As a demonstration, I weighed a 2L bottle, some water and alkaseltzer = 155.45g
Then the alkaseltzer was put in, and capped.
We observed bubbling, the a.s. disapearred; it just looked like water at this point.
It was reweighed. The mass now was the same 155.45g
The cap was loosened, a hissing was heard.
It was reweighed. The mass in now 155.27g
The mass of the gas was 0.18g
Conclusion: Matter can not be created or destroyed; gas has mass
Notes: this was a chemical change, a new substance substance, the gas, carbon dioxide was formed
Carbon dioxide is odorless, colorless, tasteless, more dense than air, and does not support combustion
Carbon dioxide is not poisonous( we inhale and exhale it), but it is not oxygen, so we would suffocate in an atmosphere of it.