Density Tubes

Beginning the density tube

We're discussing density in science, so to explore it a bit, we used three different solutions and determined their relative density. Before class I prepared three solutions. Solution #1 was 400mL of water and 10 drops of blue food coloring. Solution #2 was 400 mL of water, 10 drops of red food coloring, and 3 tablespoons of salt. Solution #3 was 400 mL of water, 10 drops of green food coloring, and 6 tablespoons of salt. The kids did not know the properties of the liquids. Their only instructions were to build the density tube, and add the liquids in a way that the layers stayed separate. All the kids began in different orders, and they all had a mix of liquids! After lots of trial-and-error, all the groups were able to get their liquids into the correct order. I discussed with each group individually why the liquids had to be ordered in this way. We discussed density, which liquid must be our most dense, and which liquid must be our least dense. We also related the density of the red liquid to the other liquids.

A completed density tube