I have reacted some copper metal with some nitric acid earlier today and I have ended up with a green solution. (Stayed green upon adding water)
But last week, I have done the exact same experiment and my result was a dark blue solution.
Is this because copper reacts differently with different concentrations of nitric acid to produce different coloured copper nitrates?
Or is the green colour due to the formation of Copper(I) Nitrate? (If this exists)
Thank you in advance.woelen - 30-8-2015 at 11:57
The green color most likely is due to formation of nitrogen oxides, which remain dissolved in the liquid and on dilution lead to formation of nitrite
ion, which gives green complexes as well.
If you use excess nitric acid and heat the liquid after all copper has dissolved, then you get a much purer product. After heating, dilute with water
and then heat to boiling again, to be sure that any nitrous acid is destroyed and converted to nitrate and nitrogen monoxide, which is driven out of
the liquid. The final result will be a purely blue liquid, which contains copper nitrate and excess nitric acid.
Under these conditions you certainly don't get copper(I). That would immediately be oxidized to copper(II).aga - 30-8-2015 at 12:01
It was a while back when i made it and i still have a jar of royal Blue crystals.ave369 - 30-8-2015 at 12:39
I've made some copper nitrate recently by reacting copper with 70% nitric acid. The solution was blue. But when I evaporated it dry in a bowl, some
(not all) of the crystals came out green.
That was a headscratcher...Texium - 30-8-2015 at 12:42
You were able to dry your copper nitrate by evaporation? I always have to dry it in a desiccator inside of the jar I want to keep it in and then put
the lid on before removing it just to keep it from liquefying... and it still gets damp.aga - 30-8-2015 at 12:54
Likely that mine are still saturated with HNO3 now i think about it.ave369 - 30-8-2015 at 13:46
You were able to dry your copper nitrate by evaporation? I always have to dry it in a desiccator inside of the jar I want to keep it in and then put
the lid on before removing it just to keep it from liquefying... and it still gets damp.
Well, it was still somewhat damp, but definitely not liquid. The consistence of clay, or something like that.aga - 30-8-2015 at 13:52
Mine is like that : like clay (wet) yet granular too.ave369 - 31-8-2015 at 23:37
I think the green color of the salt is caused by a small amount of unreacted nitric acid that permeates and wettens the "clay".Volanschemia - 1-9-2015 at 04:28
Excess Nitric Acid won't cause a green colour. It is most likely, as woelen said, due to dissolved NOx forming nitrites,
which in turn form complexes.AJKOER - 1-9-2015 at 05:50
I would appreciate if someone would try to resolve the issue of unwanted NO, NO2, nitrite or free HNO3 in the aqueous Cu(NO3)2 by the following
procedure:
1. Add a small amount of CuCO3 not to exceed the total expected moles of the impurites mentioned above or the capacity of the vessel to address the
corresponding moles of CO2 released. Quickly close the vessel (to retain the CO2).
2. Apply pulse radiation (short microwave bursts) or uv treatment (vessel or its cover must permit penetration of the uv rays) being mindful of the
volume of expected gas generated in the closed vessel.
3. Periodically shake the solution mix (not stir).
4. Stop after numerous iterations or when solution color suggests only Cu(NO3)2 is present.
Optionally, upon release of CO2 gas at conclusion of treatment, measure volume of gas released as an indicator of the level of impurities.
I will reveal my understanding of the underlying chemistry, if there is any interest, upon the procedure performing at all satisfactory.
[Edited on 1-9-2015 by AJKOER]Marvin - 1-9-2015 at 05:55
I ended up with a mixture of copper and sodium nitrate after electrolysis which I tried to separate by fractional crystallisation. What was odd was
the solution was blue when cold and green when hot.
The water of crystallisation seems important and pH may matter. You may also find that the reduction produces ammonium salts, I'm unsure if this is
favourable with copper, aside from colour this might make the solution dangerous to crystallise.
Colour changes are not too unusual with copper. Anhydrous copper (II) sulphate is white. The form we know and love is blue and some of the
intermediate hydrates I think are green or yellow. I am surprised the solution stayed green when water was added.Metacelsus - 1-9-2015 at 10:26
Blue when cold, green when hot: it sounds like the formation of a complex is being affected by temperature.
In fact, in my high school chemistry class, the tetrachlorocuprate complex was used as an example of how temperature affects reaction equilibrium. DraconicAcid - 1-9-2015 at 13:24
Colour changes are not too unusual with copper. Anhydrous copper (II) sulphate is white. The form we know and love is blue and some of the
intermediate hydrates I think are green or yellow.
No- the monohydrate is white, and the trihydrate is a light blue. I made them for the carnival.
