Some Notes on Density and Molecular Structure

In the classes in the week of 31 Jan., we will perform the Discovering Density experiment and consider some extensions to the experiment. For instance, can you think of a variant to the basic design of the Discovering Density experiment that will enable us to determine how density varies with increased salinity (i.e., increased salt content in a solution)?

A very important extension, one with implications for many areas of science, is to consider the effects of temperature on density? Does the density of water, or air or other substances vary as the temperature? Think of how you might show this with the Discovering Density experimental design, and then think of areas of science in which these density variations are important?

Finally, we will do the following experiment as a means of demonstrating that different molecules have different shapes.

Each group should take two graduated cylinders, and fill each carefully to the 25 ml mark. Predict what will happen when you pour carefully the water from one cylinder to the other; what is your prediction for the final reading of the combined contents?

Now, repeat the experiment, only this time put 25 ml of water in one cylinder, and 25 ml of isopropyl alcohol in the other? What is your prediction for the final reading on the graduated cylinder when the contents are combined? How can we explain what we have observed?