Chemistry
posted by Amy .
1.) A convenient method of determining the volume of a container of irregular shape is to fill it with a liquid of known density and measure the mass. An empty Erlenmeyer flask marked "10 mL" weighs 26.3251 g. When filled with mercury, with density = 13.5340 g/mL (at 25.0 C), it weighs 176.2510 g.
a.) Calculate the true volume of the flask.
b.) The flask is considered "empty," but it in fact contains air, which has a density = 0.0012250 g/mL. When it contains a gas at 100.0 C, its mass is 26.3415 g. Calculate the molar mass of the gas.
c.) Elemental analysis of the gas shows that it is composed of 85.63 % C, 14.37 % H, and no other elements. What is the molecular formula of the gas?
I'm stuck on a.) and I can't continue to the next part. Any help is appreciated!

I don't think the answer to a is used in the other questions.
mass Hg + flask = 176.2510 g.
mass empty flask = 26.3251

mass Hg 176.251026.3251 = ?
volume = mass/density = substitute and solve for volume 
For the true volume of the flask I got 11.0777 mL.
For part b.) I am trying to use the formula:
molar mass = mRT/PV, however I don't know what number to substitute for V.