + 5H
battery
O
O(l )
very reliable;
yielding a very
4
3
4
2
inexpensive;
low energy
durable
density
+
+
‒
‒
→ nLi
+ 6C + ne
+ nLi
+ ne
→ Li
One type
Li
C
CoO
CoO
Rechargeable;
Expensive
n
6
2
n
2
of lithium
reliable; very high
battery
energy density
Zinc-Air Batteries
S
T
PECIAL
OPIC 6.3
One type of battery being considered for use in electric cars
materials would need to be removed to be recharged.
is the zinc‑air battery, in which zinc acts as the anode and air
You could stop at your local zinc station, have the spent
provides the oxygen for the cathode reaction. This battery
electrolyte and zinc oxide particles quickly suctioned from
is low in mass because of its use of oxygen as the cathode
the cells and replaced with a slurry of fresh particles and
reactant. The overall reaction is
electrolyte, and be ready to go another 200‑300 miles. The
zinc oxide would be taken to a central plant where it would
2Zn(s) + O
(g) → 2ZnO(s)
2
be converted back to zinc metal and returned to the stations.
Most of the batteries being considered for electric cars take
Vans powered by zinc‑air batteries are already being used
by the European postal services. In 1997, one of them made
several hours to recharge, a major drawback in comparison
a 152‑mile trip from Chambria, France, over the Alps to
to the ease of refilling a gas tank. It is possible that the use
Turin, Italy. It not only succeeded in crossing the 6874‑ft
of zinc‑air batteries will avoid this problem. The reactions
peak but also averaged 68‑mph on the highway.
are not directly reversible in the zinc‑air batteries, so the
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