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Copper nitrates

Little_Ghost_again - 29-12-2014 at 05:24

Hi
The reasons dont matter but I ended up with a mix off nitric acid acid (it started out as 30% strengh) and sulphuric acid (96% and only a smallish amount in the solution).
I decided rather than throw it away I would dissolve some of the huge amounts of waste copper wire I have, from there I would use electrolysis and collect the fine copper powder that drops off one the electrodes.
I assumed I would get copper (i) nitrate and then copper sulphate. this is what happened.....................
I got a funny smell almost like chlorine or a swimming pool, it wasnt that strong, the copper in the solution had started to fiz small bubbles and the solution gradualy went a deep blue, this morning the solution was still fizzing but had gone a deep green (Copper (ii) nitrate??), there seemed to still be as much copper wire as when I started though ??
I added a tiny amount (15ml) 96% sulphuric acid and the solution went half deep blue and half lighter blue, one half looks like copper (i) nitrate and the other half looks like copper sulphate.
Once the fizzing slow down again I will decant off and add more sulphuric acid, I will then try and use electrolysis to get my copper powder, I did this with copper sulphate solution a few months back and got fine copper powder, this time I ll have a test tube under the electrode to catch it more easily.
I still cant get pictures as I would love to post the colours of this, but why did it go from deep blue to deep green over night?

CHRIS25 - 29-12-2014 at 06:24

I suspect, and bravely so I might add, that the green is copper sulphate. Cu3(SO4)(OH)4. Personally this makes sense to me (amateur speaking here) seeing that you added a DILUTE nitric acid to the solution whereas the Sulphuric acid was concentrated, both are oxidizers and I would suspect that the sulphuric acid won, so to speak, and produced copper sulphate, but not the expected blue, Green due to the binding of an Hydroxide molecule. Anyway this would be my answer in a classroom. Happy to be corrected. (PS, the green patina on copper found away from the sea is not Necessarily always a copper chloride or a copper carbonate as appears, it can be a copper sulphate)

[Edited on 29-12-2014 by CHRIS25]

Amos - 29-12-2014 at 07:58

Anhydrous copper nitrate is greenish, so perhaps as the reaction has continued, all of the water available to hydrate the copper nitrate formed has been used up? Yes, copper(II) sulfate will take priority as a salt of the stronger acid, but if you had more nitric acid than sulfuric acid present then the majorit of the solvated anions are still nitrate and not sulfate. This also seems to make sense to me because you said the reaction won't seem to continue further. Perhaps the solution is too saturated for the copper salts formed to come into solution and keep the reaction moving forward?

Metacelsus - 29-12-2014 at 08:36

The smell was probably nitrogen dioxide.

Little_Ghost_again - 29-12-2014 at 08:37

I added more sulphuric acid and it turned dark blue again, currently its starting to turn green and still loads of copper in the beaker so I will keep going.
Very interesting. The sulphuric acid is 96% and I would say the nitric acid I added a little while ago is 50%.
The bubbles had slowed right down so I am guessing that the water was almost used up so that would make sense. in the end it wont really matter seeing as soon as all the copper has dissolved (really surprised that there dosnt seem to be much copper used) I will add sulphuric acid to make sure its all sulphate, then I will you electrolysis. Seems a bit mad I know but when I did it last time with weak copper sulphate I ended up with a very very fine copper powder, its the copper powder I am after, yes I could get it other ways but this is really interesting watching the colours change.
It started really slow and nothing at all happened for around 2 hours! Then it started to slowly go blue, after a while it really took off and fizzed, at the moment there are so many small bubbles it looks almost like a precipitate in the beaker but there isnt any, Its on the point of turning from blue to green.
Way more fun than using a single acid lol.
The beaker is 1ltr so there is a fair amount of it, I put in loads of copper wire but even so I was expecting loads to have been used by now, maybe I should try and use electrolysis while this is going on.
The smell I wasnt expecting, its really chlorine like but I dont see how

Copper nitrate advice

Little_Ghost_again - 29-12-2014 at 08:41

Hi
I mentioned in another thread making copper nitrate crystals and trying to actually grow one to a large size. I have 50% and 30% nitric acid here, which should I use and how dilute should I make it to get some decent copper nitrate to start with, I am looking at making around 1-1.5 ltrs of it to start with then I will put in a desiccator to get a seed crystal and take it from there.
The aim is to get as large a crystal as I can grow over 6 weeks

gdflp - 29-12-2014 at 08:55

Copper(I) nitrate doesn't exist for very long, the cation is immediately oxidized to copper(II) by the anion. And the only oxidizer present strong enough to oxidize the copper was nitric acid, I don't believe sulfuric acid is a strong enough oxidizer to oxidize copper. My guess is that initially, since 30% nitric acid won't dissolve copper very quickly, only a small number of copper ions were in solution and there was enough water present to hydrate them. As the reaction continued however, more and more copper(II) ions came into solution and there wasn't enough water to complex with them, hence the solution turned green as it does when a piece of copper is added to conc. nitric acid. Finally, when the sulfuric acid was added, the greater number of sulfate ions formed an equilibrium of copper sulfate, overwhelming the green color and turning the solution blue. I have no idea why two layers formed, other than you didn't mix the solution well enough when you added the sulfuric acid. Were the layers immiscible?

[Edited on 12-29-2014 by gdflp]

CHRIS25 - 29-12-2014 at 09:22

I would use 50% without doubt. Conc nitric is 16 M roughly, I just used an 8 M on 32 g of cleaned copper. That took approx 20/30 minutes to dissolve. It just so happens that 8 M is 50%. You do not want to add water, risk of OH in the solution as you evaporate. Plus use ratio 4 mol Acid to 1 mol copper. You will get a lot, seriously a lot of brown fumes for about 10 minutes, after which it will die down. Anything here help?

Little_Ghost_again - 29-12-2014 at 10:41

Quote: Originally posted by CHRIS25

I would use 50% without doubt. Conc nitric is 16 M roughly, I just used an 8 M on 32 g of cleaned copper. That took approx 20/30 minutes to dissolve. It just so happens that 8 M is 50%. You do not want to add water, risk of OH in the solution as you evaporate. Plus use ratio 4 mol Acid to 1 mol copper. You will get a lot, seriously a lot of brown fumes for about 10 minutes, after which it will die down. Anything here help?

Yes thanks alot, it might also explain some the odd results from my other experiment,

Little_Ghost_again - 29-12-2014 at 10:48

Quote: Originally posted by gdflp

Copper(I) nitrate doesn't exist for very long, the cation is immediately oxidized to copper(II) by the anion. And the only oxidizer present strong enough to oxidize the copper was nitric acid, I don't believe sulfuric acid is a strong enough oxidizer to oxidize copper. My guess is that initially, since 30% nitric acid won't dissolve copper very quickly, only a small number of copper ions were in solution and there was enough water present to hydrate them. As the reaction continued however, more and more copper(II) ions came into solution and there wasn't enough water to complex with them, hence the solution turned green as it does when a piece of copper is added to conc. nitric acid. Finally, when the sulfuric acid was added, the greater number of sulfate ions formed an equilibrium of copper sulfate, overwhelming the green color and turning the solution blue. I have no idea why two layers formed, other than you didn't mix the solution well enough when you added the sulfuric acid. Were the layers immiscible?

[Edited on 12-29-2014 by gdflp]

Yes the layers mixed, whats more odd is even after 24 hours the copper hasnt dissolved, there are streams of small bubbles coming off the copper to the point that you cant really see inside the beaker! but the colour goes from green to blue and back again, I am starting to wonder if the copper somehow regenerates back onto the wire??
I am at a complete loss as to why the copper is still there looking almost as good as when I put it in!
Is they anyway hydroxide could be formed like this? it was mentioned in another thread and I have added water to this one, at the moment its in the process of going a deep green. I must try and get a pic of this its really amazing to watch the amount of bubles of being produced and yet very little copper being used up.

Bert - 29-12-2014 at 10:53

Let's merge threads to make it a little easier to understand all this-

CHRIS25 - 29-12-2014 at 11:02

Excuse the interjection, but since anhydrous copper nitrate was mentioned I thought I would post this image to ask what the turquoise green is. Now I have read that anhydrous can not be made by gentle heating of the copper nitrate solution, which is what I have just finished doing, I have 111 g of perfectly deep blue copper nitrate, probably the tri or hexahydrate, but off-centre from where the candle was directing its heat this blue-green very hard solid perfectly round crust had formed about one inch diameter. The whole perimeter was the expected blue hydrate, but this piece was rock solid. My immediate thought was anhydrous, because of the colour. But it can not be right? Unfortunately I had broken the piece up before realising this thread otherwise I would have photographed it as it was in the beaker. The photo has not done justice to how much green there was, a lot more than what you see here.

Yep, the green is a copper hydroxide, or more accurately copper nitrate with (OH). It was insoluble in water breaking down into lime green particles. So that means that the rest of my copper nitrate is probably trihydrate since expected yield and actual yield with 3H2O calculated in are very close.

[Edited on 29-12-2014 by CHRIS25]

blogfast25 - 29-12-2014 at 11:47

I've heard of a copper tribasic nitrate, Cu(NO3)2.3Cu(OH)2 and this could be it or similar. Copper nitrate hydrate doesn't like excessive heating. Just separate the blue from the green and you're good to go with the blue.

To know with certainty which hydrate (tri or hexa) it is, you'll have to use your favourite titration method.

[Edited on 29-12-2014 by blogfast25]

CHRIS25 - 29-12-2014 at 11:59

Yes I agree I should have written the formula you wrote this is what I meant actually. I have separated it from the rest, but I had to keep heating to guarantee a product without 20 water attached to it, only lost 11 g anyway. My favourite titration method, you mean the one that kept not working...

still have to re-do those, keeping getting side-tracked with too much reading.

blogfast25 - 29-12-2014 at 12:57

This would be a good opportunity to use that method (that works perfectly, trust me

) because your nitrate is a pure substance.

Assume it's the hexahydrate, as a hypothesis. Based on that prepare accurately a 0.1 M Cu<sup>2+</sup> solution from your nitrate. Titrate with KI and sodium thiosulphate (starch indicator).

If found molarity is 0.1 M, it's the hexahydrate.

If the product was pure trihydrate, the molarity found would theoretically be 0.122 M.

[Edited on 29-12-2014 by blogfast25]

Little_Ghost_again - 29-12-2014 at 13:50

I am going to take a pic in the morning, I have separated some the liquid out, it stopped fizzing and was green in colour but still almost all copper still present, I added a little more nitric acid with some water added and it turned dark blue, I have also added added more water and nitric acid to the one with copper in and there isnt much fizzing, my guess is if I add more sulphuric it will start up again, but first I am going to use electrolysis on the small portion I have separated and see what happens.
I am also going to stop messing in the morning and make some copper nitrate and other copper compounds before I go and get charged!!

Little_Ghost_again - 31-12-2014 at 12:40

I might have found a way to get some pics on tomorrow, I took some the blue solution and put to one side, I also added 50ml conc nitric to the large beaker with copper metal in and another 15ml of conc sulphuric acid, the bubbles started again and it went cloudy with no brown gas but it did get the chlorine like smell (not exactly like swimming pools but close) over night it changed again from the deep blue to the emerald green, I will take pics of both and see what you think it is.
I guess the next step is to put a little of both solutions in a desiccator and see what crystals form, maybe I can get an idea of what it is from the shape of the crystals? I am sure the deep blue is copper nitrate so that should be easy as the crystals once out the desiccator should absorb water and go mushy while if its copper sulphate they shouldnt do this.
The green one I am guessing at the following......................
If its copper (i) nitrate then again the crystal should take water and go mushy and probably blue?
If its copper (I) sulphate then the crystal should stay as it is??

There is still plenty of copper wire in the beaker and at no point has a brown gas been off. It probably isnt interesting to most people but I am totally amazed by this as it hasnt done anything I was expecting it to do.

One last question .....................
Will copper asprinate form crystals? I am after a crystal collection and that would make a good addition

blogfast25 - 1-1-2015 at 07:30

Quote: Originally posted by Little_Ghost_again

If its copper (i) nitrate then again the crystal should take water and go mushy and probably blue?
If its copper (I) sulphate then the crystal should stay as it is??

In both cases copper(II) salts will form, not copper(I) which is very prone to oxidation to (II).

Little_Ghost_again - 5-1-2015 at 12:20

Quote: Originally posted by blogfast25

Quote: Originally posted by Little_Ghost_again

If its copper (i) nitrate then again the crystal should take water and go mushy and probably blue?
If its copper (I) sulphate then the crystal should stay as it is??

In both cases copper(II) salts will form, not copper(I) which is very prone to oxidation to (II).

So copper (II) can also be deep emerald green then? Unless I guess one has gone to copper oxide ?????
I am really tied up but do have some pics to get posted and do have some the green stuff in the desiccator, I am using sodium chloride with rice mixed in under the bowel with the solution in (cheap and was to hand) so its a bit slow evaporating

DraconicAcid - 5-1-2015 at 13:15

Quote: Originally posted by Little_Ghost_again

So copper (II) can also be deep emerald green then? Unless I guess one has gone to copper oxide ?????

Yes- particularly if there is chloride present. Copper(I) salts are generally white unless impure (apart from the oxide, which is red).

Little_Ghost_again - 9-1-2015 at 13:26

Nothing to report so far, solutions in desiccator and very very slowly the solution level is dropping, no crystals yet and I didnt heat or boil off any solution first.
I am also using salt and rice (heated up on a coal fire first to dry out) as the desiccant so it will be slow. The deep blue one looks like it may have a tiny crystal forming but hard to tell through the glass, the desiccator is starting to form a vacuum so I guess its heading the right way.

Little_Ghost_again - 3-10-2015 at 12:36

so finally a update and some pics, the pics are not great sorry about that!
The beaker has been left on the window sill all this time and not touched, there is till copper in there and now some deep blue crystals on the bottom that are stuck fast, the strange bit is the colour of the liquid and the fact there seems to be be a white powder in the solution on top of the crystals.
The white stuff that looks like the outside of the beaker is dirty is in fact on the inside glass of the beaker.

The solution I put in the desiccator has produced blue crystals that when exposed to air see to melt a bit, I had to take the lid off shoot the pics quick and put the lid back on. There are some green very small crystals (no idea what they are), there is one large crystal in the bowl but every time I change the desiccant it melts a bit and takes a few weeks to grow again.
I honestly thought the solution would be dry by now. In the beginning I had water condensation droplets inside the desiccator, I am not sure if you can see it in the pics but now the droplets are a blue colour!! I havnt splashed anything its something thats only happened in the last few weeks hence why I decided to post an update. It likely I will empty the beaker and try and somehow get the crystals out, I dont see much point carrying on with this. The beaker still gives off small bubbles.

Little_Ghost_again - 3-10-2015 at 13:53

A couple of more close up pics

aga - 3-10-2015 at 14:15

Should have photoshopped out the flower petals before doing the Zoom on the same image.

Devil is always in the details.

Little_Ghost_again - 3-10-2015 at 14:43

Quote: Originally posted by aga

Should have photoshopped out the flower petals before doing the Zoom on the same image.

Devil is always in the details.

dont you like the petals? it was an old bowl re purposed for crystallizing

. The pics were a screen shot but they dont seen to come out as big on here so I zoomed in and did another capture.
I cant get the colour balance right with this camera, I might try the jpeg option next time and see if it gives a more accurate colour.
On my screen they dont look as blue as they do when you actually see them.