States of Matter—Liquid Nitrogen Demos
Questions about changes in the states of matter are demonstrated using liquid
nitrogen. These demonstrations were led by GK-12 Fellows with access to liquid
nitrogen and with adequate experience to use it safely in the classroom. These
demonstrations can be used in conjunction with the States of Matter—Dry Ice and Water
activity (also found on the GK-12 web page) which contains additional related
background information.
Grade Level Used
The demonstration can be used for all ages.
Objectives
-Demonstrate/observe how a very cold
liquid acts and its affect on the physical
properties of common objects
Duration (Prep/Activity):
Demonstration: 15 min/30 min
Materials
-Dewar of liquid nitrogen, gloves, tongs
-Small open dewar
-Tygon tubing and hammer
-Fresh cut flowers
-Small balloons
New Mexico Science Standards
Strand II: Content of Science
Standard I: Physical Science
K-4 Benchmark I: Recognize that matter has different forms and properties.
5-8 Benchmark I: Know the forms and properties of matter and how matter interacts.
9-12 Benchmark I: Understand the properties, underlying structure, and reactions of
matter.
Preparations
1. Cut a foot-long section of tygon tubing.
2. Blow up a couple of balloons.
3. Pour some liquid nitrogen into a small open dewar.
Focus Question: How do materials change from one state of matter to another?
Demonstration
As you are preparing the experiment, talk to the students about the safe handling of very
cold liquids and solids. They will see you use gloves, tongs, etc. so that you do not come
into direct contact with the liquid nitrogen. Be sure students are not in a position to
touch the liquid nitrogen or to be splashed by it.
1. Let the students observe pouring LN2 from large dewar to small, open dewar and
ask what it looks like (clear liquid/water).
2. Ask students to guess why the liquid is “smoking.” Explain that the “smoke”
coming off of it is water vapor from the air condensing—you are making clouds.
Gaseous nitrogen is invisible.
3. Flower (taking something from a liquid/solid state to an all solid state): Pass
around a couple of flowers so that students can confirm they are real, soft and
pliable. Holding a flower by the cut end of the stem, dip the flower into the LN2
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and wait until it quits bubbling. Pull the flower out and shatter it on a table so all
can see. Talk about what the LN2 did to the flower and how.
4. Balloon (taking something from a gaseous state to a liquid state and back again):
Ask the students what they think will happen if an inflated balloon is put into the
LN2. Using the tongs put the balloon into the LN2. Hold it there until it
noticeably shrinks. Remove it from the LN2 and hold it up so that everyone can
see it “re-inflate”. Discuss why it shrunk and re-inflated. (What’s inside the
balloon? What happened to it in the LN2? What happened when it came out of
the LN2? Condensation and evaporation of the air inside.)
5. Fountain (evaporating the LN2): Put one end of the Tygon tubing into the LN2
while holding the other end up and pointing it away from you. If this is done
well, it will result in a LN2 fountain. LN2 is evaporating as it goes up the tube
from the cold end to the warmer end. The vapor comes out quickly, entrapping
some liquid droplets causing a siphon so that a visible fountain results. If it stops,
take the tube out and let it come to room temperature, then try again.
6. Making predictions: Have a variety of objects or have students volunteer objects
to dip into the liquid nitrogen. Ask students to predict, and justify their
predictions based on earlier demonstrations, what will happen to each object. If
you use small cookies or crackers, the students can eat the frozen snack and blow
out “smoke.”
Follow-up Questions
1. What are the three states of matter?
2. How does a material change from one state to another?
3. Compare how objects respond to being placed in liquid nitrogen to being placed
in liquid water. What accounts for the differences?
4. Explain the changes in state in the liquid nitrogen fountain. Does water behave in
the same way?
Teacher Background Information
There are three states of matter: gas, liquid, and solid. At room temperature we
are surrounded by air (in the gaseous state), which is made up of ~79% nitrogen and 21%
oxygen. Water, Gatorade, coffee, and sanitizer are all liquids at room temperature. The
walls, carpet, desks, pencils, erasers, crayons are all solids at room temperature. Room
temperature (RT) is around 65-75ºF or 15-20ºC, depending on the air conditioning or
heating, the number of warm bodies in the room, the time of year or time of day.
There is another state of matter called a plasma, but is often left out of discussion
because under typical conditions is unstable and usually not observed. That said, you see
a plasma when you see a lit “neon” sign. The tube is filled with a noble gas (neon, argon,
helium, krypton, xenon) and a voltage is applied. The resulting charged gas gives off a
colorful glow depending on the element used and is a plasma.
With increasing temperature, a solid starts to become a liquid. The temperature at
which this begins to happen is called the melting point temperature. Similarly, as the
temperature decreases and a liquid starts to become a solid, the temperature is called the
freezing point. For most elements and some compounds, these two temperatures are the
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same.
As the temperature continues to increase, the liquid will start to boil or evaporate.
This is the same temperature at which the gas phase will begin to condense for most
elements and compounds.
Keywords
States of Matter
Solid
Liquid
Gas
Temperature
Melting (point)
Freezing (point)
Condensation
Evaporation
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