Pepsi & Pub Drafts
Just drop, without explanation of any kind, a Pepsi and a Diet Pepsi into
an aquarium or visible sink full of water. The kids are shocked at 1st to
see the Diet Pepsi float while the regular Pepsi sinks like a rock. (You
can even ask them to predict what will happen BEFORE you do this demo.)
Have them explain it. Again, kids answers are sometimes amazing. Then
discuss with them the variation in density between the corn syrup used in
regular and the powdery sweetener used in Diet drinks. This can also lead
into a discussion of the meaning of the stupid term "fluid ounce".
Kids think that's a measure of weight. It's not, since both cans would
then have the same weight (mass), but they obviously don't. It's a volume
measure. If you had 12 ounces of water, it would occupy the same space as
the soda in these cans.
Pub Draft: Check
with your building Principal and/or Dept Head on this one for clearance
first. You can demonstrate a pretty amazing little trick with a Guinness
Pub Draft can. (Yes, it's a beer-like substance. And if you can't figure
out what to do with it AFTER this demo, send it to me for proper
disposal....)
Note the Caffrey's is floating upside down???
ALERT ALERT! As of the Fall of 2000, Guiness Pub Draft cans no longer use "mounted" Nitrogen cannisters.They went the cheap route, like everyone else is and now use the floating plastic Nitrogen balls that erupt upon opening. A good substitute is Caffrey's Pub Draft cans. They still install a mounted pellet.
Caffrey's is a nitrogen-injected beverage. Place the can in
the aquarium right side up. It will slowly invert itself to end up with its bottom just barely sticking out of the water. What's this
about? A small nitrogen cartridge is in the bottom of the can! So, in
essence, the bottom of the can is air filled making the can slightly top
heavy. Further discussion of the cause of the capsule rupture, is also
worthwhile. (Opening the can relieves the cans pressure and causes the
seams of the capsule then to separate under the higher pressure inside
now...). Reminder : Get someone's permission to use the beer can.
I then use the tragic
incident of the mass deaths that occurred in Camaroon, Africa in 1984 AND
1986. This info is reported in depth in the Sept 1987 National
Geographic pp404-420. I use the National Geographic CD Collection to view the pictures and charts of the rticle on the student's computer monitors. A common highly carbonated volcanic lake is situated
ABOVE an inhabited valley. Some shaking in the lake's bed from a small volcanic tremor that released a land slide caused the water
to stir up. The CO2, which was dissolved in the colder waters at the
bottom, which CO2 will do - dissolves in colder, undissolves in warmer,
hence the 'burp' of the soda drinker - undissolved upon warming toward the
top of the lake. A huge CO2 cloud then rolled down the volcano's side into
the sleeping villages and killed all in its path. Why did it 'roll' down
the mountain? CO2 has a density of 1.97 and air is only 1.29. So the denser
CO2 will actually SINK in air. Poor folks didn't know what hit them.
A secondary quik and fun demo with this to drive home the point that CO2 dissolves more readily in COLD water is to do the following. Refrigerate or put on ice several sodas and leave an equal number of sodas sitting out in a warm room. During class, pass out the cold sodas to some kids and tell them to 'pop' their cans all at the same time. A minor 'popping' will be heard. Now, pass out the warm (and oftimes shaken - HeeHee...) cans to the other kids. Ask them to do the same. A huge pop followed by foaming occurs! Kids love this. You can also have a "burping" contest. Have a kid from the 'cold' group compete against a kid from the 'warm' group. It's interesting to see the warm one always burps more and quicker.
