One of our housemates decided to pour battery electrolyte (which is 30-40% sulfuric acid) into a motorcycle battery on our back porch next to our laundry washer and dryer. He did so extremely sloppily, and we don't know exactly what he might have spilled the acid on.

Is the acid safe to touch after it dries, or is it still a safety hazard?

If it isn't safe when dry, what can we do to neutralize the acid? I know baking soda can neutralize acid, but I'm not really sure how to easily coat an entire porch in baking soda.

My boyfriend suffers from severe, debilitating OCD with a chemical contamination obsession, so this is an absolute nightmare for him. Thank you in advance for any help you may have!

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    $\begingroup$ Roughly speaking, sulfuric acid never dries (much like oil). It just penetrates deeper down, or possibly gets neutralized with something. Baking soda will do. $\endgroup$ Sep 27, 2017 at 5:44
  • $\begingroup$ Pour water over suspicious places, mop it up and wash out the cloth you used. Use gloves if you feel safer, but it's not really necessary. Or rather have your sloppy housemate do it. $\endgroup$
    – Karl
    Sep 27, 2017 at 8:27
  • 3
    $\begingroup$ Please do use gloves. $\endgroup$ Sep 27, 2017 at 9:34

2 Answers 2


Sulphuric acid won’t dry — meaning evaporate; what water does when one typically thinks of drying — at any noticeable rate. It will, however, given time penetrate deeper into the material if the material is porous or susceptible to degradation.

Depending on how much sulphuric acid was actually spilt, I suggest either mopping up the area with lots of water (if not much was spilt) or first semi-generously applying dry baking soda to the area. Once the baking soda has stopped generating bubbles immediately on application, you can use normal amounts of water for wiping up.

While I would love to suggest you get the sloppy housemate to do it, I think you might be disinclined because they again will do it sloppily.


Definitely hazardous, and also for reasons totally missed by the existing answer and all the comments. Sulfuric acid used in batteries is always contaminated with small but non-negligible amount of dissolved lead, as spongy lead metal and lead dioxide are used as electrodes in those batteries. Sulfuric acid is corrosive but non-toxic; neutralizing it with baking soda removes the property of being corrosive and thus makes it safe. Lead and its compounds, however, is toxic; there is no way to simply neutralize it in a simple way analogous to sprinkling baking soda. Be careful and do such things in remote place away from anyone's belongings to avoid contamination next time.

  • $\begingroup$ Based on the description, he was loading electrolyte into a battery not taking it out, so the spilled bit would never have been in the battery and exposed to lead. $\endgroup$
    – Andrew
    Apr 7, 2022 at 22:36

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