edited - - ~ - bv - -
tested demonstrations Like Dissolves Like: Dry Gas Submined by:
Fred H. Greenberg SUNY College at Buffalo Buffalo. NY 14222 Checked by:
James W. Long
University of Oregon Eugene. OR 97403 A demonstration of solubility that captures student attention is provided by a comparison of commercial gasoline additives containing methanol (e.g., Prestone Gas Dryer and Gas Line Anti Freeze, Union Carbide Corp., Danbury, CT 06817) and isopropyl alcohol (e.g., Isopropyl Gasline Anti-Freeze, Berkebile Oil Co., Somerset, PA 15501). In each of two 50-mL graduated cylinders with ground glass joints is placed 1mL of a dilute aqueous solution of Crystal Violet (-lo3 M) followed by 10 mL of 2,2,4-
654
Journal of Chemical Education
GEORGE L. GILBER; Denison Univemity Granville, OH 43023
trimethylpentane, a substitute for gasoline. The deeply colored water represents the water that has collected at the bottom of a car's gas tank. Ten milliliters of a methanol-based dry gas or methanol itself is added to one of the graduated cylinders, which is stoppered, inverted and then placed upright giving a deep purple bottom layer of methanol-water and a colorless upper hydrocarbon layer. Presumably, a gas tank containing added methanol must lead to the burning of a methanol-water mixture for which the automobile engine was not designed. In the other graduated cylinder, after adding 10 mL of 2-pmpanol or a 2-propan01 dry gas, and treating as before, the purple color is evenly distributed throughout, which shows that a mixture of gasoline, 2-propanol and water can be homogeneous and is expected to be the more effective fuel. The point is made that both alcohols are solvents for water through hydrogen bonding, but that associated %propanol-water, having two more carbons than methanolwater, is the more hydmcarbon-like and will be soluble in gasoline.
