12AX7
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Sulfate curiosity
Ya know I was thinking, does bisulfate hydrolyze to sulfuric acid, or sulfate, in dilute solution?
I was thinking if you took a relatively insoluble (i.e., very dilute) bisulfate and recrystallize it a bunch of times. If things work out right, it
could be you first remove some small amount of sulfate product, leaving the solution richer with bisulfate and, eventually, sulfuric acid.
I'm guessing all bisulfates always crystallize stoichiometrically and don't much do something like this (I mean, besides something obviously prone to
hydrolysis like say, titanium(IV) or (if it exists proper) manganese(III) sulfate), since all sulfates (not counting insolubles) are reasonably
soluble; this would have to require a rather insoluble sulfate compared to the bisulfate.
...Just metaphysical, tired ramblings contemplating a crop of most likely ammonium bisulfate (I'm recrystallizing the junk left from "solar-still"
distilling nitric acid from fertilizery salts). Speaking of which, does ammonium bisulfate form tabular hexagonal crystals with alternately angled
sides? How about sodium or potassium bisulfate? Do ammonium and potassium form a solid solution here?
Tim
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guy
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It would be hard since the reaction with water and bisulfate stays to the left. Ka = 1.0 e-2
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12AX7
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So about that salt I'm crystallizing...
| Quote: | Originally posted by 12AX7
Speaking of which, does ammonium bisulfate form tabular hexagonal crystals with alternately angled sides? |
Hmm, on closer inspection, octahedra with truncated faces for some reason. A few crystals grew edge-wise showing the octahedron's faces better.
Relatively low solubility (10~20g/100ml). No sign of efflorescence, yet. Haven't checked melting point or solubility vs. temp.
FWIW, taste is bitter, sour, slightly astringent and slightly sweet too. Ammonium bisulfate I would think would be a lot more sour..?
Tim
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not_important
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Ammonium sulfate solubility is 43 g/100 cc at 20 C, the acid sulfate is higher, something like 100 g/100 cc. Taste should be saline-sour. The crystal
form might not match the standard from-water one, as the other dissolved salts could modify the crystal form. Recrystallization of a bit from water
would be interesting.
Potassium and magnesium sulfates are fairly bitter.
I don't know if there is a NH4KSO4, or mixed (NH4,K)HSO4. The ion sizes are similar, so a mixed salt wouldn't be surprising.
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12AX7
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That soluble? I recall it was like 10. Oh well. I may be SWAGging it badly, but I'm pretty sure it's relatively low solubility. I know it's not
sodium sulfate, that crystallizes different and loses moisture madly.
Hm, K2SO4 is listed as low solubility and no hydrate, but I'm pretty sure I'm seeing truncated octahedra and not a rhombic pyramid or something.
'Spose I'll have to check with base to see if it's an alum, too.
Tim
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unionised
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There's another way to look at this. Use a different solvent rather than trying to find a salt with the solubility you want.
Sodium bisulphate in alcohol gives a solution of acid and a ppt of sodium sulphate.
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not_important
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The crystal form is a puzzle. Going by what you said, I assume that you used a mixed fertiliser as the NO3 source, and so have several cations and
maybe extra anions. That's why I suggested trying to recrystallise a bit of them, many mixed salts are only stable in certain ranges of mother liquor
composition so recrystallising from plain water breaks up the mixed salt.
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