Posted by Lee on Wednesday, May 11, 2011 at 9:50pm.
A 1.00 L sample of a pure gas weighs 0.785 g and is at 733.4 torr and 29.2 degree celcius.
a) what is the molar mass of the gas?
b) if the volume of the temperature are kept constant while 0.400 g of the same gas are added to that already in the container, what will the new pressure be?

Chemistry  DrBob222, Wednesday, May 11, 2011 at 10:01pm
Note the correct spelling of celsius.
1). Use PV = nRT and solve for n = number of moles, then n = grams/molar mass. You have n and grams, solve for molar mass. Don't forget to convert T to kelvin and P to atmospheres.
2) Add 0.400 g to grams already there, use the molar mass from the first part to convert grams to moles, then use PV = nRT and solve for pressure in atmospheres.