Catalysis and Cleanliness
t~
Submitted by: Joseph E . Johnston,' Eastern District High School, Brooklyn, New York 11211 Checked by: Robbyn L. Ramp, Hiram College, Hiram, Ohio 44234
PREPARATION
Two factory-fresh 8-in. test tubes, dichromate cleaning solution, concentrated HCI, 2 g SnCl,, silver mirror solution (see for example, T.D. 12-19, " ~ k s t e dDemonstrations in Chemistry," by Alyea and Dutton). (CAUTION: DO NOT STORE ARlRlONIACAL SILVER NITRATE) DEMONSTRATION
Rinse one test tube with distilled water for control. Rarely dissolve 2 g SnCh in distilled water. The solution soon becomes cloudy, add concentrated KC1 to just clear up the precipitate, then add distilled water to makc a total of a little less than 200 ml. Fill the second test tube with the tin solution, allow it to stand for a minute or two, empty, rinse, and clean
with dichromate solution, then rinse with distilled water four or five times. Add silver mirror solution to each test tube. REMARKS
A mirror will start to form in the treated tube in a short time and will be complete before the mirror starts to form in the untreated tube. Warming the tubes in a beaker of warm water accelerates the mirror formation. I t is practically impossible to thoroughly clean a piece of chemical glassware as is shown by the catalytic effect of the stannous chloride film that still remains on the surface of the cleaned test tube. 'Present address: 194 Riverside Dr., Apt. lC, New York, N. Y., 10025.
Volume 46, Number 8, August 1969
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A547
