The construction of a voltaic pile (battery) is a simple laboratory activity that commemorates the invention of this important device and is of great help in teaching physics. The voltaic pile is often seen as a scientific toy, with the “pile” being constructed from fruit. These toys use some strips of copper and zinc inserted in a piece of fruit to produce a low-intensity electrical current to power a digital device. In a voltaic pile of this type, the zinc acts as an anode while the copper acts as a cathode. The reduction reaction [i.e.,2H+(aq)+2e⇋H2(g)] occurs on the copper (the cathode). The two electrons that are needed for the reduction are taken from the metal (copper), which remains positively charged, while the anode is the zinc, which is oxidized through the reaction Zn∘(m)⇋Zn+2(aq)+2e⁠, and the two electrons remain on the metal, which is negatively charged. If the two pieces of metal are connected by an external conductor, electrons flow from the zinc to the copper. The electromotive force of this system is about 0.76 V, which is the reduction potential of zinc, as can be found in the table of standard reduction potentials.1 

Topics
Electrical equipment, Electromotive force, Electrical circuits, Electrochemistry, Batteries, Education
1.
One basic point to note is that Volta's pile, even though it contains copper and zinc, is not a copper-zinc battery. In Volta's pile, unlike in the copper-zinc battery (as in the Daniell cell), there are no copper ions. The copper sheet is in contact with a cloth moistened with an aqueous solution that contains an electrolyte but that (unless contaminated) does not contain Cu2+ copper ions, and thus cannot be reduced to Cu∘. If there are no copper ions, one lacks one component of the redox couple and thus the reduction potential of copper should not be considered. It is the H+(aq) ion that is reduced and the metallic copper acts only as a carrier of electrons. We could actually use other metals in the pile and, unless there is polarization phenomena, the emf will remain at about 0.76 V, which is the standard potential of the Zn half-element.
2.
A.
 
Volta
, “
On The Electricity Excited By The Mere Contact Of Conducting Substances Of Different Kinds
,”
Philos. Trans. R. Soc. London
 
90
(
2
),
403
–
431
(
1800
). An English Translation Can Be Found In Bern Dibner, Alessandro Volta And The Electric Battery (Franklin Watts, New York, 1964), Pp. 111–131.
https://doi.org/10.1098/rstl.1800.0018
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3.
H.
 
Davy
 “
Outlines of a view of galvanism, chiefly extracted from a course of lectures on the galvanic phænomena, read at the theatre of the Royal Institution (1801)
,”
J. R. Inst. Great Britain
 
1
(
1802
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4.
Ibid.
© 2013 American Association of Physics Teachers.
2013
American Association of Physics Teachers
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