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gapingthingsUrban and Civil

Nov 15, 2013 (3 years and 1 month ago)

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Liquid Nitrogen Demonstrations

Safety Notes & Concerns


Liquid nitrogen is a dangerous material. The following is an

excerpt from the Air
Products Nitrogen Material Safety Data

Sheet:


T
he entire contents of a 10 Liter dewar being spilled in a

unventilated
274 square foot room with an 8 foot ceiling

would reduce oxygen levels
below the 19.5% level where Air

Products recommends the use of a
respirator. Since many

rooms are larger than this, suffocation does not
represent

a major danger. When tran
sporting the liquid in a car,

however,
it is probably a good idea to open a window.


The possibility of freeze burns represents a much more

serious danger and is

therefore our first concern. This does

not mean that the demonstration itself is
dangerous, bu
t it

does mean
you must be careful
. Dangers include:




Nitrogen can spatter (possibly in eyes) while being

poured.



Flying chunks of frozen objects could cause eye

injury.



Children (being curious) will want to reach out and

touch nitrogen or other cold
objec
ts.

As mentioned

above, contact with nitrogen can cause tissue damage,

and this must be
prevented.

Therefore specific safety precautions should include:



A
dults must stress to children the importance of not

touching frozen objects
or nitrogen.



Wear
goggles whenever pouring or dumping nitrogen.



Nitrogen can spatter into the eyes, and potentially

blinding pieces of frozen
things can fly around when we

drop it.



Use a glove and / or tongs to handle any object going

into or out of nitrogen and
to carry th
e nitrogen

dewar.




(more) Liquid Nitrogen Demonstrations

Safety Notes & Concerns


A
dults should familiarize themselves with the following first

aid instructions
(excerpted from the Air Products Nitrogen

Material Safety Data Sheet) for
cryogenic freeze bu
rns just

in case the worst happens:

If cryogenic liquid or cold
boil off contacts a

worker's skin or eyes, frozen tissues should be

flooded or soaked
with tepid water (105
-
115F, 41
-
46C).
DO NOT USE HOT WATER
. Cryogenic burns

which result in blistering or
deeper tissue freezing

should be seen promptly by a
physician.

Remember to stress the importance of not touching liquid

nitrogen or
frozen objects.


See also Liquid Nitrogen Safetygram (in pdf format


see

below) from Air Products
and Chemicals, Inc.

Note
:
the Liquid Nitrogen Safetygram above requires Adobe

Acrobat Reader
which
is available for free download.

Download Adobe Acrobat Reader
















T
he

in’s and out’s


of
L
iquid
N
itrogen


First of all...liquid nitrogen is not a toy! Be certain to read

the safety

precautions
prior to its use and never never never allow children to

play with this!!! With that
being said, here’s the details...


Nitrogen is the major component of our air (79%). Even though

nitrogen is a gas at
room temperature, it is possi
ble to contain it as a

liquid if its temperature can be
reduced to
-
196°C. any object (solid,liquid or gas) that comes in contact with liquid
nitrogen that is above

this temp
erature will cause it to boil!


Liquid nitrogen is stored in a dewar flask which i
s like a well
-
insulated

thermos
bottle. Never use a thermos bottle to store liquid nitrogen!

The dewar allows the
nitrogen gas to escape. If the gas is not

allowed a chance to escape, it
can cause
the flask to explode!
Where do you get liquid nitrogen? Yo
u may try the following

sources:




A local college or university. Make a contact with their chemistry

department; this may prove used for many other things and ideas as

well.



A high school in the area may have a Dewar flask which you can share.



Local
industry such as oil companies, welders or welding suppliers, food

companies, meat packers that use freeze drying, frozen food

processors or
distributors, research labs, steel or metal processing

companies, Air
products companies, airports, etc...



A
local
hospital or dermatologist



Be safe...wear goggles and gloves at

all t
imes...respect the nitrogen!

The Boiling Tea Kettle

The boiling tea kettle is a simple but effective demonstration.
C
arefully

pour some nitrogen into
a whistling tea kettle and put the
top back

on. The kettle will instantly begin to whistle and
"steam" will be visible

shooting out of the kettle. At this point the tea kettle looks and acts

just
like the kind that kids are used to seeing when water has been

heated to a boil. The nitrogen i
s
boiling just like water would when

heated. What has heated the nitrogen to boiling? The room

temperature kettle! If your group is quiet and you remove the lid or

the whistle from the kettle
you can hear the nitrogen boil.


In a matter of moments after th
e nitrogen has been added to the

kettle frost will begin to
accumulate on the side of the kettle. Since

the frost gives the kettle a white coating, using a
colored kettle

works best. After the nitrogen has left the kettle the frost will melt

and
further wa
ter from the air will condense on the kettle and the

kettle will be well coated with
moisture. So be sure to leave the kettle

in a visible place while doing something else to allow
time for the

frost to melt. Often a student will notice the change.




“Cla
y” nails

Because liquid nitrogen is so very cold, things that are normally soft

are changed in surprising
and amusing ways. Blu
-
Tack, normally like

putty, can be shaped by hand into the shape of nails,
which when put

into liquid nitrogen go hard (as nails)

and can then be hammered into

the wall
(well, if the wall is fairly soft). Of course, liquid nitrogen

soon evaporates and the nails warm up,
and nails made of Blu
-
Tack

turn back into ordinary soft Blu
-
Tack, leaving a situation which seems

to other people
IMPOSSIBLE! How has someone made a nail of soft Blu
-
Tack and nailed it into the wall?











Shrinking Balloons

This is a very popular one. Pour some liquid nitrogen into the ice chest.

With gloves begin taking
balloons and putting them into the ice
chest.

As they get down into the nitrogen it is best to use
tongs to push

them all the way down.

As the nitrogen cools the air in the balloons the air
molecules slow

down their movement and the balloon begins to shrink. Many kids will

think that
the air ha
s left the balloon. As you begin to fill the ice

chest with balloons the first ones in will
shrink but the next layer or

so may need to have nitrogen poured over them. Be careful, if the

balloons are sticking up over the top of the ice chest some of the

po
ured nitrogen will spill
outside the chest. So it is best to add more

nitrogen before the balloons begin to pile up.


Once you have added enough balloons to the chest you can begin to

take them out. Only use
tongs to remove the balloons. The

balloon will b
egin to re
-
inflate immediately as you take it out
of the

ice chest and moments after you have pulled out a balloon it is

completely safe to touch
and shortly after looks and behaves like a

normal balloon.

Repeated freeze/thaw combinations
will be more tha
n most balloons

can handle and some will pop on the re
-
inflating.




Ping Pong Ball Spinner


Before doing the demo get a ping pong ball. The ones with the

patterns on them work best for this. If you only have white
ping pong

balls use a marker to add
some colors or pattern to
one. Use a

straight pin to poke a tangential hole in the ping
pong ball.


Use tongs to submerse the ball in the nitrogen (it will want to
float).

Hold it under for 30 seconds or so. During this time nitrogen is going

into the ho
le in
the ball.

Use the tongs to remove the ball and place it on to a table (it may

help to have
something to contain the ball and keep it from rolling

away). The nitrogen in the ball should heat
up and convert to a gas.

This expands and is forced out of

the hole. Because the hole was poked

on a tangent as the gas rushes outward it causes the ball to spin
-

usually at a high rate of
speed. Occasionally the ball needs to be "jump

started." You can do this be briefly and gently
touching the palm of

your han
d to the top of the ball. This provides some additional heat to

get the ball rolling or rather spinning. This works just like a rocket

and occasionally the ball will
be lifted into the air by the rocket

action (if the hole ends up on the bottom).



Making
Ice Cream with Liquid Nitrogen

Mix together the following ingredients:

250 ml
heavy cream/half
-
and
-
half

150 ml

whole milk


75 grams sugar

3 ml vanilla


Blend all of these ingredients together to make a smooth mixture.

Place this blended mixture
into a metal bowl and add between 750
-
1000 mL of liquid nitrogen slowly while constantly
stirring with a

wooden spoon until the desired consistence has been achieved. Do not

add any
more liquid nitrogen then or the iced cream wil
l solidify!

If

the ice cream melts, just add a
little more liquid nitrogen and stir!

The liquid nitrogen absorbed the heat from the blended

mixture. As this happened, the liquid nitrogen boiled off

taking the heat into the atmosphere
and away from the

cream! Remember...liquid nitrogen boils at
-
195 degrees

Celsius (and room
temperature is normally around 25

degrees Celsius
!)


Racquetball in Liquid Nitrogen

Warnings: See warnings for liquid nitrogen. When the racquetball

shatters, pieces may travel a
lon
g distance. Be sure to throw it up in a

safe place. Make sure that members of the audience do
not pick up

broken pieces of the racquetball. Always use glove to handle the

racquetball after it
has been in the liquid nitrogen.


The racquetball is a solid, bu
t the bonds are loose enough for the ball

to flex and bounce. When
the ball is made very cold, the bonds are

much tighter; therefore, when the ball hits the floor,
instead of

flexing and absorbing the force, the ball shatters.


The Physics: There are many
different kinds of bonds that hold

molecules together. The
stronger of these bonds are what hold solids

together. However, there are different levels of
bonds. Obviously, the

bonds inside of steel are stronger than the ones inside a racquetball.


The bonds

in a racquetball allow it to flex. When a racquetball is

dropped under the influence of
gravity, it gains some kinetic energy.

Under normal conditions, this energy is absorbed by the
deformation,

or flexing, of the racquetball when it comes in contact wi
th the

floor. The
racquetball then returns to its original shape returning the

energy back to kinetic energy. This
is what causes it to bounce. When

the racquetball is made very cold, the bonds become much
stronger

and the racquetball lo
ses its flexibility
. Because the ball can no

longer deform to
absorb the energy, the energy of ball act directly

on the bonds; thus, breaking them.

Okay… What about the FIRE demos? Well, first you
need to understand a few things…


The rate of a chemical reaction can be sped

up by increasing the
reactant’s…

Surface area, Temperature
and
Concentration

In this chapter you are going to look at a very fast reaction between
oxygen and a
fuel
. A fuel is matter that gives off energy when it
burns. You have learned about a fuel in

the last chapter


wood!
Burning wood is an exothermic reaction because it releases heat energy!
Other fuels include oils and gasoline!

The very fast chemical reaction that
takes place between oxygen and a fuel
is known as
combustion


(“kom
-
bust
-
shun”).




i
s caused by combustion between
these two reactants!

B
esides oxygen and a fuel, what else do
all chemical reactions need? That’s
right!




The
activation energy

that is needed
to create fire is in the form of heat.
This heat can come from a lot of different places. A match, an electric
spark and
friction

(“frick
-
shun”; heat from two objects rubbing
together) are three common forms of heat! All of these things c
an
provide the activation energy needed to start a fire.

Once the activation energy starts to pull apart the atoms
inside the reactants, a fire will continue to burn as long as
there is fuel and oxygen.

Most of you have watched someone start a wood fire be
fore. Did the
wood burst into flames as soon as a match was brought close to it? Of
course not! It takes a little time for the wood to absorb enough heat
energy to start splitting apart its molecules.



Here is the chemical equation for
heating up

a piec
e of wood:


(There are a lot of atoms inside one molecule of wood, huh?)

Once you add enough heat to wood it turns the wood black and starts to
smoke, right? If you keep adding just enough heat to the wood to turn
it completely black, it will stop smoki
ng and form...


That’s right! The
charcoal

you use to make BBQ is really
just wood that has been
heated up so much that it
does not have any more smoke
to give off! That is why a
charcoal fire does not give off
a lot of smoke!

But what would happen
if you heated up that charred wood/charcoal a little
more?

In order to answer that question, we have to look at the smoke (CH
2
O)
we have created along with the charcoal (C
50
H
10
O).

When smoke gets heated, its atoms start to split apar
t and begin to
react with the oxygen in our air! Here is the chemical formula...


When smoke is heated, it reacts with oxygen to form water, carbon
dioxide...


This heat helps to keep the smoke reacting with the oxygen to produce
even
more

heat! And you should know by now that the rate of a
chemical reaction can be increased if
you increase
the temperature of the reactants!

So... are you saying the smoke
is the real fuel during
combustion? Yes it is!


The carbon in the charred wood can
also react with the oxygen in the
air. But this is a much slower reaction. It still can produce a lot of
heat


which is why we use it in our BBQ grills! That is why the charcoal
will turn bright orange after it is done burning for awhile. When they
tu
rn this color, the carbon inside the charcoal is reacting very well with
oxygen and is very hot! But since it is a slower reaction, it sends off a
lot of heat over a long time. This is very helpful when you are using
charcoal to cook your food!

Only some

compounds can be broken down to produce a lot of heat
during combustion. As you know, not everything in the world will burn.
For example, you cannot boil water and watch the steam burst into
flames!
Although it would be really cool!

The compounds tha
t go through combustion very well contain carbon and
hydrogen. Compounds with these two elements can be broken apart and
mixed together very easily with oxygen to form the products of
combustion (carbon dioxide
and water) very easily!
Gasoline burns very

well
because it is a
hydrocarbon
, which is a
compound made with only
carbon and hydrogen atoms.




Because of the dangers associated with the fire
demos, I have a small problem in writing them
all down. This is not to keep any information
from you, bu
t they can be a little dangerous and
should not be performed by any children. If
you are interested in obtaining a detailed list of
the fire demos, email me at
mrq@eequalsmcq.com

and I will be happy to
send you th
e links to these activities!


Be safe and enjoy!