In praise of two-litre soda bottles

I have been in this business too long not to know a good thing when I see it. And when I see an empty, clear, 2-L soda bottle, I grab it. At home, we’re not soft drink-people; I have been known to raid my neighbours’ recycle bins and to hover outside class parties in our Lower School.

These simple-looking containers, made of polyethylene terephthalate, are the stuff of carbonated beverages —and chemistry education.

Fig. 1. Polyethylene terephthalate, a polyester (condensation polymer)

And the price is right.

These ubiquitous bottles merit a Wikipedia entry,1 for heaven’s sake. They can be used for everything from water purification2 to a pair of makeshift sandals — I’ve seen people wearing them in Tanzania.³

These bottles changed the soft drink industry. They hold a lot but have a relatively small footprint — perfect for expensive shelf space in grocery stores.

For a chemistry teacher, a 2-L bottle can be used to:

• cut the bottom off to get a well-plate in which to carry out micro-titrations or small-scale aqueous reactions
• use a club soda bottle to store just about any aqueous solution. Remove the original label, give the bottle a quick rinse, and indicate the new contents.
• contain gases other than air. Compare the mass of a sealed bottle that contains air to a bottle filled with, say, natural gas or propane or carbon dioxide (from sublimated dry ice) and you’ve got a relative molar mass calculation ready to happen. If students know the total volume of the bottle and the average molar mass of air, they can determine molar mass of whatever gas is in the bottle.
• put dry ice in the bottle, seal it and leave it in a fume-hood behind a safety shield with the plexiglass window lowered. As the CO2 sublimates, the bottle will expand — and eventually explode. If you get the quantity right, you’ll be able to see liquid CO₂ — fabulous when studying phase diagrams.
• show how NaOH reacts with CO₂(g). Pour about
  30 mL of 6 mol/L into a carbon dioxide-filled bottle and seal it. Shake the bottle — and watch its volume dramatically decrease, courtesy of CO₂(g)  + 2NaOH  →  Na₂CO₃  + HOH(l).   

Gentle readers, I invite you to submit other uses for empty 2-L soda bottles. 

References

1. wikipedia.org/wiki/Two-liter_bottle

2. http://rethinksurvival.com/sunlight-equals-potable-water-infographic/
   

3. http://newsroom.blogs.cnn.com/2009/11/12/shoes-for-africa-sat-nov-14-at-10-p-m-et-on-cnn/