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Sometimes when atoms come together to form a molecule, one end of the molecule has a positive charge and one end of the molecule has a negative charge. When this happens the molecule is a polar molecule. Molecules that do not have two electrical poles are called non-polar molecules.
This experiment will show you how polar molecules and non-polar molecules behave when added together. If two kinds of molecules are added together that are both polar molecules, they will mix. They are miscible. Miscible means that the two things can mix together. If two non-polar molecules are added together they will also mix and are miscible. However, if a non-polar molecule and a polar molecule are added together, they will not mix together. This is called imiscible. Imiscible means that the two kinds of molecules CANNOT mix together.
- Plastic Bottle
- Vegetable Oil
- Food coloring
- Measuring Cups
- Alka Seltzer
Fill the bottle about 3/4 of the way up with vegetable oil. Fill the bottle the rest of the way up with water. Now add some drops of food coloring. Close the cap on the bottle and shake it up. What happens?
Break the alka seltzer tablet in half. Open the bottle and drop in one half. What happens? Once the bubbles settle down drop in the other half. What happens again?
Water is a polar molecule. Vegetable oil is a non-polar molecule. These two substances do not mix together, they are imiscible (they will not mix together). That’s why you see the blobs of water bobbing around in the oil. Food coloring is a polar molecule so it WILL mix with the water. The water and the food coloring are both polar molecules will mix together. That’s why the water blobs turn the color of the food coloring and the oil does not.
The alka seltzer just makes the bottle more fun because it makes the colorful water blobs move without shaking the bottle. The alka seltzer tablets dissolve in the the water and make carbon dioxide gas (like we saw vinegar and baking soda do in the Exploding Ziploc experiment). The carbon dioxide gas bubbles attach to the colorful water blobs and make them float to the top of the bottle. When the gas bubbles pop there is no gas bubble to hold up the water blob, so it slowly floats back down to the bottom of the bottle.
Here are some website and books that will give you good directions for making your own lava bottle and understanding molecules and polarity:
- National Geographic for Kids: Groovy Lava Lamp
- Steve Spangler Science: Make Your Own Lava Lamp
- Science Bob: Blobs in a Bottle
- Exploratorium: Glitter Globe
- Glasgow Sciece Center: Lava Lamp
- Science Rocks! Fizzy Fountain (pages 24-25)
- Naked Eggs and Flying Potatoes: Bubbling Lava Bottle (pages 36-39
- Super Simple Wthings To Do With Bubbles: That’s Lava-ly! (pages 16-17)
Science Experiment Idea: Make several different lava lamps using different liquids for the water. Try vegetable oil and water, like our experiment today. Then try vegetable oil and rubbing alcohol or vegetable oil and orange juice or vegetable oil and olive oil. See if you can determine which substances are miscible when added together. Which ones make a good lava lamp and which ones don’t?
Words to Know:
Polarity – When atoms align.
Atoms – The smallest, most basic unit of matter. An atom is made up of a nucleus surrounded by electrons.
Molecules – At least two atoms held together by a chemical bond.
Polar Molecule – A molecule that has two opposite electrical poles. One end of the molecule has a positive charge and one end of the molecule has a negative charge.
Non-Polar Molecule – A molecule that does not have opposite electrical poles.
Miscible – Able to mix when added together.
Imiscible – Not able to mix when added together.