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Any chemists/biologists to explain to me this weird thing that happened?

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So, awhile back I found some old papers that had gotten wet and then suffered mildew damage. Since they were sentimental, I packed them in a plastic bin (the lid was on but it was not airtight) and put a liberal amount of baking soda in with them. Then the bin sat and I forgot about it for gosh, nearly a year!


Fast forward to today. The bin was not opened till now, and has been stored at room temperature, not exposed to water (although I live in a pretty humid area and its been a muggy summer). When opening the bin, a lot of mildew smell is gone, the papers are bone dry, and the baking soda of course has gotten everywhere. This is the weird part, though - on the outside and top of the bin, not the inside, are droplets that appear like beaded condensation, of a clear liquid that feels mildly greasy. It has dripped onto some of my other things, though it doesn't appear to have caused any damage beyond spreading a faint odor. Weirdly, it has a mild vinegar-y smell, sort of tangy but not sharp - it doesn't smell like the mildew at all.


What odd chemical reaction is causing this? I have a zillion of these bins, and this is the only one doing this, so I assume its some sort of reaction caused by the baking soda. Is this water, or chemicals from the plastic, or something else entirely? Should I be worried about its toxicity? From what little I remember, baking soda is a base, so is this acid from somewhere fleeing the baking soda on the inside of the bin? I don't have enough knowledge, but I'm fascinated.

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I'm no chemist but I can say is that baking soda is known to absorb obtrusive odours, including mildew ones, which could explain the lack of odour (source.) But i'm not sure if it would have killed the mildew.


As for the 'vinegary' liquid i'm not sure but it does sound a bit strange. Could you make the assumption that the baking soda reacted with some kind of acid?


Might be a good idea to ask reddit or stackexchange for help if your question doesn't get answered here. :)

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So yes as stated above.  Baking soda is a base.  If it comes into contact with an acid, if there's enough baking soda, it will neutralize the acid.  However the product of an acid-base neutralization reaction is simply a salt and water.  So I think it is safe to say, the substance on the lid is not water, since you are describing it as something quite different.

Additionally, an acid would not "flee" from the base! So I wouldn't say it's straight acid on the lid either.  Acids and bases readily react to become more stable (neutralizaton) and they aren't going to repel each other or anything of the sort.
I am not too sure about the biology of mildew.  I would say whatever liquid/substance etc that was there from the mildew got broken down by the baking soda, simply evaporated and had nowhere to go.  I would be cautious at least of the liquid but I can tell you it's probably not an acid that will hurt you.  Especially if you added a lot of baking soda.

I'm no expert but that's what I can tell you for certain with my basic college chem knowledge.

I second taking this question to Reddit.  They have great chem/bio forums. (-:

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