COORDINATION COMPLEXES AND EQUILIBRIUM Submitted by: Donald J . Shombert, Douglass College, Rutgers University, New Brunswick, N. J Checked by:
Willard D. Houston, Wadsworth High School, Wadsworth, Ohio
PREPARATION
Have available dil. (0.1 M ) copper sulfate, conc. ammonia, two test tubes with corks, and two carefully cleaned iron nails. All dirt and grease must be removed and the nails then etched in conc. HC1 until hydrogen is briskly evolved. The nails are then rinsed with distilled water. DEMONSTRATION
The two test tubes are half filled with the dil. CuSOn solution. Concentrated ammonia is added to one tube until the deep blue complex is formed, then a few drops in excess are added. An equal volume of distilled water is added to the other tube. A nail is placed in each tube and the tubes are tightly stoppered. After a few moments the tubes are displayed to the
students and then passed around the class. The test tubes should be carefully tilted so the solutions can run to the other end while the nails remain in place. REMARKS
Red light is so strongly absorbed by the solutions that a copper deposit cannot be seen through the liquid. When the nails are exposed, one is seen to be covered with a red deposit of copper while the other is still bright iron. Students should explain the behavior in terms of equilibrium, Le Chatelier-Braun's principle, and coordination complex formation, as well as the following equations Fe(s)
+ Cu2+(aq)= FeR+(aq)+ Cub)
CuW(aq)
+ 4NHs(aq) = Cu(NHMt(aq) Journal of Chamicol Educolion
A784
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Journal of Chemical Education
Noocmber 1370
