In the Laboratory
Removing Silicone Grease from Glassware Thomas H. Lowry Department of Chemistry, Smith College, Northampton, MA 01063 A recent note in this Journal (1) described the use of 5% aqueous hydrofluoric acid for removing silicone grease residues from round-bottom flasks. A safer and more convenient alternative is a saturated solution of sodium hydroxide in ethanol. C AUTION: Eye protection must be worn at all times when handling solutions of sodium hydroxide. Avoid contact with skin and clothing. In case of contamination, wash affected areas thoroughly with water. Ethanol is flammable; use in a well-ventilated area away from sparks and flames.
The solution is readily prepared by warming sodium hydroxide pellets in 95% ethanol and is stored in a screwcap polyethylene bottle. It is poured into the flask to be cleaned and heated on a steam cone or water bath for a few minutes, then returned to the storage bottle. The item being cleaned is rinsed thoroughly with water. No filtering is needed, and although the solution turns dark soon after being prepared, it can be kept indefinitely and used repeatedly without losing its effectiveness. It does not etch glass even after contact times of several hours and is an extremely effective general cleaning solution for glassware. Literature Cited 1. Reilly, T. J. J. Chem. Educ. 1996, 73, 381.
Vol. 74 No. 7 July 1997 • Journal of Chemical Education
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