Question

A teacher assigns the following experiment to a class. Draw an outline of a bird's feather, and color one half of the outline with a thick coat from a wax crayon. Leave the other half uncolored. Next, sprinkle a few drops of water on both halves of the feather. You will observe that the water soaks into the plain paper. The waxy coat, however, allows the paper to remain dry. Water forms tiny beads on top of the wax instead of soaking through it.
The results of the experiment MOST STRONGLY support which conclusion about the polarity of lipid molecules?

A. Lipid molecules are polar because they mix poorly with liquids, such as water.
B. Lipid molecules are polar because they adhere tightly to smooth surfaces, such as paper.
C. Lipid molecules are nonpolar because they repel water molecules, which also are nonpolar.
D. Lipid molecules are nonpolar because they repel water molecules, which are polar.

Answer 1

The correct answer is option (D) Lipid molecules are nonpolar because they repel water molecules, which are polar.

Lipids are organic compounds made up of fatty acids and glycerol. A glycerol is a organic molecule with three hydroxyl groups and a fatty acid consists of a long hydrocarbon chain attached to a carboxyl group.

Lipids are hydrophobic, nonpolar molecules with no charge on their ends. Waxes are long chain nonpolar lipids. The water repelling property of the waxes prevent the water sticking to it and appear as water beads on its surface. The hydrophobic hydrocarbon tail of the fatty acids are hydrophobic in nature making them repel water. The presence of wax on the surface of the plants and animals protects them from dehydration.

Thus, the nonpolar property of lipids make it insoluble in the polar solvents like water as there is no interaction or sharing of electrons between them.