chemistry
posted by Jesse .
a 256 mL sample of an unknown gas was collected over water at 23 degrre celsius and 750 mmHg. the gas has a mass of 0.80 grams. what is the molar mass of the gas? (the vapor pressure of water at 23 degree celsius is 21.0 mmHg)

Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass and solve for molar mass.
In the gas equation, for pressure substitute for P = (75021/760)
Don't forget T must be in kelvin. Volume must be entered in L.