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Author: Subject: Zinc + acid = weird smell
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[*] posted on 14-11-2020 at 15:16
Zinc + acid = weird smell


I did some reduction of molybdate in HCl using zinc. And I smelled something weird - similar to smell of H2S. Recently I smelled it when I reduced chrome alum in HCl, but I thought that it was H2S because of sulfate reduction. But when I reduced molybdate, there wasn't any sulfate present. I use the same zinc for reductions quite a long time and I never smell this "H2S" during reaction with HCl. It should be 99% zinc. Is there any common impurity in zinc which cause this smell?

[Edited on 14-11-2020 by Bedlasky]

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[*] posted on 14-11-2020 at 15:32

It's not sulfates that cause this, but sulfides. They're commonly present as iron sulfide and zinc sulfide in the zinc powder. Maybe your molybdenum had such a contamination too, you don't need more than a couple hundred micrograms of it to cause such a smell, as our receptors are very sensible to hydrogen sulfide.
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[*] posted on 14-11-2020 at 21:51

Interestingly, this subject is discussed in this paper from 1861

Some interesting observations (not all related to that paper) - it appears that the main impurity in Zinc is Lead. Also, most Zinc is smelted from Zinc Sulfide. Last, but not least - the odor of H2S can be detected at 130 parts per billion.
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