Homework Help: chem

Posted by ~christina~ on Monday, September 3, 2007 at 11:17pm.

1.) When determining the melting point it's described in my text as recording 2 points in the melting process.
a) when the first drop of liquid is seen
b) when all of the compound is liquified

and since I have to determine the melting point of sulfanilamide pure and impure (I get the pure after crystalization and the impure is the before sample)

My question pertains to should I trust the temperature that is stated on the web. Secondly when seeing the "first" drop of liquid from the compound does it litterally present itself as a drop of liquid (descriptions in books can be misleading sometimes)

2.)What will happen if you choose a solvent whose boiling point is higher than the melting point of the compound to be crystalized?

-I was confused as to what was said before ...so..I'll propose my thoughts before I have to hand this in tommorow...

I think that if the boiling point is higher than the melting point wouldn't the solution boil before the compound to be crystalizes melts at all? (I thought about this awhile and it should be but isn't in my text)

chem - DrBob222, Tuesday, September 4, 2007 at 12:01am
1. It will be obvious when the first crystal melts. It may not be a "drop" as such so it isn't literal but you can't miss it. As for the literature mp, no, I wouldn't trust them for your samples. They will be good boundaries to guide you but the mp of your samples will depend upon the purity, both before and after recrystallization.
#2 I will leave. I know you and Bob Pursley have talked about it.
chem - ~christina~, Tuesday, September 4, 2007 at 12:03am
Thanks Dr.Bob for all your help, I'll make note of that when I do lab tomorrow =D

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