[CHM 330] Homework Question

[Andrew J. Pounds]

On 10/19/25 19:51,  wrote:
> Good evening Dr. Pounds,
> I hope you are well! I'm struggling to get an answer for chapter 6 
> question 5 part D on osmotic pressure. Would you be able to explain 
> this part?
> Thanks!
>
> Get Outlook for iOS <https://aka.ms/o0ukef>

So in the ideal case the vapor mole fraction would be the moles of 
mannitol over the moles of mannitol + the moles of water.  If you 
multiply this by the vapor pressure of water you get the amount the 
vapor pressure of the water was lowered by the presence of the 
non-volatile mannitol.

Use the observed vapor pressure that was given to determine the observed 
vapor pressure lowering, and then the mole fraction of mannitol.  Once 
you have the mole fraction of mannitol you can do a little algebra

mole fraction of mannitol = moles manitol / (moles water + moles mannitol)

to determine the moles of mannitol in the solution.  You don't have the 
volume of the mannitol, but in this case it is negligible compared to 
the 1000 ml of water. Then set up the Osmotic pressure equation

Pi V = nRT

I found it easiest to compute the Osmotic pressure in atmospheres and 
then convert to Pascals.


-- 
*/Andrew J. Pounds, Ph.D./*
/Professor of Chemistry and Computer Science/
/Director of the Computational Science Program/
/Mercer University, Macon, GA 31207 (478) 301-5627/
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