Preserving CuCl

[xeluc]

I just made some beautiful white CuCl. It is currently under water and seems decently stable. However, the container I used to decant liquid got some CuCl on the edges and it has turned a light olive Green color. I have to assume that the rest will too when dry. What is the best way of keeping my CuCl white?

[RyanJ]

I just made some beautiful white CuCl. It is currently under water and seems decently stable. However, the container I used to decant liquid got some CuCl on the edges and it has turned a light olive Green color. I have to assume that the rest will too when dry. What is the best way of keeping my CuCl white?

 

Copper (I) oxide is available from chemical supply houses and possibly from ceramics suppliers. It is a red powder, which can be dissolved in hydrochloric acid. It forms a colorless solution, when absolutely no oxygen is present, otherwise a dark brown solution is formed, containing a dark mixed valence copper (I)/copper (II) complex. The exact nature of this dark compound only is understood partially, see riddle on copper (I) and copper (II). Copper (I) oxide is an interesting chemical for the home lab, but performing experiments with this is really difficult, due to the extreme sensitivity of aqueous copper (I) compounds to oxygen from the air.

 

Looks like you can't - apparently its reacts with Oxygen.

 

Source: http://81.207.88.128/science/chem/elem/elements/Cu/index.html

 

Cheers,

 

Ryan Jones

[Borek]

Looks like you can - just separate it from oxygen

 

Perhaps keeping it under some oil, like pure sodium?

 

Best,

Borek

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[xeluc]

yes, I beleive I will do that. Thanks borek.

[woelen]

yes, I beleive I will do that. Thanks borek.

In fact, xeluc, you can't without really good lab facilities. Storing under oil is a real pain. Sodium comes in nice large lumps, CuCl is a powder. If you dry it, it will become darker already. Adding oil to the wet stuff will be a REALLY messy crap.

 

Have a look at my site. I purchased some CuCl from a good chemical company and this is the best they could offer me.

 

http://woelen.scheikunde.net/science/chem/compounds/cuprous_chloride.html

 

If chemical companies are selling this as the best they have, then forget about making a purer compound at home. Even this sample was a rip off already. Making CuCl of this purity already costs almost $1 per gram on a commercial scale.

[RyanJ]

Looks like this stuff is really hard to keep in its pure form then. Is it best just to buy this stuff as you need it?

 

Cheers,

 

Ryan Jones

[xeluc]

hm... I noticed that for a few hours while I was waiting for my CuCl precipitation to fall tothe bottom, the Powder was snow white. Within 10 minutes of decanting however, things were a different story. My crap is a lot darker than yours.. What if I put some CuCl that has not been dried (white) ins a Vial and heat up a tub of water to drive out disolved gases, then screw on the cap of the vial under water, to eliminate any air inside. The point here is not to make something where I can use CuCl for experimentation, I jsut want a pure sample. When it is created, it is EXTREMLY pure, theres nothing saying I can;t at LEAST get a product simlar to yours Woelen. I'm thinking however that CuCl will also react with water. Of course this must be a much slower process as I havn't seen this take place. A MSDS did say it reacts with moisture. Maybe only in the presence of Oxygen though? Can someone second this?

[woelen]

CuCl does not react with water. If you keep out oxygen rigorously, then it can be kept indefinitely, either dry or moist. The compound itself is stable, the pain is just in its extreme sensitivity towards oxygen, when it is wet or moist.

 

I recognize very much of your struggling with the stuff . I've done this many times myself and I could make beautifully white stuff, but as soon as I tried to make it dry, it became greenish/brown and it was spoiled within seconds. Finally I've given up and I bought some of the stuff (now approximately 1 year ago). The purchased stuff keeps fairly well and it does not degrade further. The stuff is not hygroscopic like CuCl2.

 

I even have tried to use acetone for cleaning up. I decanted most of the water, added acetone to it (which dissolves most of the water and remains of acid), decanted the acetone again, added new fresh acetone and decanted that and did a final rinse with diethyl-ether. But even that method of drying did not give me a nice white powder. If you really want nice white CuCl, then you have to work in an all-inert gas apparatus. That, however, is beyond the possibilities of what a home chemist can afford. So, I've given up on this .

 

@RyanJ: I purchased some, as you have seen on the picture. It remains like this and does not deteriorate further. So, you can buy some of this stuff, but do not expect it to be 100% pure when you receive it. It will contain quite some contamination with copper (II). If you want to perform experiments with CuCl, then you can also make it in a wet environment. Xeluc has done so and indeed you can obtain snow-white stuff as long as it is kept under water. I think it is best that Xeluc gives details on how he made his CuCl.

[xeluc]

Well actually, I used one of your experiments, Woelen . In a container of conc HCl, I threw in a lot of Copper wire (better surface area for reacting) and some CuO to get Cu2+ Ions into solution (Cu(OH)2 or CuCl2 would work fine too, I just used what I had at the time). From there the Cu2+ Ions Oxidized the Cu into Cu+. After all traces of Cu2+ were eliminated I Transferred the HCl solution from my 20 Ounce bottle (Parents don't liek my chem experiments. They don't understand and therefor assume I'm making Meth ) to a more open container, where the Cu+ Ions would be oxidized further back to Cu2+ Ions. Then the now-brown solution was transferred and sealed back into teh plastic bottle. The bottle was sealed to aleviate excess HCl vapors. The Liquid would again becoem clear as Cu2+ ions were oxidized to Cu+. After each sucessive transfer, my solution became more and more conentrated wit Cu Ions. Originally I was going to use this as a source of CuCl2, but after beign enlightened by Woelen, I thought it'd be SO awesome to have a pure sample of CuCl. When the defining moment came, when I saw that glorious white precipitate come form a yellow/clear liquid, it was nice to say the least. It's 64 degrees F in my house right now, Oil prices in USA are too high for dad to turn on the heater . As a result, things evaporate slowly. Currently, I have a Dark olive green shell wiht some brown in it. When it is broken, white pure CuCl can be seen. Once this is all dried, I will end up re-inserting it into my CuCl-synthesizer and try again. So Woelen, can i have a reasonably pure sample of CuCl with my method stated in my above post?

 

EDIT: It seems as if you answered my question in your previous post. So, why do YOU not do this? I am sure you would like a more-pure sample... If you have tried for so long I can reasonably say you would have tried this yourself, and if it had worked, you would have a picture of THAT instead of the olive green sample you have. So..... ???

 

EDIT 2: Why is it that I answer my own questions right after I post them. I re-read your post and you mentioned drying the with acetone. Well, I don't understand how that would help you.. Other than causing it to dry faster than when in water therefor maybe minimizing corrosion? Anyhow, after reading that part, it seemed like you were geared torwards a dry specimen (can I say specimen or is that only for live things..). In which case, my method would not be satisfactory for your needs.

 

Hey, what if you kept the cap pf a vial full of water/CuCl slightly loose, boiled hte water away and as soon as the last of the visible water boiled away, you sealed the vial. It would be a slight vaccum with H2O Vapor, but if done right, little or no O2. Also, your vial would be seamingly dry, save maybe a LITTLE moisture that would condense... But I think that's pretty close. Who knows, just a thought. Don't knwo if it's feasable but I cant see why not. Other than maybe the CuCl goign everywhere during boiling. But the end result would be white or only very slightly oxidized CuCl...

[woelen]

The reason that I used acetone and ether rinses was to make the stuff dry as fast as possible. Once it is thoroughly dry, it is not so sensitive to aerial oxidation anymore. But even the tiniest traces of water make it very vulnerable and that is why I did not succeed in making a sufficiently pure sample. Even under acetone it changes color .

 

CuCl is somewhat soluble and the dissolved matter is what is oxidized so easily. I think it has to do with the larger contact area of the dissolved matter and the fact that the dissolved matter is complexed: CuCl2(-) is so sensitive towards aerial oxidation....

 

Your idea of boiling away water from a sample in a loosely capped container may work. I personally never tried that. I'll try such a thing at a test tube scale and I'll let you know. I can imagine, however, that at higher temperatures the CuCl hydrolyses and that it becomes contaminated with oxide and hydroxide ions.

 

My aim indeed is a purely dry sample. I do not like wet samples of chemicals. Look at my sample of vanadyl sulfate on my website, it has a really nice color, but still it is ugly with all the water around.

 

 

One of my chemistry books states the following way of preparation:

 

Dissolve 40 grams of copper (II) chloride in 200 ml of concentrated hydrochloric acid and add 100 ml of water. Add a large amount of copper wire or thin foil and heat on a waterbad. Wait, until the liquid has become colorless.

Prepare two liters of oxygen-free water and cool down to a few degrees centigrade.

Pour the colorless solution of copper into the water. A white and heavy precipitate is formed.

 

In a dimly lit room, suction filter the white precipitate and rinse it with dilute oxygen-free sulphuric acid (acid: water = 1 : 20) and then rinse with oxygen-free absolute alcohol (methanol also will do, is much cheaper). Next, transfer the still wet crystalline mass to a drying chamber, which is pre-heated already and kept at a temperature close to 100 C. Drying must be done as fast as possible. Once the crystals are absolutely dry, they quickly must be transferred to a thoroughly dried container, which is capped immediately and tightly closed.

 

When the crystals have to remain white instead of brown or green, then the container must be filled with a dry and inert gas, such as N2, CO2 or a gaseous hydrocarbon.

 

If I read this, then I think that for the home chemist this hardly is feasible. Making all your solvents and acids free of oxygen is not easy. You can boil them for a while to drive off oxygen, but on cooling down, they readily absorb some oxygen from the air again.

[xeluc]

Ok, well I'm gonna do some experiemtning and see what works best. After all, if it DOESN'T work, I can just re-disolve it ;-)

 

Also, I believe CuCl is absolutly not soluble in alcohol. Unless the whole azeotrophism thing messes it up, I think that would work to keep it under. I'm ok with liquids in my samples..

[woelen]

Xeluc, finally I've done an experiment, which I promised you to do. I made some nice white CuCl by adding a concentrated solution of a copper (I) salt to a lot of water. For you the preparation of the snowy white stuff is quite familiar now I guess.

 

Next, I decanted the very light blue solution above the white crystalline precipitate and I rinsed with water. Next, I decanted again, leaving a wet white solid with a very thin layer of water above it.

 

This stuff, I heated until all water has evaporated. The results are really disappointing. I get dirty brown solid, with even black crap in it. Remarkably, on cooling down, the stuff became a little lighter and the black color disappeared. Finally, I had a light brown solid, but certainly not the beautiful white solid I had before.

 

Now comes the most remarkable part. To this brown crap I added a little water again. And guess what happened . The solid becomes snowy white again within seconds. This REALLY surprised me.

As expected, the solid does not dissolve.

 

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Next, it became time to sit down and think . I have the following theory on these observations.

 

1) The nice white stuff is not as pure as we think it is. We always make it from a strongly acidic solution, which also contains quite some Cu(II) ions.

2) On dilution with water, the CuCl crystallizes and the solution becomes waekly acidic with low chloride concentration. The dark brown multivalency complex cannot exist under these conditions anymore, the copper (I) precipitates in CuCl, the small amount of copper (II) goes in solution as blue aqua ions.

3) Some of this blue copper (II) material is attached/embedded in the CuCl-crystals. This makes them optically very white. Some yellow/brown impurities are masked by the blue color. This principle of optical whiteness also is deployed by certain brands of clothes washing soap to make things look brighter and cleaner than they actually are. Our CuCl crystals may look so beautifully white, due to this copper (II) impurity.

4) Also some acid is embedded in the precipitated CuCl crystals.

5) On heating to dryness, the copper (II) in the mix forms brown copper (II) chloride. The black stuff may be transient copper (II) oxide, which disappears again because of some HCl still present in the crystal mass. I also go quite some white fumes during the heating.

6) What is left behind is copper (I) chloride, with some copper (II) chloride and possibly a very small amount of acid left.

7) On addition of water, the copper (II) chloride becomes very light blue again and partly goes into solution. With the traces of acid left, the liquid does not become turbid. The CuCl again looks snow-white again.

 

I invite you to try this yourself. It is really remarkable to see all of this. If you heat the white crystals be careful to use heat resistant glassware. I used a wide testtube.