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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Monoamine on April 24, 2021, 06:04:17 PM

Title: Any help? My metal thermometer probe dissolved!
Post by: Monoamine on April 24, 2021, 06:04:17 PM
I was distilling some aqueous hydrobromic acid (HBr) and the metal thermometer probe that I had in it dissolved and turned the whole solution dark brown, almost black...  :o Is this dangerous? Can I fix it somehow?
Title: Re: Any help? My metal thermometer probe dissolved!
Post by: Monoamine on April 24, 2021, 07:45:12 PM
Ok, could this be it?: The iron somehow catalyzed the formation of Br2? When I took a bit of the dark red/brown/black liquid and added enough sodium thiosulfate (Na2S2O3), it became sort of milky turquoise green, and all the black/red disappeared.
Title: Re: Any help? My metal thermometer probe dissolved!
Post by: Monoamine on April 24, 2021, 09:13:07 PM
Nice... now my whole clothes smell like rotten eggs. Probably nothing to do with hydrogen sulfide... This is why I love chemistry  :D
Title: Re: Any help? My metal thermometer probe dissolved!
Post by: Monoamine on April 24, 2021, 09:42:33 PM
Okidoki now there's definitely some sulfur depositing in the condenser. Reminds me a bit of yellowstone national park.  ;)
Title: Re: Any help? My metal thermometer probe dissolved!
Post by: Orcio_Dojek on April 25, 2021, 03:43:37 AM
Iron did not catalyze formation of Br2, as it is reducer not oxidant: Fe + 2 HBr --> FeBr2 + H2

Dark brown colour could come from FeBr3 if HBr was contaminated with Br2 or FeBr2 oxidized.

Na2S2O3 reacted with remainder HBr and also reduced FeBr3 back to FeBr2:

Na2S2O3 + 2 HBr ---> 2 NaBr + S + SO2 + H2O

2 FeBr3 + 2 Na2S2O3 ---> 2 FeBr2 + Na2S4O6 + 2 NaBr

Solution was milky green because of presence of Fe2+ (green) and coloidal S (white).

Could it be dangerous? Yes - if thermometer was filled with mercury, then the mercury is still there as it will not react with HBr as iron.
Title: Re: Any help? My metal thermometer probe dissolved!
Post by: Corribus on April 26, 2021, 09:15:40 AM
OP identified the thermometer as a metal probe thermometer - which seems to be consistent with what looks to be a probe thermometer in the background of the picture. Unlikely it has anything to do with mercury.
Title: Re: Any help? My metal thermometer probe dissolved!
Post by: Monoamine on August 24, 2021, 05:21:09 PM
Thanks for the reply. Yes it was just a metal probe, not filled with any mercury. Also, I'm still alive  :)