Erupting Lava Bottle

Combining the effects of the fact that oil and water don't mix with the effect of baking soda and acid makes a beautiful display as the colored water gets pulled through the oil, and gives a quick lesson in density.
Take any plastic bottle and fill it about three-quarters full with ordinary vegetable oil.
Fill to the top with water. Add about 10 drops of food coloring. Break an Alka-Seltzer tablet in half, or in quarters if your bottle is small. Drop it into the bottle.
Please excuse the fact we couldn't get all of the label off the bottle!
Watch for the bubbles start to rise. It looks a lot like an erupting volcano.
You can put the top on your bottle, if you are afraid of spills, or leave it off and keep adding more Alka-Seltzer when the bubbles stop rising.
The fizzing caused by the Alka-Seltzer is carbon dioxide gas which forms bubbles that rise up through the bottle. Water is more dense than oil but when the gas bubbles attach themselves to blobs of water, the blobs and the bubble together are less dense than the oil, so they float upward. At the surface, the bubbles pop and the blobs of water sink back down again.

After adding the Alka-Selzer tablets a while, it will begin to get cloudy. Just stop until it clears up again, and then you can begin adding more.

Although this looks like a lava lamp, the real lava lamps are made from colored wax that rises and moves through the water as the lamp heats up. The wax expands more than the water and becomes less dense than the water and floats to the top. At the top the wax cools, becomes less dense and sinks again.

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