Liquid Nitrogen

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Revision as of 03:27, 9 September 2015 by imported>Morganp (→Bimetallic Plate)
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Physics and Chemistry
States of Matter, Properties of Matter
Grade Range
Elementary School, Middle School, High School
Format
Stage

UNDER CONSTRUCTION

Materials

  • Liquid Nitrogen
  • Thermos container for presenting
  • Tongs
  • Balloon
  • Bimetallic Strip
  • Racquetball
  • Flowers OR Bananas
  • Nail
  • Hammer
  • Green Board
  • Ladle
  • Small Blast Shield

Safety Precautions

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. LIQUID NITROGEN CANNOT BE TOUCHED WITH BARE HANDS! KEEP AWAY FROM ANY BARE SKIN!

A proper storage container is essential for transporting, transferring, and handling liquid nitrogen. These arrangements must be discussed with the supplier. Be sure not to store the liquid nitrogen in a container that can be sealed. The container may explode and can possibly inflict injury. Liquid nitrogen is stored in a Dewar, which will keep it cold for long periods of time. However, even in a Dewar, liquid nitrogen warms up and evaporates.

When working with liquid nitrogen, proper safety equipment MUST be used: safety goggles and thermal gloves must be worn at all times by all people working around the liquid nitrogen. It should be noted that most thermal gloves designed to work with liquid nitrogen will allow liquids to pass through them and saturate the material. Extreme caution should be exercised so that no liquid nitrogen contacts the gloves, as severe frostbite WILL occur.

Liquid Nitrogen is many times colder than most people have experience with and they do not comprehend how cold it is. Be sure to take special care with liquid nitrogen around younger students. Never keep it within touching distance and never leave a Dewar of liquid nitrogen unattended. It should be explained to audiences that a trained person using safety gloves and goggles must handle liquid nitrogen carefully. NEVER use liquid nitrogen in a demonstration without gloves and safety goggles.

Do not let students touch the ball or hoop after it has been taken out of the liquid nitrogen. Be extremely careful with the ball and hoop when using it in a glass (silvered or non-silvered) Dewar. You should NOT allow the hoop to come into contact with the Dewar sides or bottom. You may wish to consider performing this demonstration in a metal mixing bowl. This warning is advised for ANY metal object that needs to be placed in liquid nitrogen.

The racquetball, flowers, bananas, and hot dogs should be handled by Science Theater performers only, and with thermal gloves at all times. Audience members may want to touch the pieces after the experience, but there is still risk of freezing-related problems. Feel free to show some of the pieces, but wear gloves at all times and tell the audience members to not touch. In addition, objects will shatter when broken. Consider breaking the objects behind a clear shield. Always keep the audience members a safe distance away.

Demonstration

Preparation: Fill the presentation thermos, and put the polystyrene lid on it, making sure it isn't tight. Set up the demonstration area, laying out the different items you need around the thermos on a table. Set a small blast shield in front of the presentation thermos. Blow up the balloon, making sure that it is just slightly too big to fit into the presentation thermos.


Molecule Dance

Note: This demonstration is great for younger audiences, but can be skipped for audiences in 9th grade or higher

  1. Call on several students to be volunteers. If it is a small assembly, you can have the entire assembly be volunteers!
  2. Have them all stand close together, and start dancing. While dancing, they can move around, spreading out and taking up more space.
  3. Have everyone stop, then tell them that they will all start "heating up". Have them start dancing again, but this time moving very quickly and taking up a lot more space.
  4. Have everyone stop, then tell them that they will all start "cooling down". Have them move slowly, and try to huddle together, taking up very little space.
  5. Have everyone stop, then tell them to go back to "room temperature". Let them move at their initial speed, and take up some space.
  6. Have the volunteers all take a bow and return to their seats.


Balloon

  1. Show the balloon to the audience, and ask them for ideas on what will happen if it were put into the liquid Nitrogen.
  2. Show that the balloon does not fit into the thermos. Using the ladle, pour liquid nitrogen on top of the balloon while it is on top of the thermos, and it will start to collapse. After pouring one or two scoops onto the balloon, it should fit.
  3. After getting the balloon into the thermos, use a pair of tongs to pull it out. Immediately drop it onto the table, and pick it up using your hands (It will be warm enough to handle). As it expands, carefully turn it over in your hands, and blow onto any spots that look frozen to help thaw it out. It should re-expand to the original size!


Banana & Flowers

Banana
  1. Show the banana to the audience, and push a nail into the side of it to show that it is a normal banana. Drop the banana into the liquid Nitrogen.
  2. As the banana cools and freezes, explain to the audience what is happening to it.
  3. After 1-2 minutes, the banana will be sufficiently frozen. While wearing the cryo gloves, pull the banana out of the thermos using the tongs. Drop it on the table.
  4. Try to stab the banana with the nail repeatedly, while holding it on the green board. After a few attempts, use the hammer to shatter the banana
Flower
  1. Show one of the flowers to the audience, and tap it gently against the blast shield to show that it is a regular flower.
  2. While wearing a cryo glove, stick the head of the flower into the liquid Nitrogen for 8-10 seconds. Pull it out, then tap it against the blast shield on the presenter's side. It will shatter!
  3. Repeat the above steps, making sure to take time to explain each part of the demonstration.

Leidenfrost Effect

Note: This demonstration works best either right before or after the Banana & Flower demonstration. Do not perform this demonstration if you have not practiced it. Please use all necessary safety precautions before performing this demonstration

  1. Show the audience your bare hand, and ask them why you wore a glove to handle the banana/Why you didn't wear a glove to handle the balloon.
  2. Explain how cold liquid Nitrogen is, and how it is dangerous to handle directly. Ask if you should stick your hand in.
  3. Hold your hand directly over the open thermos. Quickly submerge your hand in the container and pull it back out. repeat this process a few times, allowing time between dips to show that your hand is, in fact, intact.
  4. Hold one hand directly over the thermos, and have the other holding the ladle. Scoop up a small amount of liquid Nitrogen with the ladle. Have the hand over the thermos open, tilted downward toward the thermos, and pour the liquid Nitrogen onto your hand. It will roll off your hand, and not hurt you!

Bimetallic Plate

  1. Show the bimetallic plate to the audience. Explain that the sides are Bronze and Nickel.
  2. Put the bimetallic plate into the liquid Nitrogen. Ask the audience if a metal can get "more solid". Explain what happens.
  3. Pull out the bimetallic plate after 10-15 seconds. It will be curled over sideways!
  4. Optional: Bring the blowtorch with you. After showing what happens with the liquid Nitrogen, heat the bimetallic plate with the blowtorch. It will bend in the opposite direction!
    1. Note: Do not put the hot bimetallic plate into the liquid Nitrogen. The rapid cooling could cause it to break!

Racquetball

9. For Bimetallic Strip:

Present the bimetallic strip to the audience and explain that is a strip that has a different metal on each side (Bronze on one side, Nickel on another). Dip the strip into the liquid nitrogen for a few seconds. It is not necessary to cool the strip completely. When the strip is pulled out, the audience will notice that the strip bends to one side.

10. For Racquetball:

Convince the audience that the racquetball is flexible by bouncing it a few times on the floor. Using tongs, place the ball in the liquid nitrogen and wait until the bubbling stops. The racquetball takes a long time to cool down (about 5 minutes), so we suggest that you talk with the audience about what is happening to the ball or perform another demo while waiting. Remove the ball and try to bounce it away from the audience or into a shield. The racquetball will break if it is thrown onto a hard enough surface. If you are in a gym, you may need to throw it against a concrete wall (away from the audience).

What to Say:

Ask the audience what they know about temperature, besides just weather. If no one answers, ask for the differences between a solid, liquid, and gas 9and plasma, if someone mentions it). You will likely get the three different states of water: Ice, liquid and steam. Then ask for volunteers and perform the Molecule Dance.

After the dance, explain that the molecules of each have a different kinetic energy, which is determined by how hot, or cold they are. The hotter they are, the faster the molecules move, and vice versa. Then it's time to get excited about Liquid Nitrogen. Stress how cold it is. "So as you can see, it's not just cool. It's cold!" 'bad pun #1' (77 degrees Kelvin, -326 degrees Fahrenheit) and make sure to warn the audience members not to try this experiment at home. A good safety pun would be: "So have any of you seen A Christmas Story? -Most will have- All right. So do you remember the scene where Ralphie's friend sticks his tongue to the pull and gets stuck? -Some chuckles, nodding of heads- Well; Liquid nitrogen will do that to you, except you'll be stuck to whatever you are touching at the time. This is why we cannot let anyone in the audience get too close to the liquid nitrogen, because we'd rather not get you stuck to the floor or something -bad pun #2-"

Start the Balloon demo. Inflate the balloon and show how the pressure increased from a greater amount of gas molecules pushing against the walls of the balloon. Ask the audience "what do you think will happen when I put the balloon in the Liquid Nitrogen?" Place the balloon in the liquid nitrogen, watch it deflate, and ask the audience if they know what caused the change. The kinetic energy of the molecules decreased from the extreme drop in temperature. The molecules slowed down, and decreased the amount of pressure inside the balloon. "To 'expand' on this idea 'bad pun #3' We will now look at bubbles!"

-Pull out the Frozen Soap Bubbles demo- "So here I have some soapy water. What do you think will happen when I put the liquid nitrogen in? -get responses- well, let's find out!" -Pour some in, watch the reaction- "So what just happened here you guys? -Responses- So you can see that the water started bubbling. Is it really hot, or is it because of something else? . . Well, keep in mind how cold the liquid nitrogen is. It's currently boiling, and turning back into a gas, so some of that gas was caught in the bubbles. However, because it is so cold it froze the bubbles! Now this is cool and all... cool? Get it? 'Bad pun #4' but we can show this in a better way. Can I get a countdown? 3! 2! 1!" -Dump the soapy water in the container, watch it explode with bubbles- "Whoa! Now THAT was awesome!"

Now switch to the Banana Demo. Ask the audience on what a banana is mostly made of. Encourage the answer of "water". Explain that the water in the banana might freeze while it is in the Liquid Nitrogen. While the Banana is freezing, you can start the Frozen Flower demo. Pull out the flower. Show that it’s normal and even ask an audience member to look at it and feel the petals and say if it’s like a normal flower. Once they agree, place the flower into the liquid nitrogen, pull it out, and bang it against a hard surface. "Poor flower petals, they didn’t stand a chance…" Ask the audience what they believe happened. Hopefully someone will say that the flower froze, which is absolutely correct! Explain that the water in the flower froze, making it more brittle. However, water expands when it freezes (unlike most other materials) which lead to the cells in the flower bursting, and the sound of shattering glass when we broke it. Take out the banana, and explain that the banana, like the flower, is now frozen. If you can, hammer the nail into the board. Then, while grabbing the hammer and pounding the banana lightly, explain that "The banana -bang- has frozen solid -bang- and clearly -bang- is no longer soft -bang- which is why -bang- we can pound it -bang- without it going to mush -whack it hard to shatter it- but we can shatter it."

If it is being performed, you would now go to the Frozen Finger demo.

Now, what would happen if we placed a part of the human body into the liquid nitrogen? Do we have any volunteers?!? … That’s alright; we won’t actually put one of you into the liquid nitrogen. Instead, who wants to see me put my finger in here? (Most will say yes, and at this time you get concerned for your well being) . . .Re-really? I was only kidding. . .I mean, do you realllly want to see me stick my finger in? (YES) oh. . okay then. . . (proceed to stick the finger in slowly, and make sure to flinch and be acting like it is the worst pain ever while explaining) "So my finger (ow!) is right now (sharp intake of breath) being frozen by the (aaaahh!) liquid N(Ow!) nitrogen (ow ow ow!) which means that the water (AAhh!) is bursting the cells (OW!) in my finger (whimpering pain, feel free to take a moment here) which means my finger (slowly pull it out) is no longer useful. . . well (pull out the hammer) let's get this over with. . . Proceed to put the finger on the wood block and, before the audience had time to react, smash it. Flinch, pull your hand away, do whatever you want to make it seem like you really did just smash your finger off. Then, stop faking and take the glove off, showing your real finger to be intact "So as you can see now, I was kidding and my finger is still here. But what about the fake finger? -Get responses- So you can see that it did freeze, and it is true that by sticking my hand it like that that my hand would freeze off like that.

As you have all noticed, we encourage safety throughout this show at all times, so that we don't risk freezing any of you and keep you safe. . . So, if that is the case, then why aren't I wearing my safety gloves all the time?" -Lead into Leiden Frost effect-. "So you may be wondering if it is actually unsafe for me to not be wearing my safety gloves all the time. Well, there's only one way to find out. Who wants to see me stick my hand in the liquid nitrogen?" -YEAH! - (feel free to make a comment about how evil everyone is, they'll chuckle at it) "Ok then, here it goes. So 3, 2, 1, -stick hand in and out quickly- huh. . .I'm not frozen. . . should we try again?" -YEAH!!- "Ok then. 3, 2, 1, -repeat- . . . I'm still not frozen . . . let's try pouring it on my hand! -Pull out the ladle- "Now there is something I Have to tell you guys. The reason why it is not freezing my hand is due to the Leiden Frost effect -have them repeat it a few times- This effect has to do with temperature. Because I am at 98.6 and it is at -326, there is a big temperature difference of over 400 degrees! This means that, when it lands on my hand, some of it turns right into a gas, and the rest of the liquid -pour it across your hand- rolls on the gas and off my hand! In fact, you can also see it roll across the floor!" -Make sure none of them touch it as it rolls on the floor-

Next switch to the ball and hoop. Show the audience that the ball fits easily through the hoop. Then ask, since the balloon deflated when placed into liquid nitrogen, what do you think will happen if we place this hoop into it as well? Let the audience answer the questions while the hoop cools in the liquid nitrogen. When it’s finished, try to move the ball through the hoop, only to discover it doesn’t fit! If you wait a little while, the ball will fit through again after it warms up. Describe how the kinetic energy of the molecules decreased again. When the kinetic energy of molecules is lower, they are more likely to take up less space than when warmed up.

Expand on the idea of thermal expansion and contraction by introducing the bimetallic strip. Point out that the strip is made up of two separate metals. Ask the audience for any predictions as to what may happen after the strip is placed into liquid nitrogen. When the strip has reached the correct temperature, pull it out part way, and present the magic of the strip bending to one side! Remind the students that the strip was composed of two different metals. The metals contracted at two different rates. The one that had a larger coefficient, according to linear expansion, contracted more and made that end of the strip bend more.

For a finale, use the racquetball demo. Start off by showing the audience the racquetball and bouncing it, stating the obvious things such as "see how it is bouncy". Then, close it inside the tongs and place it within the liquid nitrogen. While it is cooling, you can explain what is going on. "So, as you all know by now, the liquid nitrogen is extremely cold. So what is happening to the racquetball?" -Chances are you will get a few people who will say that it is freezing- "well, keep in mind that a racquetball is made of rubber, which cannot freeze. Also, it is not a metal, so although it will contract, it won't contract enough to show a difference. So what do you think will happen to the ball then when I pull it out? -get a mix of answers, edge people towards saying that it will not bounce- "So have any of you ever put a rubber band in a freezer? -Some yes- and what happened to the rubber band? It didn't stretch as well, right? Well, there is a reason for that. Rubber and other elastic materials are affected strongly by temperature. If you were to take a bouncy ball and play with it on the hottest day of the year, it will bounce higher than if you were to try bouncing it in the middle of winter." At this point, the ball should be ready, so pull it out and gently drop it on the table. It will go -thud- and barely bounce back. "So as you can see, the ball is no longer going to bounce. Instead" -chuck it all the wall/floor, and it shatters- "the ball has lost so much elasticity, that it can no longer handle hitting the floor/wall! It shattered!" -gather up the pieces of ball, and place them on the table. Kids can look at them once they warm back up- "So as you can see, the ball shattered when I threw it. What made it so the ball could no longer bounce? (Liquid nitrogen, extreme cold) Exactly. This poor ball hit the floor like your grandmother's fine china. . . Which I STRONGLY suggest never dropping. EVER." "So what what on earth was that loud sound when the ball hit the ground? Well that was related to the pressure inside the ball. See, a racquetball is hollow and has a certain pressure inside of it at any given temperature. When it gets colder, the pressure decreases as well, because the molecules aren’t hitting the sides as quickly anymore, like with the balloon. So when the ball broke, what you heard was all of that compressed air decompressing. The ball could not deflate like the balloon did earlier because it is not flexible enough to do so."

Close the show, and at this point, you would have someone else start with closing remarks as you prepare the Liquid Nitrogen Ice Cream.

Substance: 

   Gold 14

   Aluminum 23

   Glass (common) 8.5

   Brass 19

   Iron or Steel 12

   Concrete 12

   Silver 19

   Copper 17

   Lead 29

Why It Is

The audience should be made aware that molecules compose all solids, liquids, and gases and that they are in constant motion. It is important that they understand that the motion of these molecules depends on the temperature of the substance. The point of this demonstration is to show how the molecules move faster when the temperature is higher and move slower when the temperature is lower. This relationship between the motion of molecules and temperature is called kinetic theory. The important thing to understand in these equations is that kinetic theory relates the temperature of a material to the average velocity of an individual particle. In other words, as the temperature of a gas is increased, then the velocity of the molecules composing that gas will increase as well. This model of temperature as it relates to the movement of molecules is a very powerful one and can be used to explain many different temperature-related phenomena. The first one is that temperature will affect the expansion and contraction of objects. This is the core concept at work in the first set of demonstrations. When a gas is cooled down the molecules will move slower and stay closer to similar molecules due to slight attractions. When a gas is heated up, the opposite occurs and the molecules will begin to move faster and overcome any attractions or interactions, moving further away from each other.

Real Life Examples

This is analogous to people in the winter, people stay inside their houses and huddle together because it is so cold. However, in the summer, people go outside and move around because it is warmer. Of course, molecules are not like people in that they do not make decisions to go out or stay in. The movement of molecules is completely dependent on their temperature. A real life example of linear expansion of different materials occurs when a glass jar has a stuck metal lid. When presented with this situation many people will try to put the jar under hot water. The hot water causes the molecules in the metal lid to move faster, causing it to expand. The jar is easier to open now because the lid is not as tight around the jar. The glass jar also expands, but not as much as the metal lid. That means that glass will expand less than any metal when heated to the same temperature.

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