Are some molecules heavier than others

A balance can be used to measure weights. Make a balance like the one shown. Tie a paper bag to each end of a meter stick. Tie another string in the middle of the meter stick and have a friend hold the string. Move the string along the stick until you get the bags balanced at the same height from the floor. 

You need to make some carbon dioxide molecules. Cover the bottom of the plastic pail with one cup of baking soda. Next pour two cups of 

A meter stick or yardstick Two grocery bags Five pieces of string 

When you have finished making your observations, pour the liquid in the pail down the sink. Rinse-the pail and the sink with water. 

Which paper bag went down - the one containing the air molecules or the one containing the carbon dioxide molecules Continue to hold the balance steady for several minutes. Do both paper bags move back to the same height  

---