Chemistry gas law problem. I need help!!

A compound of P and F was analyzed as follows: Heating .2324 g of the compound in a 378 cm^3 flask turned al of it to gas, which had a pressure of 97.3 mmHg at 77 degrees C. Then the gas was mixed with calcium chloride solution which turned all of the F to .2631 g of CaF2. Determine the molecular formula of the compound.

I have no idea how to do this or even where to start... can you help me by explaining to me how to do this? My chem teacher said we'd need to do gravametric analysis.... Thanks so much if you can!!

molecular weight of the gas:

(97.3 / 760) (0.478) = (n) (0.08206) (350)

n = 0.001684967 mol

0.2324 g / 0.001684967 mol = 138 g/mol

We will use this to move from the empirical formula to the molecular formula.

amount of F:

0.2631 g times (38.0 g / 78.074 g) = 0.128055 g

This is the gravimetric factor you teacher referred to. (38.0 g / 78.074 g) is the decimal percent of F in CaF2.

moles F:

0.128055 g / 19.0 g/mol = 0.00674 mol

moles P:

0.2324 g minus 0.128055 g = 0.104345 g

0.104345 g / 31.0 g/mol = 0.003366 mol

empirical formula:

P ---> 0.003366 / 0.003366 = 1
F ---> 0.00674 / 0.003366 = 2

PF2

get molecular formula:

PF2 weighs 31 + 38 = 69

138 / 69 = 2

PF2 times 2 = P2F4 <--- That's your answer

Here's another P2F4 problem for your dining pleasure:

http://answers.yahoo.com/question/index?…