Subject: Is mass conserved in a reaction between vinegar and baking soda?

My students were performing a lab to investigate the concept of conservation of 
mass.  When they mixed baking soda and vinegar (as well as hydrochloric
and sulfuric acids) in a sealed plastic bag, the products invariably
lost a small amount of mass.  We discussed bouyancy of the gas evolved, but
decided that carbon dioxide was heavier than air, not lighter.  I could
not explain this loss of mass.  Any ideas?

Our procedure;
1. place approx 4 grams of baking soda in a ziplock bag.
2. fill a micropipette with vinegar, place in bag.
3. mass the system.
4. without opening the bag, squeeze the pipette and mix the reactants.
5. after two minutes, mass the system again and compare masses.

Thanks!

Gary K. Webber

Re: Is mass conserved in a reaction between vinegar and baking soda?