Extensions:

Hands and Minds on Sugar and Oil:
Let students discover that a solution of salts conducts electricity but not sugar. Ask their opinion about why ionic solutions conduct electricity but solutions of polar organic molecules such as sugar do not. After all, they both are water-soluble (hint: ions carry true charges, are polar molecules which are overall electrically neutral or charged?).

Experiment with oil to fix the idea of hydrophobicity. Shake the test-tube. Observe how over time what first looked as a solution is separating into two phase ­ water and fat. Why?

Building Lipids. Students can also build a matchstick model of a polar lipid structure in order to discover lipid vesicles, prototypes of our cell membranes, and films: Using red-tipped matchsticks, they could begin by deciding whether the red tips are hydrophobic (dislike water) or hydrophilic (attracted to water.). Then see how many arrangements they can make. There are at least three possible arrangements (films, spherical micelles or inverted micelles). These represent 2-Dimensional arrangements. Once students have come up with a structure, they should quess out what the shape would look like in 3-D.

Thematic Connections

Breathing and disease theme: Red blood cells are needed to carry oxygen because oxygen barely dissolves in water. Hemoglobin dissolves more easily and is designed to carry the oxygen. CO2 is more soluble and in fact is carried back partly in the blood stream and partly by the hemoglobin. In anemia a patient has fewer erythrocytes with hemoglobin in the blood serum, or has erythrocytes with less hemoglobin in them. Therefore there is less oxygen getting into the tissues.

Sense receptors theme: Ions in solution in our cells act as triggers for all of our nervous signals, (e.g., sight, smell, touch, TASTE)

Evolution: The Earth's oceans contained enormous quantities of dissolved salts and organic materials, from which living cells eventually emerged. Read about the early materials.

Benzene vs. Phenol Compare these two formulas. Guess which is completely water insoluable and which is soluble.

 

Additional Resources

Read about Solutions

Picture: Interactive Physics: Solubility
http://www.concord.org/~barbara/workbench_web/solubility.html