Sciencemadness Discussion Board

What is this? (copper inorganic compound)

DrMario - 10-10-2014 at 06:37

This is how I obtained the content of that jar: I made a saturated aqueous solution of sodium hydrogencarbonate (NaHCO3) and put some random pieces of copper into it. These were various copper plates and wires. All reasonably pure, but all, more or less, covered by cupric oxide.

I closed the jar and left it there for several weeks, maybe a month or more. The copper plates became even darker, but the solution became this bright blue.

What do you think this might be?

copper-NaHCO3.jpg - 1.3MB

Endo - 10-10-2014 at 06:46

I suggest this would be a good post for a beginnings question.

The light blue solution is typical of the copper 2+ ion in solution. The blue color is due to the formation of the complex ion [Cu(H2O)4]2+. Tough to see what the precipitate looks like. If it is gel like it is probably a copper hydroxide or if not more likely a copper carbonate, or a mix of the two.

:)

DrMario - 10-10-2014 at 07:02

Quote: Originally posted by Endo  
I suggest this would be a good post for a beginnings question.

The light blue solution is typical of the copper 2+ ion in solution. The blue color is due to the formation of the complex ion [Cu(H2O)4]2+. Tough to see what the precipitate looks like. If it is gel like it is probably a copper hydroxide or if not more likely a copper carbonate, or a mix of the two.

:)


First of all, the precipitate is just undissolved NaHCO3
It's not a beginner's question, since not even you know what exactly is going on. Yes, the cation is clearly Cu2+ - and then?




[Edited on 10-10-2014 by DrMario]

hyfalcon - 10-10-2014 at 07:17

If you don't have references on the chemistry, then it belongs in the beginners section.

Endo - 10-10-2014 at 07:21

Hmmm,

Your question was
Quote:

The copper plates became even darker, but the solution became this bright blue. What do you think this might be? </quote>



I felt I answered your question clearly. The bright blue color is the complex ion of Cu2+ in solution.

You will need to specify another question if you want more information. -- <b> and then?</b> is a bit of a mystery to me. For now you have a soup of ions in solution: The copper complex ion [Cu(H2O)4]2+, Na+, and because of equilibrium a range of different carbonate polyatomic ions in various proportions, and water. It appears you have removed the copper metal.

So, in a closed container, with nothing to drive the reaction that formed the Cu2+ in the first place (no copper metal), this jar will remain sky blue on your shelf doing very little until you change the conditions and drive an equilibrium in one direction or the other by adding something to the reaction mix. So your answer to "and then?" is very little.

AsocialSurvival - 10-10-2014 at 07:29

Copper (2+) carbonate. Air oxidizes Copper, and formed Copper Hydroxide reacts with Sodium bicarbonate to form Sodium Carbonate and Copper Carbonate.

You can make your solution even more dark blue and concentrated if you add Carbon Dioxide to it, because Copper bicarbonate will form which is much more soluble.

For example only 10 mg of Calcium dissolves per liter of water in the form of carbonate, but 95 grams of Ca dissolve in same amount of water if bicarbonate.

Test it by drying, the remaining powder will look green, not blue, trust me!

[Edited on 10-10-2014 by AsocialSurvival]

Amos - 10-10-2014 at 07:42

Sodium bicarbonate dissociates, creating a low concentration of OH-. Because copper(II) oxide and copper(II) hydroxide are both amphoteric, they will dissolve in greater amounts than usual with more OH- present. Don't be deceived by the color, though; it's unlikely you have a very significant amount of copper(II) in solution. It's still overwhelmingly sodium carbonate/bicarbonate.

DrMario - 10-10-2014 at 07:46

Quote: Originally posted by AsocialSurvival  
Copper (2+) carbonate. Air oxidizes Copper, and formed Copper Hydroxide reacts with Sodium bicarbonate to form Sodium Carbonate and Copper Carbonate.

You can make your solution even more dark blue and concentrated if you add Carbon Dioxide to it, because Copper bicarbonate will form which is much more soluble.

For example only 10 mg of Calcium dissolves per liter of water in the form of carbonate, but 95 grams of Ca dissolve in same amount of water if bicarbonate.

Test it by drying, the remaining powder will look green, not blue, trust me!

[Edited on 10-10-2014 by AsocialSurvival]


Thanks a lot.

What is the reason these bicarbonates are so much more soluble than carbonates? Also, I was under the impression that copper carbonate was practically insoluble in water - so is it possible that there already is copper bicarbonate in the solution?

DrMario - 10-10-2014 at 07:47

Quote: Originally posted by No Tears Only Dreams Now  
Sodium bicarbonate dissociates, creating a low concentration of OH-. Because copper(II) oxide and copper(II) hydroxide are both amphoteric, they will dissolve in greater amounts than usual with more OH- present. Don't be deceived by the color, though; it's unlikely you have a very significant amount of copper(II) in solution. It's still overwhelmingly sodium carbonate/bicarbonate.


OK, thanks, this answers my question quite thoroughly!

Amos - 10-10-2014 at 08:11

Quote: Originally posted by DrMario  
Quote: Originally posted by No Tears Only Dreams Now  
Sodium bicarbonate dissociates, creating a low concentration of OH-. Because copper(II) oxide and copper(II) hydroxide are both amphoteric, they will dissolve in greater amounts than usual with more OH- present. Don't be deceived by the color, though; it's unlikely you have a very significant amount of copper(II) in solution. It's still overwhelmingly sodium carbonate/bicarbonate.


OK, thanks, this answers my question quite thoroughly!


Also, I don't know that copper bicarbonate exists by any means, even in solution. I think bicarbonate is restricted to group 1 and 2 elements.

AsocialSurvival - 10-10-2014 at 08:22

Quote: Originally posted by DrMario  
Quote: Originally posted by AsocialSurvival  
Copper (2+) carbonate. Air oxidizes Copper, and formed Copper Hydroxide reacts with Sodium bicarbonate to form Sodium Carbonate and Copper Carbonate.

You can make your solution even more dark blue and concentrated if you add Carbon Dioxide to it, because Copper bicarbonate will form which is much more soluble.

For example only 10 mg of Calcium dissolves per liter of water in the form of carbonate, but 95 grams of Ca dissolve in same amount of water if bicarbonate.

Test it by drying, the remaining powder will look green, not blue, trust me!

[Edited on 10-10-2014 by AsocialSurvival]


Thanks a lot.

What is the reason these bicarbonates are so much more soluble than carbonates? Also, I was under the impression that copper carbonate was practically insoluble in water - so is it possible that there already is copper bicarbonate in the solution?


Yes, you can't have any bicarbonate as long as you have one hydroxide (in case of elements with oxidation states +1 and +2), but it can be formed by absorbing additional CO2 from air. You can imagine those two chemicals seperately, after long period of time, both Sodium hydroxide and Copper hydroxide will become bicarbonates, because they absorb it from air.

But don't try to get dry Copper bicarbonate, because it only exists in solution, just like Calcium bicarbonate (the alkali metals however can be isolated dry).

Why?

Well, because Carbon dioxide forms acid with water, and obviously the more CO2 is the more acid is formed, just like adding more NO2 to water to make more Nitric acid.

The easiest and best way to make bicarbonate is to hold that solution in closed bottle full of CO2 above it, and then periodically add more CO2. That will raise partial pressure of CO2 which will dissolve more Copper as bicarbonate. However, if you start from Copper metal, you will still need access to Oxygen so it can oxidize Copper. best to do this method on already made Copper hydroxide or carbonate.

Practicaly, mother nature did that so that you can grow plants 2 times faster than usual, if you increase CO2 concentration in air which is neccessary for photosynthesis, it will absorb more nutrients from soil in needed proportion.

[Edited on 10-10-2014 by AsocialSurvival]

blogfast25 - 10-10-2014 at 11:11

Quote: Originally posted by No Tears Only Dreams Now  
Sodium bicarbonate dissociates, creating a low concentration of OH-. Because copper(II) oxide and copper(II) hydroxide are both amphoteric, they will dissolve in greater amounts than usual with more OH- present. Don't be deceived by the color, though; it's unlikely you have a very significant amount of copper(II) in solution. It's still overwhelmingly sodium carbonate/bicarbonate.


Is the right answer. Copper is slightly amphoteric and in alkaline conditions forms cuprate anions: Cu(OH)<sub>4</sub><sup>-</sup>(aq). These are intensely deeply blue coloured and even just a bit of them will colour your solution light blue. As 'TNODN' claims: there isn't much copper that actually entered the solution.

Copper carbonates or bicarbonates are irrelevant here because the copper is solvated as anions. It's a slow process and as the OP wrote it took weeks. As a practical way of dissolving significant amounts of copper, forget it.


[Edited on 10-10-2014 by blogfast25]

DrMario - 12-10-2014 at 02:05

Thanks guys/gals.

Before I get rid of the contents of this jar, is there any experiment worthwhile doing?

blogfast25 - 12-10-2014 at 03:27

Quote: Originally posted by DrMario  
Thanks guys/gals.

Before I get rid of the contents of this jar, is there any experiment worthwhile doing?


Take a small amount and slowly neutralise it with strong HCl (lots of bubbles). At the end of that you should have a faintly green solution of cupper (II) chloride.

xfusion44 - 12-10-2014 at 04:15

What would I get if I were to connect power to the copper leads in DrMario's case? (NaHCO3, water, copper leads) I assume that I would get copper carbonate, but faster, right?

unionised - 12-10-2014 at 05:09

A solution of bicarbonate left lying around won't have a lot of hydroxide in it, but it will contain carbonate ions.
Coper forms a complex ion with carbonate and My guess is that's the most likely cause of the blue colour.

AsocialSurvival - 12-10-2014 at 05:26

Quote: Originally posted by xfusion44  
What would I get if I were to connect power to the copper leads in DrMario's case? (NaHCO3, water, copper leads) I assume that I would get copper carbonate, but faster, right?


Right! Electric current speeds up oxidation!

[Edited on 12-10-2014 by AsocialSurvival]

unionised - 12-10-2014 at 06:30

After a while the copper would dissolve from one electrode and be plated out at the other. The net concentration of copper in the solution would remain unchanged.
Not really very useful unless you are seeking to electrolytically refine copper.

DrMario - 12-10-2014 at 06:53

Quote: Originally posted by blogfast25  
Quote: Originally posted by DrMario  
Thanks guys/gals.

Before I get rid of the contents of this jar, is there any experiment worthwhile doing?


Take a small amount and slowly neutralise it with strong HCl (lots of bubbles). At the end of that you should have a faintly green solution of cupper (II) chloride.


I appreciate the idea, but the outcome seems a bit too obvious. I'd rather do an experiment that determines the anions present in the solution, or perhaps something that would determine the exact complex. I do have some EDTA-Na 2 available. And of course ammonium hydroxide, the Big Three acids etc.

AsocialSurvival - 12-10-2014 at 07:22

Quote: Originally posted by unionised  
After a while the copper would dissolve from one electrode and be plated out at the other. The net concentration of copper in the solution would remain unchanged.
Not really very useful unless you are seeking to electrolytically refine copper.


Not really! That is only correct for more soluble Copper salts. In this case, Hydrogen would reduce and only a fraction of Copper at a time (which is present in microgram to miligram quantities in solution). And Copper would rather get oxidized than Hydroxide aka Oxygen from water.

I tried this many times, and collected lots of Copper carbonate (blueish green or greenish blue in solution, green when dry).

[Edited on 12-10-2014 by AsocialSurvival]

Amos - 12-10-2014 at 07:30

Quote: Originally posted by DrMario  
Quote: Originally posted by blogfast25  
Quote: Originally posted by DrMario  
Thanks guys/gals.

Before I get rid of the contents of this jar, is there any experiment worthwhile doing?


Take a small amount and slowly neutralise it with strong HCl (lots of bubbles). At the end of that you should have a faintly green solution of cupper (II) chloride.


I appreciate the idea, but the outcome seems a bit too obvious. I'd rather do an experiment that determines the anions present in the solution, or perhaps something that would determine the exact complex. I do have some EDTA-Na 2 available. And of course ammonium hydroxide, the Big Three acids etc.


I mean, what you have there is pretty straightforward. Just because it's changed in color doesn't mean the composition has changed much at all, and I doubt you have significant enough amounts of copper in there to do much experimentation on in the realm of solid compounds, but complexing in solution can be explored. Adding HCL or even just salt will make it turn green, adding ammonium hydroxide will produce a precipitate of Cu(OH)2 in small amounts and in larger ammounts form the tetraammine copper(II) complex, which is ultramarine blue. If both of these happen with the same solution, you can pretty much bet that what's in solution is the [Cu(H2O)6]2+ complex, as the H2O ligands very readily detach themselves to make room for others. This is the same thing you usually get with solutions of copper(II) salts. If you had some new and different complex, it might not react so readily.

[Edited on 10-12-2014 by No Tears Only Dreams Now]

xfusion44 - 12-10-2014 at 11:25

Quote: Originally posted by AsocialSurvival  
Quote: Originally posted by xfusion44  
What would I get if I were to connect power to the copper leads in DrMario's case? (NaHCO3, water, copper leads) I assume that I would get copper carbonate, but faster, right?


Right! Electric current speeds up oxidation!

[Edited on 12-10-2014 by AsocialSurvival]


I'm asking that, because I already done this and I could copper plate key :)