Dancing Spaghetti 

Parts:

1000 mL beaker filled with 750 mL water

4 Tbsp white vinegar

1 Tbsp baking soda

Thin spaghetti broken into 10-15 approx. 1 in.-long pieces

Food coloring (optional)

 Procedure:

Dissolve baking soda in water.  If using, add several drops of food coloring.  Add pasta pieces and then vinegar.  Over the course of several minutes, the pasta will start rising to the top of the solution and then dropping back down to the bottom in a cyclic dance.  This cycle can continue for many minutes.

 Explanation:

The spaghetti pieces are denser than water, so they normally sink to the bottom.  When the baking soda (base) and vinegar (acid) mix, they react to form carbon dioxide.  Bubbles of carbon dioxide stick to the pasta and, together, they are less dense than the water so they rise to the surface.  Once there, many of the bubbles pop, so the spaghetti returns to the bottom where it can collect more bubbles.
Soda Can Crush 

Parts:

Empty, clean soda cans (also works with larger cans)

Water

Stove or hot plate

Bowl of ice water

Tongs

 Procedure:

Put a small amount of water into each soda can (just a little more than it takes to cover the bottom of the can).  Heat the cans on the stove until water vapor can be seen coming out of the top (keep children away from the heat).  Allow the vapor to flow for at least 30 seconds.  Gently grab the can with the tongs near the bottom and quickly invert the can into the ice water.  The can should immediately collapse.

 Explanation:

As the water boils inside the can, it becomes steam/water vapor which eventually pushes most of the air out of the can.  When the can is inverted into the ice water, the steam rapidly condenses back into water leaving a vacuum inside the can (the water can’t be pulled into the can fast enough).  The air pressure in the room is more than sufficient to crush the can.  This experiment can actually be done with 55-gallon oil drums, though that scale is much less practical for a classroom.
Mentos Fountain 

Parts:

Roll of mint Mentos (not any other kind)

2-liter bottle of diet soda (diet is better because sugar soda leaves a sticky mess)

Test tube large enough to hold the roll of Mentos

Plastic card (such as a driver’s license)

 Procedure:

This demonstration should be done outside (unless you want a really big mess in the room).  Unwrap the Mentos and stack all of them into the test tube.  Open the bottle of soda.  Cover the test tube with the card and invert it on top of the soda bottle.  Slide the card out of the way, allowing all of the Mentos to fall into the soda bottle and quickly move out of the way.  A large plume of soda (can reach at least 20 feet) will burst out of the bottle.

 Explanation:

Soda contains a large amount of dissolved carbon dioxide—this is what makes it fizzy.  Normally, the carbon dioxide slowly escapes from an open bottle as bubbles gradually form on the smooth bottom and sides of the bottle and rise to the surface.  Mentos are covered with countless microscopic cracks that serve as points of “nucleation” for the carbon dioxide to come out of the soda.  With all of those nucleation sites, much of the carbon dioxide comes out of the soda all at once and erupts out of the bottle, bringing quite a bit of soda with it.