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Q & A: hot green water

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Most recent answer: 10/22/2007
Q:
our teacher did this experiment where he filled up 2 beaker with hot water and 2 beaker with cold water. then he put green food coloring in one of the hot water beakers and green food coloring in one of the cold water beakers. Then he put the green hot water beaker and flipped it upside down onto the cold water beaker, but nothing happended. Then he took the green cold water beaker and placed it upside down onto the hot water beaker and it turned green. And now i need help writing a lab about it. How do i do that, can u help me?
- Alex (age 14)
Sunrise Mountain High School, Peoria, AZ
A:
Alex- That's a nice experiment. The idea is this. Hot water is a little less dense than cold water. That means that the same weight of water uses up a little more space when it's hot than when it's cold. Most materials are like that- they take up a little more room when they're hotter, because the atoms and molecules jiggle around more and don't stick quite as tightlt to each other.
Denser things sink into less dense things. That's why steel will sink in water but styrofoam will float on top. So you can see that the hoter water should float on top of the cold water- which is just what you actually saw. When the cold water is on top, it sinks. Maybe it breaks up into little streams as it sinks, helping mix the green dye around.Anyway, a lot of the green dye will make it toward the bottom.

Mike W.

(published on 10/22/2007)

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