Bandil (Hive Bee)
08-23-02 10:27
No 348046
      CuCN to NaCn  Bookmark   


How would one go about changing CuCN to NaCN? Swim thought of adding equimolar amounts of NaCl in a aq. soln, precipating the Cu(I)Cl and evaporating the water to give the NaCN. Would NaOH work or would that form soluble complexes with the copper?


08-23-02 11:26
No 348057
      NaOH  Bookmark   

Are you sure that CuCl would precipitate? I think that NaOH is better. No complex will be formed. Actually the initially formed CuOH will turn into Cu2O after some time... both CuOH and Cu2O are insoluble and could be filtered off...
BTW, you should be aware that cyanides are pretty nasty stuff. Don't get yourself (or somenoe else) killed!
(Hive Bee)
08-23-02 13:03
No 348079
      I just discovered that CuCN has a VERY low sol.  Bookmark   

I just discovered that CuCN has a VERY low sol. in water. Its around 10^(-10)... is it still possible to do the conversion with NaOH... and how would one do it practically??


(Hive Bee)
08-26-02 14:53
No 349167
      Swim has no other option than to use CuCN...  Bookmark   

Swim has no other option than to use CuCN...

Could any of you please give me a ref to a practical conversion between the two. Swim's method for converting is currently:

Dissolve x moles of NaOH in water
Put x moles of CuCN in this soln

stirr and wait for some oxide to precipate.

Would this work for converting og would the soln remain unchanged with CuCN as the precipate?

Thanks alot in advance!

(Stoni's sexual toy)
08-26-02 18:23
No 349215
      There is a procedure being used in traditional ...  Bookmark   

There is a procedure being used in traditional old-school qualitative analytical chemistry, the shit you are bothered with first at the local universities since it frustrates so many wanna-be chemists that many will quit voluntarily.

When you want to identify the anions of insoluble inorganic compounds mix them with an excess of Na2CO3 and some water, heat for a while, filter the insolubles out and perform your tests on the Na2CO3-solution. Since carbonates of most metals are usually very much insoluble it is possible to convert not-quite-as-insoluble-but-still-hardly-soluble metal compounds into the carbonates, leaving the anions as the sodium salts which can be easily identified by standard procedures.

Sounds kinda confusing? Ok, here's an example: We have an inorganic sample believed to contain PbSO4, which is pretty much insoluble in water and therefore can't be easily analysed. Since PbCO3 will be several magnitudes more insoluble the very slight solubility of PbSO4 will be enough to convert part of it into the carbonate:

PbSO4 + Na2CO3 --------------> PbCO3 + Na2SO4

After filtering out the Pb salts the Na2CO3 mixture is carefully neutralised with a suitable acid, and the SO4(2-) can be detected by standard reactions, e.g. forming a precipitate with barium nitrate solution.
(If this PbSO4 example happens to be an exception which does not work then I'm sorry, but I guess you got the idea)

There's only one problem: this whole thing doesn't go anywhere near completion in a realistic timeframe, and when decomposing CuCN with Na2CO3 (or NaOH, which should work just the same, it all depends on molar saturation concentrations) you will end up with a mixture of lots of Na2CO3 (/NaOH) and a little bit of NaCN, which is probably completely unusable for your intended reaction.

I'm not fat just horizontally disproportionate.
08-27-02 21:50
No 349730
      I don't know...  Bookmark   

I've never actually done such a thing, but there is a chance that the decomposition of the CuOH would draw the equilibrium in the desired direction. A simple test could clarify that...