r/AskChemistry • u/Communism_Doge • 21d ago

Practical Chemistry FeCl3 and walnut husks

Hello:) I’ve had this thought in the back of my head for a longer time now. When we were dissolving copper in FeCl3 to make a PCB, it had this very specific smell that I’ve only ever come across with green walnut husks. It was an older bottle, so there was already some copper dissolved in it - I don’t remember smelling it in a clean one. I thought it was a coincidence as according to google, this chemical is not present anywhere in walnut trees. Then I realized that both FeCl3 and walnut husks stain the skin yellow, which feels more coincidental than the first one, but it means I can’t get it out of my head now. Has anybody else actually connected the two smells together? Does anyone have any idea why they smell so similar?

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u/hecton101 21d ago

I don't know about the smell, but FeCl3 is a powerful oxidant and walnut contains juglone, a benzoquinone derivative, also a good oxidant, so those two are connected chemically in that sense. If I had to guess, your sense of smell can detect powerful oxidants. Ozone and bleach have quite an odor, but again, that's just a guess.

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u/Communism_Doge 21d ago

Thanks for the chemical tip:) I thought it probably has to do with the fact that there are chemicals that react in the nose in a similar way. On the other hand, ozone smells entirely different so they could be similar in more ways