Ciao Summer Science Explorers!
Maybe you have seen a lava lamp before – but if you haven’t you are missing out on an iconic symbol of the 1960’s and 70’s. Traditional lava lamps are made with clear glass container containing a clear liquid (usually water) and a colored wax with an incandescent light bulb underneath the glass container. As the light is on, it will heat up, melting the wax and causing the cool bubbling affect as the wax’s density decreasing as it warms and then increases as it cools off and sinks back down, only to warm again at the bottom.
The problem with old-fashioned lava lamps is they can get really hot – plus they are a little pricey! Today we are going to make our own, not hot lava lamp!
- Baby Soda Bottle w/Cap (or an empty clean regular soda bottle)
- Food Coloring
- Vegetable Oil (cheap is fine)
- Alka-seltzer Tablet
- Fill the bottle approximately 3/4 full with vegetable oil. Be careful not to spill!
- Slowly pour water into the bottle until the bottle is full but not overflowing. Where does the water go?
- Add several drops of food coloring to the bottle (you want nice dark color). Do they mix with the water or the vegetable oil? Why do you think this is?
- Break up your Alka-seltzer tablets into a couple of large chunks and drop one or two into your bottle. What happens!?
- When your lamp has finished fizzing you can put your bottle cap on the bottle to save it until later. If you want to see your lava lamp action again all you have to do is drop in a few pieces of Alka-seltzer!
What’s Going On Here?
Alka-seltzer is an effervescent antacid which produces bubbles of carbon dioxide when exposed to water. In your soda bottle, the water is more dense than the vegetable oil, and is therefore on the bottom. However, all the little carbon dioxide bubbles grab small amounts of the colored water and WHOOSH! whisk it up to the top. Once the bubble escape into the atmosphere the water will float back down to the rest of it’s buddies.
Now you may have noticed that the food coloring didn’t interact with the vegetable oil at all. This is because the food coloring is a water based product, and just like the water itself, it refuses to mix with the vegetable oil. Even if you were to cap the bottle and shake it vigorously, the color would remain in the water. This is because of the structure of the molecules in the oil and the water. Water is a polar molecule, meaning that it has a slight positive and slight negative charge on it’s two ends. Oil on the other hand has no charge, and is therefore repelled by the charge of the water. We say that oil is “hydrophobic” which literally means, when translated from latin, “scared of water”! Are you hydrophobic or hydrophilic (love of water)?