testimento
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The solubilities - which one crashes out first?
I was beginning to wonder how the solubility function actually works. I have solution that contains partially unknown stuff, but I have a reason to
suspect that it contains ammonium nitrate, urea, ammonium phosphate and most likely something else too.
Well, since ammonium nitrate and urea solubilities are quite high, up to 1kg/100ml, and ammonium sulfate is low, it lays between 70 and 100g per 100ml
from 0 to 100 degress C. When the solution is concentrated, what will happen:
1) will the less soluble compounds always crash out before the more soluble
2) will the more soluble salts remain liquid and take the place of the less soluble stuff by chemically forcing them out of the liquid?
To make sure what I mean, is that if you have stuff dissolved in water which solubility is 50g/100ml and you put in something that has solubility of
100g/100ml, will it kick the lesser out, or will they be mixed?
I actually evaporated the liquid down, and in the half-way, a batch of gunk crashed out which I filtered, and after that the liquid stayed clear as
long as I kept it hot(UAN solubility, 10kg/liter). I began to suspect that this very crop was actually the bunch of these less soluble salts that were
kicked out by the UAN. Could I be right?
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chemrox
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look for a text called: "semi-micro qualitative analysis"
isn't this posted in the wrong section?
[Edited on 31-12-2013 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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bfesser
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Thread Moved
30-12-2013 at 17:50 |
elementcollector1
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They will initially be mixed - only way to separate is by converting one of them to something insoluble or fractional crystallization.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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DraconicAcid
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As far as I understand it, it's complicated.
If you have two dissimilar solutes (say, benzoic acid and sodium chloride), the presence of one will not affect the solubility of the other, if the
solutions are dilute. You can heat the solution up so that both solutes are dissolved, cool it down until the solution is supersaturated with the
less soluble material, which will then precipitate.
If the solution is very concentrated in the more soluble solute (using the solutes mentioned above, say 20% sodium chloride), then the solubility of
the less-soluble solute will change because you're not dealing with a true aqueous solution anymore- the more soluble solute changes the
characteristics of the solvent. Benzoic acid will be much less soluble in 20% aqueous sodium chloride than in water; it will be far more soluble in
20% aqueous ethanol than in water.
If both solutes are ionic, then a high concentration of one will make the other more soluble (due to a change in the ionic strength) *unless* they
have ions in common ("common ion effect"). Silver acetate is not very soluble in water- it will be even less soluble in a solution containing sodium
acetate or silver nitrate (you can look up the concept of Ksp, or solubility product to understand exactly why). You can easily demonstrate this by
adding a few drops of conc. hydrochloric acid to saturated sodium chloride- the salt precipitates out.
In the example you suggest, ammonium sulphate and ammonium nitrate have the ammonium ion in common, so you would expect that ammonium sulphate would
not dissolve so well in a concentrated solution of ammonium nitrate. However, the solubility of both are quite high. If you had a solution
containing 200 g of ammonium nitrate per 100 g of water, that's over 20 moles per litre! That's 2.5 moles of ammonium nitrate for about 5.6 moles of
water, or just over one molecule of water per ion. That's not going to have the same solvent characteristics as water.
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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testimento
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Thanks for responses,
The other problem is that I don't know exactly what the stuff has eaten before I got my hands into it. Probably it contains more or less everything
that one could believe to be needing when fertilizing his garden. All I know that it has slightly less than 50% of it's mass consisting of nitrogen
containing products, or N rating of 10, of which nitrates 6% and urea 4%, or something like that. But what supports my suspicions is that when I
filtered the liquid and boiled it down, it was all clear until just about half-way down, all of a sudden, stuff began to crystallize out of it, and I
kept cooking it for a while until I started to suspect that the amount won't increase and I filtered the all-watery, still-nearly-boiling liquid
through a filter and put it back to boil, and after that it stayed all clear until I took it off to cool, and then it began to phlegmatize, as AN and
urea would do.
So, I think that the batch that came out from it, contained pretty much all of the phosphates, sulphates and other useless products. I need to perform
some tests on it, but if it doesn't work, I'm gonna go the hard way, then. 
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Fantasma4500
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Quote: Originally posted by DraconicAcid  | You can easily demonstrate this by adding a few drops of conc. hydrochloric acid to saturated sodium chloride- the salt precipitates out.
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damn. for +7 years i didnt know how the natural salt crystallization was done, we were with class on some trip to an island where they crystallized
salt from very concentrated saltwater, they mentioned something about hydrochloric acid and at this time i didnt even know if hydrochloric acid was
etching - lol
kept me wondering why they would add that to NaCl solution as i started understanding chemistry
bam.
answer out of nowhere.. actually thought about the question of this thread several times myself
however, what if you lead anhydrous HCl into a saturated solution of NaCl? would it rather accept the HCl to bind with the water instead of the NaCl?
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blogfast25
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| Quote: Originally posted by Antiswat | | however, what if you lead anhydrous HCl into a saturated solution of NaCl? would it rather accept the HCl to bind with the water instead of the NaCl?
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No, this too causes the NaCl to precipitate out. Gassing concentrated solutions of chlorides with HCl is a method of precipitating these chlorides.
Works for NaCl, AlCl3, ZrOCl2 and probably quite a few others.
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testimento
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Is there any data is it possible to separate sodium chlorate and sodium chloride by concentration? By meaning, are the chloride and chlorate salts
both soluble, because chlorate will dissolve up to 230 grams per 100ml at 100c where chloride is only 35g. By my idea the chloride could be separated
by concentrating the solution until it will contain mostly chlorate and the chloride would crash out.
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phlogiston
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For seperations by crystallization like the above (depending on the relative amounts of chloride and chlorate) you can also exploit the difference in
solubility with temperature.
The solubility of sodium chloride is almost the same at 100 deg C (390 g/l) and at 20 deg C (359 g/l), where for sodium chlorate there is a big
difference (2040 g/l and 959 g/l respectively).
So if you (1) boil the solution down until it is saturated with sodium chlorate (2) hot filter any sodium chloride that crystalised during boiling
down and then (3) allow to cool, the crop of crystals that you get is going to be mainly sodium chlorate.
Optionally, adding a little bit of hot water after filtration will reduce yield but improve purity depending on the relative amount of sodium chloride
present.
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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testimento
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http://www.oocities.org/capecanaveral/campus/5361/chlorate/r...
This seems to be most interesting page. If I understand it correctly, it indicates that a cooled solution of sodium chlorate solution containing
sodium chloride, can be carefully concentrated with sodium chloride and then further injected with conc. sodium chloride solution in order to
precipitate most of the sodium chlorate.
In practice, one would make conc. NaCl and electrolyse it for a time and gradually add more NaCl into it as it goes, and then cool it down and add
NaCl as long as it will dissolve or sodium chlorate begins to crystallize and then drive up the solution with conc. NaCl to precipitate most of the
chlorate. It could be then filtered and dried in oven.
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jock88
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The third post in this thread explaines how simply systems work in good detail.
http://www.sciencemadness.org/talk/viewthread.php?tid=29164
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zed
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Don't know what you are attempting to do. Are you attempting to recover some particular reagents present in the solution, or do you just want to
identify them?
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