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In our neighborhood, the week of Halloween is a little chaotic as the kids are so excited about trick-or-treating and their costumes. It's hard to get them to concentrate on their studies or on their normal household activities. However, Halloween is the perfect opportunity to introduce a little Halloween science into the home. This Halloween experiment is easy to do and fun for all: mixing a potion of Witch’s Brew to create your own Lava Lamp. 

Concept:

This experiment confirms what you already know, molecules of oil and and molecules of water do not mix. It very simply demonstrates the concept of density for different liquids. Density is the mass of a substance per unit volume into a particular area… or a comparison between an object’s mass and volume. The exact same volume of two liquids may actually have different masses, so they would have different densities. That’s why vegetable oil floats on top of water, and water sinks because it is heavier.

Objective: Identify the change in density when different liquids are mixed together and observe the changes in the state of matter in a mixture.

Materials:

One clean, 16 oz plastic soda bottle with cap
Vegetable oil (no need for the good stuff here…)
Food coloring
One Alka-Seltzer tablet
Water

Procedure:

1. Fill the bottle 3/4 full with vegetable oil.

2. Fill the rest of the bottle with water almost to the top, but not overflowing.

3. Add about 10 drops of food coloring. Be sure to make the water is fairly dark in color. Notice that the food coloring only colors the water and not the oil…

4. Divide the Alka-Seltzer tablet into 8 pieces.

5. Drop one of the tiny pieces of Alka-Seltzer into the oil and water mixture. Watch what happens. When the bubbling stops, add another chunk of Alka-Seltzer. Repeat until you have used all 8 pieces.

6. Wait until the Alka-Seltzer had dissolved and the bubbling has completely stopped. Screw on the soda bottle cap. Tip the bottle back and forth and watch the wave appear. The tiny droplets of liquid join together to make one big lava-like blob.
    

Questions:

Why does the water separate from the oil?

What about the bubbles? Why do they float up?

Why do they go right back down after floating to the top?

What would happen if you left the cap on the bottle after adding the Alka-Seltzer? (**Don't try this! Just think about what would happen.)

The Alka-Seltzer tablet reacts with the water in the bottle to make tiny bubbles of carbon dioxide gas. These gas bubbles attach themselves to the blobs of colored water and cause them to float to the surface because the carbon dioxide gas is far less dense than both the water or the oil. When the water/gas blobs reach the surface, the gas bubbles pop due to the expanding gas. The colored blobs of water, still being more dense than the oil, sink back to the bottom of the bottle.

Answer to last question: A big, huge, oil & water, blobby mess!

EERIE GREEN PUMPKINS

All your neighbors will have Jack-O-Lanterns that glow orange with regular candles (we had a pumpkin one year that was big enough to warrant using a Coleman lantern!!), but why not try a Jack-O-Lantern that glows green! Best of all, the green glow is simple and safer than traditional candles.

Purchase two large glowing light-sticks per pumpkin at any Halloween party store or regular hardware store. (Available in 3 colors online at Arbor Scientific.) Activate the light stick and attach them to the inside of the pumpkin lid by unbending large paperclips to secure them.

Lightning at your finger tips!

If you enjoyed this experiment, check out our Plasma Globe, no mad scientist’s lab is complete without one! This globe creates a dramatic display of light inside a hand-blown glass sphere by blending specially formulated inert gases.

Go there now!

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