My physics teacher put water in a flask on a burner and when it reached boiling he took it off the burner left it on the counter for a couple seconds then put a rubber stopper on top of it.
Then he flip it upside down onto a platform that held it in place.
Then he placed ice cubes on the top of the flask and it started boiling.
2007-01-13 13:22:58 · 6 answers · asked by Karim S 2 in Science & Mathematics ➔ Physics
This is a neat trick, and it's explainable!
The temperature at which water (or any substance) boild depends on the pressure under which the water exists. In an open flask, the water would be at normal pressure, so it would boil at a temperature we'd expect it to. As pressure decreases, the boiling temperature goes down.
Once a stopper was placed in the flask, it became a closed environment, but still under standard pressure. Since the water in the flask was hot, water vapor would have displaced much of the air in the flask (before a stopper was put in, really). So when we stopper the flask we have a closed environment of hot water and water vapor.
Placing an ice cube on the surface of the flask causes a temperature change. Heat moves out of the flask and into the ice cube. The water vapor will be cooled quickly, and it will condense back into liquid water. Since the flask is closed, no air can rush in to take the place of the water vapor, so now we have water in a vacuum, more or less. A vacuum would have very little pressure, or no pressure, and so the boiling point of water drops significantly. The hot water, at this pressure, is more than hot enough to boil, and so it does.
Presto!
Dry Ice will not mimic the appearance of boiling water if it is not placed inside the water. In this experiment, it is not. However, dry ice could be used for this trick in place of normal ice, and it should work similarly. Dry ice is, after all, very cold. But this trick works just fine with normal frozen water ice.
2007-01-13 13:43:13 · answer #1 · answered by The Ry-Guy 5 · 2⤊ 0⤋
An old trick. . .
When he boils the water most of the air in the flask is replace with steam and water vapor. When he plugs the flask the air is kept out and the water vapor is trapped.
Now, when he lowers the temperture of the vapor (notice that the put the ice on top), the vapor condenses to water and your pressure drop. The water at the bottom is still near boiling and as the pressure drops so the the boiling point.
The water boils. . .
2007-01-13 21:39:04 · answer #2 · answered by Walking Man 6 · 2⤊ 0⤋
If the pressure is low enough water can boil at pretty much any tempeture, including below freezing. It usually sublimes at low tempeture and pressures, if fact Ice can directly sublime without melting. Water is one of the few substances that can eist in all thrre phases at the same tempeture
In this particular demonstration, the air above the boiling liquid was cooled causing the pressure to drop, and the still hot liquid to reboil
2007-01-13 21:30:19 · answer #3 · answered by walter_b_marvin 5 · 2⤊ 0⤋
atmospheric pressure being very little inside the flask (after it cools) the ambient temprature of the room is sufficent to boil the water. In space, the vacuum doesn't kill people, their blood boils.
2007-01-13 21:30:25 · answer #4 · answered by emkay4597 4 · 2⤊ 0⤋
You are probally mistakin they are used to cool down boiling water. I hope i helped. I know thats what they are used for i never knew people tried to use them to boil water unless u are talking about dry icel. :)
2007-01-13 21:29:44 · answer #5 · answered by Anonymous · 0⤊ 2⤋
You sure it wasn't dry ice instead of ice cubes? Dry ice will do that.
2007-01-13 23:12:46 · answer #6 · answered by darksam3 1 · 0⤊ 3⤋