Conductivity
in Various Media
Introduction:
The purpose of this demonstration is to demonstrate how ions
in a solution complete an electrical circuit. In this experiment,
a connection is made between a power source and a light bulb
by inserting two copper electrodes into various solutions (salt
water, sugar water, distilled water, soda and/or various acids).
Commercially available "light Spheres" are also used
to show that the human body can also be used to complete a
circuit.
Materials:
- Distilled water
- Tap water
- Soda, vinegar, or other acidic
medium
- NaCl or Epsom salt
- Sugar
- Orange, lemon, potato, apple (any
one of these will do)
- Rubber gloves
- Conductivity apparatus (requires
110 volt outlet)
- Metal rod
- Wood rod
- Light sphere
- Paper towels
- Overhead slide
Procedure:
First it may be helpful to show that
a metal rod conducts electricity but a wooden rod does not.
Then it can be shown that distilled water does not conduct,
but tap water will. It should be noted that tap water may
not always conduct well enough to light up the light bulb.
By adding salt (NaCl or Epsom salt) to the distilled water
you can show that it will now conduct electricity. This experiment
can be repeated using sugar. It may be a good idea to ask
for predictions first. You can also test the cola or acid
to see how well it conducts. The fruits or vegetables can
also be tested. When testing an orange or lemon, you may
have to mash the fruit a bit to allow the juices to flow
between the electrodes. Often, if the electrodes are in
different segments of the orange or lemon, it will not
conduct very well, again, you may have to mash it up a
bit.
The second demonstration that can be
done uses the commercially available light spheres. By touching
the two metal strips on the sphere, you are connecting a
circuit that will light up a small light bulb inside the
sphere. This can also be done by lining up several people
(holding hands) in a circle and having the first person touch
one metal strip and the last person touching the other metal
strip. The electricity should conduct between the people,
completing the circuit.
Helpful Hints:
- Once it has been demonstrated that sugar
will not conduct electricity and salt will, it will be helpful
to discuss what causes a solution to conduct. You may have
to remind the students what an ion is.
- There are overheads
available to help the students understand do in the presence
of electricity.
- If you are using soda, ask the students
which of the ingredients conducts electricity, remind them
that sugar does not conduct.
- If you are using a potato,
remember that it is the starch that is conducting electricity.
Be sure to wipe the copper electrodes after each use.
Safety:
- When doing this demonstration, you should
wear the provided rubber gloves to prevent any shock.
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