jimmyboy
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Metathesis reactions
Right now i have decided to mess with a solubility reaction between ammonium sulfate and potassium nitrate - i decided since AN (ammonium nitrate) is
the only compound soluble in alcohol i would use it to extract but have found that it isnt as easy as all that and have gotten very small yields - i
was using denatured alcohol for this but now i believe that the exchange simply cannot take place without water present - i thought this would be a
simple route but not so - right now i am thinking of trying to mix molar amounts of am sulfate and pot nitrate and then add just enough water for one
mole of AN - or just mix the two together in water until completely dissolved and then add alcohol until i see precipitate of potassium sulfate - one
question - when a ionic compound hits the point where it precipitates/crystallizes - does it completely fall out of the water or is there a azeotrope
type mixture of the ions still present in the solution after it has fallen out? any help is appreciated
Thanks
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12AX7
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When something "precipitates", it's just like the weather term (except in water, not air). In the case of weather, the air no longer
has solubility for the moisture level and rain or snow falls out... in the solution, all ions mingle and whichever combination is least soluble
precipitates out, usually as an extremely fine powder which takes some time to settle. If you are doing precipitation on cooling (making a
concentrated solution at boiling temp, then cooling), the particles will grow a bit on cooling and leave larger crystals (depending on how fast it is
cooled).
Tim
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neutrino
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After something crystallizes, there’s always some of it left in solution (unless it was boiled to dryness, in which case there is no solution). Say
you have a saturated solution of a salt at 70*C with a solubility of 100g/L. Cool this down to 30*C and the solubility should drop, say to 10g/L.
Every liter will precipitate 90g of solid, but the rest will still be in solution.
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jimmyboy
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So say if there are two salts totally dissolved in a solution at 70*C - if the first salts solubility is 10g/L and the second is 30g/L both at 30*C
then when it is cooled down there will be 10 grams of the first and 30 grams of the second still in the solution respectively. Neither has totally
precipitated out.
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neutrino
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That’s the right idea, but there’s also the common ion effect. If the two salts share a common ion, the more soluble one will force the less
soluble one to precipitate. I’m not sure if potassium and ammonium do this and give you a complex system (ammonium has the same charge and almost
the same size as potassium).
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12AX7
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Yep, for instance you can mix solutions of sodium carbonate and magnesium sulfate, both of which are soluble, and on contact, magnesium carbonate
precipitates (leaving sodium sulfate in solution). Magnesium carbonate is slightly soluble, so a small amount remains in solution, depending on just
how soluble it is, and at what temperature.
Tim
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jimmyboy
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What do you mean common ion? there are 4 ions i see - ammonium - potassium - nitrate and sulfate - neither compound has anything in common - i am
going to try mixing first in water then try to "Salt out" with alcohol - anyone know the effects of alcohol on a solution if the compounds
arent soluble in alcohol? what - maybe a 50/50 solution of water/alcohol will make it all precipitate out
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neutrino
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Ammonium ions tend to mimic alkali cations, especially K<sup>+</sup>.
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jimmyboy
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I went ahead and tried mixing in water first - then adding methanol making it 50/50 methanol/water - the solution instantly turned frothy white -
looks like a milkshake - i dont see any separation as of yet - for some reason i feel all i have done is made the ammo sulfate and pot nitrate
xtallize - superfine crystals but no ammo nitrate nonetheless
hmm i guess everyone was too bored with my question to tell me that this reaction wouldnt work
[Edited on 31-3-2005 by jimmyboy]
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chloric1
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Dont give up
jimmy
I have been doing something very simular. Epson salts with sodium bromide to make magnesium bromide but my yeilds where low too. Go ahead and
separate the precipitate and then soak it in pure methanol for about 3 days. Then decant the methanol from any solids left behind and evaporate. No
sulfates should be left in the final product. Separations such as this are A LOT of work. But, for the home chemist they are quite feasable. You
should next try mixing concentrated ammonium chloride solution with sodium nitrate solution. sodium chloride separates as finer crystals. then add
your solvent
[Edited on 3/31/2005 by chloric1]
Fellow molecular manipulator
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jimmyboy
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well i didnt really give up - i just have the wrong starting materials - i could get ammo nitrate with ammonium sulfate + calcium nitrate - but not
potas nitrate since it is way too soluble - hmm ammo chloride and sodium nitrate you say - hmm why would NaCl precipitate out ?- all the ions in that
reaction are fairly soluble - ammo chloride i could make - but hmm sodium nitrate isnt a commonplace chem - i only have a limited amount of salts to
play with since i only buy the common ones - the only route to calcium nitrate would be acids which i am trying to avoid but that is another idea
Another idea would be to mix kno3 with calcium chlorate made with the hypochlorite and drop kclo3 out with cold leaving calcium nitrate - hah what a
pain though - but feasible - any other possible suggestions?
The phosphorus joke cracked me up by the way 
[Edited on 2-4-2005 by jimmyboy]
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jimmyboy
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bump
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jimmyboy
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hmm trying to salt out the same mixture by adding nacl - will see what happens
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