Posted by **Kamila** on Monday, March 21, 2011 at 11:40pm.

A container holds 1.00 mol O2, and the pressure in the container is 2.00 atm. A student adds 60.0 g of gas Y to the container. The total pressure (of O2 and gas Y) is 3.00 atm.

What is the molar mass of gas Y?

(V and T constant)

- chemistry -
**Joanie**, Monday, March 21, 2011 at 11:55pm
Ok so i also was going to ask this question but I THINK i figured it out.

remember that mols and pressure are proportional. if 1 mol of O2 gives 2 atm of pressure, then how many mols of a gas gives 1 atm of pressure? (because the total is three, so we just need to find out how to get that extra atm of pressure). so i set up a proportion. 1mol/2atm=Xmol/1atm and i got .5 so then i set up 60g Y/.5 mol and i got 120. it makes sense but im not sure if this is how it was supposed to be done. i did get the right answer so i hope i helped a little!

- chemistry -
**DrBob222**, Tuesday, March 22, 2011 at 12:39am
Yes, 120 is correct.

I worked it with mole fractions.

XO2 = (PO2/Ptotal) = (2/3)

Xunk = (Punk/Ptotal) = (1/3)

Then for oxygen, (1 mol)

(mol O2/(mol O2 + mol unk) = 2/3

Solve for mole unk, then moles = g/molar mass and solve for molar mass.

Your solution is more esoteric than mine.

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