EDSE 452/453: Science Activity Homemade Lava “Lamps”

Christy Cachero

Curriculum Fit:

Grade 8 Science – Unit A (Mix and Flow of Matter)

Outcome 3: Comparing densities of different liquids, and methods of altering the density of a fluid.

Required Materials:

• clear glass or jar
• vegetable oil
• water
• salt
• food coloring

Procedure:

1. Fill the glass or jar half-full with water. Ask the students to predict what they think would happen if vegetable oil was added to the water. Wherever possible, ask the students to explain their predictions using “scientific” terms as practice.
2. Add between 1/3 – 1/2 cup vegetable oil to the glass or jar. Ask for observations. Allow everything to settle before proceeding to Step 3. Ask students to predict what would happen if food coloring was added to the mixture.
3. Add a couple drops of food coloring to the liquids. Ask for observations. Ask students to predict what would happen if salt was added.
4. Shake some salt into the glass or jar. What happens to the food coloring? What happens to the salt?
5. Keep adding salt for as long as you want the action to occur.

Explanation:

The definition of density is mass per unit volume. The oil will float on the water because it is less dense than the water. In other words, in a comparison between equal volumes of oil and water, water will be the heavier of the two. The density of water is used as the reference and is assigned a density of 1 g/L. Thus, anything that is denser than water will sink in water, and anything that is less dense than water, such as oil, will float in water.

Because the oil layer is on top of the water, salt added to the mixture will be added to the oil first. Salt is heavier than water and will therefore sink. As it does, some oil is dragged down with it. The salt will begin to dissolve in the water, releasing the oil blob. Because of its density, the oil will return back to the top of the water.

Source:

This activity was created by Eric Muller and was taken from the Exploratorium's Science Explorer website (http://www.exploratorium.edu/science_explorer/volcano.html).