cyclonite4
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xCuSO4 + yCa(OCl)2 ----> ?
Today, I accidently spilled a saturated solution of Ca(OCl)2 on some CuSO4.5H2O and noticed a reaction producing gases, and leaving behind a green
solid and a black solid. I didn't attempt to identify the gas by smelling because it was produced at a high rate and if it was chlorine, it could
have had some nasty effects.
Does anyone know what the byproducts of this reaction could be, or whether it was caused by some kind of impurity (both chemicals were obtained from a
hardware store)?
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budullewraagh
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the green indicates the presence of cuprous (Cu+) cations. this means they were reduced from cupric (Cu+2) cations. the only gas i could imagine
being evolved would be Cl2...unless it was H2O being released due to great enthalpy change. did you happen to notice any of the properties of the
gas?
im just about positive CaSO4 was produced unless the gas was Cl2 in which case CaSO3 was evolved. it would make sense that a copper hypochlorite
would be produced but with the gas evolved i cannot be so sure. if it was water, it works out. if the gas was not, it would be chlorine, indicating
that the sulfate reduced to sulfite.
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cyclonite4
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There was a change in enthalpy (negative/exothermic), by feeling the side of the glass I determined it to be about the same as the hydrolysis of NaOH
(in terms of heat). When the gas stopped being produced, I noticed a chlorine after-smell, but this could of been the hypochlorite [Ca(OCl)2 has the
same odour in solution].
Any ideas as to what the black solid could be?
\"It is dangerous to be right, when your government is wrong.\" - Voltaire
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unionised
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"the green indicates the presence of cuprous (Cu+) cations."
No, it doesn't. Most Cu(I) compounds are white.
The green colour is more likely to be due to Cu++ complexed with Cl, or to the hydroxide.
I can think of a couple of gases that might be released, chlorine or oxygen. Catalytic decomposition of hypochlorite to oxygen is well known. Lats
time I saw a reference to it they used Co++ as the catalysy, but I think other transition metals might do the job too.
Large quantities of chlorine are distinctly greenish (hence the name)
Ca(OCl)2 tends to be quite alkaline so precipitation of basic chloride or hydroxide would be expected. Copper hydroxide is fairly easy to dehydrate to
the (black) oxide by heating. The heat generated by the reaction might well have done this.
As for the idea that sulphite might be made, how? you have mixed a couple of fairly strong oxidants.
budullewraagh, what were you thinking here?
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cyclonite4
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| Quote: | Originally posted by unionised
Copper hydroxide is fairly easy to dehydrate to the (black) oxide by heating. The heat generated by the reaction might well have done this.
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The black solid was a precipitate, floating on top of the solution.
I believe it was probably Oxygen gas because even though i didnt sniff the gas produced, I had the glass sitting a few metres away from me, and
couldnt smell chlorine.
\"It is dangerous to be right, when your government is wrong.\" - Voltaire
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chemoleo
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I agree with unionised, and dont really see where you got the idea of Cu+ from. The hypochlorite is an OXIDANT, which then seemingly causes the
reduction of Cu2+ to Cu+?? The hypochlorite would cause the REVERSE reaction!
CuSO4 will catalyse the decomposition of the Ca(OCl)2, to CaCl2 and O2. Nascent O2 has some pungent odour to it by the way... so you could be fooled
into thinking it contains chlorine.
Normally I would have assumed thought that this reacts on to CuCl2 (green), and CaSO4.
Theory doesn't match with experiment, however, with the black precipiate appearing. It could be CuO of course, but where does the Cl2 go? I
can't see Cl2 evolving while a hydroxide is present.
Instead, I would suspect that the Ca(OCl)2 contains a percentage of Ca(OH)2, as it normally is never 100% chlorinated. This would then explain the CuO
appearing.
Try dissolving the black precipitate in dilute HCl, you should get a deep green solution.
[Edited on 9-1-2005 by chemoleo]
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BromicAcid
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Out of curiosity and readily available reagents I just tried this, in the cold.
To about 50 ml of water was added a gram or so of Ca(OCl)2, not all of it dissolved nor did I expect it to. In a test tube 5 ml of a saturated CuSO4
solution was made. Upon mixing the resulting solution was a green color and was opaque, there was no gas evolution, possibly due to the cold
temperatures. The solution still smelled distinctly of hypochlorite. The reaction probably entails:
Ca(OCl)2 + CuSO4 ---> CaSO4 + Cu(OCl)2
The cupric hypochlorite being somewhat unstable and decomposing along either of two paths to produce the chloride or the oxide.
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chemoleo
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Yes, but I believe he used more concentrated conditions, i.e. solid CuSO4 (?) and a saturated (whatever that is) solution of hypochlorite.
This would drive the temp up, 1) liberating O2, and producing the CuO - both which wouldnt happen when dilute. What do you think?
Never Stop to Begin, and Never Begin to Stop...
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chloric1
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Let us not forget Copper sulfate is a salt of a strong acid by a weak base. Copper sulfate is hence hydrolysised to make faintly acidic solutions.
If this reagent was in excess stoichemetrially, then no hydroxide would be present and chlorine would be as easily librated as oxygen. Years ago I
remember mixing sodium hypochlorite solution with copper sulfate and actually getting a brown precipitate. I remember reading somewhere in the
literature of a copper dioxide or peroxide that was quite unstable. The reference said it was made by oxidizing cupric ions.
Fellow molecular manipulator
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cyclonite4
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Yes thats right chemoleo, saturated Ca(OCl)2 and solid CuSO4 pentahydrate (blue when hydrated, white when not).
I might try this again with proportions that support the theories developed so far. I'm a little short of memory right now, and I can't
remember how to test for chlorine or oxygen gas, anyone know any easy tests (qualatative, not quantitive)?
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Esplosivo
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Chlorine turns moist red litmus paper red and then bleaches it (if in high enough concentrations).
The simplest test for oxygen is the good old glowing splint experiment, that when immersed in an oxygen enriched environment it will start burning.
This test can be masked by water vapour or other gasses though. I don't know any other simple test for oxygen that could be carried out.
[Edit: Removed some inaccuracies]
[Edited on 10-1-2005 by Esplosivo]
Theory guides, experiment decides.
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cyclonite4
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Geez... I guess I forgot about the chlorine test, one of the last things we did in school before the holidays started. I guess the oxygen test is
kinda obvious  , but the gas in the reaction was being produced so fast, that it
may become dangerous.
\"It is dangerous to be right, when your government is wrong.\" - Voltaire
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cyclonite4
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Here are some photos of the end products. I included three because they are all a bit difficult to see because they photo was taken at night with an
IR illuminator.
BTW chemoleo, a saturated solution means the maximum amount of solute dissolved in a given solvent.
\"It is dangerous to be right, when your government is wrong.\" - Voltaire
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symboom
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Here is copper sulfate with sodium hypochlorite
Produces green percipitate
Which I dont know what is it
[Edited on 9-10-2016 by symboom]
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Texium
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Probably copper oxychloride (basic copper(II) chloride). It's an insoluble light green compound that often forms when you add oxygen to alkaline or
neutral Cu2+ in the presence of chloride. The hypochlorite solution provides the oxygen, the alkalinity, and the chloride all at once. http://www.sciencemadness.org/smwiki/index.php/Copper_oxychl...
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Texium
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Thread Moved
9-10-2016 at 07:24 |
AJKOER
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The action of copper sulfate on calcium hypochlorite was reported by A.J. Balard over a hundred years ago. It forms CaSO4 and copper hypochlorite
which eventually decomposes into copper oxychloride and oxygen:
CuSO4 + Ca(OCl)2 = Cu(ClO)2 + CaSO4 (s)
Lets assume that the Bleaching Powder also contains some Ca(OH)2:
CuSO4 + Ca(OH)2 = Cu(OH)2 + CaSO4 (s)
The decomposition of the unstable copper hypochlorite:
Cu(ClO)2 + 2 H2O + Cu(OH)2 = CuCl2.Cu(OH)2 + 2 H2O + O2
Reference: "A comprehensive treatise on inorganic and theoretical chemistry", Volume 2, by Joseph William Mellor, page 271. To quote:
"R. Chenevix notes the ready solubility of cupric oxide in chlorine water, and P. Grouvelle found that the soln. obtained by passing chlorine into
water with cupric oxide in suspension possessed bleaching properties, and these were retained even after the soln. had been boiled for a quarter of an
hour. A. J. Balard found that the distillation of P. Grouvelle's liquor furnished some hypochlorous acid and a green oxychloride, 3CuO.CuCl2.4H20, was
formed in the retort. A. J. Balard prepared a soln. of cupric hypochlorite by dissolving cupric hydroxide in hypochlorous acid. It is also made by the
action of cupric sulphate on calcium hypochlorite. A. J. Balard found that copper filings are partially dissolved by hypochlorous acid, the soln.
after standing some time contains cupric chloride, and deposits a green pulverulent cupric oxychloride."
[Edit] If no Ca(OH)2 is present in the Bleaching Powder, then the chemistry gets more complex. Look to an iron impurity in the salt or added water.
Then, on boiling O2 participiates in an autoxidation with the transition metals (Fe, Cu, Mn,..) producing the superoxide radical anion that feeds a
Fenton-type reaction creating the missing OH-. Please see my comments and references provided at https://www.sciencemadness.org/whisper/viewthread.php?tid=53... and together with radical reactions cited at https://www.sciencemadness.org/whisper/viewthread.php?tid=66... . In particular, Wikipedia (see https://en.m.wikipedia.org/wiki/Dicopper_chloride_trihydroxi... ) notes the following commercial aeration method for the production of copper
oxychloride:
CuCl2 + Cu + 2 NaCl → 2 NaCuCl2 (eq.6)
6 NaCuCl2 + 3/2 O2 + H2O → 2 Cu2(OH)3Cl + 2 CuCl2 + 6 NaCl (eq.7)
In the current context, the formation of cuprous may be governed by a coupled redox equilibrium, and not the action of copper metal on a cupric salt:
Fe2+ + Cu2+ ↔ Fe3+ + Cu+
Interestingly, a small presence of iron metal could form Fe2+ from Fe3+, and the coupled redox above would then produce the required cuprous for the
Fenton-type reaction to form OH-. Iron metal, given sufficient time, could also displace copper from its salts liberating Cu which could act on cupric
forming cuprous.
[Edited on 17-10-2016 by AJKOER]
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