SME
Grade 10 Science · Problem type
Standard cell voltage
Use this for “What voltage does a zinc–copper cell give?”: E°cell from the two metals’ reduction potentials.
Diagram
Zinc (−0.76 V) has the lower reduction potential, so it is the anode: it is oxidized and its electrons flow through the wire to copper, the cathode (0.34 V).
E°cell = E°cathode − E°anode = 0.34 − (−0.76) = 1.10 V.
This is an example. Type your own values to start a new problem.
E°cell (V)
=
E°cathode (V)
−
(
E°anode (V)
)
Formulas
E°cell = E°cathode − E°anode
1.1 = 0.34 − (−0.76)
Assumptions
•
Each metal stands in a 1 M solution of its own ion at 25 °C; the potentials are the standard table’s.
•
The metal with the higher reduction potential is the cathode, where reduction happens.
•
E°cell = E°cathode − E°anode, and it is positive for a working cell.
Step-by-step
WE KNOW
E°cathode = 0.34 V, E°anode = −0.76 V
FIND
cell voltage (E°cell)
Step 1 · Find cell voltage (E°cell)
Use E°cell = E°cathode − E°anode
The cathode’s pull for electrons minus the anode’s: the bigger the gap, the bigger the voltage.
E°cell = 0.34 − (−0.76)
0.34 V is copper’s and −0.76 V is zinc’s: a zinc–copper cell with zinc the anode
E°cell = 1.1 V
Check
Put the numbers back in. Both sides should match.
1.1 = 0.34 − (−0.76) ✓
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