Lava Lamp Lab!

Learn how to create your own lava lamp using 5 basic materials!

Materials:

  • Oil (we used vegetable oil)
  • Water
  • Food dye
  • Alka-Seltzer tablets
  • A tall, clear container

Instructions:

Fill approximately 2/3 of the container with oil. Fill the rest of the container with water, but be sure to leave room at the top– the liquid gets pretty turbulent. The water should sink to the bottom of the container. Add food dye to the mixture. We added three drops, but the quantity added depends on the desired color of the lamp. The dye will only color the water, and won’t touch the oil.

After the dye settles and the water is fully colored, add in the Alka-Seltzer tablets. We recommend breaking the tablet into pieces, as too much of the tablet can agitate the liquid excessively. Experiment with the amount of Alka-Seltzer tablet you add!

So… what’s happening?

A combination of things, really.

1) Water is denser than oil. This means that water has a greater amount of mass per volume than oil.

Say you have one container that holds exactly one liter of oil and another that contains precisely one liter of water, and you want to find the density of the liquids in each container.  Let’s say that the containers are identical, and therefore have the same mass.  The mass of the containers would throw off our calculations of the masses of the liquids.  However, since the ratio will remain intact between the calculated densities of the two liquids, we can still accurately compare them. 

The equation for density is below:

Since both containers contain the same amount of fluid, or the same volume of fluid, in this instance, the masses of the two containers containing the liquids truly determine the density of the two liquids.

If we were to measure the mass of both containers on a balance (not a scale—that’s weight), the water would have a higher mass than the oil.  In the example below, the mass of the container with the water was 1150 grams compared to the oil’s mass of 950 grams.  Therefore, the density would be higher for the water than for the oil.

In other words, there will be less space between individual water molecules and more water molecules packed in the container than oil molecules.  Because of this, the water sinks to the bottom of the container, and the oil floats on top.

2) Water is a polar molecule and oil is non-polar. This means that within a water molecule electrons are unequally distributed, so some parts of the molecule are partially positive (hydrogen) and some are partially negative (oxygen)– see below.

Water Molecule

Because of this uneven charge, water can break apart other polar molecules, like salt and sugar. However, when it comes to substances mixing together, like tends to go with like. This means that water likes to mix with other polar substances but not with non-polar substances.

Similarly, oil can mix with other non-polar substances, but stays away from polar substances; in fact, it is described as “hydrophobic,” or water-fearing, and is repelled by water.

Vegetable oil, what we used in our lava lamp experiment, is a triglyceride, and as such is made up of three fatty acid chains and a glycerol. The fatty acids, made up of hydrocarbon chains, contribute greatly to vegetable oil’s hydrophobic nature.

Vegetable Oil Molecule (Triglyceride)

This leads to the oil and water separating from each other, and explains why the food coloring only dissolved in the water.

Interestingly, if you shake the oil and water together, they momentarily “mix” together before separating. This process is called emulsion, in which tiny droplets of oil are dispersed throughout the water. This is why you have to shake oil and vinegar dressing before applying it to a salad, as otherwise you’ll be left with an oily salad.

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