weiming1998 - 14-6-2012 at 06:48
I have read this thread (http://www.sciencemadness.org/talk/viewthread.php?tid=20392), so I tried to make some of that copper salt described in the thread with sodium
metabisulfite.
As I don't have it, nor do I have Na2SO3, but I do have Na2S2O3, I combined that with some sodium bisulfate and lead the resultant SO2 through Na2CO3
solution. Wikipedia says that S2O5(2-) hydrolyzes into HSO3- in solution (http://en.wikipedia.org/wiki/Sodium_metabisulfite), so I thought the SO2 can eventually react with the Na2CO3 to make Na2SO3, which can then react
with more SO2 to form NaHSO3, which I might be able to use to prepare the copper salt Cu3(SO3)2.2H2O, a mixed-valence compound, described on the
thread I have posted earlier.
Nevertheless, after I finished making my mix of sulfites, I poured it into concentrated CuSO4 solution. It made a khaki-green precipitate that had
some interesting properties, which I'll describe below.
1, This precipitate slowly decomposes in boiling water to red Cu2O, indicating that it is likely to be a Cu(I) compound
2, It reacts with Na2S2O8 to form a (strangely) colourless solution, which upon acidification, became blue.
3, It dissolves in vinegar to form a blue green solution, which is copper acetate.
4, It reacts with NaHSO4, to form some SO2 gas that I can smell, and a white precipitate (more like a fine suspension)
The question is, is this some kind of complex, Cu(I) sulfite, or something else altogether? Again, a search on the net yielded useless results about
CuSO4 and Na2SO3.
Eddygp - 14-6-2012 at 10:50
It looks like an alkaline, maybe of carbonate nature salt. Try melting it to see if it decomposes, and try to have a look at the products (precipitate
it out of the solution and dry it first). Umm, a pH indicator when reacted with Na2S2O8? Had a check... it may be similar (structurally) to some sort
of cuprocarmine.
weiming1998 - 15-6-2012 at 01:30
It is not a pH indicator when mixed with Na2S2O8. It seems to detect the presence of oxalic acid well. When some of the khaki-green precipitate is
mixed with persulfate, a colourless solution results that turns blue instantly with oxalic acid, but not with other acids, even mildly reducing ones
like citric acid.
And also, this precipitate oxidizes in air to form a blue-green crust-like substance that floats on water.
AndersHoveland - 15-6-2012 at 02:39
This would be the reaction I would expect between copper sulfate and sodium bisulfite:
3 CuSO4 + 10 Na2S2O5 --> Cu3(S2O3)2 + 10 Na2SO4 + 8 SO2
I would think it might produce a mixed oxidation state copper double salt of thiosulfate.
[Edited on 15-6-2012 by AndersHoveland]
Eddygp - 15-6-2012 at 13:05
You invented the oxalometer! Congratulations! 
EDIT: Uhh, no sarcasm involved 
[Edited on 15-6-2012 by Eddygp]