ACS at the State Fair

Density Demo

Chemicals:

trichloroethylene (Carbo-sol from Sunnyside), mineral
spirits, water, food coloring. All chemicals can be bought at hardware
stores or grocery stores.

Materials:

test tube, test tube caps, pipettes, test tube rack,
necessary safety supplies

Note:

Methylene chloride or 1,1,1-trichloroethane will also work
for trichloroethylene. Hexane will work for mineral spirits

Caution: Eye protection should always be worn when handling chemicals. Adult supervision is required.

Procedure:

Using a pipette add a small amount of trichloroethylene to a test tube. A small amount is 2-3 cm in height. Talk about it.
Using a pipette very gently add a small but different amount of mineral spirits to the surface of the trichloroethylene. Point out the boundary and talk about this and get responses. Although these two will mix if shaken, they will stay separate if added gently.
Carefully add one drop of a water solution of food coloring to the test tube. It will float in the middle. Talk about this and get responses. Add drops of solutions of different colors of food coloring. If you are careful, you may see several drops of varying colors floating side by side.
Using a pipette slowly drop in water drop by drop allowing everyone to see the process and get responses as this happens. Add enough water until the two clear liquids are clearly separated.
Ask what will happen if this is shaken. Then cap the test tube and shake vigorously. Ask for responses.
If the colored water is on the bottom, add enough trichloroethylene until it reverses. If the colored water is on the top, add enough mineral spirits until it reverses. The mineral spirits will have to be added to the bottom layer by pushing the pipette through the colored water and injected directly to the bottom layer. The trichloroethylene will make the organic layer more dense, and the mineral spirits will make it less dense, each affecting the final position of the water layer and the organic layer in the test tube.

Topics that can be discussed are density, miscibility, meniscus, etc

----Contributed by Frank Salter, Mark Twain Section