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blogfast25
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Ceric Ammonium Sulphate: attempted preparation
I’ve attempted to prepare ceric ammonium sulphate (CAS) - (NH4)4Ce(SO4)4.2H2O (CAS 10378-47-9) by means of a brute force fusion, with
stoichiometry:
CeO2 + 2 H2SO4 + 2 (NH4)2SO4 = (NH4)4Ce(SO4)4.2H2O
For that purpose 10.0 g of reagent grade CeO2 (a light yellow, very fine powder), 7.7 g 2 (NH4)2SO4 (the stoichiometric amount) and 7 ml of 95 % H2SO4
(approx. twice the stoichiometric amount) were mixed in a 250 ml RBF and an air cooled refluxer was fitted to it. The reagent mix was a viscous slurry
and had already heated up significantly during mixing.
The RBF was heated on an oil bath for about 20 minutes, starting at RT and ending at about 250 C (bath temperature). The run was ended because a
striking colour change from a light yellow paste to a reddish brown cake (appearing quite dry and immobile) had taken place.
This was then allowed to cool, then force cooled on ice bath. Slowly about 35 ml of cold DIW was added and much of the cake dissolved to form an amber
looking liquid, presumed a solution of CAS with excess H2SO4 and (NH4)2SO4. It was clear though that much of the initial CeO2 was still present as
unreacted oxide. This was separated from what was presumably ceric ammonium sulphate solution by filtering. The unreacted amount of CeO2 will be
determined tomorrow.
The last bits of this reddish cake/crust was dissolved in a bit of hot water and added to the filter. This is the perfectly transparent solution
obtained (still during filtering), about 40 ml at the end of filtering:
The same solution during boiling: it appears to be slightly thermochromic, it is darker coloured at BP than RT:
At about 25 ml during boiling in, the first turbidity was observed and boiling was stopped (beaker was taken off the heat). After a bit of cooling,
the beaker was ice cooled. A crop of rather non-descriptive small red/amber crystals of presumably CAS was obtained.
Of the original solution (pre boiling) about 1 ml has also been transferred into a test tube. Three drops of 35 % H2O2 were needed to reduce all the
Ce(IV) to Ce(III) and thus a colourless solution resulted. To that some K2SO4 solution was added and the white and poorly soluble potassium cerous
sulphate double salt precipitated, this typical is of REs (III).
To follow:
• Yield determination
• Second attempt with larger amount of H2SO4 and longer time/higher temperature.
[Edited on 15-6-2013 by blogfast25]
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platedish29
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Hey there, blogfast!
Cool idea!, if those are the crystals to pick doesn't it comes as a homogenous goopy mass of the material??
anyway I think you should try higher temperatures with less solvent, and czochrawski it off, I put my pets it won't work out pretty good fella 
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elementcollector1
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I'd like to see how much ceria went unreacted - I'm planning to do the same with my ceria/sulfuric acid/alcohol mix.
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smaerd
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Neat blogfast, did you create this procedure yourself or was it based on any literature?
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blogfast25
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In the mean time, there’s been a development. When I went back to check on the ice bath and crystals later on last night, the crystals had
redissolved completely. On heating they reappeared. So this material has an inverted solubility-temperature dependence (like many RE sulphates) and
this can be used to isolate/recrystallise the substance.
I can also confirm its thermochromic nature: solutions darken noticably when heated and I believe this might explain the inverted
solubility-temperature dependence, by means of structural changes at higher temperature, affecting both colour and solubility.
This is the first crop of crude CAS (still wet) obtained exploiting the poor solubility at BP (bottom of a 250 ml beaker):
Lovely vibrant colour!
Huh?
I should know the answer by tonight. Guessing by unreacted CeO2 filter cake volume I’d say about 50 %.
It was based on a similar procedure of mine to synth ferric ammonium sulphate.
[Edited on 15-6-2013 by blogfast25]
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platedish29
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Are you not familiar with the czocrawski process for crystal growing?
Sorry I misstyped pets what so thereof should be "bets"
Nice work! Are those simmetrical crystals or just lumps? can you wash/ isolate those crystals out?
[Edited on 15-6-2013 by platedish29]
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elementcollector1
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50% sounds about right to me.
I wonder if a few recrystallizations would make the product look less glompy.
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Endimion17
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I hope you'll get some decent crystals. I've only seen dusty CAS so far.
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blogfast25
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The unreacted CeO2 of the first run weighed in at about 6.7 g, so barely 33 % actually dissolved. Shockingly bad, really…
The second run was as follows: 14 ml of conc. H2SO4 and 2 hours of runtime, starting at RT and ending at 266 C.
This time I actually got a bit of bubbling from start to finish. Here’s the RBF after cooling:
After chilling, 50 ml of DIW was added on ice bath. Again unreacted CeO2 was prominently present. But is does look less. Actual numbers tomorrow.
After filtering - solution strength is in the order of about 0.5 M Ce4+:
The same solution when boiling:
I believe the colour change must be due to two different structures being in equilibrium:
CAS, yellow/amber ↔ CAS, amber/red
If ΔH = Hamber/red - Hyellow/amber > 0 (endothermic), heating would then push it to the right. ‘Amber/red’ could then also be less soluble
than ‘yellow/amber’. The first crystals crop had also lightened considerably overnight.
The boiling CAS solution started bumping badly after the first turbidity showed, even with boiling pebbles, so it’s now evaporating on steam bath.
Czocrawski? I’ll have to look it up.
But getting decent crystals may prove difficult…
I’m also a bit baffled at the colour of Ce (IV). The electron configuration of Ce (0) is:
[Xe] 4f<sup>2</sup> 6s<sup>2</sup> (others claim [Xe] 4f<sup>1</sup> 5d<sup>1</sup>
6s<sup>2</sup> but that doesn't really change anything here)
That would indicate that Ce (III) would have one lone 4f electron (and thus be coloured) and Ce (IV) none, which would make it colourless. But reality
is the other way around... 
[Edited on 15-6-2013 by blogfast25]
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12AX7
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Perhaps Ce forms a complex with H2O (or O or OH) and the shared electrons are doing the color (which could be f or d orbitals, depending on how it
works out). Dunno. Could one make an analogy to, say, VO4(-)? Analogies don't really have to be helpful, since the color could vary continuously
between electronically similar species; isoelectronic configuations will be structurally similar (in molecular and spectral order).
Interesting if the color could be better resolved -- you should be able to observe two peaks of different proprotion if the two-species theory is
correct (which could easily be analogous to Co(OH, H2O) species), and there should be time required for the interconversion (the Co change takes
seconds or minutes I think; in contrast, most Cr complexes for example are rather persistent). Perhaps it can be quenched and the color change
observed over time. If the absorption peak is narrow enough to resolve to sufficient resolution, but it merely moves with temperature, that would
pretty well show it's one substance changing continuously.
Also, is the solid salt a single form, or does it have different allotropes?
Tim
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watson.fawkes
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It's the Czochralski process, pulling crystals from a melt. Melting point of ammonium cerium(IV) sulfate dihydrate is listed on the Sigma-Aldrich site as
"130 °C (lit.)", presumably because they haven't measured it themselves.
I have to wonder if all the ammonia you added is still in the reaction mixture. You may have significant amounts of cerium (IV) sulfate. It's
decomposition point is 350 °C, per Wikipedia. A melting point test would give you some idea of what you've got.
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blogfast25
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If only I knew, Tim. When it first settles at BP it’s kind of wine red, but after cooling overnight it comes out basically amber, so it’s entirely
possible that it has at least two allotropes. The latter is also the colour of the photo in Wiki, for what it’s worth…
Quote: Originally posted by watson.fawkes  | | I have to wonder if all the ammonia you added is still in the reaction mixture. You may have significant amounts of cerium (IV) sulfate. It's
decomposition point is 350 °C, per Wikipedia. A melting point test would give you some idea of what you've got. |
266 C is still a long way away from 350 C. Also, nothing left the flask and on opening I couldn’t smell anything.
An MP determination may be made but I really need to recrystallise it first.
You don’t have an explanation for the Ce (III)/Ce(IV) colour conundrum I presented above?
Today I'm running a test WITHOUT ammonium sulphate, so that might shed some light on it too.
[Edited on 16-6-2013 by blogfast25]
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woelen
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Cerium compounds can have quite different colors, and the presence of ammonium ion has a great influence on the color.
I have ceric sulfate 4-hydrate, which is bright yellow (somewhat like PbI2). This compound only dissolves sparingly in water. Its solutions are bright
yellow as well.
I also have ceric ammonium sulfate, which is orange. Solutions of that are yellow as well.
Finally, I also have some ceric ammonium nitrate. This compound also is orange, just like the sulfate. Apparently, the ammonium ions make ceric ions
appear more orange than yellow.
The orange color of your solid material is quite close to the color of my ceric ammonium salts.
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watson.fawkes
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| Quote: Originally posted by blogfast25 | You don’t have an explanation for the Ce (III)/Ce(IV) colour conundrum I presented above?
Today I'm running a test WITHOUT ammonium sulphate, so that might shed some light on it too. |
I don't have an
explanation. I know better to trust my intuition when f-orbitals are involved. Having said that, there's one part of the color conundrum that's likely
important. Both oxidation states absorb ultraviolet strongly, and physically that's tantamount to a range of colors that humans cannot see. The color
we can see should be considered a tint on top of that.
As for the thermochromic behavior you say, my first hypothesis is that the preferred coordination state changes with temperature. There are 8 ions to
a single cerium, and I doubt all of them act as direct ligands. The Wikipedia page on cerium mentions that ammonia complexes of lanthanides are dark
brown, so it's a reasonably hypothesis that the darker solution you saw was one where ammonia was coordinated to the cerium. The lighter solution
would be that where the sulphate was the ligand. I don't know if that's true, but it's a start for a literature search.
The other thing that occurs to me is that it's conceivable (though I don't know any mechanism) that some of ammonia has oxidized to nitrate. Might
test for nitrate and/or nitrite presence to rule it out.
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12AX7
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It could be informative to slowly recrystallize the substance at low and high temperatures, in order to grow crystals of an observable size (and also
because large crystals of anything are cool  ). The habit should be different
if the crystals are different, and thermochromism of the crystal will be more easily observed than in a polycrystalline mass. Well, maybe you have
(or can make) a microscope with a heated stage -- in any case, recrystallization is of course a good idea for purity if nothing else.
I would be very surprised if ammonia were present as a complex: boiling sulfuric acid was used! It would have to be a very strong complex indeed
(which I suppose isn't impossible), but still, it would be obvious from the formula if ammonium is not present. An ammonium complex is impossible, as
far as I know.
How does ammonium sulfate behave? Does it ultimately decompose to N2, H2O and SO2 at, what, like 400C+? Most ammonium salts sublimate, which is a
reversible reaction (perhaps with NH3 + H2SO4 in the gaseous phase for this one). I would expect similar behavior here, leaving CeO2 behind in
addition.
Tim
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watson.fawkes
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| Quote: Originally posted by 12AX7 | | I would be very surprised if ammonia were present as a complex: boiling sulfuric acid was used! It would have to be a very strong complex indeed
(which I suppose isn't impossible), but still, it would be obvious from the formula if ammonium is not present. An ammonium complex is impossible, as
far as I know. |
It's certain that any thermodynamic analysis of the complexation system must include the
state "not complexed". I didn't mention that before; my oversight. It's also conceivable that the ligand geometry changes between 4-ligand and
6-ligand.
Upon seeing the figure the abstract for this paper, A hexanuclear cerium(IV) cluster with mixed coordination environment, I was astonished. The core is six Ce atoms bridged by 8 oxygen atoms in the
shape of a rhombic dodecahedron. The coordination number of the Ce ions is 8. There are three nitrate ions in the complex, acting as bidentate ligands. After
seeing something like this, I'm keeping an especially open mind about what's going on here.
More directly relevant to the matter at hand is the 1945 paper Spectrophotometric Studies on Cerium (IV) Sulfate Complex Ions.
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Fantasma4500
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i believe i have some magnetic metal mixture thats also thermochromic, magnet pieces found very close to big copper wire spools in LCD TV
when i neutralized the chlorides with still HCl in it, it heated up and it became a clear much darker colour, after more carbonate was added it
precipitated out
it has the same flouroscent glow
who knows how many things it could be.. brilliant colour anyways, ill make a tonne of it and store it in a bottle because its so pretty (:
more than abit offtopic i know, sorry.. never heard about thermochromic effect before
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blogfast25
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The unreacted CeO2 from run #2 was only 0.75 g, so about 90 % dissolution had been achieved.
The products obtained from both runs are substantially different in colour (left: #1; right: #2):
The third run was as follows: 10.0 g CeO2, no ammonium sulphate, 22 ml of conc. H2SO4, 1 hour runtime.
The amount of non-digested CeO2 has yet to be determined but seems negligible going by filter cake. After filtering:
The same solution near BP:
This was then boiled in for what felt like an eternity, when bumping started and a large crop of material dropped out over the course of about 1
minute:
This lightened a lot on cooling.
A small sample of this product was dissolved in iced water, it dissolved completely.
Tests using Ce(OH)4:
The crops of ‘CAS’ products of run #1 and #2 were combined and dissolved in cold water and neutralised with 0.89 SG NH3, ceric hydroxide
precipitated. This was then copiously washed with hot water:
Dissolution tests with this ceric hydroxide proved it dissolves easily in hot 50 % H2SO4, hot HNO3 70 % and hot HCl 37%. In all cases similar looking
solutions were obtained and all were thermochromic.
Here is a Ce(NO3)4 solution at RT:
In the case of hot HCl, the dark red slowly fades to colourless, and chlorine could be detected:
2 Ce(IV) + 2 Cl(-I) == > 2 Ce(III) +Cl2(0)
This reaction was fairly slow. It's a fairly wasteful way of preparing CeCl3 solutions.
So, ceric sulphate, ceric ammonium sulphate, ceric nitrate and ceric chloride solutions all show the same colour and thermochromism.
This strongly suggests the thermochromism is more or less independent of sulphate ions, nitrate ions, chloride ions or ammonium ions.
One final observation: the wet Ce(OH)4 responds slightly to UV light… like Nd(OH)3
[Edited on 16-6-2013 by blogfast25]
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woelen
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Nice results. Your observation confirms the colors of the chemicals I have. Without ammonium ions you have a bright yellow compound, with ammonium
ions you get the orange/red stuff.
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blogfast25
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| Quote: Originally posted by woelen | | Nice results. Your observation confirms the colors of the chemicals I have. Without ammonium ions you have a bright yellow compound, with ammonium
ions you get the orange/red stuff. |
But run #1 AND run #2 both were prepared with ammonium sulphate present!
Also, the colour of the solutions (and their thermochromism) seem totally indifferent to the type of anion. Some more experiments tomorrow.
I think this CeO2 may contain small amounts of another RE, not sure which though. Now it turns out the Ce (III) chloride has a yellow/greenish tinge,
but not like ferric yellow though. And the Ce(OH)4 really does respond to saver bulb light differently than incandescent light, no question about
it...
Hot glacial acetic acid didn't manage to dissolve the Ce(OH)4, so it probably isn't worth trying NH4HF2 either... I wish I had me some perchloric
acid. 
[Edited on 17-6-2013 by blogfast25]
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kmno4
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Just a literature note about sulfate Ce(IV) colours (in attachment).
Complete ebook (old, 1919, mentioned here http://www.sciencemadness.org/talk/viewthread.php?tid=14145&... ) is available from archive.org.
Attachment: pp.pdf (152kB)
This file has been downloaded 790 times
Слава Україні !
Героям слава !
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blogfast25
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Thanks kmno4, I already have it but it's good to be reminded.
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elementcollector1
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Lanthanum, maybe? Try treating a salt of the mix (the nitrate, maybe?) with concentrated HNO3 - apparently cerium is insoluble here, and can be
separated.
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woelen
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by woelen | | Nice results. Your observation confirms the colors of the chemicals I have. Without ammonium ions you have a bright yellow compound, with ammonium
ions you get the orange/red stuff. |
But run #1 AND run #2 both were prepared with ammonium sulphate present!
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Sorry for the misread, I understood you did one run with ammonium sulfate and the other without.
It still may be that the orange stuff contains a lot of ammonia while the yellow stuff does not. You can easily test that by adding some of the solid
to wet solid crunched NaOH and carefully smell the mix.
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blogfast25
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| Quote: Originally posted by woelen | Sorry for the misread, I understood you did one run with ammonium sulfate and the other without.
It still may be that the orange stuff contains a lot of ammonia while the yellow stuff does not. You can easily test that by adding some of the solid
to wet solid crunched NaOH and carefully smell the mix. |
It was run #3 that was without ammonium. That product is indeed yellow, much like #1.
But I won't be pursuing CAS anymore. Instead I'll try and prepare a bit of ceric ammonium nitrate and maybe the ceric magnesium nitrate hydrate. And
some boring cerous sulphate too.
I really want try and identify the contamination, assuming there really is one. I'm pretty sure I'm not 'seeing things'...
As far as I'm concerned the tell tale signs are Nd(III) or Pr(IV).
[Edited on 18-6-2013 by blogfast25]
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