OctanitroC
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Strontium Acetate Solubility?
Hey, I've been conducting quite a bit of experimentation with acetic acid and characterizing various acetate salts. Today I took my (easily more than
halfway to oxide) bits of strontium I had and dissolved them in hot white vinegar. I was a bit concerned I might run into problems with sugars and
other crud from the vinegar, but I haven't had any problems so far. The exotherm was enough to drive the solution to boiling, and I kept it on heat
while adding enough vinegar to mostly clarify the solution. I then filtered it hot and let it cool, expecting to let it evaporate like Cu(OAc)2
solution. I was surprised when it immediately started crystallizing! So my question here is this: Does anybody have a reliable solubility curve for
strontium acetate? The only one I found showed a normal curve up to around 30 degrees C then retrograde up to 100 C, but that doesn't fit at all with
what I saw when I redissolved the crystals. I'm going to try to recrystallize and take some pictures tomorrow to post - the crystals grow as fairly
compact masses of really thin square plates. Quite beautiful actually, they remind me of tiny clear wulfenite crystals. But as far as solubility goes,
does anybody have good data? I don't have the CRC handbook on me or I'd look it up there, so I've just been shooting in the dark as far as volumes of
water to add when recrystallizing.
And then I discovered this charming young man had stolen my kidney!
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blogfast25
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Apparently the salt is a hemihydrate.
My CRC ('86) doesn't mention even a single data point on its solubility.
One product data sheet I found claims that it 'dissolves in 2.5 part of water'.
Do you have any idea of the concentration you achieved?
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OctanitroC
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Unfortunately not...I didn't dry the crystals completely and I don't have a good sub-gram balance in any event. I got the solution maximally saturated
at 100 C then decanted off of the excess Sr(OH)2 then let it cool to room temp then put it in the refrigerator. So I should have gotten the difference
in solubilities between 100 and roughly 0 C for around 50 mL of solution.
And then I discovered this charming young man had stolen my kidney!
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OctanitroC
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Here are the pictures I took of the second crystallization I did this morning (sorry for the crappy resolution, had to use iPad camera). Any idea what
crystal habit they are?
And then I discovered this charming young man had stolen my kidney!
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blogfast25
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Nice crystals indeed!
Weigh everything, then filter off the crystals and dry an weigh them. That should at least give a good idea of solubility at 0 C. If that value is
small then solubility at higher temperature doesn't matter so much because on recrystallization you'll always get back most of the crystals.
It'd be nice to see what happens in a third crystallisation: by then they should be very pure!
[Edited on 15-3-2014 by blogfast25]
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Zyklon-A
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From Wikipedia: 37, 42.9, 41.1, 39.5, 38.3, 36.8, 36.1, 36.2, 36.4, g/100mL
-----------------------0 °C, 10 °C, 20 °C, 30 °C, 40 °C, 60 °C, 80 °C, 90 °C, 100 °C.
[Edited on 15-3-2014 by Zyklonb]
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OctanitroC
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I found those on Wikipedia too, but if they're correct, I shouldn't have been able to precipitate any. Hmm. I added my crystals back to the filtered
supernatant I had then added just enough water to re-dissolve them, I'm going to see if I can grow some larger crystals by slow evaporation, then I'll
try some solubility measurements. Thanks!
And then I discovered this charming young man had stolen my kidney!
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Boffis
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Quote: Originally posted by OctanitroC  | | I found those on Wikipedia too, but if they're correct, I shouldn't have been able to precipitate any. Hmm. I added my crystals back to the filtered
supernatant I had then added just enough water to re-dissolve them, I'm going to see if I can grow some larger crystals by slow evaporation, then I'll
try some solubility measurements. Thanks! |
You haven't got strontium acetate crystals! What you have got is strontium hydroxide in one or more of its hydrates. Strontium hydroxide has a steep
solubility/temperature relationship ie the solubility increases very rapidly with temperature, on cooling it crystallises not the acetate. You will
need to cool the solution and make it acid with excess acetic acid and then evaporate it slowly in a warm place or on a water bath to get the
hemihydrate. Or you can evaporate the water at low temperature over silica gel. You can also steepen the solubility gradient and salt out the acetate
by adding excess glacial acetic acid (personal experience). Interestingly I recently acquired an old jar of BDH strontium acetate which claims to be
the dihydrate so low temperature evaporation may give this hydrate, but I haven't tried it.
Strontium hydroxide octahydrate can be grown into large tetragonal prisms with a perfect basal cleavage by slowly cooling (solubility about 48g per
100ml of water at 100C and only 0.5 at 10 C)
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OctanitroC
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Ohh, that would make a lot more sense. I really need to get a hold of some GAA... So the solution I ended up with the white vinegar is mostly Sr(OH)2
with some of the acetate in there as well? I should have checked solubility on the hydroxide, I was assuming the Sr metal, at least, would
preferentially react with the acid because I expected the hydroxide to have a comparable solubility to Ca(OH)2, since that has a negligible solubility
in the first place AND is retrograde. But it looks like it acts almost exactly like Ba(OH)2 instead. And then I have the whole problem of there having
been mineral oil soaked into the powdery SrO that was coating the metal (since I stored it under oil), so I've got a persistent layer of organic mung
on my solution that's gone white from oxide or hydroxide. I might just scrap what I have and start over with SrCO3 and GAA, I'd really like to compare
the acetate crystals to the hydroxide ones without worrying abut cross-contamination.
And then I discovered this charming young man had stolen my kidney!
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blogfast25
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Well done, Boffis!
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Boffis
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Even dilute 3-5% acetic acid will dissolve Sr(OH)2 and its hydrate and also strontium oxide (which was at one time available on ebay). Metallic Sr
reacts with water to form the hydroxide without any acetic acid being present so you need to check your final solution is slightly acidic (Sr
hydroxide is strongly alkaline).
I tried dissolving strontium carbonate in 1pt by volume of glacial acetic acid and 2 pts water but I found that commercial SrCO3 dissolves rather
slowly and requires long heating and never completely dissolved. I mean to test the carbonate to make sure it is not contaminated with sulphate but I
haven't gotten round to it yet. The SrCO3 fizzed at first then just settled to the bottom, stirring and heating did not seem to improve the situation.
The SrCO3 is "pyro grade" material from an ebay site. I would be interested to hear from anyone else that has had this problem.
An alternative method of crystallising Sr acetate may be to add alcohol. I haven't tried this with alkaline earth acetates but I did try it with
nickel acetate and it DIDN'T work. Nickel acetate also has a very flat solubility/ temperature curve so it too is can't be recrystallized by simple
cooling and if boiled down at atmospheric pressure you get an insoluble basic salt that is hard to redissolve in excess acid. An interesting feature I
observed when recrystallizing nickel acetate from strong acetic acid was the very slow rate at which it crystallised, complete crystallisation even at
4-5 C takes a month (!) so maybe I didn't leave the alcoholic mixture long enough.
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OctanitroC
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That's quite a good idea! I've noticed that my copper carbonate I prepared from CuSO4 + NaHCO3 behaves similarly to your nickel acetate...basic salts
are a pain to put up with.
I wanted to check with you before I try this: I was thinking I would take the crude solution of acetate and hydroxide I have and filter it into Na2CO3
solution to precipitate the carbonate. That would get rid of my insolubles and oily residue on top of the solution and leave any alkali salts in
solution, and since SrCO3 is nearly insoluble it would drop the strontium out of solution. Then I could decant from that, filter and redissolve in
vinegar, which would hopefully prevent any formation of hydroxide. Then I could try precipitation with ethanol. From what you said about the nickel
acetate it seems that precipitation time is highly variable (I've used ethanol to crash tetraamine copper sulfate before and that's nearly
instantaneous and makes a really fine powder).
But as far as the precipitation and redissolving goes, that shouldn't give me any pesky side reactions, right?
And then I discovered this charming young man had stolen my kidney!
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blogfast25
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| Quote: Originally posted by OctanitroC | | I was thinking I would take the crude solution of acetate and hydroxide I have and filter it into Na2CO3 solution to precipitate the carbonate.
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Assuming the carbonate is much more insoluble than the hydroxide you don't even need to filtrate: the hydroxide will convert to carbonate. See also
Ca(OH)2 + K2CO3 === > CaCO3 + KOH, the well known method for preparing KOH solutions from simple chemicals.
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Subcomputer
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Boffis - I tried dissolving ebay SrCO3 with white vinegar and noticed a very similar result, finely divided white sludge that didn't seem particularly
reactive to adding more white vinegar after removing the supernatrant. The same SrCO3 could be reacted down to only a small amount of leftover with
HCl. Mine was definitely contaminated with sulfate by the smell in this and other experiments. I'm tempted to see if woelen's sulfate removal method
for BaCO3 will also work for Sr, since SrCl2 can be easily rendered back into SrCO3. I did get crystals via slow evaporation of the acidic
supernatrant, by means of a mason jar with a filter paper for a lid over several months, though now I guess I should dissolve a few to test their pH.
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