20.7 The Fruit Powered Clock

Chemical Concept Demonstrated: Electrochemical cells

Demonstration:

A zinc probe has been soldered to one of the leads from a digital clock; a copper probe has been soldered to the other. The probes are inserted into a fruit or vegetable. A jumper wire that is soldered to pieces of zinc and copper metal is then inserted so that the zinc end is next to the copper probe and the copper end next to the zinc probe.

Observations:

    The clock turns on.  The clock can run for up to a week.

Explanation (including chemical equations):

    Because the digital clock requires a potential of at least 1.2 V, the pair of zinc-copper cells must be connected in series.  A zinc probe has been soldered to one of the leads from the digital clock and a copper probe has been soldered to the other lead.  These probes are inserted into the fruit or vegetable of choice roughly 1.5 inches apart.  A jumper wire that is soldered to pieces of zinc and copper metal is then inserted into the fruit or vegetable so that the zinc end of the jumper wire is 1/4 inch from the copper probe from the clock and the copper end of the jumper wire is a similar distance from the zinc probe from the clock.

    The resulting zinc-copper cell can be inserted into a variety of fruits and vegetables to determine the presence of electrolytes.