What do you predict would happen if you conducted this experiment using sulfur hexafluoride (sf6) which is much heavier than methane or butane?

The volume of SF6 would be larger and this would affect the pressure in the flask .

Explanation:

If we conducted an experiment using same number of moles of sulfur hexafluoride (SF6) ,methane or butane, there will be no any effect on temperature, pressure  and volume. But if we conducted an experiment using same weight of sulfur hexafluoride, methane or butane, there will be some effect on temperature, pressure and volume.

Hope that helps!