Question

The density of chloroform at a pressure of 220 mmHg and 25 degrees celsius is 1.42 g/L. Calculate the molar mass of chloroform.

My set up is:

mol*K .289 atm 1 1.42g/L
------------- ------------ ------ ---------
.08206Latm 1 298K


What I am unsure of is if this is the right way to take this since 1.42 is not in liters but grams per liter.

Answer 1

I don't think that will get it. You can modify the ideal gas law of PV = nRT for density as follows:
n = g/M where M is molar mass substitute for n to get
PV = gRT/M or
PVM = gRT.
Then P*M = gRT/v but g/v is density in g/L so
P*M = dRT
and M = dRT/P
M = 1.42*0.08206*298/(220/760)

Answer 2

I wasn't in class when my teacher taught me this, and she did not go over the material well, so how were you able to go from PV=nRT to M=dRT/P?

Answer 3

Go back and re-read my original response. I showed you how I did it; i.e., I didn't just pull it out of the air. I derived the equation for you. I started with PV = nRT, substituted grams/molar mass (g/M) for n, rearranged to get P*M = gRT/v, noted that g/v = density = d and that ends up with P*M = dRT. Then I solve for M = dRT/P.

Answer 4

Oh I see now. I read it as each step you had was just different equations that you combined, not as a series of steps. Thank you!