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Bp and mp

by tipton12
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tipton12
#1
Mar10-05, 12:32 PM
P: 20
does anyone know why it is important to have the melting point of a solute not be higher than the boiling point of the solvent during recrystallization? --having a little trouble rationalizing this.
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The Bob
#2
Mar10-05, 12:54 PM
P: 1,116
Is this not because the pattern will be from a liquid a solid and then to a gas if you decrease the temperature???

The Bob (2004 )
dextercioby
#3
Mar10-05, 01:03 PM
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Are u sure you're asking a right thing...?I mean according to me,it should be the other way around.The solvent (water,e.g.) must have the boiling point temp.less than solute's melting point,AT THE SAME PRESSURE...

Daniel.

tipton12
#4
Mar10-05, 02:04 PM
P: 20
Bp and mp

Ok, you're right dextercioby. I had it the other way around. Oops! But I still am not clear on the reasoning. Here is the website I read it from:
http://www.ux1.eiu.edu/%7Ecfthb/clas...3/Quiz2key.htm
tipton12
#5
Mar10-05, 02:07 PM
P: 20
I only assumed that if the bp of the solvent was higher thanthe mp of the solute than the compound you're trying to isolate will have already melted and mixed completely with the solvent.
dextercioby
#6
Mar10-05, 02:32 PM
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Nope,recrystallization of a solution means:
boiling of the solvent------------->recrystallization of the solute.
Since you want the solute to be solid (that means "recrystallization"),you need to boil the solvent.Ergo,its boiling point < the melting point of the solute (at the same pressure);

Daniel.


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