One suggestion is to watch the reaction take place
in a closed container on a scale. Consider putting
the vinegar and baking soda in separate partitions
in the container, sealing the container, checking
the mass, then tipping the container to mix the
reactants. The final mass should be unchanged.
Why seal the container? Mass conservation is
easy to show when all the products are solids or
liquids, but for this reaction we would like to
account for the carbon dioxide produced as well.
Fortunately we don't expect buoyancy to play a
role since CO2 is still 1.7x denser than air, so
the scale will probably do a good job. (It's still
worth testing, though!)
You can show this with the following:
1. Repeat the experiment in a number of different
containers (glass, ceramic, metal, plastic). This
will tell the students that the container isn't
part of the reaction, since you can do it in
2. Do the reaction inside of a plastic bag.
This will fill up the bag as the carbon dioxide
gas is released.
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