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Bleach Crystals

November 8, 2005

What’s left when bleach evaporates? A listener asked, and science reporter Bob Hirshon has the answer.


Where’s the bleach? I’m Bob Hirshon and this is Science Update.

Mary Beckman of Idaho Falls left some bleach out overnight. In the morning, the liquid had evaporated and all that was left were some crystals. She called to ask us:

What are they? And, if I put the water back in there, can I dissolve them? Can I get my bleach back?

Chemist Joe Merola from Virginia Tech says bleach is a solution of a salt called sodium hypochlorite. When the water evaporates, it breaks down into other salts, including sodium chloride.

JOE MEROLA (Virginia Tech):
So part of the crystals that she’s seeing is just plain old table salt—rock salt—sodium cloride.

So all Mary will get if she dissolves these crystals is salt water.

If you have a mystery substance, call us at 1-800-why-isit. If we use your question on the air, you’ll win a Science Update mug. I’m Bob Hirshon, for AAAS, the science society.