Boiling water fogging up?

Question

For an experiment, I had to boil water in a beaker on a bunsen burner. But the beaker fogged up on teh OUTSIDE of the beaker, not the inside...I would understand if it fogged up on the inside, because of the heat and cold, but why on the outside? And my teacher himself said it was on the outside, so it's not a mistake.

Answer 1

You can best answer this yourself, because you were there and saw it happen.  It can happen pretty easily though.  When you start the water and the beaker are cold.  Possibly very cold, depending on where you got the water.   When you put the burner under it there are two things that can happen.  1.  There's water on the bottom of the beaker from some splashing when you filled it, this evaporates when the flame hits it, and recondenses on the beaker.   This can happen on a hot plate, too.

2.  This can't happen on a hot plate, but happens all the time with a flame.  What's a flame?  Burning methane.  What are the products of combustion?  CO2 and water.  Hmm.  Water.   Yes, the flame produces water vapor, and that can condense on the cold beaker until the beaker warms enough from the flame to prevent it.