guy - 4-3-2006 at 21:50
NaSCN (25% tinted blue, from a weed killer) was added to CuSO4 crystals. Immediatly a dark red (maroon) solution is formed.
On addition of acetic acid (from vinegar), a green solution was formed.
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In another experiment, the CuSO4 / NaSCN solution was treated with excess 10% ammonia solution, a turquoise solution was obtained.
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In another experiment, the CuSO4 / NaSCN solution was treated with excess concentrated NaCl solution, a precipitation of a maroon sludge was formed.
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In another experiment, the CuSO4 / NaSCN solution was treated with excess strong NaOH solution, a light green solution was obtained with a slow
formation of a yellow/brown precipitate.
~~~~~~~~
In another experiment, the CuSO4 / NaSCN solution was diluted, light green color is formed.
Does anyone have any idea what these compound are? The internet only has results for Cu(I) thiocyanate. I have never seen a green copper ammonia
solution before neither. Copper does certainly behave funny.
Pictures:
CuSO4/NaSCN(left) and w/acetate(right)<a href='http://putfile.com/pic.php?pic=3/6223383910.jpg&s=x10' target='_blank'><img
src='http://x10.putfile.com/3/6223383910-thumb.jpg' alt='Click to enlarge'></a>
w/ ammonia<a href='http://putfile.com/pic.php?pic=3/6223393528.jpg&s=x10' target='_blank'><img
src='http://x10.putfile.com/3/6223393528-thumb.jpg' alt='Click to enlarge'></a>
w/ Chloride<a href='http://putfile.com/pic.php?pic=3/6223403865.jpg&s=x10' target='_blank'><img
src='http://x10.putfile.com/3/6223403865-thumb.jpg' alt='Click to enlarge'></a>
w/ hydroxide<a href='http://putfile.com/pic.php?pic=3/6223463989.jpg&s=x10' target='_blank'><img
src='http://x10.putfile.com/3/6223463989-thumb.jpg' alt='Click to enlarge'></a>
diluted<a href='http://putfile.com/pic.php?pic=3/6223433936.jpg&s=x10' target='_blank'><img
src='http://x10.putfile.com/3/6223433936-thumb.jpg' alt='Click to enlarge'></a>
12AX7 - 4-3-2006 at 22:44
Isn't that a reducing agent? I'd think the precipitate at least would be something like colloidial (or finely powdered) copper, or cuprous oxide.
Tim
guy - 4-3-2006 at 22:58
Which precipitate? The one in NaOH? That one resembles Cu2O more. The original solution is a really clear dark red. Is still had some undissolved
particles.
The_Davster - 4-3-2006 at 23:06
The reaction of ferric compounds with thiocyanate forms a blood red solution, this has been used a test for iron. It works by the thiocyanate acting
as a ligand. I imagine something like that is at work here.
Your thiocyanate is from weedkiller, is it used as-is or was it purified first?
I have a feeling that Cu2+ is being reduced to Cu+ which then forms the ligand with the excess thiocyanate.
I think it explains all your observations.
guy - 4-3-2006 at 23:38
I used the weed killer as is. I don't know how to purify it.
How does the fact that the copper is in the +1 state explain a green copper/ammonia solution, or a green copper/hydroxide or a green copper/acetate
solution?
*Note: The original blue color looks like a copper sulfate color.
[Edited on 3/5/2006 by guy]
The_Davster - 4-3-2006 at 23:49
I could be wrong...
The thiocyanate ligand being replaced by ammonia could explain the colour change. Addition of hydroxide could have either broke up off the thiocyanate
ligand precipitating Cu2O, or precipitated some sort of thiocyanocopper(I) hydroxide or oxide.
Seeing as your acetate solution is side view I cannot really make out the relative colour, but I am thinking that it did not actually react, but just
the acetate solution diluted the solution. But if I am wrong on the colour judgement that shoots this little explanation to hell
guy - 4-3-2006 at 23:58
The acetate one definetley has a different color. It is a forest green (kind of dark-ish), while the others a like "normal" green.
The colors might not be completely accurate because of the initial blue dye from the product. Can anyone duplicate this experiment, possibly using
purer materials?
unionised - 5-3-2006 at 01:12
Thiocyanate reduces copper(II)
Cu++ + 3SCN- --> CuSCN + (CN)2
Hydroxide replaces SCN
CuSCN + OH- --> CuOH + SCN-
loss of water gives the oxide
2CuOH --> Cu2O +H2O
Many of these compounds- possibly all of them - are soluble in NH3 soln as varous complexes.
Air rapidly oxidises Cu(I) to Cu(II) - especially in solution as NH3 complexes.
Since I have no idea what the other stuff in the weed killer is I think it might explain some of the other colours . Maroon/red is also consistent
with traces of iron in the mixture. Another possibility is disproportionation of Cu(I) to give Cu(II) and metalic Cu as a reddish ppt.
guy - 5-3-2006 at 02:18
For the solution with NaOH, why would the precipitation of CuOH take so long? After about 30 minutes, only a little precipitate was formed. The
solution was still very green. And it was a strong NaOH solution too.
I don't think that the Cu+ disporportinates, because on diluting, it turns to a clear green again.
[Edited on 3/5/2006 by guy]
12AX7 - 5-3-2006 at 09:19
Copper complexes do tend to be soluble in base, if they don't decompose (Fehling's solution for instance).
Tim
woelen - 6-3-2006 at 02:55
I personally have done quite some experiments with copper (II) and thiocyanate two years ago or something like that. I put the results of this
experiment in my electronic logbook, which now is part of my website. I used pure chemicals, not stuff from weed-killers. The results are quite
different from yours, I did not get red colors. I expect the dye and other ingredients from the weed-killer to interfere in your experiment.
Have a look at my results:
http://woelen.scheikunde.net/science/chem/exps/expshow.cgi?i...
http://woelen.scheikunde.net/science/chem/exps/expshow.cgi?i...
I have had a correspondence with someone from Usenet (Farooq) who thinks the black material is a copper (II) thiocyanate complex/precipitate of
Cu(SCN)2, which is darkgreen in solution. Indeed, thiocyanate slowly reduces copper (II) to copper (I) and this results in formation of white CuSCN.