bolbol
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Ammonia smell from Copper/zinc compounds?
I had a metal composed of zinc and copper dissolved in nitric acid and I neutralized it with NaOH to precipitate out everything and after the reaction
was over and the precipitates were out I noticed an ammonia smell from the solution. Not as intense as a 10% ammonia solution but definitely an
ammonia smell.
What could be causing this?
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deltaH
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According to the wiki on zinc nitrate, using conc. nitric acid and zinc metal reduces some of the nitrate to ammonia. You should use dilute nitric
acid to avoid this if you wish to. I've recently reported this on another thread.
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Shivachemist
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No, it mainly happens with dilute nitric acid and even with very dilute nitric acid. Zinc dissolves in dilute nitric acid and reduces nitric acid to
nitrous oxide whereas very dilute nitric acid reduced to hydroxylamine and ammonium nitrate along with Zinc nitrate. I think ammonium nitrate in the
mixture reacts with Sodium hydroxide to give ammonia. The same happens with tin and Iron too. This is probably due to the liberation of nascent
hydrogen (powerful reducing agent). However, concentrated nitric acid dissolves zinc and produces Zinc nitrate with the liberation of Nitrogen
dioxide. But, this will not happen with Copper.
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bolbol
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This was actually done using fairly conc nitric acid... Any body knows an easy way to separate the two compounds of copper hydroxide and zinc
hydroxide?
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Shivachemist
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oh, NO2 was evolved during the reaction? Well, separating these compounds is difficult. Having said that, how about adding more Sodium hydroxide to
dissolve Zinc hydroxide (due to the formation of Sodium zincate) and remove copper hydroxide using filter paper ( as it is only very sparingly soluble
in Sodium hydroxide solution) and then you can recover the Zinc ion by adding soluble carbonate solution. But, I will tell you if I find a better
solution for this.
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bolbol
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yes NO2 was evolved only at the beginning tho. And yes I read on wikipedia that adding more OH- will dissolve the zinc hydroxide back but I wasn't
sure how I'd recover that from the NaOH.
Only acid bases I have currently are vinegar, ammonia, nitric acid and sodium bicarbonate... and arsenic acid lol
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Amos
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I can't tell you how to separate zinc and copper hydoxides without converting the copper hydroxide back into copper metal, but if you're interested in
that, add just enough acid(hydrochloric is a good one for this purpose) to dissolve the mixed hydroxide, and then add zinc metal to displace copper
from the solution. When you're done, there should be a water-clear solution of zinc chloride with a pile of copper metal at the bottom. Zinc hydroxide
can be precipitated out by the addition of NaOH or ammonia, and the spongy copper metal obtained can be cleaned of any remaining zinc with dilute
hydrochloric acid. If you don't have hydrochloric acid, it's almost vital that you do obtain it somehow.
I wouldn't recommend gdflp's method as zinc hydroxide also dissolves in ammonia to form an ammine complex, just as copper hydroxide does.
[Edited on 2-4-2015 by No Tears Only Dreams Now]
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Shivachemist
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FYI: Zinc hydroxide is amphoteric in nature and dissolves in excess of ammonia solution too (due to the formation of complex). So, I afraid this won't
work.
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gdflp
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Deleted my last post so as not to cause confusion. Sorry about that, I was having another stupid moment
[Edited on 2-4-2015 by gdflp]
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blogfast25
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Quote: Originally posted by Shivachemist  | | This is probably due to the liberation of nascent hydrogen (powerful reducing agent). However, concentrated nitric acid dissolves zinc and produces
Zinc nitrate with the liberation of Nitrogen dioxide. But, this will not happen with Copper. |
'Nascent hydrogen' is a myth that's been put to bed a long time ago, shiva.
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