Could you help me create an experiment to determine the molar m of CO2?

This means that I have to experimentally come up with some grams and moles. We are using alka seltzer tablets. I have only one day left to work on this lab, so it has to be done within an hour. I've already tried using a eudiometer and water trough to measure the volume of the carbon dioxide and from there the moles, but there is too much carbon dioxide produced. Then I cut the pieces into quarters but then no gas of the reaction was coming out into the cylinder. And despite this, I still haven't figured out how to experimentally determine the amount of grams of a gas. Could you please help me figure out what I could do?