posted by Dani .
A hot-air balloon has a volume of 4.000 x 10^5 L at 30 degrees celsius and a pressure of 748 mmHg. If the average molar mass of air is 29.0 g/mol, what is the mass of air in the balloon?
Use PV = nRT and solve for n = number of moles. Then n = grams/molar mass and solve for grams.
Don't forget T must be in kelvin and P should be in atmospheres.