Hands-on-Science: Make your own salt volcano

What do you need?

  • Glass Jar or Clear Drinking Jar
  • Glass
  • Vegetable Oil
  • Salt
  • Water
  • Food Coloring (Optional)

Caution

Be careful with the glass

Instructions

  1. Pour about 3 inches of water into the jar
  2. Pour about 1/3 cup of vegetable oil into the jar. When everything settles, is the oil on the top of water or underneath it?
  3. (Optional) Add one drop of food coloring to the jar. What happens? Is the drop in the oil or in the water? Does the color spread?
  4. Shake salt on top of oil while you count slowly to 5.
  5. Add more salt to keep the action going for as long as you want.

To see the science behind this activity, go to Exploratorium Science Explorer.

What did you learn?

DENSITY – Low density liquids will rise above the higher density liquids

While water often mixes with other liquids to form solutions, oil and water does not. Water molecules are strongly attracted to each other, this is the same for oil, because they are more attracted to their own molecules they just don’t mix together. They separate and the oil floats above the water because it has a lower density.  The food coloring only mixes with the water and goes through the oil to reach the water.

Real World Applications

Variation

Would you like to make your Lava Lamp bubble? How would you do that?

  1. Get a glass jar with lid or a tube and fill it 3/4 full with oil (use some cheap vegetable oil).
  2. Add couple of tablespoons of water to the tube.
  3. Add 10 drops of food coloring.
  4. Divide an Alka-Seltzer tablet into 4 pieces.
  5. Drop one piece into the oil and water mixture.  What happens?
  6. When the bubbling stops, screw the soda bottle cap on and seal with duct tape. Be sure the bubbling totally stops.  Did you notice the fizz? This will take a few minutes. Turn the test tube slowly back and forth to see your lava lamp flow.

Oil and water molecules are so attracted to themselves that they do not mix together, even though they will mix with other substances. Oil has a lower density than water so it floats on top. The food coloring only mixes with the water and goes through the oil to reach the water. The alka-seltzer reacts with the colored water to make bubbles of carbon dioxide gas. These bubbles attach themselves to the blobs of food colored water and causes them to float to the surface. When the bubbles pop and the carbon dioxide escapes, the blobs sink back to the bottom.

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