Can Crush (Demo)
A can is crushed by dipping it in water.
Reference: “Chemical Demonstrations, Volume 2,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1985; p. 6.
Add about 10 ml of water to an empty aluminum soda pop can.
Heat the can on a hot plate until steam comes out of the opening for twenty seconds.
Using tongs, quickly lift the can and invert it in a pan of cold water.
Explanation: The steam replaces the air in the empty can while it is being heated. When the can is inverted in the water, the vapors condense quickly and crush the can. Gas occupies much more volume than a liquid.
Tips:
Matter Action (Hands-on)
Students act out volumes of matter.
Reference: None
Pack the students as close to each other as possible.
This represents a solid.
Have the students start moving around each other, but still touching each other.
This represents a liquid.
Move the students apart so they are evenly distributed throughout the room.
This represents a gas.
Explanation: The students are molecules in different phases. Explain the relative energy, movement and volume of each phase.
Tips: Perform this activity at the beginning so the students can relate to an experience and refer back to this activity while performing the other activities. This can also be done at the end to reinforce the concepts presented during the other activities.
Balloons (Demo)
A balloon is inflated and deflated several times without blowing into it.
Reference: “Simple Science Experiments With Everyday Materials,” by Muriel Mandell, Sterling: New York, 1990; p. 53.
Pour 300 ml of vinegar into a plastic, 2-L pop bottle.
Fill a deflated balloon with baking soda (sodium bicarbonate).
Attach it to the top of the bottle and lift the balloon so the solid falls into the bottle.
The balloon should inflate.
Tie off the inflated balloon and place it in a large shallow pan.
Pour liquid nitrogen over the balloon until it deflates.
Pick up the balloon and allow it to warm to room temperature.
As it is inflating, shake the balloon to indicate a solid is in the balloon.
Repeat as desired.
Explanation: The baking soda reacts with the vinegar to produce carbon dioxide which inflates the balloon. When liquid nitrogen is poured over the balloon the carbon dioxide cools down and deposits as dry ice. When the balloon warms, the dry ice sublimes and reinflates the balloon.
Liquid Nitrogen (Demo)
Properties of things that are very cold.
Reference: “Chemical Demonstrations, Volume 2,” by Lee R. Summerlin, Christie L. Borgford and Julie B. Ealy, Second Edition, American Chemical Society: Washington, 1988; p. 20.
Procedure: Bounce a racquetball and place it in a 600-ml beaker.
Pour enough liquid nitrogen into the beaker to cover the ball.
Using tongs, hold the ball under the liquid nitrogen until the rapid boiling stops.
Take the ball out of the beaker a drop onto a hard floor.
If the floor has carpet, you may have to throw it to the floor.
Have other things available to freeze and break. Flowers and grapes are good.
Allow plenty of time to freeze large pieces of fruit such as bananas.
Explanation: Liquid nitrogen is very cold (-196 °C). It changes the properties of many materials. The flowers and fruit are changed because the water in them freezes. Ice is a good insulator, so it takes longer for larger pieces of fruit. The rubber is brittle because the energy is removed from the polymers and won’t move to compensate for the force applied to them when the ball is dropped.
Tips: Make sure the beaker you use is 400 mL when freezing the racquet ball. Otherwise, the tongs may be too big to take the ball out of the beaker.
Questions Students May Ask: Why do things freeze?
