[ch3mwannabe]

I did an experiment on the resolution of tris(ethylenediamine)cobalt(III) ions. We had tris(ethylenediamine)cobalt(III) chloride trihydrate and reacted it in solution (at about 80 degrees C) with silver (+)-tartrate and isolated crystals of the (+)Co(en)3.(+)tart.Cl (ie the (+)(+)diastereoisomer).

The crystals were then dissolved in 5M HCl and NaI was added. A few mL of ethanol to was added complete the precipitation of the (+)tris(ethylenediamine)cobalt(III) iodide.

My question is, why do we dissolve the crystals in concentrated HCl? Could someone illustrate the reason with an equation to help me better understand it? Thanks!

[Arkcon]

There are a few reasons I can think of, many of them not really germane to the preparation of a complex.  However, lets work together, to try and figure it out ...

Does the particular concentration chosen 5M HCl, tell you anything?  Is that, for example, the best way to get the lowest pH?  And what is the reaction that is happening, at this step?  What does the NaI do?

[vex]

Are you sure that you're getting the cobalt(III) species back out? I would expect the HCl/NaI mixture to be pretty reducing...