Ethylene Glycol Freezing point

[IanMiller]

I'm trying to figure out the freezing point og ethylene glycol/water solution at various mass % concentrations. Heres the problem: What I remember from Highschool Chemistry is freezing point depression is calculated by Delta F.P= Kfreezing*molality. That will produce a freezing point that decreases with increasing molality. However I have read that at a mass % of about 71% the freezing point will begin to rise again. Why doesn't the equation reflect this and what property of Ethylene Glycol causes this behavior. I pulled some values out of a book for the freezing point, but they differ from the calculated values I get using the previous relation. They start out tracking pretty close but by a 60% solution the book value is -60.21 degrees f and my calculated value is -48.90.

Thanks for the help.

Ian

 

[25362]

Freezing-point depression's formula:
delta T_f=(E_f)(m)
is applicable to ideal solutions (i.e., follow Raoult's Law). Ideal solutions are defined as those in which forces of attraction between all molecules are identical.

Most non-electrolyte solutes agree quite good with this Law for low concentrations. Higher concentrations deviate more and more from ideality, although non-electrolytes such as EG show good correspondence at relatively higher concentrations. The value for the cryoscopic constant of water (E_f)=1.86
mass% molality actual FPD, deg.C calc. FPD
1 0.163 0.3 0.3
10 1.79 3.37 3.33
20 4.027 7.93 7.49
40 10.741 23.84 20.0
60 24.166 51.23 44.9

Showing that as the concentration rises so does the deviation from ideality (the van't Hoff factor is 1.14 for 60% mass solutions).

Since all the particles in solution cause FPD, apparently at higher-than-70% concentrations either the alcohol hydrolyses less or there is some association between molecules e.g., as a result of hydrogen bonding, a fact that reduces the number of "particles" affecting this colligative property, and the FPD becomes narrower.

 

[hydrae]

IanMiller
For a more pracital solution: look in ASHREA's Handbook of fundumentals, the chapter on brines, secondary coolants(chapter 18 in my edition) for charts, tables, and descriptive detail.
Hydrae

 

[maxoverdrive]

I have a chart that I will gladly send you if you send your email address to moverdrive_34436@yahoo.com. also it equates to brix (a sugar measure if you have a low brix refract.

 

[jmw]

Visit

http://www.houghtonchemical.com/fluid/wintrex