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Dan Vizine
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Think small college, early 70's, freshman lab....nope, just eyeballs.
It worked remarkably well.
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blogfast25
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A remarkable exercise for a freshman lab, IMHO.
Maybe I'll have to reconsider and clean our local tobacconists out of ferrocerium.
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Dan Vizine
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Y'know, I could be wrong about the stationary phase. I really can't remember if it was ion exchange resin or something like alumina. It could even
have been silica gel for all I know, although alumina maybe makes more sense.
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eidolonicaurum
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So how would a chromatography column be set up? Is it simply a long tube (how long?) filled with aluminia, silica gel, resin of some sort, etc.? I am
a complete novice when it comes to these sorts of things.
[Edited on 11-4-2014 by eidolonicaurum]
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blogfast25
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Quote: Originally posted by eidolonicaurum  | So how would a chromatography column be set up? Is it simply a long tube (how long?) filled with aluminia, silica gel, resin of some sort, etc.? I am
a complete novice when it comes to these sorts of things.
[Edited on 11-4-2014 by eidolonicaurum] |
My Shriver and Atkins 'Inorganic Chemistry' practically gives a recipe for it. I'll try and dig it up tonight.
[Edited on 11-4-2014 by blogfast25]
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Dan Vizine
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by eidolonicaurum | So how would a chromatography column be set up? Is it simply a long tube (how long?) filled with aluminia, silica gel, resin of some sort, etc.? I am
a complete novice when it comes to these sorts of things.
[Edited on 11-4-2014 by eidolonicaurum] |
My Shriver and Atkins 'Inorganic Chemistry' practically gives a recipe for it. I'll try and dig it up tonight.
[Edited on 11-4-2014 by blogfast25] |
Quite generally, here is how you prepare a chromatographic column.
Just as you said, a chromatography column is nothing more than a long tube with some kind of stopcock at the bottom to control flow. The amount of
material the column can handle at once is a function of the column's diameter. The degree with which it can separate different materials is a function
of the column length.
To fill a chromatography column, follow this procedure. If the column has a fritted glass disc at the bottom, you're good to go. If it doesn't, you
need to make a ball of glass wool and push it down there. The function of this is to keep the stationary phase (the solid) inside the column and out
of the stopcock. Next, take a large beaker and fill it with somewhat more adsorbent than your column can hold (this is dry packed material, it will
settle). Add enough of whatever solvent you intend to run the column with (called the eluent) and stir the mixture until you have a slurry free of
bubbles. That bubbles thing doesn't sound too important, but it is. In fact, uniformity is probably the single most important aspect of filling the
column. Discontinuities between successive pours should be minimized as much as possible. Pour some of the slurry into the column with the bottom
stopcock opened. As the liquid level runs down low enough to allow an additional pour of the slurry to be made, do so. Rapping on the side of the
column with a cork ring or your knuckles helps the solids settle evenly. The top surface should be absolutely flat when the column has been totally
poured. Close the stopcock when you have added sufficient stationary phase. Leave enough space at the top of the column for solvent to be added,
several inches at least. Cover the top of the adsorbent with a layer of heavy sand, maybe a quarter of an inch to a half an inch thick. Alternatively,
take a piece of filter paper the same diameter as the column and punch dozens of tiny holes in it with a pencil point. Lay this on top of the
adsorbent. Either of these methods serve to defuse the stream of fresh solvent added to the top of the column.
Dissolve the material to be separated in the minimum amount of solvent. This is crucial because the width of the band of material you apply to the top
of the column has everything to do with how well it will separate. The thinner the band, the cleaner the separation generally. Using a pipette, slowly
add this material to the top of the column. Open the stopcock and allow this band to slowly adsorb into the top layer of the stationary phase. Follow
this by fresh solvent also added by a pipette for fine control. Once the band has started moving down the column, you can pour additional solvent in
from a beaker. An elegant solution to this need to add solvents regularly can be achieved using a separatory funnel. Fill the separatory funnel all
the way with solvent. Put the stopper in and use supports to position the drain of the separatory funnel an inch or two above the sand in the column.
Open the stopcock of the separatory funnel slowly. At first solvent will flow out somewhat quickly, this will rapidly come to a stop due to the vacuum
generated inside the funnel. When the level of the liquid in the chromatography column goes below the tip of the separatory funnel, air leaks back in
and solvent comes out until it once again prevents air from getting in. This process repeats over and over and will maintain a level of liquid inside
your chromatography column without continual work on your part.
The stationary phases which are commonly used are neutral alumina, basic alumina, silica gel, reverse phase silica gel and ion exchange resins. This
is not an exhaustive list, many things can be used as adsorbents but these are the most common. Refer to the literature for the stationary phase most
appropriate to the materials you are separating. Silica gel generally has the best resolving power. However silica gel is considered to be slightly
acidic and is not appropriate for all compounds. Alumina, any of the kinds, generally interacts with most organic molecules less strongly than silica
gel. They also will allow chromatography of things which fall apart on silica gel. Reversed phase silica gel is a specialty product and very
expensive, you don't need to consider this. Ion exchange resins look like little tiny plastic beads. Their most important use is for ionic compounds.
Not only can they be used to chromatograph materials but they will also swap out the anion or cation depending if you are using an anion exchange
resin or cation exchange resin.
The polarity of the solvent used to elute the material down the length of the column determines how fast the material moves, how well it separates
from other materials as well as the broadness of the band as it moves. Solvent mixtures are very frequently employed. Sometimes the relative amounts
of two solvents are varied as the process proceeds, but this complication is generally not needed for regular organics. It seems to enjoy more use
with biologicals. The solvent must have good solubility for your compound and must have sufficient polarity to allow you to run the column in a
reasonable length of time with reasonable volumes. As the solvent runs out of the bottom stopcock, you collect it in many small fractions. The
contents of these fractions are assayed by any one of a number of methods. Being primarily an organic chemist, I heavily favor thin layer
chromatography plates. You simply make a spot of each fraction at the bottom of the plate, put the plate into a jar containing a tiny bit of solvent
in the bottom, and as the solvent absorbs up the length of the plate it performs a mini chromatography. You examine the plates by shortwave or
longwave ultraviolet light, by placing them in a chamber filled with iodine vapors, by spraying them with a mixture of alcohol and sulfuric acid and
then heating them until the organic compounds char, by examining them with UV/VIS light, by spraying with o-vanillin/alcohol/sulfuric acid and heating
or any other method you can think of which will allow you to discriminate among them. There are developing reagents which will detect non-aromatic
hydrocarbons, even alkanes. Fractions containing comparably pure material are combined and evaporated to give you back your purified component.
This was dictated using voice recognition, so if you see any craziness, blame it on that. I'll undoubtedly edit this as the day goes on and I find
more errors.
[Edited on 11-4-2014 by Dan Vizine]
[Edited on 11-4-2014 by Dan Vizine]
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Bert
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The term "elute" eluded the voice (non) recognition software-
Rapopart’s Rules for critical commentary:
1. Attempt to re-express your target’s position so clearly, vividly and fairly that your target says: “Thanks, I wish I’d thought of putting it
that way.”
2. List any points of agreement (especially if they are not matters of general or widespread agreement).
3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
Anatol Rapoport was a Russian-born American mathematical psychologist (1911-2007).
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Dan Vizine
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I can't even find the word elute in there. Although "eluant" is spelled wrong, eluent is correct.
Ohhh! Now I see it, thanks.
[Edited on 11-4-2014 by Dan Vizine]
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blogfast25
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From 'Inorganic Chemistry' (Shriver and Atkins, third edition), my interpretation:
For resin, sodium polystyrene sulphonate can be used. If I’m not mistaken that’s box standard Dowex ion exchange resin, normally used to exchange
cations for H<sup>+</sup>. Soak in brine to ‘load’ fully with Na<sup>+</sup>. Then wash with deionised water, then with
eluent solution.
Eluent solution is an ionic citrate, lactate or better a 2-hydroxy isobutyrate, probably about the same concentration as the RE solution.
Load the column (a burette, for instance) with resin, add eluent (note the volume used), then load the top with dissolved Ln<sup>3+</sup>
salts. A second burette, ‘coupled’ to the first one could be used to administer the eluent. Open stopcock of the top one fully, then open stopcock
of the column to get a steady drip.
It works because of the competing equilibria: ion exchange of Ln<sup>3+</sup> with the resin and complexation of the
Ln<sup>3+</sup> by the complexing agent. The smallest (thus heaviest) REs elute out first.
Quite doable. Another one on my ‘list of things to do before I leave this mortal coil’…
[Edited on 11-4-2014 by blogfast25]
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eidolonicaurum
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Could I therefore use a burette filled with silica gel beads as the stationary phase to separate these rare earths? And what else could I use this set
up to separate, eg could a mixture of d-block salts be separated using this method?
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Chemosynthesis
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Excellent post, Dan!
One caveat about the wool plug for an unfritted column is to only use a small amount. It's to keep sand from etching your stopcock, so a tiny amount
to just keep your packing level is sufficient. Do not forget it or you will create a permanent leak (until you replace the stopcock).
Silica and alumina are pretty standard column materials for column chromatography. One tip I learned is that you can pour a thin layer of sand on top
of your packed column prior to adding more solvent, to avoid disrupting the evenness the top of the packing. It's not necessary, but can be helpful
to keep bands straight, and narrow down your fraction selection/maintain resolution.
Do not let your column dry out with product inside. You need to keep the solvent level above your stationary phase by refilling. The thin sand
toplayer trick can help out there. If you have to leave a column overnight, try to wrap it in foil and foil/parafilm the top to keep your solvent
system from evaporating. The easiest way I am familiar with to unpack a column is a very light stream of compressed air through the tip, with the
column aimed into a trashcan. If you have compressed gas that is unreactive to your chromatography system, check out flash chromatography. I always
hated gravity chromatography because of the time consumption. I ran plenty in synthesis before getting into better funded labs and switching fields.
Edit- check out these articles... you might need to manually run a gradient, which I always found annoying, or run multiple columns. Silica gel with
nitric acid eluent is mentioned. I haven't run that system before, so be careful when mixing since you might heat the column. DMSO and silica, if I
recall correctly, can heat up. I remember seeing people crack columns that way.
http://pubs.acs.org/doi/abs/10.1021/ac00277a069
http://www.chemeng.lth.se/exjobb/E546.pdf
[Edited on 11-4-2014 by Chemosynthesis]
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eidolonicaurum
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If I had, say, 100ml of substance in solution, how would that be processed in a burette sized column? Would I pour it in bit by bit and separate the
whole lot at once or put some in, separate the components, add more and repeat the process?
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blogfast25
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I don't see how alumina or silica, without some surface treatment, can possibly retain RE ions.
In Seaborg's 'The Transuranium Elements' there are plenty of references to separating REs or actinides using Dowex-1 or Dowex-50 resins and 0.2 M
citrate buffer as eluent. Not a word about alumina or silica though. Chemosynthesis' second reference does use silica gel and di-(2-ethylhexyl)
phosphoric acid (good luck getting that!) as eluent.
Dowex style ion exchange resins aren't hard to obtain.
| Quote: Originally posted by eidolonicaurum | | If I had, say, 100ml of substance in solution, how would that be processed in a burette sized column? Would I pour it in bit by bit and separate the
whole lot at once or put some in, separate the components, add more and repeat the process? |
That wouldn't work: for a 25 ml burette you would have to concentrate all substances in a few ml at most. For a 100 ml you'd need a much wider column
bed, like several cm radius.
[Edited on 11-4-2014 by blogfast25]
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Chemosynthesis
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You almost have to do it at once or your different materials can begin to overlap among samples. The only way to do them piecemeal is to know your
resolution, theoretical plates, etc. I never did any of that.
Dissolve your substance in just enough solvent to get an even coating of your sand. I always liked using the sand topcoat because, as I alluded to,
this step can depress some sand, but should leave the stationary phase flat. Flat, narrow/sharp bands are key in any kind of chromatography,
including gel electrophoresis, which I am finishing a bunch of right now. Once you have your coating, you should very gently try to pour on your
solvent, possibly using a stir rod or something to disperse the pressure along your column wall. I would rotate my stirring rod around to avoid
hammering one of sand with solvent.
Once you fill up pretty high, you are now ready to open the stopcock and fill up your tubes. If you run a lot of tubes, you need a big rack and a
couple hours time, possibly. Make sure you have a system of tube filling order. Always go left to right, or always zig zag. Whatever you like...
keep it consistent so you never lose track of your tube count. Just as Dan Vizine said above with TLC being an excellent way to determine your
solvent system... TLC is also an excellent way (only way?) to determine your fractions. TLC every single tube you fill, and make notes on which
eluents are in which tubes. Discard/keep accordingly.
Hopefully I remembered all that accurately. I haven't done the synthesis/purification/characterization side in awhile, but want to get back into it.
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Dan Vizine
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Thanks, Chemosynthesis, likewise with your contributions.
Blogfast, At a very basic level, all a molecule needs to be retained on any of these phases is a dipole moment or a charge or even high
polarizability. Even alkanes don't have Rf values of 1.0 in all solvents.
For those who may not know the term, Rf = distance material moves on a tlc plate divided by the distance the solvent traveled. Generally, higher
polarity = lower Rf
But actually, eidolonicaurum, this is something you will need to read about to do. Our explanations will not be good enough given the time &
space, etc. Blogfast's specifics are a push in the right direction. Dowex is the most universally used ion exchange resin and it is tiny golden
colored beads. Columns will run very quickly. This is not always the best thing, resolution may suffer and you'll want to throttle the flow a bit in
all likelihood.
Btw, Silica gel (SiO2) and alumina are white powders.
Every chromatography I've ever done which had water as a co-solvent on silica gel always brought a tiny amount of an inorganic residue with it.
You won't have this problem at all with Dowex beads.
To totally change the form of the resin, run 5 bed volumes of an aqueous soln of the desired ionic form through the column followed by 3 volumes of
distilled water. More washing is better if you have the time/ambition.
[Edited on 12-4-2014 by Dan Vizine]
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Chemosynthesis
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I appreciate it! Posters like you and Blogfast are the reason I joined instead of lurking.
You just convinced me to get a copy of that book. I had a different upper level inorganic text in undergrad and let someone borrow it, and this is
exactly the kind of text I need lying around to refresh the Jahn-Teller effect and orbital mixing for ideas on what do with the
PrCl<sub>3</sub> I was going to use in a catalysis.
Thank you.
Good call. I forgot to mention as per my
"Model Calibration of Chromatographic Separation of Rare Earth Elements" by Frida Ojala Department of Chemical Engineering, Lund University January
2010 link that di-(2-ethylhexyl) phosphoric acid (HDEHP) reagent was cited as being able to separate lanthanides on silica columns with the nitric
solvent front. Maybe not the best idea.
[Edited on 12-4-2014 by Chemosynthesis]
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blogfast25
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A bit more from Atkins and Shriver: an admittedly somewhat oversimplified guide to colours of the Ln<sup>3+</sup> aqua ions, in function
of the number of 4f electrons:
0 or 14: colourless
1 or 13: colourless
2 or 12: green
3 or 11: red
4 or 10: pink
5 or 9: yellow
6 or 8: pink
7: colourless
So at Gd<sup>3+</sup> the colour series more or less turns back on itself. It also means that out of the 14 elements, 9 have colourful
aqua 3+ cations, 5 don't.
Dan, I appreciate your point about alumina/silica, but in the case of cations, a cation exchange resin really does sound like the logical choice. As
you also pointed out.
And some more from The Transuranium Elements: for the actinides/lanthanides they used a Dowex-50 resin, which is essentially a sulphonated cation
exchange resin, somewhat old fashioned probably (this is pre-war research). A 0.2 M ammonium citrate/citric acid buffer (pH about 3.5) was used as
eluent solution, at 100 C (87 C for the actinides). A remarkable similarity in the elution behaviour between the two series was observed.
I'm not sure what the purpose of the temperature is: affecting Rf values probably.
It also describes experiments with Dowex-1, using 13 M HCl as eluent.
[Edited on 12-4-2014 by blogfast25]
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Brain&Force
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Here are the colors of different lanthanide compounds:
Lanthanum: colorless (0 f-electrons)
Cerium(IV) sulfate: yellow (0 f-electrons)
Cerium(III): generally colorless, except cerium(III) oxide is yellow(?) (1 f-electron)
Praseodymium(III): pale green - limeade color (2 f-electrons)
Neodymium: varies depending on light source: reddish-magenta to lilac in sunlight, colorless in CFL light (3 f-electrons)
Samarium (III): pale yellow (5 f-electrons) Fluoresces deep red(?)
Samarium(II): blood-red but unstable (6 f-electrons)
Europium(III): colorless to pale pink (6 f-electrons) Fluoresces red
Europium(II): yellow (7 f-electrons) Fluoresces blue
Gadolinium: colorless (7 f-electrons)
Terbium(IV) oxide: black (non-stoichiometric)
Terbium(III): colorless (either 8 f-electrons or 7 f-electrons and a d-electron, I've see both) Fluoresces green
Dysprosium: colorless (9 f-electrons) Fluoresces yellow(?)
Holmium: varies depending on light source, yellow in sunlight, pink in CFL light (10 f-electrons)
Erbium: pink (11 f-electrons)
Thulium: either colorless or green(?) (12 f-electrons) Fluoresces blue(?)
Ytterbium(III): colorless (13 f-electrons)
Ytterbium(II): green (14 f-electrons)
Lutetium: colorless (14 f-electrons)
Would separation through magnetism be feasible at all? Just an idea...
At the end of the day, simulating atoms doesn't beat working with the real things...
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blogfast25
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No idea.
Incidentally, the 4 % Ho oxide in HClO4 standard for spectrophotometers is decidedly pink, at least as shown in Wiki...
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elementcollector1
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Half off-topic, but I just calcined a (presumably) 2:1 mix of Ce and La oxalates to oxides. What should I do to separate these two? According to the
Wiki page, cerium salts are insoluble in nitric acid, but I'd rather avoid that, as I don't have any nitric acid and don't want to go to the trouble
of distilling it for this one purpose.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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Chemosynthesis
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| Quote: Originally posted by elementcollector1 | | Half off-topic, but I just calcined a (presumably) 2:1 mix of Ce and La oxalates to oxides. What should I do to separate these two? According to the
Wiki page, cerium salts are insoluble in nitric acid, but I'd rather avoid that, as I don't have any nitric acid and don't want to go to the trouble
of distilling it for this one purpose. |
This has a good procedure of the type you describe... which unfortunately, uses nitric acid.
http://link.springer.com/article/10.1007%2FBF00468565#page-1
Seems better than my next alternative from Indian Journal of Chemistry Vol. 44A, March 2005, 497-503... which suggests
N-phenylbenzo-18-crown-6-hydroxamic acid, or the solvent impregnated resin of http://dx.doi.org/10.1016/j.seppur.2013.07.047
and similar un-home-friendly sounding reagents here:
http://dx.doi.org/10.1016/j.hydromet.2003.10.008
I hope I'm wrong, but it looks like nitric might be your best bet. That or borrow a gas centrifuge.
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blogfast25
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| Quote: Originally posted by elementcollector1 | | Half off-topic, but I just calcined a (presumably) 2:1 mix of Ce and La oxalates to oxides. What should I do to separate these two? According to the
Wiki page, cerium salts are insoluble in nitric acid, but I'd rather avoid that, as I don't have any nitric acid and don't want to go to the trouble
of distilling it for this one purpose. |
Try fusing the oxides with an excess NaHSO<sub>4</sub> for about an hour or so. This should convert the
La<sub>2</sub>O<sub>3</sub> to the La sodium double sulphate which is very poorly soluble. Assuming the Ce was present as
CeO<sub>2</sub> that should convert to Ce(SO<sub>4</sub> <sub>2</sub> which is relatively soluble.
This is assuming the calcination of the oxalates to oxides was successful.
[Edited on 13-4-2014 by blogfast25]
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12AX7
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Regarding scandium, AFAIK, its use in aluminum alloys is as a modifier, similar to titanium. Titanium finds use as a grain refiner: it is present as
fine TiSix (TiSi2 comes to mind?) intermetallic grains, which have low solubility in molten aluminum and act as nucleation agents, resulting in a
finer, stronger crystalline structure on casting. The amount is usually < 0.1%. This is probably less important for rolled or wrought products.
My short understanding of odd Russian alloys is limited to this: they used lithium-aluminum alloys in rocket parts (skin, structural?). Whether these
(or any other military or special purpose) alloys contain Sc, I don't know.
Tim
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elementcollector1
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| Quote: Originally posted by blogfast25 |
Try fusing the oxides with an excess NaHSO<sub>4</sub> for about an hour or so. This should convert the
La<sub>2</sub>O<sub>3</sub> to the La sodium double sulphate which is very poorly soluble. Assuming the Ce was present as
CeO<sub>2</sub> that should convert to Ce(SO<sub>4</sub><sub>2</sub> which is relatively soluble.
This is assuming the calcination of the oxalates to oxides was successful.
[Edited on 13-4-2014 by blogfast25] |
Well, I obtained a tan / light brown powder of a very smooth, almost liquid consistency, so I think that a major portion got converted at the very
least.
I'll have to prepare some NaHSO4, then.
Another odd thing happened while I was doing the same with what I'm fairly sure was neodymium oxalate (all these white powders!). At first, it went
rather smoothly, and the compound turned consistently dark gray. However, upon further heating around the edges of the crucible (this was done with a
blowtorch), a whiter substance began to appear. Curious, I heated the gray compound further until all of it was the white compound. What could this
be? In addition, it appears the white compound partially melted - upon scooping into water to check for solubility, some of the substance had
collected into 'chunks'. So far, it does not appear to be soluble, so I am very confused.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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blogfast25
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NaHSO4: pool supplies, if I'm not mistaken.
I wouldn't worry too much about that colour change: it could be caused by all sorts of things like the last but of volatile contamination blowing off.
It's very hard to tell what it is precisely and colour is deceptive in any case, probably more so at high temperature. If it's nice and white it's
probably fairly pure. Iron would tinge it red to brown for instance.
[Edited on 14-4-2014 by blogfast25]
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