There are three major ways of producing energy – combustion, nuclear fission and electrochemical cells.  Electrochemical cells are also called voltaic cells and batteries in which chemical energy is converted into electricity.  In these chemical reactions, electrons are passed from one element or compound¹ to another.  The flow of electrons constitutes the flow of an electric current.

¹Compounds are pure substances that are composed of more than one element in a definite proportion.  For example, water is made of the element hydrogen and oxygen in a ration of 2 hydrogen to 1 oxygen.  That is why water is known to be "H two O" or having a fomrula of H₂O

Demo 11          Money Is Power            

Materials:  pennies (2), dimes (2), paper towel, salt, water, multimeter with millivolt scale

Precautions:  none

Disposal:  Throw the salt wet paper towel in the trash and keep the coins.

Procedure:  Clean the coins with detergent using a toothbrush.  Fold the towel into three or four layers.  Cut three squares to about the size of the coins.  Wet them and sprinkle some salt over them.  Sandwich the wet paper towel between the coins: dime/penny/dime/penny.  Set the multimeter to the lowest millivolt range and measure the voltage by touching the probes of the multimeter to the surface of the upper and lower coins.

Explanation:  This is a voltaic cell named after Alessandro Volta (1745-1827) who in 1790 invented it by sandwiching salty wet cardboard between alternating pieces of zinc and copper.  The zinc metal passes electrons through the salty wet cardboard to the copper metal, and the flow of electrons can be measured by the multimeter.  Can you tell which coin passes electrons to which one in the cell you just built?

Precautions:  None

Disposal:  Throw lemons away with trash.

Procedure: Insert a penny and a galvanized nail into each of two lemons and connect the two lemons in series.  Connect the + pole of a memory capacitor to the penny and the ─ pole to the nail.  The voltage should range from 1 to 1.5 volts.  Let the capacitor charge for at least three hours.  Then use the capacitor to run the buzzer.  For connections see pictures below.

Explanation: The zinc metal on the surface of the galvanized nail loses electrons.  The electrons pass on to the acid (hydrogen ions) in the lemon.  The flow of electrons goes from the galvanized nail to the acid, to the copper penny, through the wire, to the capacitor.  When enough electrons are stored in the capacitor, you can drive the buzzer with them.  Thus, chemical energy is converted into electrical energy, into mechanical energy, into sound energy.  (This demonstration was presented by Ron Perkins and Mark Straus at CHEM ED '89)