Sciencemadness Discussion Board - CuSO4 + NaHCO3 a bit of help please with products..

CuSO4 + NaHCO3 a bit of help please with products..

binaryclock - 19-4-2013 at 13:33

Can someone explain the reaction of copper(ii) sulfate and sodium bicarbonate to me? this is the accepted solution:

CuSO4 + 2NaHCO3 -> CuCO3 + CO2 + H2O + Na2SO4

I would of thought that the products would be CuCO4, and NaSO4.

Sorry for my ignorance, I'm reading tons about all this in different books just need a bit of help once in a while.

Thanks

DraconicAcid - 19-4-2013 at 13:37

You can't make CuCO₄ or NaSO₄. Both the carbonate ion (which has three oxygens) and the sulphate ion have a negative two charge, so have to be balanced with cations that have a total charge of +2. One copper(II) ion will work, but sodium has a charge of +1, so you need two of them.

vmelkon - 19-4-2013 at 13:38

You need to learn about cations and anions.
The charge on Cu is 2+.
The charge for SO4 is 2-.

Therefore copper sulfate is CuSO4.

Carbonate is CO3 with charge of 2-.
There is no such thing as CO4. Draw the anion and see for yourself.

Sodium sulfate is Na2SO4 because
The charge on Na is 1+.
The charge for SO4 is 2-.

12AX7 - 19-4-2013 at 13:44

"CuCO4 and NaSO4" typo right?

The equation is correct.

Water can be ignored, since you usually do such a reaction in a huge excess of water to begin with. Also, the CO2 leaves fairly easily, but not instantly, so it's of some consequence in the reaction.

Among the more subtle things which can happen:
- Copper forms a carbonate complex, meaning, copper is actually soluble in strong carbonate solutions -- not like calcium, for example, where you can force more out of solution by Le Chatelier's principle.
- Copper does not (or doesn't normally) form a stable carbonate, but rather a basic carbonate, with some mixture of OH and CO3 present. As a result, more CO2 will be given off than expected, particularly on boiling.
- CO2 and carbonate have a fairly slow reaction equilibrium, so to drive the reaction forward, you often heat the solution to speed it up. This also reduces the solubility of CO2 in H2O, and pushes end products to more stable forms (perhaps resulting in a lower basic carbonate, i.e., with more OH and less CO3 in it).

Tim

bfesser - 28-7-2013 at 07:32

Quote: Originally posted by bfesser

In my experience, copper(II) sulfate will react with sodium bicarbonate, precipitating copper(II) bicarbonate (rxn. I), which quickly decomposes (rxn. II) to copper(II) carbonate.<ol type="I"><li>CuSO4(aq) + 2 NaHCO3(aq) → Cu(HCO3

2(s) + Na2SO4(aq)</li>
<li>Cu(HCO3

2(s) → CuCO3(s) + CO2(g) + H2O</li></ol></strong

Hexavalent - 28-7-2013 at 09:07

Where is the reference for this?

bfesser - 29-7-2013 at 15:08

My original reference was an email I received from a university professor many years ago—lost to time, I think.

Here are a few documents I found with a <a href="http://scholar.google.com/" target="_blank">Google Scholar</a> <img src="../scipics/_ext.png" /> search:
<a href="http://dx.doi.org/10.1016/0043-1354(71)90049-2" target="_blank">Copper/bicarbonate equilibria in solutions of bicarbonate ion at concentrations similar to those found in natural water</a> <img src="../scipics/_ext.png" />
<a href="http://www.researchgate.net/publication/11682690_Complexation_of_Copper(II)_with_Carbonate_Ligands_in_Aqueous_Solution_A_CW_and_Pulse_EPR_Study/ file/79e4150ef416c86083.pdf" target="_blank">Complexation of copper (II) with carbonate ligands in aqueous solution: A cw and pulse EPR study</a> <img src="../scipics/_pdf.png" />

And I found this interesting paper while searching:
<a href="http://libinfo.uark.edu/aas/issues/1941v1/v1a21.pdf" target="_blank">Crystals of an insoluble carbonate of copper grown under a soda solution</a> <img src="../scipics/_pdf.png" />

I probably should have just written it as one equation with two arrows, having the bicarbonate species in square brackets, to indicate an inferred unstable species.

[Edited on 29.7.13 by bfesser]