Varmint
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Stump remover (KNO3) purification...
I haven't searched the entire forum, but I like what I see, and am afraid I'm so far below the net qualification of the participants, its not funny.
Still, I hope to learn a lot, and eventually contribute in a meaningful manner.
My goal is to get back into chemistry. I was very fond of it in HS, spent my working career in electronics, and now I'd like to get back into what I
consider my first "love".
My interest tends towards "energetics", but I feel I've got a lot of re-learning before I set off in that direction.
Anyway, I noticed something while looking for tips on KNO3 "stump remover" purification. I know people are generally in a hurry, especially when they
expect things to take multiple passes, but this is ridiculous...
They start out with say 100ml of water (should be DI or distilled but rarely is stated as such), heat it up, saturating the solution with enough stump
remover that crystalization occurs with as little as a degree or two drop.
Why so fast? The beaker is positively loaded with suspended nucleation sites, the SIO2 anti-caking agent + other garbage, coupled with over-zealous
saturation.
As it turns out, purification using this method is fruitless, at the root of each and every crystal is that which you seek to remove.
So, I did it differently. I saturated to about 1/3rd of what most folks "brag" about getting dissolved, filtered it 3 times with quality lint-free
filters, and used a brand new erlenmeyer of high quality.
Then I boiled it down to 1/3 volume, hung a string in it like I was making rock candy, let it cool, and was rewarded with an incredibly beautiful
"chandelier" hanging from the string.
My mistake was the erlenmeyer, it eventually grew to where I couldn't get it out without crushing a good bit of it. It should be noted the evironment
(soulution/flask) were so clean, that prior to my breaking it trying to get it out, not one crystal formed anywhere else.
So it was a simple process to further reduce the remainder by boiling, and "string" it again.
Yield? 91.7% dry weight. If I was smart I would have weighed the filters before/after, but I'll try and do that next go-round.
So, while I doubt this is really any news to anyone here, I felt like posting just to let you know I'm lurking if nothing else.
DAS
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annaandherdad
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Hi, Varmint, like you I'm an older guy who just got back into chemistry after a long career in something else. I used to enjoy it very much in junior
high. I've had a lot of fun doing simple experiments. And this web site has an incredible amount of information in it, and some of the members are
extraordinary scientists. For example, it's always a pleasure to read what woelen has to say, or to look at his web sites.
What you say about purifying KNO3 makes a lot of sense. You need to filter it before crystallizing it, and if it's supersaturated you won't be able
to filter it. Similar problem with purifying copper sulfate by crystallization (I mean, cheap copper sulfate like you get in the gardening store).
Any other SF Bay chemists?
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amazingchemistry
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I'd say you're doing good by filtering it before recrystallizing it. If you know there is SIO2 in there, my guess would be that it won't dissolve,
while the KNO3 will, so it should be easy to remove. However, I thought that for best results, solvents for recrystallization had to be picked so that
your product dissolves when the solvent is hot, but not when it's cold. Do you know what other possible impurities are there? I'm thinking a
solvent-pair recrystallization would work too, depending on the impurities present.
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elementcollector1
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KNO3, as I've heard it, is one of the best examples of recrystallization in water: very soluble when hot, much less soluble when cold.
Recrystallization once or twice should be absolutely fine.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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Varmint
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Amazing:
I agree, there is no guarantee I'm "clean" yet, and if I was seeking reagent grade I'd realize the folly and not have even started.
Rather my goal was to get rid of the obvious, rather than making the mistake of simply recapturing the SIO2 as many others had done.
As I started to indicate, proper science would have been to weight the filtered solids, continue the concentration/stringing (or resort to spontaneous
self-seeding generating the last KNO3 crystals), then boiling off the water to try and decipher the remnant composition.
Having no idea what the remaining contaminants would be (prior), I couldn't even guess at an appropriate solvent would have been, so my thought was to
determine it after the fact as best I could in order to provide an enhanced process next go-round.
Thanks for the feedback (and to Anna's dad as well), I appreciate hearing from you. The funny part about chemistry is, even after all we know, all
the work that has gone on before, enhanced processes are still being developed with regularity, indicating we don't knoe everything yet, ergo, this
branch of science is no where near closed.
DAS
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amazingchemistry
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My first thought was that simple recrystallization wouldn't work because being an ionic solid, KNO3 would still dissolve in cold water. I'm also
thinking that if you have KNO3 in stump remover form you could also have various other nitrates and potassium and sodium salts that could interfere
with the process.
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blogfast25
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Quote: Originally posted by amazingchemistry  | | My first thought was that simple recrystallization wouldn't work because being an ionic solid, KNO3 would still dissolve in cold water. I'm also
thinking that if you have KNO3 in stump remover form you could also have various other nitrates and potassium and sodium salts that could interfere
with the process. |
Wiki's solubility table is a reasonable resource for water solubilities of common salts:
http://en.wikipedia.org/wiki/Solubility_table#P
For KNO3: 141 g / 100 g (of water) @ 100 C; 22.4 g / 100 g (of water) @ 0 C. As far as solubility differentials go this is as good as it gets for
thermal re-crystallisations. The nitrate left in the mother liquor after cooling isn't lost of course and can still be recovered as crude KNO3.
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Bot0nist
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This is a good starting project, and recrystalization skills are indespensable in chemisrty work ups. If you are planning to use the
KNO<sub>3</sub> for a nitric acid synth (I only assume because you said you like entergetics) then the stump remover is likely pure enough
for that outta the contianer. Further purification never hurts though.
I simply dissolve the stump remover in an excess of water, filter the solution to remove unsolubles, boil down till saturation, then I place the
beaker in a still place where it will be undisturbed for 12 to 24 hours. This grows nice crystalls. Putting the beaker in a pre heated thermos to slow
the cooling down even more makes for some really impressive crystal growth.
Good luck friend, and welcome to SciMad.
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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