Root Beer Recipe
A great demo of Henry's Law or just good chemistry fun!
The recipe for root beer is:
1 gallon water
1 lb sugar (or sweeten to taste)
1 oz root beer extract
1 lb dry ice
Mix ingredients and put dry ice into mix. Cover mixture. It takes about 45 minutes to work. Ratio this up as you need.
Comments: I use a container that is translucent so that you can see the dry ice sublimating. Tall, round, cylinder water coolers work very easily though. You can screw the lid on tight enough to allow for some pressure release, but still carbonate the drink. You can get the extract at Food Lion and should be able to get it at any grocery, it's with the vanilla and other spices.
Chemistry: Henry's law says that the greater the pressure of the gas above a liquid the more gas will dissolve in the liquid. Soda is carbonated by dissolving carbon dioxide at high pressures into the soda mix. In this demo you use the sublimation of dry ice (-109°F) to obtain the carbon dioxide gas. You need to partially (but to be safe not totally) contain the gas to build up the gas pressure and force more CO2 into the root beer mix.
Ron Robertson, Chemistry Dept.