Carbon and Zinc
The common carbon zinc battery can be cut open and studied without encountering toxic chemicals.
Be careful of sharp edges. Wear work gloves.
Wear eye protection.
Pry the D-cell battery open with the needle nose pliers, The battery is a cylindrical metal case bent over at the ends. Use the pliers to straighten the bends and push the innards out through the end you have opened.
Use the pliers to pry the bottom off the 9 volt battery. The sides are folded over the bottom. The top is the end from which the terminals stick out. When you have folded back the bottom, push the battery stack out from the top.
To Do and Notice
Notice that the D-cell has a central carbon rod surrounded by a black paste inside a metal can.
Notice that the 9 volt battery is made up of 6 smaller cells connected together. Use a voltmeter to measure the voltages inside the 9-volt batterys stack of cells. Notice that each one produces about 1.5 volts.
Whats Going On?
Chemical reactions take place between the paste and both the central carbon rod and the zinc metal lining the steel case of the D-cell. The net effect of these reactions is the removal of electrons from the carbon and the addition of electrons to the zinc. To the outside world, the case of the battery thus becomes a source of electrons, negative. While the central electrode becomes a sink of electrons, and therefore positive.
A source of electrons is called a cathode. To help
you remember this, recall that electrons were originally discovered
as cathode rays being emitted from the negative cathode of vacuum
tubes. A sink of electrons is an anode.
Notice the possible confusion in these definitions: If you are interested in the chemistry inside the battery then the electrons leave the positive carbon electrode making it a cathode, if however you are interested in the external interactions of the battery the positive cathode is a sink of electrons and so becomes an anode for outside observers.
Alkaline cells produce more power than regular
cells. To do this they use more corrosive chemicals. they produce
essentially the same voltage as regular cells however they can make
Return to Day 15
Scientific Explorations with Paul Doherty
30 May 2000