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Station 3: Liquid
Nitrogen
1.
FREEZE FLOWERS, TENNIS
BALLS, RUBBER HOSE
What happens to flowers when immersed in
liquid nitrogen? Have students do this. What do you hear when the
flowers are immersed in the liquid nitrogen? What does it sound
like? Is the liquid nitrogen boiling?
What about a racquet ball? Show how
bouncy the racquet ball is and then put it in the liquid nitrogen.
Leave it in liquid nitrogen until the end of their time at this
station.
What about a Rubber hose? Show how stretchy it is. Put part of
the hose in liquid nitrogen. What are the changes in properties?
Have students stretch the frozen
hose.
Mention the space shuttle application.
What is liquid nitrogen? How cold
is it?
Temperature at which
water boils? 100
oC
Temperature at which water freezes? 0
oC
Temperature of
liquid nitrogen? -197
oC -->
very cold!
What is
the fog above the liquid nitrogen? Condensed water vapor.
Put
some liquid nitrogen in a tea kettle. Have the students look inside
the kettle and see the bubbling liquid. Is the liquid nitrogen
boiling? Close the lid and hear the kettle whistle. Don’t we need
heat to boil liquid nitrogen? Are we providing heat? Where does
the liquid nitrogen get the heat? It absorbs heat from the kettle
and from the air around the kettle. Even from water molecules in
the air. See the water condensing on the kettle? When we take heat
from gaseous water molecules, they condense to form droplets of
water
2.
SHRINK A BALLOON
SHAPED LIKE A DOG, AND MAKE IT COME BACK TO LIFE
Show them a balloon filled with
air: How does the balloon stay blown up? Atoms and molecules move,
collide with the walls of the balloon, cause pressure inside the
balloon.
What
happens when we put a balloon filled with air in the hot sun? Why?
Atoms and molecules speed up, increasing the number of collisions
with the walls, increasing pressure.
What
happens when we put a balloon filled with air in liquid nitrogen?
Why? Put balloon in liquid nitrogen. Have students do this also.
Shrinks => molecules slow down
How
does a microwave heat food?
Water molecules absorb radiation.
This causes the water molecules to rotate more. The rotating water
molecules collide with other molecules in food, this increases the
motion of molecules in food (it increases the energy, which makes
the food hot. Temperature is directly proportional to average
kinetic energy. When the temperature of a given substance is high,
the kinetic energy of the atoms and molecules of which the substance
is made is also high.
3.
WHO WANTS TO CONDENSE THEIR BREATH? MAKE IT INTO A LIQUID AND
SOLID
Blow up
a balloon with air (5-6 inches in diameter, not bigger!) and put it
on a test tube.
What is in the air that you blew into the balloon?
N2, O2, CO2, H2O
and whatever else is in the air you breathe out.
What is in between the gas molecules in air?
Nothing - it is just empty space.
How
much space is between the molecules in a gas? Do an experiment to
show this.
Immerse the test tube with the balloon on top in liquid nitrogen.
What
will happen?
As
the gas cools, the molecules slow down. The volume of the balloon
decreases and eventually completely deflates.
This
takes a little while so do the next activity and come back to this
later.
Remove the test tube from the liquid nitrogen.
What
is inside the test tube? liquid and solid
What
liquids? N2(l), O2 (l),
What
solids? CO2 (s), H2O (s)
How
much space is between the liquid and solid molecules?
Not much - they are in direct contact with each other.
How
does the volume of liquid and solid in the test tube compare with
the volume of gas in the balloon?
The volume of liquid/solid inside the test tube is much smaller than
the volume of gas in the balloon. Thus, there is lots of space
between the molecules in the gas.
4.
CAN WE BLOW UP A BALLOON USING LIQUID NITROGEN?
At room
temperature and pressure nitrogen is a gas. Put ~ 200-300 mL of
liquid nitrogen in a plastic water bottle using a funnel. Put a
balloon over the top and secure balloon. What is happening?
In one
bottle, put in ~200-300 mL water. Put a balloon on top. What is
happening?
In
another bottle put some chunks of dry ice. Put a balloon on top.
What is happening?
water
---> stays in the liquid phase ---> balloon does not inflate
liquid nitrogen ---> nitrogen gas ---> blows up balloon fast
dry ice (solid) ---> carbon
dioxide gas ---> blows up
balloon slowly
Ask students
How can we speed this up?
Liquid
nitrogen absorbs heat from the container and the surrounding air
molecules outside the container to form the nitrogen gas. Energy is
required to pull the N2 molecules apart. It blows up the
balloon, so energy in the form of heat is converted to energy in the
form of work.
heat
---> work
Go back and finish the third activity – what happened to your
breath inside the balloon?
5.
Break the racquet ball.
Use tongs to take the very cold racquet ball out of the
liquid nitrogen. Hold the racquet ball at about your eye level and
drop it. It shatters. Students can each take a piece of the ball
to keep. CAUTION: the pieces of the ball are very cold.
SAFETY:
Drop the frozen racquet ball -- throwing it with too much force
can cause pieces to fly up and hurt someone. | 