<%@ Register TagPrefix="uc1" TagName="TopSubBanner" Src="../../CommonControls/TopSubBanner.ascx" %> <%@ Register TagPrefix="uc1" TagName="TopBanner" Src="../../CommonControls/TopBanner.ascx" %> <%@ Register TagPrefix="uc1" TagName="Instruction" Src="../../CommonControls/Instruction.ascx" %> <%@ Register TagPrefix="uc1" TagName="LeftColumnNav" Src="../../CommonControls/LeftColumnNav.ascx" %> <%@ Register TagPrefix="uc1" TagName="Footer" Src="../../CommonControls/Footer.ascx" %> <%@ Register TagPrefix="uc1" TagName="RightColumnNav" Src="../../CommonControls/RightColumnNav.ascx" %> <%@ Page Language="vb" AutoEventWireup="false" Codebehind="default.aspx.vb" Inherits="StoreFront.StoreFront.DefaultPage" EnableViewState=True TargetSchema="http://schemas.microsoft.com/intellisense/nav4-0"%> Arbor Scientific - Coolstuff Newsletter - Volume 8

CoolStuff Newsletter Article Vol. 8, April 2003

Chemistry: Gas Laws Smorgasborg

With a Special Contribution from Patti Carlson ~ New Trier High School, Winnetka IL.

In this issue we welcome the contributions of Patty Carlson, Chemistry Teacher and colleague from New Trier High School and we continue with the discussion of the Learning Cycle from the last issue of CoolStuff. The activities that follow represent the exploratory phase of the learning cycle approach.  These activities introduce students to the behavior of gases in different situations so that they may draw their own conclusions before being given formal instruction in gas laws. For the complete story on the "Learning Cycle" phases, click here.   ~ Chris Chiaverina

One of the challenges of teaching chemistry is making the invisible world seem real and relevant to our students. Labs present the best opportunity to demonstrate this, but too often we, out of necessity, begin each lab with a litany of “don’ts” (don’t eat food in the lab, don’t touch the acids, don’t look at the bright light being given off, etc) and it is rather rare that the material we study in chemistry lends itself to an experiential approach. I put this lab together because I was so inspired by Chris’ “smorg” concept. I wanted to see if I could generate the same kind of enthusiasm and elicit the “ah-ha” moments from my chemistry kids as he routinely does with his physics students.

The active engagement with the phenomena in this lab is important in helping students confront their own preconceptions and or misconceptions and allows them to test their personal theories. The hardest part is resisting the temptation to give students the “answers” because they are so excited and get deeply involved in developing such interesting (read wacky) explanations.

The fun of watching the kids jump up, shouting a Seinfeldian “Get out!” when someone actually breaks a meter stick in two, listening to the surprised shrieks of students who successfully propel a potato slug across the room and watching happy students munch popcorn while they try to figure out why the kernels pop are all worth the extra set-up time you’ll need to devote to this lab. Give a few kids some mole money (extra credit) to stay after school and help you clean up. Have fun!

Patty

Gas Laws Smorgasbord

Station 1     The Cartesian Diver

Key Concept ~ When the pressure on a gas is increased, its volume will decrease.

Set up a Cartesian diver in a soda bottle.  Fill the bottle with water all the way to the top.  Fill the diver with just enough water so that it barely floats on the surface.  When the bottle is squeezed, the pressure increases on the air trapped in the diver.  When the density of the air (gas) changes (increases), the diver sinks to the bottom (whether the bottle is sealed or not). Releasing the bottle releases the pressure.

Instructions:

The "diver" is the little tube half-filled with water inside the large plastic bottle. Note the position of the diver inside the bottle as the bottle sits on the table.

Questions:

Now, squeeze the plastic bottle.  What happens to the diver? 

Now, take your hands off the bottle. What does the diver do now?

What do you think causes the diver to behave this way?

 

 

Station 2    Microwave Popcorn

Key Concept ~ When the temperature of a gas is increased, its volume will increase.

Students will be micro waving small amounts of popcorn in a clear bowl.  Popcorn pops when the moisture inside boils and expands, bursting the kernel open.

Instructions:

Place about two tablespoons of popcorn in the clear plastic bowl. Put the top on the bowl and place in the microwave. Close the microwave door and turn the microwave on high. Watch as closely as you can as the popcorn kernels begin to pop, but of course DO NOT OPEN THE DOOR! As soon as the vigorous popping stops, turn off the microwave.

Questions:

Describe what you see (yeah, I know, but try).

What do you think makes the popcorn pop?

Put your popcorn in a paper bag and then squirt in some butter if you wish.

 

Station 3  Balloon and the Flask (or Hot Air Ballooning)

Key Concept ~  When the temperature of a gas is increased, its volume will increase.

Place 10 mLs. or so of water in an Erlenmeyer flask. Stretch an un-inflated balloon over the mouth of the flask (250 mL. flask). 

Place the flask next to a hot plate with a thermal (oven) glove so that students can move the flask easily from the hot plate to the ice water.  Students will see how an increase in temperature can cause in increase in the volume of a gas.

Instructions:

Place flask on hot plate and let water boil.

Questions:

What happens to the balloon? Why?

Now, put the flask in a beaker of ice and let it cool.

Now what does the balloon do? Why?

Photo from University of Wisconsin Chemistry Department

 

 

Station 4     Life in a Vacuum!

Key Concept ~  When the pressure on a gas decreases, its volume will increase.

This station can use a large vacuum chamber or the small vacuum chamber and Vacuum Pumper shown.  Provide a balloon with a small amount of air tied inside.  The balloon needs to be small enough that it won't seal against the sides of the chamber.  Students will observe an increase in volume when they decrease the pressure in the chamber.

Instructions:

Observe as a partially inflated balloon is placed inside a Vacuum Chamber, in which the air is slowly evacuated. To do this, simply drop the balloon into the chamber. Place the lid and hand pump on the top and pump the air out. Repeat with a marshmallow and shaving cream. IMPORTANT: clean up your mess!!!!!

Questions:

What happens to all of these objects?

Why do you suppose this behavior occurs?

 

Station 5    Iron Man (a.k.a. Magdeburg Hemispheres)

Key Concept ~ The earth's atmosphere exerts pressure on objects.

Students will observe the strength of atmospheric pressure in this memorable demonstration.

Instructions:

Take the two black rubber cups and slap them together quickly with a lot of force. Now, try to pull them apart using the handles. Ask a friend to pull one end and you pull the other.

Questions:

Can you pull them apart? Why or why not?

Now, "burp" the cups, i.e., allow air to come in the center by peeling the sealed cups from each other.

Now what happens? Why?

 

Water is colored and in a clear beaker for photo. Never let students drink from beakers!

 

Station 6    This Sucks! I'm under so much pressure!  (Impossible...Science CAN'T suck!)

Key Concept ~  The earth's atmosphere exerts pressure on objects.

This station has a few steps. It's important that you assure that students follow the progression of tasks as laid out. This helps build the acquired knowledge to make the final conclusions.  Hopefully, students won't spill any water, but it might be a good idea to set up this station over a sink.  Also make sure each student uses a dry card.

Instructions:

Pour some tap water into one of the cups provided. Obtain a straw and sip some water.

Why does this work?

Now, suck up some water and place your index finger over the top of the straw. Lift the straw out of the cup.
 

What happens? What causes the water to remain in the straw?

Fill a Styrofoam cup brim full (overflowing) and place an index cards securely on top. Make sure there is good contact between the card and lip of cup. Now, gently turn the cup sideways.

What happens to the water?

Now, gently turn the cup upside down and carefully let go of the card.

What happens to the water now? How is this possible?

 

Station 7   Mass a Gas

Key Concept ~  Air is a form of matter and has mass that can be measured.

Along with understanding atmospheric pressure, students can discover that air has mass.  As shown in the photo, a liquid crystal temperature strip can be added to show the rise in temperature when the bottle is pressurized.

Instructions:

Attach a Pressure Pumper to an empty two-liter pop bottle.  Measure the mass of the bottle to at least the nearest 0.1 gram.  Record the mass below.

Pump the pressure pumper 200 times and record the mass of the bottle again.

Questions:

What happened?

Why did the mass change?

Remove the Pressure Pumper and record the mass of the bottle again.  Explain what happens.

 

 

I didn't use meter sticks for this because of cost constraints.  I used pieces of scrap wood having meter stick dimensions. Also, the student-performed meter stick Karate demo could be potentially risky. Students can get overly exuberant when performing this demo with possible harm to themselves and those around them. I would suggest that a warning or perhaps that students be supervised when carrying out this activity. Safety Glasses are a must.

Station 8   Ruler of the World!

Key Concept ~  The earth's atmosphere exerts pressure on objects.

This is another demonstration of the strength of atmospheric pressure.  Students won't believe that the air is stronger than they are!  Note: The meter stick will break.  Breaking a meter stick makes this activity really memorable, but you might want to use another thin piece of wood.

Instructions:

Take a meter stick and place it on a desk so that it extends a bit over the desk. Place two full sheets of newspaper over the section of the meter stick that remains on the desk. Smooth the newspaper out several times so it lies on the table as flat as possible.

Questions:

Now, try to karate chop the meter stick. What happens?

Why were you able to do that?

Why is the newspaper important?

 

 

Station 9   Super Duster & Office Buster

Key Concept ~  When the volume of a gas increases, its temperature will decrease.

Obtain a can of compressed "air," such as those used to clean electronic equipment.  As you depress the nozzle, the gas inside (typically an HFC) responds to the reduced pressure by "boiling" or rapidly turning into a gas.

This is an endothermic process so the can gets extremely cold (can even cause frost-bite if you hold it too long.) I like the students to relate this to the phenomenon of water boiling at lower temperatures at high altitudes due to the lower pressure. (Lots of campers know this very well.)

The classic Drinking Bird uses a similar concept and makes a good companion to this station.  Simply challenge the students to explain the bird's motion.

Instructions:

Wrap your hand around one of the duster cans.  Make sure your palm is in complete contact with the can. Now, depress the nozzle.

Questions:

What do you feel?  Why?

Shake the can.  What do you notice?

Try to explain what happens when you depress the nozzle.

 

Information on the Drinking Bird

For Java applets distributed on this web page
Copyright (C) 1998 Michael Fowler [email protected]

Dr. Michael Fowler
Physics Building
University of Virginia
Charlottesville, VA 22901

 

Station 10  Computer Terminal ~ Have an Applet!

Key Concept ~  When the pressure on a gas increases, its temperature will increase.

Load the applet from the link below.  It has a one-dimensional model of a gas under pressure. 

Instructions:

Watch the single gas molecule in the applet.  Hit the red “compress” button to lower the piston.

Questions:
 
What happens to the volume as the piston is lowered? Why?

What happens to the atom velocity as the piston is lowered?

What happens to the temperature as the piston is lowered?

Now, hit the red “expand” button. What happens to the atom velocity and temperature?

What is going on here? Try to explain in your own words.

 

Station 11  Nice shot Spud!

Key Concept ~ Pressure and volume are inversely related. The volume of a gas decreases as the pressure that the gas exerts increases.


The potato launcher is great for demonstrating this  concept because there is a section of trapped gas between the two potato chunks that gets increasingly compressed as the dowel pushes one chunk nearer the other. Eventually the pressure being exerted on the plug end chunk becomes so great that it is fired out of the "launcher". If a good seal is not made when loading the potato pieces the launcher won't work. Caution** Be sure to demonstrate this station to students first and warn against pointing the launcher at anyone! (under penalty of bodily torture to the Perp!)

Instructions:

"Stamp" a plug of potato with each end of the Potato Launcher tube. Use the plunger to firmly push one plug into the tube. Try to aim the other plug at the target. Do NOT aim the launcher at a person!

Questions:

What happened?

Why did/didn't it work?

Push the plunger all the way through to empty the launcher for the next group.

 

Slip a large washer on to the dowel and use the duct tape to secure. This forms a good hand protector when pushing the plunger in.

 

Ok the smorgasbords' done...what now?

After the gas laws exploratory activity, the teacher must decide how to best help students make sense out what they just encountered in the laboratory.  Along the way, basic principles, terminology, and mathematical relationships must be introduced.  (See Concept Development)

One way to accomplish these objectives is to use lecture demonstrations to drive the concept development.  Lecture demonstrations allow the teacher to revisit the phenomena introduced by the exploratory stations in an engaging way. 

Many times students miss some important aspect of an activity.  Therefore, it is often good for the teacher to repeat some of the activities done by the students as class demonstrations.  In this way the teacher can focus student attention on the essential element of selected activities.  Drawing on students to explain what they see and why they think it happens gets them actively involved in a communal learning process while allowing the teacher to assess understanding.

In addition to revisiting smorgasbord activities, the teacher can further amplify basic principles through the use of novel demonstrations.  These demonstrations may be used further clarify concepts and illustrate real-world applications of the basic principles being studied.

The demonstrations described below should be performed by the teacher.  The use of hot and very cold objects prohibits hands-on student involvement.  Furthermore, students should wear safety glasses when these demonstrations are being performed by the teacher.

 

Photo from University of Wisconsin Chemistry Department

Dry Ice Ballooning

Put on thermal gloves. CAREFULLY break off a piece of dry ice and place inside an un-inflated balloon. Pinch the balloon closed and wait a few minutes.

Questions:

What happens?

Explain.

 

Egg over easy!

Pour 7-10 mls. of water into an Erlenmeyer flask (1000 mL. flask) . Place on hot plate, let water boil away. Immediately after the water has boiled off, remove from heat (remember to use thermal gloves!) and place a well-greased, hard-boiled egg on the mouth of the flask. Observe.  After students have had a chance to answer the questions, ask for a volunteer to try to get the egg back out.

Questions:

What happens to the egg? Why?

Propose a way to get the egg out of the flask without cutting it.

Describe the method you saw used to get the egg out.

 

Photo from University of Wisconsin Chemistry Department

 

 

Photo from University of Wisconsin Chemistry Department

Click here to see

the "Ultimate Crashed Can Demo"

 

 

You Can Do it!

Place about 7-10 mls of water in the empty pop can. Place can on hot plate and turn heat on high to let the water boil off (the length of time will vary) After the water has evaporated, immediately grasp the can with thermal (oven) gloves and invert it into the beaker of cold water.

Questions:

What happens to the can? Why?

Why was it important to put water in the can before heating it?

Watch what happens when the can is lifted out of the water.  Explain your observations.

Here's an idea for keeping students minds on topic even after they leave your classroom. It might even get them to see other events in real life that help make the connection to new knowledge.

 Video Clips (Extra Credit)

Check out  the movies “Total Recall” and “License to Kill” . See if you can locate the scene's that would apply to these questions.

In Total Recall, what is happening to Arnold when his helmet cracks? Why?

In License to Kill, what happens to the bad guy’s head in the pressure chamber? Why?

 

Our next smorgasbord will take your students on a journey through the world of light, color and perception. By way of hands-on experiments and take-home devices, they will learn how light is produced, beamed, blocked, bounced and bent.  Your students will discover what it takes to become invisible, how sound may be carried on a light beam, and why the myriad colors on a television screen are really just in your head. Through some visual foolery, your students will experience the perceptual paradoxes that occur when the brain is unable to make sense of sensation.  When they complete the color and light smorgasbord, they may find that they have found a new way of "seeing the light."
 

Regards,

Next Issue:   Light & Color (Can you really see the light?)

 

About Patty Carlson:

I have known and worked with Patty Carlson for over a decade and feel privileged to teach and grow with her. Patty is an energetic, creative, and caring professional who has earned the respect of her students and the admiration of her colleagues. She relates well to students, knows her subject inside and out, and is enthusiastic about sharing her knowledge with others. Patty is intrigued by the simplest things, which, I believe, explains her success. She seems more fascinated with the natural world around her each day and she shares this growing sense of wonder with her students.

Patty's creativity is evident in her teaching. The lessons, laboratory activities, and field experiences she has prepared for her students are as effective as they are unique. Emphasizing a constructivist approach, Patty allows her students to develop their own worldview through interactive experiences both in and outside the classroom. She is convinced that a solid conceptual foundation is a prerequisite for understanding. Whenever possible, she takes her students beyond the confines of the school to perform fieldwork. Such activities stress higher-level thinking skills as well as demonstrate the application of science in the real world.

Chris Chiaverina