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

More Density

View of our jars from the top

A fuzzy side view of our jars.

As we continued our exploration of density, we began another investigation using three jars of unknown liquids. The kids didn't know the contents of the jars until after the investigation was completed. Jar #1 contained 60 mL of dish soap (blue liquid). Jar #2 contained 60 mL of baby oil. Jar #3 was nothing but air, which is why I covered it in foil. I didn't want to spoil the surprise. Some kids knew right away there was nothing in it, but some were convinced I had put something in there! The groups all measured the mass of each jar using the triple beam balance. Then they added the jars to the tub of water to observe which was the most dense/least dense. All groups came to the conclusion the blue liquid had the most mass and was the and most dense, while the foil-covered jar had the least amount of mass and was the least dense.

We then discussed why it was so important both the liquids have the same volume. If the volumes are different, we wouldn't know if the blue liquid was, in fact, more dense, or if there was just more liquid in the jar.