Sciencemadness Discussion Board

Copper and Ammonia

IceDahl - 6-3-2016 at 05:56

Is it possible to dissolve copper or at least copper compounds in ammonia. What would i get if i dissolve for example copper chloride in ammonia. I could not find much info about this.
Note: By ammonia i mean ammonia in a water solution.

Amos - 6-3-2016 at 07:12

Yes, copper compounds will dissolve in aqueous ammonia with few exceptions. If you were to add ammonia solution to a solution of copper(II) chloride, you'd first encounter a pale blue precipitate of copper(II) hydroxide, and the supernatant would contain ammonium and chloride ions. With some stirring and the addition of more ammonia, the copper(II) hydroxide will dissolve to yield a deep royal blue color indicative of the copper(II) tetraammine complex, [Cu(NH3)4]2+, and the ammonium and and chloride ions from earlier will still be present in the solution as well as some hydroxide ions.

PHILOU Zrealone - 7-3-2016 at 08:33

If you put copper wire with aqueous ammonia and air into a closed recipient with a screew on top.
Shake it from time to time and open to allow fresh air to enter (oxygen is consumed by the reaction)...the ammonia solution will turn bluer and bluer with time...you finally end up with dark blue Cu(NH3)4(OH)2 ...the crystals of those burn with a blue-green flame.

aga - 7-3-2016 at 11:16

I tried that with a piece of copper pipe suspended above some conc ammonia.

The Blue colour of the drop of liquid that forms under the copper pipe is the most beautiful blue i have ever seen.

MeshPL - 7-3-2016 at 12:15

Electrolysis of copper electrodes in ammonia solution also produces tetraaminacopper (II) hydroxide, although after some point the copper starts plating on the cathode and reaction practically stops. Could be an interesting way to do copper plating though.

moonfisher - 11-3-2016 at 16:19

I second aga, it is a stunning blue, like the finest gentiana. Sometimes, copper (ii) boride looks a little like it, but not really.

chemrox - 11-3-2016 at 18:02

Quote: Originally posted by MeshPL  
Electrolysis of copper electrodes in ammonia solution also produces tetraaminacopper (II) hydroxide, although after some point the copper starts plating on the cathode and reaction practically stops. Could be an interesting way to do copper plating though.

Would this be a PTC? and could one use Cu/NH4 in dissolving metal reductions?

Metacelsus - 11-3-2016 at 21:23

The reducing potential of Cu is not very good, when it comes to reducing organic compounds. In fact, copper(ii) is sometimes used as an oxidant (for example, in Fehling's solution / Benedict's reagent).

[Edited on 3-12-2016 by Metacelsus]

AJKOER - 21-3-2016 at 05:42

A source reference detailing the underlying mixed chemistry involving Cu/NH3/H2O/O2 or H2O2 and a touch of sea salt, which is a good electrolyte for the spontaneous electrochemical aspects of the reaction. Interestingly, the mechanics of the reaction was debated by pundits for many decades. The link below also contains a picture of some of my efforts:

https://www.sciencemadness.org/whisper/viewthread.php?tid=64...

Warning: Do not apply an electric current to an ammonia solution in air and allow the pH to drop. Apparently, an acidified NH4NO2 solution is prone to detonation such that researchers avoid such situations. See my prior comments on this topic at https://www.sciencemadness.org/whisper/viewthread.php?tid=63...

[Edit] Similar comments per Wikipedia on NH4NO2, to quote:

"Ammonium nitrite solution is stable at higher pH and lower temperature. If there is any decrease in pH lower than 7.0, It may lead to explosion. It is desirable to maintain pH by adding ammonia solution. "

Link: https://en.m.wikipedia.org/wiki/Ammonium_nitrite

[Edited on 21-3-2016 by AJKOER]