[Chemistoftheelements]

Hi, I remember performing a practical once whereby ammonia solution was added to a solution of Nickel(II) chloride, with a purple precipitate appearing. This has always stuck with me as an example of an insoluble complex, and noting that many other ammonia complexes are soluble, it has now got me wondering why some complexes of any kind dissolve whilst others don't. Could anyone who has more theory please recommend to me something which would help me understand why some complexes dissolve and others don't in water under standard conditions? I realise this may be a bit involved, so I was thinking of a textbook or an area of inorganic chemistry which covers this? Many thanks.

This post has been edited by Chemistoftheelements: 10 January 2012 - 10:29 AM

[Greg Boyles]

Chemistoftheelements, on 10 January 2012 - 10:16 AM, said:

Hi, I remember performing a practical once whereby ammonia solution was added to a solution of Nickel(II) chloride, with a purple precipitate appearing. This has always stuck with me as an example of an insoluble complex, and noting that many other ammonia complexes are soluble, it has now got me wondering why some complexes of any kind dissolve whilst others don't. Could anyone who has more theory please recommend to me something which would help me understand why some complexes dissolve and others don't in water under standard conditions? I realise this may be a bit involved, so I was thinking of a textbook or an area of inorganic chemistry which covers this? Many thanks.

Is nickel diamine what ever insoluble is it? We did the copper ammonia thing in high school and I mucked around with it at home but it never occured to try it with nickel salts or anything else.....not that such salts are easily available at the super market or the garden centre.

Chemistry is fun - it was my all time favourite subject at high school. I learned quickly about house hold use of assorted chemicals because I was always on the look out for a cheap source of them to experiment with.

[John Cuthber]

Greg Boyles, on 10 January 2012 - 01:13 PM, said:

Is nickel diamine what ever insoluble is it?

What?
I can't even parse that.


Anyway, nickel salts form a precipitate with ammonia solution, but they dissolve in an excess of aqueous ammonia.
The solution looks a lot like the copper ammonia complex.

Have a look here
http://www.public.as...nal/nickel.html

This post has been edited by John Cuthber: 10 January 2012 - 07:20 PM

[Chemistoftheelements]

John Cuthber, on 10 January 2012 - 07:17 PM, said:

Anyway, nickel salts form a precipitate with ammonia solution, but they dissolve in an excess of aqueous ammonia.
The solution looks a lot like the copper ammonia complex.

Have a look here
http://www.public.as...nal/nickel.html

Thank you, that was interesting and informative.

Greg Boyles, on 10 January 2012 - 01:13 PM, said:

Is nickel diamine what ever insoluble is it? We did the copper ammonia thing in high school and I mucked around with it at home but it never occured to try it with nickel salts or anything else.....not that such salts are easily available at the super market or the garden centre.

Chemistry is fun - it was my all time favourite subject at high school. I learned quickly about house hold use of assorted chemicals because I was always on the look out for a cheap source of them to experiment with.

Yes, it's insoluble enough for the NiCl2 to be amost completely recoverable, as I recall. You can drive the ammonia off in a fume cupboard, which was, infact, part of the practical. I wasn't sure of the formula for a long time, but it's a very striking experiment, and the kind of demonstration which could be used more widely in schools and colleges to encourage people to participate in chemistry.

This post has been edited by Chemistoftheelements: 10 January 2012 - 08:04 PM

[Greg Boyles]

John Cuthber, on 10 January 2012 - 07:17 PM, said:

What?
I can't even parse that.


Anyway, nickel salts form a precipitate with ammonia solution, but they dissolve in an excess of aqueous ammonia.
The solution looks a lot like the copper ammonia complex.

Have a look here
http://www.public.as...nal/nickel.html

I thought he meant that the coordination complex itself was insoluble.

Interesting, pretty much the same colour as the copper coordination complex.

What else apart from Ni, Ag and Cu forms a complex with ammonia?

It always intrigued me as to why say iron does not form a complex with ammonia. Why is that?

This post has been edited by Greg Boyles: 11 January 2012 - 05:12 PM

[mississippichem]

Greg Boyles, on 11 January 2012 - 05:07 PM, said:

I thought he meant that the coordination complex itself was insoluble.

Interesting, pretty much the same colour as the copper coordination complex.

What else apart from Ni, Ag and Cu forms a complex with ammonia?

I'm sure that many metals do. I know at least platinum and ruthenium from my personal work experience. Surely almost all d-metals will in some form or fashion though.

[Greg Boyles]

mississippichem, on 11 January 2012 - 05:12 PM, said:

I'm sure that many metals do. I know at least platinum and ruthenium from my personal work experience. Surely almost all d-metals will in some form or fashion though.

I am pretty certain that iron does not form a complex with ammonia.

[Chemistoftheelements]

All I know is that when I've neutralised Fe(II)+ containing solutions with aqueous ammonia, I've gotten a precipitate. Whether that precipitate is Fe(OH)2 or whether it's a hydroxide- ammonia complex, I don't know- the observation that some ammonia- containing complexes are soluble whilst others aren't makes it difficult to tell, and a frustration for me. I'd like to be able to predict theoretically how some complexes (and not just ammonia- containing ones) dissolve in water under standard conditions.

Anyway, here's very likely what the ammonia- nickel chloride complex which I mentioned is: http://www.periodict.../028/index.html




It's about the fifth picture from the bottom.

[mississippichem]

Greg Boyles, on 11 January 2012 - 05:24 PM, said:

I am pretty certain that iron does not form a complex with ammonia.

I'm pretty certain it does, according to Housecroft's Inorganic Chemistry.

"Iron(II) halides combine with gaseous to give salts of that decompose in aqueous media precipitating "

So they do. But not in water.

This post has been edited by mississippichem: 11 January 2012 - 07:35 PM