How do batteries' performance vary with time on the shelf?
Keith,
Most commercial batteries (dry cells) are composed of solids whose
activities are nearly constant, hence their potentials don't diminsh MUCH
as the charge goes down.
But if you have access to a millivolt meter, have the kids get a
collection of metal strips .. e.g. Mg, Zn, Sn, Cu, Ag, Au (jewelry will
do) and Pt if you can lay hands of a piece of wire. Connect the Mg to
the negative terminal and the other metals in succession to the positive
terminal, then immerse in a solution of an 'inert' electrolyte. NaClO4
is best. NaCl will react with the Ag and NaNO3 does funny things with Pt.
Ask them to explain the sign of the potential .. reverse leads if
they doubt it .. and the magnitude with different metal pairs.
Discover how batteries WORK.
John Cooper, Chemistry, Bucknell University, Lewisburg PA 17837-2005
jcooper@bucknell.edu 717-524-3673