9 volt battery
clear plastic cup (short and wide; 8 ounce supermarket deli containers are great)
2 short pencils, sharpened on both ends (must have graphite leads - warning- some golf pencils have plastic
leads- test the brand of pencils before Science Club)
foam holder, (cut from foam meat tray as shown)
1 teaspoon salt
2 test tubes
Butane lighter or match to test for hydrogen gas
one drop blue food color, diluted in a cup of water
Mix up a solution with 1 spoonful salt and a half cup water.
Stir till dissolved.
Poke the pencils through the foam
holder as shown, so they are the same distance apart as the terminals of the 9 volt battery.
Set foam holder/pencil assembly
in the plastic cup. Balance the 9 volt battery on the pencil leads and
put a small rubber band around the battery to hold it to the foam holder (rubber band should not be tight, so that gravity
will hold battery terminals against pencil leads.) The battery must be above water level.
You should see bubbles rising from
the submerged pencil leads. If not make sure the battery terminals are resting on the pencil leads.
Here is the tricky part: fill the test tubes with water and, while holding your finger over the opening, turn it upside down in
the cup, releasing your finger when the test tube top is under water. This is
so the test tube remains filled with water (If your plastic container is big enough, you can lay the test tube down in the
cup under water and then turn it upside down. Might also be easier to do if you remove the battery/pencil apparatus
temporarily) . A piece of tape on the edge of the cup will hold the test tube in place.
Repeat with the second test tube.
Position the test tubes over the
pencil tips to catch the gas bubbles. When they are half or more full you can test the solutions.
Don't make this a demonstration. Give every kid in the Science Club thier
own apparatus. HANDS ON!
Make sure the room is
well ventilated - the chlorine is gas is poisonous, though the quantity we create is harmless.
Which battery terminal
created the most gas bubbles: plus or minus?
You can put a drop of
food coloring in the salt solution and watch it bleach out from the chlorine bubbles. Also note how the chlorine generating
pencil tip wood bleaches out.