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Splitting Water: Electrolysis Experiment
All you need in order to see electrolysis in action is a battery and a couple pencils! (Adult
supervision required.)
Materials:
What to do:
 - Fill the beaker or glass with warm water.
- Carefully remove the erasers and metal sleeves so you can sharpen both ends
of each pencil. These pencils are your electrodes. The graphite in them
will conduct electricity, but won't dissolve into the water.
- Cut a piece of the cardboard to fit over the beaker, then punch two holes in
the center of the cardboard about an inch apart. Push the pencils through the holes and set them in the glass. They
should extend into the water, but not touch the bottom of the glass. The
cardboard will hold them in place.
- Connect each pencil to the battery with an alligator clip lead attached
to the exposed graphite (pencil lead). If you don't have alligator clip
leads, use two lengths of wire and strip an inch of insulation off each end.
Wrap the wire around the graphite of each pencil and connect the wires to
the battery. You may need to use tape to hold the wires in place.
What's happening?
As soon as you connect the wires to the battery, you will see bubbles appearing
around each of the pencil tips in the water and floating upward. Those bubbles
are the components of water—hydrogen and
oxygen gas—that have been split apart by the electricity as it travels through
the water from one pencil to the other. The pencil attached
to the negative terminal of the battery collects hydrogen gas while the one
connected to the positive terminal collects oxygen. Does one pencil collect more
bubbles than the other? Which one? Why do you think this is? (Hint: Water's chemical name
is H2O because it has two hydrogen atoms to every one
oxygen atom.)
Further experimenting:
- Try adding an electrolyte to the water in the beaker. Water
doesn't conduct electricity that well by itself, but you can speed up the
process by adding some table salt to the water. Do the bubbles form more rapidly
when you do this? (Safety Note: using salt may produce small amounts of
chlorine gas, similar to the amount present when using bleach.)
- Try different types of batteries. Can you make electrolysis happen with
a 1.5-volt battery? What about if you add an electrolyte?
- With some
real electrolysis equipment you can collect the two gases
in test tubes to measure the different amounts produced and test their
different reactions to a flame.
- For electrolysis to work as true renewable energy, you need to use a
clean energy source to run the reaction. Do this project again using
solar cells instead of a battery.
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