Timeline for Does adding salt help water boil faster?
Current License: CC BY-SA 2.5
7 events
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| Oct 6, 2010 at 19:05 | comment | added | dmckee --- ex-moderator kitten | Be very careful with the experiment that @chris suggests. Vibrations in the vessel can also nucleate the boiling, and people have been hurt when apparently quiescent liquids suddenly boil over. Ideally you would wear a full face shield, rubber apron and long rubber gloves. (I superheated half a cup of half-and-half and set it off in the middle of the kitchen, once. Splashes went five feet in every direction and the spousal unit and I both got multiple small burns.) That said, this is a fantastic demo. | |
| Sep 3, 2010 at 15:03 | comment | added | Chris Cudmore | Try this in the microwave: Use a pyrex measuring cup, and nuke a cup of water for about 2 minutes. Watch during the last minute, so that you can time when it starts to boil. Lets assume 1:45. Now, do it again, but only nuke it for 1:40. Take it out, and add a spoonful of salt (Stand back!!!!) It should explode into a boil. What happened is you actually raised the temperature of the water above 100 deg. But the boiling action requires nucleation points (salt crystals!) In the pot on a stove, the bottom is above 100, but the top isn't. Adding salt causes the bottom to nucleate. | |
| Sep 3, 2010 at 3:43 | comment | added | daniel | bingo. adding salt to water that is almost at the boil makes it appear as though it has hit the boil; in reality it's just causing some oxygen to fall out of solution, and you'll note the temperature does not jump above 100C. | |
| Sep 3, 2010 at 3:20 | comment | added | Michael Natkin | @dmckee - I think that is right as well; it isn't that you've suddenly reached the boiling point, you just release a bunch of bubbles of oxygen that are trying to come out of solution. | |
| Sep 3, 2010 at 2:17 | comment | added | dmckee --- ex-moderator kitten | I would assume the instant boiling is an effect of adding nucleation sites, though this too is speculative. | |
| Sep 3, 2010 at 2:13 | comment | added | Jay | I suspect it is because as the salt is dissolved, that portion of water (salty) is now denser and remains at the bottom of the pan and gets more exposure to the heated bottom. Pure speculation though. | |
| Sep 3, 2010 at 1:54 | history | answered | user2215 | CC BY-SA 2.5 |