[zulu]

hi,

we made an exp. in a lab class, but i'm not sure about the conclusion...

here's the procedure:

- fill 4 test tubes with around 1-2 ml of nickel(ii)nitrate solution each
- add some concentrated ammonia solution drop by drop to the first tube until the color changes
- again, add concentrated ammonia solution drop by drop to the sec. test tube until the color changes, and then dilute the solution with water
- with regard to the third test tube, first again add concentrated ammonia solution drop by drop until the color changes, but then add a drop of ethylenediamine
...and so on

i observed different color changes, but my problem is, i don't know for what that stands for, what happened, whats the objective of this exp.? :/

[Alberto_Kravina]

By adding ammonia VERY SLOWLY to a Ni²⁺-solution you'll get a green precipitate (nickel hydroxide), if you add excess ammonia the ppt. is dissolved as a tetrammine complex. I don't know what exactly happenes when you add ethylene diammine...
Maybe by diluiting the second test tube the Ni(OH)₂ precipitates again....  

[Yggdrasil]

You could try relating the colors of the complexes to the order of the ligands in the spectrochemical serries.

[plu]

Have you thought about what complexes form?  In your first test tube, you only added ammonia.  What complex does that form with nickel?  In your second test tube, you added water after the ammonia.  How does that affect the nickel-ammonia complex?  In your third test tube, you added ethylene glycol.  Does that change the complex perhaps...?  

[pantone159]

Ethylenediamine (not ethylene glycol) also forms a complex with Ni.  
Do your results suggests that this complexes less strongly, or more strongly, than NH3?

Supposedly, you can observe a series of ethylenediamine (en) complexes, from Ni(en)⁺⁺, Ni(en)₂⁺⁺, up to Ni(en)₃⁺⁺.
I haven't messed with en myself, so I can't comment on how easy it is to see the separate ones.