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jamit
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Wow, that is beautiful. What did you do ' chemcam' to make copper nitrate like that?
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chemcam
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Well thank you, what I did was use steam to evaporate the excess water from the solution and when I saw crystals forming I took the heat away and let
it further crystallize over night. It was a solid-like mush the next morning so I stirred it to get the shapes seen in the photo then just let it air
dry for a couple more days.
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zirconiumiodide
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Impurity formed upon Drying Copper Nitrate
So over the course of several months i have managed to dry some Copper Nitrate solution i produced by the reaction of Copper Carbonate with Conc.
Nitric Acid to form some nice crystals but upon crushing they were still quite moist. To try and rectify this i placed back in my dessicator box and
left to dry further for a couple of weeks. But DISASTER! Some of the Copper Nitrate, although a nice powder now has decomposed to a red Cupric Oxide
which adds a rather unwanted impurity to my product. There is only a bit of this impurity as far as i can see and i don't want to ruin the otherwise
fine product further so as far as i can see i have three options...
1) Ignore the annoying impurity and store anyway
2) Add a very small amount of HNO3 via pipette or store for a few days under Nitric Acid fumes
3) Filter of the impurity
2 will probably work but don't want to damage the product further and 3 is undesirable as will have to go back through the drying procedure which took
months so might just have to ignore the impurity 
The reason for this decomposition is probably because i dry my chemicals in a desicator box on the window sil and the direct sunlight probably
catalysed the breakdown.
Any suggestions would be greatly appreciated, cheers
ZnI4 
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Texium
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That's certainly odd... the red copper oxide would be cuprous rather than cupric, so if that's indeed what it is then you would have had to have some
other impurity in there with it capable of reducing the copper(II) to copper(I). Where did your reactants come from? That could potentially help
determine what the problem might be.
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zirconiumiodide
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Copper Nitrate was produced from 69% HNO3 with Copper Carbonate.
Copper Carbonate was produced from Copper Sulphate by reaction with Sodium Carbonate. Very little Sodium Sulphate should be in the product as Copper
Carbonate precipitate was rinsed with water, so product should be reasonably pure.
I decided to store the Copper Nitrate anyway as the decomposition appears to have only occured on one side of the evaporating dish containing the
compound and is limited to the surface. Probably <1% of the Copper Nitrate has decomposed. Upon grinding with pestle and mortar the resultant fine
powder is only slightly tinted by the impurity.
Thanks for the response and correction zts16. As the impurity is red it is as you suggested more likely to be cuprous oxide as appose to cupric oxide
which is black.
I think the sunlight (or heat from it) catalysed the breakdown as the side decomposed was that on the window side of the dish. I can't think of any
impurity in the product that would catalyse the breakdown. This decomposition was completely unexpected - i know high temperatures decompose Cu(NO3)2,
but sunlight? 
As not as much damage as previously thought has been done to the compound i will put up with the impurity. But in the future i will have to make sure
that i carry out the final drying of the crystals out of direct sunlight, if i make some more of this compound 
ZnI4
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woelen
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I hardly can imagine that copper(I) is formed in your situation. The red stuff really must be some other impurity. I can imagine it is some iron
compound. Cheap copper sulfate can contain some ferrous sulfate (I had a sample from a pottry supplier which gave a red color with thiocyanate,
besides the black precipitate of cupric thiocyanate).
 Btw, zirconiumiodide = ZrI4, not ZnI4
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Texium
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Quote: Originally posted by zirconiumiodide  |
Thanks for the response and correction zts16. As the impurity is red it is as you suggested more likely to be cuprous oxide as appose to cupric oxide
which is black.
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Yeah, I'm sorry, I was not actually suggesting that I thought that you had copper(I) oxide, I was just
trying to show how it would be very unlikely. Now that I have returned to re-read my previous post, I see how that could have been misleading.
I agree with woelen about the iron impurities. You never really know what's going to be in the store-bought stuff. Most of the time when I use mine,
there are little bits of mystery compounds left over in the product that I can't explain, unless I use the stuff I've recrystallized.
Do the thiocyanate test on a solution of your copper sulfate if you have the means to. In fact, what might be better would be to just test your
copper(II) nitrate solution to see if the iron impurities made it all the way through.
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zirconiumiodide
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Don't know why i've been putting Zn instead of Zr! Must be writing these posts
late at night. Either that or Zinc impurity!
I was very shocked by what seemed like decomposition. But why else was it only seen on the sunlit side and surface of the product?
Also there have been no signs of impurity up until this point. Two weeks ago they were lovely (all beit damp) blue crystals ..So can only believe that under very dry conditions and under direct sunlight although
slow, decomposition occured over the course of the two weeks it was drying.
Copper Sulphate used is meant to be high purity - bought of ebay. But saying that seems to have some insoluble (and probably soluble) impurities!
Haven't currently got thiocyanate as still working in a rudimentary home lab set up and building up my stock of chemicals so will have to wait a few
months before performing this test when i get some Potassium Thiocyanate.
ZrI4
[Edited on 16-7-2014 by zirconiumiodide]
[Edited on 16-7-2014 by zirconiumiodide]
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Texium
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Well, the impurity could be more soluble than the copper nitrate, thus being hidden when the crystals were still wet and only coming out of solution
when they were more dry. It's really very unlikely that your copper nitrate is actually decomposing. You'd get a definite odor of NO2
coming off of there if it was.
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zirconiumiodide
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Impurities would have been seen throughout the compound as the Copper Nitrate was powder dry, and not just restricted to the surface as this was. And
on one side, answer that question?
Decomposition can't keep being dismissed in the light of the evidence!
If i had blow torched it i would expect the same thing, probably more extreme, but there would be decomposition on the surface and on the side i
blowtorched.
There was some tinting of the NaOH drying agent yellow suggesting gas may have eminated from the compound but any NO2 gas present in the drying box
would have been absorbed by the NaOH meaning there could have been very little present upon opening of the box. It may also have occured days before
the box was opened giving ample time for the gas to be absorbed.
The only way to be certain, even though from the evidence i'm quite sure it was decomposition, would be to repeat what occured by placing a small
amount of pure Cu(NO3)2 in direct sunlight under the same conditions.
But generally i decided to raise this issue not only for suggestions on how to cure my now tainted Copper Nitrate but also to warn people against
making the same mistake i did as it was totally unexpected. 
ZrI4
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hyfalcon
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| Quote: Originally posted by zirconiumiodide | Impurities would have been seen throughout the compound as the Copper Nitrate was powder dry, and not just restricted to the surface as this was. And
on one side, answer that question?
Fractional crystalization
ZrI4 |
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