Since we are running a little behind, I performed the gas volume lab as a demonstration. Since the students just reasoned through the alka seltzer reaction in the mass lab, it was only a short logic jump to knowing the mass of gas created when a tablets dropped in water. The gas collection seemed to blow their minds. Most students reasoned that the gas would be less dense than water, but the estimates were in the .2-.5g/ml range. Our quick calculation yielded .002 g/ml!
Here’s the set up pic from out teacher notes: