Date: Sat, 17 Feb 2001 17:10:10 -0500

Author: "Dwight K. Souder"

Subject: Re: Liquid Nitrogen

Post:

I just recently did some LN2 demos a couple of weeks ago. I did the samethings
as you, but I also added some new stuff. Here they are:

1. Take a mylar balloon of helium and pour the LN2 over it. The balloon will
shrink. Let it warm up and expand and it'll begin to float. I use this to
explain density.

2. I demonstrate some of the properties of superconductors.

3. Demonstrate the properties of "happy" and "sad" balls. The rubber ball
that doesn't bounce (sad ball), will after being cooled. The rubber ball that
does bounce (happy ball), will not shortly after being removed from the liquid.

4. Get some dry ice and put it in a rubber balloon and tie it off. Pass the
balloon around and the heat from the students' hands will cause the balloon to
expand and the solid CO2 to phase change to a gas. Immerse the balloon in LN2
and it will collapse. Shake the balloon, and you can hear the rattling of the
solid CO2.

5. With the dry ice, put it in a bucket of water and allow it to make its
fog. Blow bubbles and allow them to float into the bucket. Due to the density
of the CO2 and coldness, the bubbles will stop falling and float on the layer
of air of CO2. If you watch carefully, the CO2 will slowly diffuse into the
bubble, causing the bubble to expand and sink.

6. Pour a small amount of of LN2 in a large cardboard box, just enough to get
it cold (below freezing). Blow bubbles, but sometimes the bubbles will freeze
and shrink. They almost look like bubbles of crinkled plastic. I've even had
floating bubbles that were partially frozen, and when you get near them, they
melt into bubbles of floating "cups".

7. For the following, use a large (1 gallon - 1.5gallon) plastic zip-loc
bags. Get a large test tube with a one-hole rubber stopper that fits properly
in the test tube. Make a hole at the far end of the zip-loc (furthest away
from the opening), but large enough so that the stopper can partially fit
through it. Then attach the stopper to the test tube. This is hard to
describe, but you'll have a test tube with a stopper in the top of it, with a
plastic bag hanging off the top of the stopper. Do this to a few others.
a. Fill one of the zip-loc bags with hydrogen. Seal the zip-loc. Place
the test tube in a container of LN2. The students should notice that nothing
really happens. The volume of the zip-loc remains relatively the same size.
b. Fill another zip-loc with oxygen gas. Seal the zip-loc. Place the
test tube in a container of LN2. After a short while, the students should
notice that the zip-loc collapses all the way. Lift up the test tube and a
pale blue liquid will be in the bottom (liquid oxygen). Take a VERY strong
magnet to it and show the paramagnetic properties of LO2.
Take a kleenex and burn it and show how quickly it burns. Take another
kleenex, soak it in the LO2. Using tongs and fire resistant gloves, light the
tissue (it may take a little while). It'll go up like a flare! Do the same
thing with small dowel rods...they'll burn like a torch! Do the same with a
marshmellow (sp?)...ultimate way of making smores. :)
c. For the grande finale....fill another zip-loc bag with methane (from
the lab stations). Seal the zip-loc. Place the test tube in a container of
LN2. The bag will eventually collapse. Lift up the test tube and a
white/clear liquid will form (liquid methane)...sometimes solid methane will
form. Wearing heat resistant gloves, goggles, and plenty of room around you,
turn off the lights, remove the stopper, and hold a flame to the top of the
test tube. The gas will light and I jokingly refer to it as my portable bunsen
burner. :) The flame will remain relatively small at the top of the test
tube. With your free hand, touch the bottom of the test tube (it'll be very
cold), be sure to hold it away from you. The liquid methane will rise up
(boil) and the flame will also quickly rise up...sometimes hit the ceiling.
I've had it at times when I had too much methane in the test tube, some of
the liquid methane will come out of the test tube and onto my gloves and
floor. I just blow them out...they don't last very long. JUST DON'T DROP THE
TEST TUBE! If you'd like, you can see a picture of it on my website (it's
still under construction). Just look under Chemistry.

I hope these help! Have fun with them, but always be cautious!

Dwight Souder
Ashland, OH
http://www.crestview-richland.k12.oh.us/Teacher/Souder/Homex.html


Glenn Knapp wrote:

> I'm getting ready to do the old liquid nitrogen thing. I've got the usual
> demonstrations - rubber ball, flowers, hot dog, grapes, banana, etc. I am
> looking for something new; any ideas would be appreciated.
>
> Also I have heard of the following, but wonder if it works and if it is
> safe. You soak a cracker (the classic graham cracker is the preferred
> wafer I believe) in the liquid nitrogen and then put it in your mouth and
> chew it up. Supposedly it does not harm the mouth but does produce a huge
> volume of water vapor that escapes through the nose and mouth during the
> chewing process. Does anyone have experience with this?
>
> Glenn

Back