Submitted by Adam Johnson / Harvey Mudd College on Fri, 02/05/2010 - 17:18
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Teaching

we are redoing our first year laboratory, and want to fix a broken experiment, and add a new one.

1)  Vanadium.  We have the students make a variety of vanadium compounds and watch the color changes during a variety of redox reactions.  I haven't taught this in a while, but I know there is a chemical reduction, bubbling air through it for an oxidation, and then finally reduction with zinc amalgam.  We'd like to remove the Zn and Hg from the lab if possible.  Does this lab sound familiar to anyone?  And do other reducing agents work?

2)  Werner compounds.  We'd like to "adapt and implement" a Werner complex lab.  Have the students make, say, cis and trans Co(en)2Cl2 or Co(NH3)4Cl2.  Ideally, the two complexes would have dramatically different colors and properties.  I suppose we could even have them make [Co(NH3)6]Cl3; [Co(NH3)5Cl]Cl2, [Co(NH3)4(Cl)2]Cl and [Co(NH3)3Cl3], or have groups make each one and compare as a class.  Any ideas?

thanks,

Adam

Tags
laboratory
Werner complexes
cobalt
redox
first year
Hilary Eppley / DePauw University
Hi Adam,
I was perusing my folder of "potential labs" for my intro course last week, and this one from the Chemical Educator on the spectrochemical series for cobalt almost made the cut (I may do it as a in class demo or mini lab activity instead).  It isn't quite what you are looking for, but it might actually serve both of your purposes at once!   http://chemeducator.org/bibs/0010002/1020115dm.htm
Sat, 02/06/2010 - 15:33 Permalink
Kurt Birdwhistell / Loyola University New Orleans

We did the following lab for several years in general chemistry.  we are not currently using this lab.

Williams, G. M.; Olmsted, J.; Breksa, A. P., Coordination Complexes of Cobalt. Journal of Chemical  Education 1989, 66 (12), 1043-45.  (Involves making 5 Cobalt complexes. )

We analyzed for Cobalt using beer's Law.  If I remember correctly we converted the Co complexes  to Co(SCN)4]2- and did the Beer's law on that complex for Co determination.  The aqua complex is a little difficult, but the other preparations work quite well.   

Kurt

Mon, 02/08/2010 - 14:39 Permalink
Nancy Williams / Scripps College, Pitzer College, Claremont McKenna College
Adam, your good neighbor and pal Andy Zanella has developed some fine cobalt preps, some of which have even been turned into real labs. At the frosh level, we have them make [Co(NH3)5Cl]2+ from Earth, Air, Fire, and Water, and this can be converted by the use of hammer and tongs into the tetreammine carbonate, or a mixture of the cis and trans bis-en-dichlorides (which are easily separable, and one is violet, the other green). We do a kinetics lab by which they take one of these isomers and approach an equilibrium mixture--easy to follow by UV-Vis.
Tue, 02/09/2010 - 11:53 Permalink
Chris Mullins / University of Kentucky

Scott,

If you don't mind sharing, I'd like to know more details about the easy to follow by UV-Vis kinetics expt. with Co-ammine complexes...

 

Thanks,

 

CSM

Wed, 05/19/2010 - 15:36 Permalink