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### Topic: finding molar mass from fp and mass  (Read 3397 times)

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#### zxwut?

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##### finding molar mass from fp and mass
« on: February 03, 2010, 09:16:34 PM »
A solution of 2.500g of BHT in 100.0g of benzene had a freezing point of 4.880 degrees Celcius. What is the molecular mass of BHT?

My first thought was to use MM of solute= [(Kb)(mass solute)(i)] / [(delta Tf)(kg solvent)] but I don't know the differential freezing point temperature. How do I go about finding that or am I totally off base here?

#### Schrödinger

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##### Re: finding molar mass from fp and mass
« Reply #1 on: February 03, 2010, 10:26:02 PM »
Your formula seems to be ok except for the fact that Kb has to replaced by Kf, since we are dealing with freezing point depression.

As for the $request=http://www.forkosh.dreamhost.com/mimetex.cgi?{+\Delta+T_f+}&hash=897a8650e6d16478354f412e4c4bfa3e$ part, you have the freezing point of the solution and you can find the freezing point of pure solvent (google/wikipedia-benzene)
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#### zxwut?

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##### Re: finding molar mass from fp and mass
« Reply #2 on: February 03, 2010, 11:09:32 PM »
Oh, I see. Thank you very much, sir.

#### Schrödinger

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##### Re: finding molar mass from fp and mass
« Reply #3 on: February 04, 2010, 12:30:39 AM »
Dude, I'm just a 17 year old.
You don't have to call me "sir"  .
Anyway, feel free to ask doubts
"Destiny is not a matter of chance; but a matter of choice. It is not a thing to be waited for; it is a thing to be achieved."
- William Jennings Bryan