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Activity: Famous Duo Splits Up |
Background
They’ve been seen everywhere together—at ice skating
rinks, in hot tubs, standing on city sidewalks, or running through
storm drains—hydrogen and oxygen atoms, bonded together to
form molecules of water. Sure, they’d disappear into thin
air for a while, even go underground. But they always returned—together.
It’s shocking to hear what’s come between them: a chemical
reaction called electrolysis.
Electrolysis is a decomposition reaction. A decomposition
reaction is a type of chemical reaction in which a compound
breaks down into its basic elements. Water is a compound made from
the elements hydrogen and oxygen.
During electrolysis, electricity causes the hydrogen and oxygen
atoms in water to dissociate, or split apart. Try
the following experiment and watch these former partners go their
separate ways.
Materials
- 1 glass beaker or jar
- 2 test tubes or clear vials
- 6-volt battery
- two 8-inch pieces of coated wire (18-22 gauge) with ends stripped
- 2 cups tap water
- 2 tbs. baking soda
- 1 measuring cup
- 1 measuring spoon
- wire cutters
Steps
-
Mix two tablespoons of baking soda in two cups of water. Stir
until the baking soda has dissolved. Then pour about 1 ¼
cups of the solution into a beaker or jar.
-
Set up the experiment as shown, leaving one of the battery
wires unconnected at this point. You will need to fill each
test tube to the top with the leftover solution, then hold your
finger over the open end as you immerse it upside-down in the
beaker of solution. Position one tube over each wire tip.
-
Connect the loose battery wire and observe what happens at
the tip of each wire in the solution. Let the reaction continue
for at least five minutes.
-
The chemical formula for a molecule of water is H2O:
two atoms of hydrogen bonded to one atom of oxygen. Look at
the test tubes.
Which test tube contains more gas? __________________________
Which test tube do you think contains hydrogen gas? ____________
Which contains oxygen gas? ______________________________
- The baking soda was added to the water to speed up the electrolysis
reaction. What would be another way to speed it up?
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