# What is the molar mass of the unknown gas?

1. Mar 8, 2005

### chemister

All of the gas inside of a flask is removed and the flask is found to weigh 123.17g. It is filled with a gas of unknown molar mass until the pressure inside the flask is 658 torr at 23 degrees celcius. The flask is then found to weigh 132.92g with the unknown gas. The unknown gas is removed and the flask is filled with water and found to weigh 1002.65g. Assuming the ideal gas equation holds, what is the molar mass of the unknown gas?

I know that the density of water at 23 degrees celcius is 0.999g/ml. Would I use the equation Density=Pressure X Mass / R X Temp.?

THANKYOU!

2. Mar 8, 2005

### dextercioby

U can easily find the mass of the gas,its density under those conditions and then use
$$\mu=\frac{\rho RT}{p}$$

Daniel.

3. Mar 9, 2005

### chemister

What Do The Different Variables Stand For In The Equation?

4. Mar 9, 2005

### dextercioby

µ is the molar mass.\rho is the volumic mass density.R is the universal gas constant,T is the absolute temperature,p is the pressure...

Daniel.

5. Mar 9, 2005

### GCT

Well, you'll need to use the ideal gas equation

$$PV=nRT$$

which of these variables is not given explicitly? The volume. How would you find the volume? hint: using the density of water and the mass of water in the flask

You can now solve for n, moles. The rest should be simple, you should now easily be able to find the molar mass on your own.