A02
Water boils at a lower temperature under reduced air pressure
This
is an experiment with very hot water: Please do it only if an adult is
present!
When water is boiling the
pressure of the water vapour equals the pressure of air. On a high mountain
the air pressure is lower than usual: The boiling point of water is less
than 100° C.
In the previous
experiment you pulled at the piston of a closed syringe with air to
reduce the pressure of this air.
Experiment:
* Left: Pour 20 ml
of boiling water into a 50-ml infusion bottle,
close it by a stopper pierced by a 100-m syringe. * Pull the piston vigorously:
Observation
right: The water cooled by transferring starts boiling again.
Explanation:
The air pressure above the hot water was strongly reduced.