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blogfast25
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Cream of tartar solubility
CoT, chemically potassium bitartrate, is only slightly soluble in cold water (1.2 g/100 g water). Does anyone know its solubility in boiling water?
I'd like to recrystallise food grade CoT.
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AJKOER
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Potassium bitartrate, also known as potassium hydrogen tartrate (KC4H5O6) per Wiki has only 0.6 grams soluble at 10 C and 6.2 g at 100 C.
Good luck.
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Hexavalent
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Hmmm....I assume that is in water?
Is there a possibility of there being another solvent for it? I would assume that the solvent would need to be fairly polar as the solid itself here
is quite polar to my knowledge.
Background info - here is an extract from the Wikipedia page on potassium bitartrate, which kinda gives a real-world 'application' of the solubility
data given by AJOKER.
"Potassium bitartrate crystallizes in wine casks during the fermentation of grape juice, and can precipitate out of wine in bottles. The crystals
(wine diamonds) will often form on the underside of a cork in wine-filled bottles that have been stored at temperatures below 10 °C (50 °F), and
will seldom, if ever, dissolve naturally into the wine.
These crystals also precipitate out of fresh grape juice that has been chilled or allowed to stand for some time.[1] To prevent crystals forming in
homemade grape jam or jelly, fresh grape juice should be chilled overnight to promote crystallisation. The potassium bitartrate crystals are removed
by filtering through two layers of cheesecloth; the filtered juice may then be made into jam or jelly.[2] In some cases they adhere to the side of the
chilled container, making filtering unnecessary.
The crude form (known as beeswing) is collected and purified to produce the white, odorless, acidic powder used for many culinary and other household
purposes."
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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unionised
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If it's already food grade, how much purer do you think you can get it?
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blogfast25
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AJ:
My figure came from here:
http://faculty.kutztown.edu/vitz/limsport/LabManual/KSPWeb/K...
Where in wiki did you get these numbers from? A flat solubility/temperature curve makes recrystallising a little harder.
Thanks, Hexa: I already saw that.
Unionised: food grade doesn’t imply purity.
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AJKOER
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My figures were listed under potassium hydrogen tartrate.
Unfortunately, only two values are given.
Link:
http://en.wikipedia.org/wiki/Solubility_table#P
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blogfast25
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Yes, I see it now. Definitely a flat-liner. 
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Hexavalent
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For water!
Again, are there no other solvents which offer better curves for recrystallization?
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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blogfast25
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Doubt if you'll find them, Hexa: this is one of those chemicals whose main application seems to be as a foodstuff.
Recrystallisation by slow evaporation of solvent is an option but it's a tad slow.
[Edited on 3-6-2012 by blogfast25]
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Hexavalent
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This is where we all need a rotavap! Sigh!
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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blogfast25
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Not to mention so much else! I could really do with one of them portable XRFs too... 
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S.C. Wack
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UTFMI
UTFMISE
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sargent1015
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All the information you could ever need. Nice.
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blogfast25
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Thanks, S.C.
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unionised
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It's not generally a bad indicator. What impurities do you expect to find?
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blogfast25
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Anti-caking agents, for instance (rice powder, see also food grade sodium bicarbonate and also ironing starch) would be a reasonable expectation.
Cream of Tartar is a natural product, derived from the production of another foodstuff, it is likely to be somewhat contaminated as such. I'm looking
into using it as a Standard Material. At least one recrystallisation would be a minimum to be 'safe'.
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AJKOER
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Could we use Sodium bicarbonate as a "salting-out" agent?
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unionised
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No
Though it might be fun trying.
On the subject of purity.
It would be instructive to do two titrations, on with the cream of tartar as purchased and one with the recrystallised stuff.
Also, since it's white (not pink or yellow) I suspect it has been recrystallised already.
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blogfast25
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Quote: Originally posted by unionised  |
No
Though it might be fun trying.
On the subject of purity.
It would be instructive to do two titrations, on with the cream of tartar as purchased and one with the recrystallised stuff.
Also, since it's white (not pink or yellow) I suspect it has been recrystallised already. |
AJ: in what context?
Unionised: and I suspect it hasn't, it's fit for purpose as obtained, I think. Could be completely wrong on that, of course.
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AJKOER
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Here is a description of salting-out in the context of proteins per Wiki.
"Salting out (also known as antisolvent crystallization, precipitation crystallization, or drowning out)[1] is a method of separating proteins based
on the principle that proteins are less soluble at high salt concentrations. The salt concentration needed for the protein to precipitate out of the
solution differs from protein to protein." Also:
"When the salt concentration is increased, some of the water molecules are attracted by the salt ions, which decreases the number of water molecules
available to interact with the charged part of the protein. As a result of the increased demand for solvent molecules, the protein-protein
interactions are stronger than the solvent-solute interactions; the protein molecules coagulate by forming hydrophobic interactions with each other.
This process is known as salting out."
More broadly, I have see a website where finding the appropriate salt and concentration to facilitate (or make more efficient) precipitation for
industry preparations was their only business.
Here is a real world example:
Link: http://onlinelibrary.wiley.com/doi/10.1002/pol.1962.12056163...
Here is another somewhat basic reference on precipitation:
http://www.monzir-pal.net/Bioseparation/Contents/Precipitati...
I am far from being an expert in this field.
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bahamuth
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From The Merck Index 14th
In my eyes Merck states that the product obtained from wine sediments is atleast 99.5% pure, and one might expect that food grade is just that or
better.
If you want it for standard it may well be that the contaminants doesn't interfere, and if it is a in-house standard it does not really matter either.
Just procure a large enough batch so you have the same standard forever....
Edit:
In regards to "salting out" I doubt it will work in the conventional way by adding a highly ionic salt as to "push" the more "hydrophobic" compound
out. Another way, which I also doubt will work is by "salting out" by the route of the common ion effect, just adding a potassium salt that has a much
higher solubility to force the potassium bitartarate to crystallize, though as I said I do not think that will work either. Slow evaporation in a
large diameter evaporating dish with a filter paper on top usually works wonders on any compound refusing to crystallize.
[Edited on 4-6-2012 by bahamuth]
Any sufficiently advanced technology is indistinguishable from magic.
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blogfast25
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Thanks for that Bahamuth.
Even 'internal' standards require good purity, as otherwise you're not sure what you're accurately weighing. Hence (e.g.) conductor copper is pure
enough to be used as a standard material but any 'high copper' alloy wouldn't ncessarily be.
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unionised
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The phrase "internal standard" has a meaning other than that which you are using. One characteristic of them is they don't need to be particularly
pure- just consistent.
You can't sensibly add sodium bicarbonate to a solution of potassium bitartrate. It will react. Acids and bases generally react on mixing.
Wine lees are generally red or brown. Since the commercial product is white it has been cleaned up. That purification is likely to be good enough for
home lab purposes.
I'd still like to see the results of the two titrations: before and after crystallisation.
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blogfast25
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| Quote: Originally posted by unionised | The phrase "internal standard" has a meaning other than that which you are using. One characteristic of them is they don't need to be particularly
pure- just consistent.
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An 'internal standard' is a bit of an oxymoron, if you ask me. That would only work if at least once you had standardised your internal standard
against an 'absolute', external standard.
Cleaned up, possibly. Would that mean you'd trust it implicitly as a standard? And what about additions to the product, post clean up? We don't know,
that do we?
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unionised
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It may be an oxymoron if we ask you, but it's perfectly well defined and commonly used in analytical chemistry.
http://en.wikipedia.org/wiki/Internal_standard
And, for the record, I have used red biro ink as an internal standard. I never bothered to find out what the dyestuff was, never mind how much of it
was present in the ink. However all this is beside the point.
We are talking about something that's not very soluble in water so there's no point adding an anti caking agent.
If they added anything I'd expect it to be labelled as such.
So, yes I'd use it as a standard- at least until I had any reason to suspect it wasn't clean.
I'd still like to see the outcome of the experiment titrating the "before" and "after" samples.
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