The standard electrode potential of zinc is −0.76 V and that of copper is +0.34 V. What is the standard electromotive force (e.m.f.) of the electrochemical cell formed when these two electrodes are combined?
A0.42 V
B0.76 V
C1.10 VCORRECT
D1.52 V
GCEChemistryRedox and Electrochemistry2021
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Why the answer is C, and why the others tempt you.
The standard e.m.f. of a cell is calculated as E°cell = E°cathode − E°anode. Copper has the higher reduction potential (+0.34 V) and acts as the cathode, while zinc (−0.76 V) acts as the anode. Therefore, E°cell = +0.34 − (−0.76) = +0.34 + 0.76 = 1.10 V. Option A is the difference of magnitudes ignoring signs, and D is the sum of absolute values minus the correct calculation.
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