[mip]

I did a prac on 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.  We isolated crystals of the (+)Co(en)3.(+)tart.Cl (ie the (+)(+)diastereoisomer).  We then dissolved these crystals in 5M HCl and added a solution of NaI.  We then added a few mL of ethanol to complete the precipitation of the (+)tris(ethylenediamine)cobalt(III) iodide.

In my prac report I have to include reasons for adding HCl and NaI and I don't really understand why we used HCl, was it to change the pH of the solution, and if so, why?

Any help on this would be much appreciated.  

[mip]

Just incase anyone else was wondering, it turns out we dissolved the isomers in HCl as it is a conc. source of chloride ions and thus (somehow) increases the solubiltity of the crystal isomers... I hope that makes sense, Im exhausted!!!

[movies]

Maybe you just need a high ionic strength in solution to help solubilize the complex.

Just guessing though, my inorganic techniques are lacking.

[AWK]

This is a classic Werner synthesis from 1912.
The complex is good soluble in water but only sparingly in medium concentrated HCl solution.
Moreover, the complex is unstable in  solution at RT, hence a precipitation should be fast

Werner, Ber. 45, 121 (1912)
Inorg. Synth. 2, 221-222, 223-225
Inorg. Synth. 6, 183-186