alexrandomkat
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sodium nitrate from suspicious CAN cold packs trouble
So I got a bunch of Walgreens cold packs which say they contain calcium ammonium nitrate (CAN) and water on the ingredients.
I saw on Wikipedia CAN can indicate either a mix of CaCO3 + NH4NO3, or a double salt hydrate: 5Ca(NO3)2 NH4NO3 10H2O
Since I could dissolve it in water easily to produce a clear solution, I figured I had the double salt on hand. My plan was to add NaOH to precipitate
out CaOH (could use for other things) and produce ammonia, then after getting the CaOH evaporate the filtrate to get the NaNO3.
I recrystallized the CAN (bc I like to torture myself, never doing that in a flask again, broke a stirring rod...). Vacuum filtered it out of the
fridge.
Trouble started occurring past this step though. So I added the CAN and dry NaOH granules in a 1L roundbottom, washed the granules out of the joint (I
really should get a funnel), and quickly popped it on my ammonia capture setup. Added water to the mix until it became a stirrable slurry, put it in a
100C water bath, and waited.
The rxn eventually solidified; I guessed this was all my sodium nitrate falling out. Water was added until this was mostly dissolved, and I waited
some more.
First mistake was that when ammonia gas flow seemed to stop after a couple hours, I put in a bit of extra NaOH through the top to make sure it was
done (I had realized I undercut the amount of NaOH because I saw the CAN was very wet, and I estimated the water as pure water rather than saturated
with CAN). This caused an ammonia + NaOH explosion... None got on me, but it was a gross stinky mess (luckily contained on cardboard I just threw
out). Could have seen that coming if I slowly added the stuff instead of chucking it in (I REALLY should get a funnel).
So I dropped NaOH in smaller quantities after that. Let it run for another few hours because the ammonia just kept on coming...
Eventually it was like 2AM, so I took off the flask and vacuum filtered the contents. Only got a tiny amount of precipitate, and it dissolved really
easily in hot water??? I was expecting CaOH -- clearly this isn't it. So I put everything back in the roundbottom and stoppered it overnight.
Next day, I was like screw it and added MORE NaOH (like... +1/2 the original amount? idk I didn't weigh it...) and water until everything dissolved,
hooked it up to my water aspirator, boiled it with hot plate on max. Went for two hours, turned one cooler of cold water into stinky ammonia water.
Went for a few more hours, this time the cooler water had little smell. Should have watched it closer because the sodium nitrate eventually crashed
out and bumped a ton, caused no issues but could've been bad.
So my thoughts are that the cold packs actually just had plain ammonium nitrate in them, not CAN as listed on the label.
So right now my stuff is sitting in a beaker, total volume ~580 mL, ~1/2 of it is a fine silt which I assume is sodium nitrate. It has a pH of ~10
according to a pH strip, rough calculation says I have about ~0.001 g NaOH. It still has a slight ammonia smell (was strong when it was warm). So what
I'm getting is that I still have not added enough NaOH to complete the reaction...
So questions:
- Does my guess about the cold packs content seem right? I didn't throw out the calcium nitrate in the recrystallization filtrate, did I?
- Nothing in solution would mess with the pH strip reading, right?
- How can I tell how much ammonium nitrate is left in solution (and if I need to redissolve some of the precipitate, since it is more soluble than
sodium nitrate)?
I want pure sodium nitrate as I will be making nitric acid from it.
My plan is to vacuum filter the precipitate, wash with cold water, add bicarb to the filtrate to stop wasting my NaOH and throw it back under vacuum,
boil until I get more precipitate, repeat.
[Edited on 6-2-2023 by alexrandomkat]
[Edited on 6-2-2023 by alexrandomkat]
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ave369
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Ca(OH)2 is not insoluble, it is somewhat soluble (~2 gram per liter) in water.
Smells like ammonia....
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MadHatter
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Calcium Hydroxide
Ca(OH)2 is relatively insoluble. 0.189 grams per liter of ice water. Solubility
decreases as temperature increases.
From opening of NCIS New Orleans - It goes a BOOM ! BOOM ! BOOM ! MUHAHAHAHAHAHAHA !
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Rainwater
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$$CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2$$
$$2NH_4NO_3 + H_2SO_4 \rightarrow (NH_4)_2SO4 + 2HNO_3$$
You should be able to extract the nitrates with hot water, if some of the calcium carbonate remain, it should not be a problem.
using an excess of sulfuric acid will trap any water produced in the reaction.
Edit
Word of warning, any Chloride salt in the reagents, will contaminate your acid with hcl. So if you're going to be refining metals with this, please be
aware. Silver nitrate can be used to test for and remove the hcl
[Edited on 23-2-2023 by Rainwater]
"You can't do that" - challenge accepted
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alexrandomkat
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I am pretty sure there is no (or maybe just tiny amounts of) calcium present in the cold packs -- it seems to be plain ammonium nitrate prills
(contrary to the ingredients listing on the box). Also Ca(OH)2 has retrograde solubility, which is why I mentioned the hot water wash. This is on the
scale of ~350g starting material in <1L volume of hot water, so I definitely would have noticed if there was any significant proportion of calcium
in it.
I think my main mistake here was adding in more NaOH before realizing that I was way farther from completion than I thought I was, to the point where
I had no idea where I was at in the reaction once I figured out the probable cause.
Ended up neutralizing with only NaOH over bicarb since I didn't want to risk the further hassle of going overboard with the bicarb (lower solubility)
and having to separate that from my nitrates. Heated flask, added NaOH, cooled to room temp and watched for the formation of ammonium nitrate needles
(repeated twice because I didn't add enough NaOH). Once no crystals formed at room temp, this was put in a fridge and I got some nice large
rectangular crystals. There was no ammonia smell upon dissolving these in hot water, so pretty sure this is the sodium nitrate.
The only problem left is that I vacuum filtered the crystals, put them in a vacuum desiccator, then forgot about them on a desk. The vacuum eventually
went away (expected) but then it rained and somehow water fucking sucked into the desiccator? Even though it was stored under a roofed patio?
So now my salt is melted and silica all wet lol.
Once I get everything dry again, are ziploc bags good enough to keep the sodium nitrate dry? Not expecting to be able to use it dry right out of the
bag, but hopefully want to keep the sodium nitrate from turning itself to slush on storage.
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Rainwater
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Mansion jars work really well. Bag it and throw it into one of them with a good lid.
If your going to store it for a long time, you can vacuum seal the jar for extra protection.
"You can't do that" - challenge accepted
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Amos
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I haven't analyzed every detail, but keep in mind that Ca(OH)2 will react just as happily with ammonium ions to produce free ammonia gas as any alkali
hydroxide will. It's a very strong base. In my experience the best way to produce ammonia gas from an ammonium salt and base is to add all of your
base at the very beginning, and limit the reaction via temperature and moisture. I will start the stream of ammonia with an ice cube, and stand by
patiently during the beginning until the flow of ammonia gas slows enough that suckback becomes an issue. That's when I add more water and then begin
heating. You shouldn't treat the liberation of ammonia like it's some easy reaction where what you put in is what you get out; it's very highly
soluble in water and participates in lots of complicated equilibrium reactions when metal cations are present.
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Amos
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When I produce ammonia and a nitrate salt from ammonium nitrate, I intentionally always add excess sodium/potassium hydroxide. It's an arduous process
removing all of the ammonia and excess base will help somewhat. Even though there is clear excess base remaining, this is no problem if you add nitric
acid to neutralize it; then you can crystallize out a pure nitrate salt. You can also make very clean nitric acid from the residue of the initial
ammonia-generating reaction(no matter how much excess base there is) if you acidify the whole thing with sulfuric acid and distill.
At each step in the process, instead of trying to be certain of the exact amount of each chemical compound present, ask yourself instead what reagent
should be present in excess to afford the smoothest reaction.
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alexrandomkat
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| Quote: |
In my experience the best way to produce ammonia gas from an ammonium salt and base is to add all of your base at the very beginning, and limit the
reaction via temperature and moisture. |
This was the original plan, I was just thrown off by the fact that I had pure NH4NO3 instead of the claimed calcium ammonium nitrate
(5Ca(NO3)2•NH4NO3•10H2O) as per the box label.
Original setup (heated ammonia generating flask + 3-way adapter with gas inlet on top for water addition / suckback control + condenser to give me
length + vacuum adapter into receiver with tube into water) was maybe overkill with the glass but worked nicely, and I feel like it would have gone
well had I had the proper amount of base in from the start.
| Quote: |
You shouldn't treat the liberation of ammonia like it's some easy reaction where what you put in is what you get out; it's very highly soluble in
water and participates in lots of complicated equilibrium reactions when metal cations are present. |
Yeah, I realized that when I was boiling my solution at pH 11-12 thinking, "when is it gonna be done..." Nope, needed more hydroxide. Plenty of
ammonium nitrate was still present. Also, I did this just because I thought it was almost done and needed a little push, but never boiling ammonia out
in the open again. Never. That was nasty.
| Quote: |
ask yourself instead what reagent should be present in excess to afford the smoothest reaction |
Glad I stuck with excess NaOH over bicarb since its solubility gives me a lot of room to go over the edge without having it come out with my final
nitrate salt upon crystallization. And I did not want to fix yet another thing.
| Quote: |
this is no problem if you add nitric acid to neutralize it; then you can crystallize out a pure nitrate salt |
Unfortunately I do not have any nitric acid yet, but I'll keep this in mind.
I think next time (if there is one) I'll try starting out with bicarb as the base since it's cheaper, cranking the heat, and once ammonia generation
stalls, finishing the reaction with a careful addition of excess NaOH and further heating all in one clean run, then neutralization with nitric acid
and crystallization.
Also since my starting ammonium nitrate is wet, maybe using bicarb won't make me rush to snap on the ammonia flask like using NaOH granules did?
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