Liquid Nitrogen
The main ideas we are trying to get across in this presentation are scientific observations and hypotheses, temperature scales, number lines and circle graphs, composition of atmosphere, relationship to periodic table and emphasis that chemicals are not necessarily poisonous and in fact are what we eat. This is also the demo where we make ice cream, and so it acts as an end of year treat for the kids.
The kids will all have a copy of THIS assignment sheet.
Introduce Yourself!
Tell the kids your name(s), what you are studying, why you are studying. Why you wanted to go to college, what you plan to do when you leave college, why you like college. Try to minimize questions about college life at this point (this shouldn't be difficult, they will probably be shy at the start), and return to this at the end.
Setup
This demo requires some setup. Put an egg in the small open container with LN2, it should look like it is boiling. Have the polystyrene container half filled with LN2 also. Have gloves and goggles at the ready. Safety is an issue here, the kids will want to touch everything. Keep them back at a safe distance, have them wear goggles.
First the egg.
Point out that it looks like it is boiling, in fact it is. Ask them what is happening. Leave the egg boiling for now.
Next, flower.
Ask them what they think will happen to a flower when placed in LN2. Ask them for a HYPOTHESIS. As always, let them think of an answer before proceeding. Freeze the flower and crush it, this is always fun!.
Next, balloon.
Again, ask them what they think will happen to a balloon when placed in LN2. Ask them for a HYPOTHESIS based on what they have seen so far! Get as many hypotheses as possible before proceeding. After freezing the baloon, show than that it returns to its normal shape, thus the air hasn't gone anywhere. You can show then the frozen air if you are quick.
Next, racquet ball.
Again, ask them what they think will happen to a balloon when placed in LN2. Ask them for a HYPOTHESIS based on what they have seen so far! Get as many hypotheses as possible before proceeding. After freezing the ball, take it and the egg outside and smash them. For safety reasons, have the kids stand as shown in the picture below. Tell them NOT to pick up the frozen ball and egg parts.
Next, the number line and circle graph.
This exercise is to get them calibrated on temperature scales and the composition of the atmosphere.
Next, nitrogen as a chemical.
Ask them whether nitrogen is a chemical, if it is, is it poisonous. They should be able to work out that if it is in the atmosphere, it can't be poisonous!
Next, the ice cream!
It takes at least 3 people to do this. Pour half the mixture into one plastic beaker, the other half into the other. It needs one person each to stir each beaker and one to pour the LN2. You need to stir CONSTANTLY, and make sure that it isn't getting icy around the sides of the beaker. Add the LN2 a little bit as a time. It takes more LN2 than you think. Even after you have made the ice cream, add some more LN2 to prevent it from melting too quickly. Serve with syrup and M&Ms.
Next, the ice cream!
It takes at least 3 people to do this. Pour half the mixture into one plastic beaker, the other half into the other. It needs one person each to stir each beaker and one to pour the LN2. You need to stir CONSTANTLY, and make sure that it isn't getting icy around the sides of the beaker. Add the LN2 a little bit as a time. It takes more LN2 than you think. Even after you have made the ice cream, add some more LN2 to prevent it from melting too quickly. Serve with syrup and M&Ms.
Wrap up.
Complete the assignment sheet. depending upon how much time there is left encourage the kids to ask questions about the demos, college life etc.
Direct the presentation in whatever direction seems most appropriate for your particular class and situation.
Ice Cream Recipe
1. One quart of half and half
2. One quart of wipping cream
3. One carton of egg substitute
4. One and a half cups of sugar
5. Six tablespoons of vanilla
This is enough for a class of ca. 30 kids.