Science Questions

What chemical leaks from batteries?

Wed, 4th Sep 2013

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Rob Waite asked:

I have a question about alkaline batteries.


I recently unwrapped a set of battery powered lights, and I saw that we had left the batteries in all year. The batteries are a well known brand and they looked like they had leaked. There was a white powder around the contacts of the batteries and also on the contacts of the lights. What is this powder? Is it harmful to touch? What would be be best way to clean this powder away? Do we need a chemical help such as lemon juice or something? Will the powder be harmful to a new set of batteries that I insert? Keep up the great work!

Rob from Leeds.


Laura - Okay, so what's actually happening here is the electrolyte from the Batteriesbattery is leaking out. So, you think of batteries, itís sort of school level chemistry that youíve got a reaction going on between two metals and there's some sort of electrolyte in the middle thatís allowing charge to be transferred between this two sides of the battery. That usually in your normal alkali batteries is potassium hydroxide usually or something like that. Eventually though, your batteries do keep reacting even if youíve not connected them up. They react very slowly, but they do leech a little bit and there could be side reactions, and eventually, these things can just sort of pop open, at which point, your electrolyte comes out.

Chris - Is it nasty?

Laura - Potassium hydroxide is not very nice. Itís an alkaline. Itís quite caustic. However, it then reacts with carbon dioxide in the atmosphere. So actually, what you're seeing is those white crystals. Thatís actually potassium carbonate and that's actually potash. Thatís the main component in potash.

Chris - Thatís good for garden.

Laura - I wouldnít suggest necessarily knocking it off and putting it in your vegetable patch or anything. But probably, donít start licking at batteries or anything like that, but just dispose of them. If there's any on your contacts or things, you can start trying to wipe that off potentially with lemon juice or something.

Dominic - And I guess even if itís potash on the surface, underneath, you've still got the potassium hydroxide you donít really want to knock that surface off.

Laura - No, quite. So, that's why you want to use say, something like a weak acid to try and neutralise it as you're washing it off. The other thing of course is that these things can start creeping in to electronics and so, you can actually Ė if you've left your batteries in something for long enough, you can start really messing around with your circuits and degrading them.


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A mixture of ammonium chloride and manganese dioxide. Can easily be removed with white spirit vinegar which will neutralise it. Then rinse with water and dry thoroughly. If it has corroded through the springs you will need to replace them. SeanB, Sun, 4th Aug 2013

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