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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: zulu on January 03, 2006, 12:14:30 PM

Title: whats the sense of this exp. (complexes)
Post by: zulu on January 03, 2006, 12:14:30 PM
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.? :/
Title: Re:whats the sense of this exp. (complexes)
Post by: Alberto_Kravina on January 03, 2006, 01:10:54 PM
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....  ???
Title: Re:whats the sense of this exp. (complexes)
Post by: Yggdrasil on January 03, 2006, 07:47:39 PM
You could try relating the colors of the complexes to the order of the ligands in the spectrochemical serries.
Title: Re:whats the sense of this exp. (complexes)
Post by: plu on January 06, 2006, 10:08:39 AM
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...?   ;)
Title: Re:whats the sense of this exp. (complexes)
Post by: pantone159 on January 06, 2006, 01:21:45 PM
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.