DFliyerz
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Accidental HF
A little while ago when I was working with trying to extract neodymium salts from a "magnet soup," I tried adding the soup to a saturated solution of
sodium fluoride. That method failed, but I later noticed that almost anywhere that the precipitate was in contact with the bottom of the beakers, it
was etched! I'm not sure what exactly it was, since I don't think HF can be formed by HCl + NaF... right?
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DraconicAcid
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Yes, it can be. Hydrofluoric acid is a weak acid in aqueous solution; if the pH of a solution containing fluoride ions is less than 4, the majority
of it will be in the form of HF.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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blogfast25
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HF is a weak acid, in Bronsted-Lowry terms. Residual acid in your magnet soup displaces the fluoride:
F<sup>-</sup>(aq) + H<sub>3</sub>O<sup>+</sup>(aq) === > HF(aq) + H<sub>2</sub>O(aq)
But even a neutral (well, alkaline actually) saturated solution of NaF will etch glass, given time.
When using water soluble fluorides, always use PP beakers.
It's also a bad idea to use 'magnet soup' to prepare NdF3. Separate the Fe and Nd first. In a highly acidic magnet soup, the solubility product of
NdF3 may not be reached, depending on actual pH.
Edit: you do mention a precipitate, so that must have been NdF3, as both Fe(II) and Fe(III) fluorides are water soluble.
What you did was potentially quite dangerous! Don't mess with NaF and strong acids unless you really know what you're doing!
If you are going to add Nd magnet soup to saturated NaF, at least part-neutralise the soup with ammonia first, so pH is about 5.
[Edited on 13-5-2015 by blogfast25]
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MrHomeScientist
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Quote: Originally posted by blogfast25  | | What you did was potentially quite dangerous! Don't mess with NaF and strong acids unless you really know what you're doing!
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Seconded. Seriously, follow the procedure we went through in the main magnet thread. Don't discount others' experiences, especially where soluble
fluorides are concerned. If you have a new approach you want to try, verify it with us first before you do anything in the lab. We aren't being
nannies; we really want to help, and keep you safe.
Also all of these magnet-related posts you have should be posted in the main magnet thread instead of starting multiple new ones.
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