nlegaux
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Unusual yellow compound...
Yesterday I made Chevreul's salt. Realizing that the supernatant was probably acidic due to the SO2 gas produced by the reaction, I neutralized it
with NaHCO3. When I did this, an unusual yellow precipitate formed and a gas was evolved. This gas put out a lit splint. I believe that the NaHCO3
reacted with unreacted complex left in solution. I tested this by creating more complex in a test tube and adding NaHCO3. Sure enough, a similar
looking yellow precipitate formed and a gas was evolved that put out a lit splint. The yellow precipitate has very fine particles that cannot be seen
at 80x magnification, and easily passes through a coffee filter. Any ideas as to what it may be?
On a side note, in an attempt to precipitate out the complex, I made the complex again and added IPA. A red crystalline precipitate that looks very
similar to Chevreul's salt formed. I yet to do any tests on it to try determining what it is, but are there any ideas as to what it may be? Sorry for
the lack of pictures, my camera stopped working recently.
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Zyklon-A
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You probaly had a reducing immpurity which reduced metabisulfite to sulfur, probably incompletely. So, it's probably sulfur, which fits the
description.
What reagents did you use?
[EDIT] Actually, I think I may be wrong. According to woelen's discription on this experiment, it may be hydrous copper(I) oxide. Perhaps you
mistakenly used sodium sulfite?
Check this out:http://woelen.homescience.net/science/chem/exps/copper_sulfi...
[Edited on 28-11-2014 by Zyklon-A]
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nlegaux
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The reagents used to make the green complex where Sodium Metabisulfite (labelled Sodium Pyrosulfite from Bonide stump-out) and Copper Sulfate (from
root killer). What is the best test to use to determine if the precipitate is sulfur or copper oxide?
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forgottenpassword
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Sulphur will burn if ignited.
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Zyklon-A
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Weird, well metabisulfite doesn't seem to decompose to sulfite, but rather sulfate, so I doubt it could be an immpurity.
If you can manage to filter the yellow powder, some tests could be done on it:
If it dissolves in HCl (aq) to give a blue solution it's probably copper oxide. I dont know what the formula is for it though so I could be wrong.
You could heat it, if it melts, starts burning and smells like SO2, it's sulfur.
[Edited on 28-11-2014 by Zyklon-A]
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DraconicAcid
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Copper(I) oxide can be yellow, and will dissolve in hydrochloric acid to give a green solution (exposure to air oxidizes the copper to copper(II),
which gives coloured chloro complexes).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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nlegaux
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I was able to decant some of the original yellow compound. I took some of this (I haven't dried it yet) and added it to 1ml of 5% HCl. I added around
3ml of suspension to it. When added, it dissolved in the HCl, leaving a colorless liquid (so it probably isn't copper oxide). Than, i took some of the
yellow precipitate in suspension from the test tube (I also didn't dry this...) and added it to 1ml of HCl. A fine white powder was produced, and a
gas was evolved. This reaction may have been between the complex and the HCl. I will start to dry both of the powders out (from the test tube and
original) so I can get better results.
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nlegaux
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I was able to filter the red precipitate from the IPA suspension, it appears to be copper metal (the way the crystals are dendrites). I attempted to
filter the suspension containing the yellow compound (not the original yellow compound) and was able to collect some, although the majority of it
passed through the filter. I disposed of both supernatants by heavily diluting them (in 1L of water) and washing them down the drain. The precipitates
are drying now.
[EDIT] The red precipitate's crystals are not actually dendrites. I looked at them underneath a microscope, and they are actually many small spheres
stuck together.
[Edited on 11-28-2014 by nlegaux]
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Amos
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Okay, I'm pretty sure you and I are dealing with the same compound, here. Adding ascorbic acid to a solution of copper(II) sulfate followed by heating
generates a fine powdery precipitate of copper metal and leaves behind a green or yellow solution, depending on the limiting reagent. Adding sodium
carbonate or hydroxide to that new solution precipitates a yellow solid very similar to what you are describing, which I believe to be hydrous
copper(I) oxide. Adding IPA to the solution generated a brick red solid, as you said, which is classic of the non-hydrous form of copper(I) oxide.
Copper(I) oxide also makes sense due to the reducing environment in which the compound was formed.
Here are some properties of my compound
- It only grudgingly dissolves in aqueous ammonia with a lot of shaking, forming the familiar tetraammine copper(II) complex.
-It turns tan to red-brown upon drying in air
-It will not dissolve to any degree in boiling household vinegar(I tried this because copper(II) carbonate will)
-It forms a superfine, powdery, copper-colored precipitate upon treatment with phosphoric acid. Perhaps it could be copper metal?
Very regrettably I do not have hydrochloric acid at this time to find out if mine reacts similarly to yours, but if you're trying to identify this
compound, you might want to produce what I've got and see if they match up.
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DraconicAcid
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Quote: Originally posted by No Tears Only Dreams Now  | Copper(I) oxide also makes sense due to the reducing environment in which the compound was formed.
Here are some properties of my compound
- It only grudgingly dissolves in aqueous ammonia with a lot of shaking, forming the familiar tetraammine copper(II) complex.
-It turns tan to red-brown upon drying in air
-It will not dissolve to any degree in boiling household vinegar(I tried this because copper(II) carbonate will)
-It forms a superfine, powdery, copper-colored precipitate upon treatment with phosphoric acid. Perhaps it could be copper metal?
Very regrettably I do not have hydrochloric acid at this time to find out if mine reacts similarly to yours, but if you're trying to identify this
compound, you might want to produce what I've got and see if they match up. |
That really does sound like copper(I) oxide. Add a bunch of salt to the hot vinegar solution- the chloride ion coordinates the copper(I) ion, helping
it dissolve (and then get oxidized by the air).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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nlegaux
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I took some of the original yellow compound (still in suspension) and added it to aqueous ammonia. It almost immediately dissolved and formed (what
looks like) the tetraamine complex. When added to vinegar, the original compound almost immediately dissolved leaving a clear solution.
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TheChemistryShack
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Have you done a flame test of the precipitate yet? I mean, of course, a small amount of sodium contamination will discolor the flame to turn it
yellow, but it is still worth a shot.
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nlegaux
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Good suggestion TheChemistryShack. Even if there is a Sodium contaminant, won't the flame still be greenish?
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Amos
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| Quote: Originally posted by nlegaux | | I took some of the original yellow compound (still in suspension) and added it to aqueous ammonia. It almost immediately dissolved and formed (what
looks like) the tetraamine complex. When added to vinegar, the original compound almost immediately dissolved leaving a clear solution.
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Are you sure it's clear, and you're not just adding too much water to see the color? I'm not saying you're wrong, I just want to be sure. Maybe
there's an aquacopper(I) complex that's clear...
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nlegaux
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I repeated the same test again. I added 1ml of household Vinegar to a test tube, and added >3ml of the original suspension. The yellow compound
dissolved, leaving a clear liquid. [EDIT] Now that it has sat for a while, it is starting to turn a light brown color...
Also, as both of the compounds (the original yellow compound and the yellow compound made afterwards) dry out, they are starting to turn a green
color.
Does anyone have any idea what the red precipitate (that formed with the addition of IPA to the green complex) with the spherical crystals may be?
[Edited on 11-28-2014 by nlegaux]
[Edited on 11-28-2014 by nlegaux]
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DraconicAcid
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Copper(I) isn't stable in solution. It will form a diammine complex and a dichloro complex, both of which are colourless, but oxidize rapidly on
exposure to air to give blue or green solutions (respectively). If copper(I) oxide is dissolved in an acid without a coordinating anion, it will
disproportionate to copper(II) and copper metal.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Amos
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Are cuprous and/or cupric sulfite recognized chemicals? Does anybody have some information on them?
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blargish
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I do not believe so. Chevreul's salt is a double salt of both, but I don't think either can exist on its own. Woelen has a great page on his website
outlining this, and the various reactions between copper (ii) and sulfite in aqueous solution: http://woelen.homescience.net/science/chem/exps/copper_sulfi...
He also encounters the yellow precipitate of hydrous copper i oxide during one of the experiments.
Edit: I guess they do exist on their own as well. Copper I sulfite is also called "Etard's salt"
[Edited on 29-11-2014 by blargish]
BLaRgISH
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IrC
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http://www.endmemo.com/chem/compound/cuso3.php
"Copper(II) Sulfite
Name: Copper(II) Sulfite
Alias: Cupric Sulfite
Formula: CuSO3
Molar Mass: 143.6092
CuSO3 is a red powder at room temperature. "
http://www.endmemo.com/chem/compound/cu2so3.php
"Copper(I) Sulfite
Name: Copper(I) Sulfite
Alias: Cuprous Sulfite
Formula: Cu2SO3"
From a different source: "Properties: White to pale-yellow hexagonal crystals. Slightly sol in water; sol in HCl, NH4OH, alkali solns. Practically
insol in ether, alcohol."
"Science is the belief in the ignorance of the experts" Richard Feynman
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Amos
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You know, I totally skipped those in the search results, figuring that it was just another of those sites that gives you the molar mass and formula of
compounds, real or theoretical...
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IrC
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Yeah it would take someone like woelen to say for sure. I only dabble in chemistry as electronics is my real existence. But I figured when the sources
say "CuSO3 is a red powder at room temperature.", and "Cu2SO3 White to pale-yellow hexagonal crystals", they must be more than merely theory. Someone
had to observe them at sometime.
"Science is the belief in the ignorance of the experts" Richard Feynman
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nlegaux
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Now that the powder (made from reacting the complex with NaHCO3) has dried out, it is a very light green color.
[EDIT] I just realized that I can take pictures with my phone... One picture is the dry powder, the other the suspension.
[Edited on 11-29-2014 by nlegaux]
[Edited on 11-29-2014 by nlegaux]
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