Electrolysis is a process of using electricity to create a chemical reaction. Here we are splitting water molecules into their individual components: and .
Since water is a relatively poor conductor of electricity and we are using a small 9 volt battery, we need to add something to the water to improve its ability to pass electricity: Salt (known by scientists as SODIUM CHLORIDE or NA CL). Salt is composed of 2 atoms: Sodium and Chloride.
In the project electricity flows down the graphite pencil leads and flows through the water/salt solution.
Oxygen molecules form as bubbles on the positive (+) terminal. They immediately combine with chloride molecules from the salt and the bubbles become gas - Chlorine is household bleach!
Hydrogen molecules form as bubbles on the negative (-) terminal.
· 9 volt battery
· clear plastic cup (short and wide; 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
· cellophane tape
· 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.
Test the solutions:
Chlorine gas is heavier than air so turn the test tube right side up. Add a few drops of water lightly colored with food color (make it almost clear with a light tint)and it will be bleached clear.
Hydrogen is lighter than air, so keep the test tube upside down. Bring a flame near the mouth of the test tube and there will be a small, pleasing explosion as the hydrogen gas ignites.