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Topic: finding molar mass from fp and mass  (Read 3349 times)

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Offline zxwut?

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finding molar mass from fp and mass
« on: February 03, 2010, 09:16:34 PM »
He asks:
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?

Offline 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 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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Offline 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.

Offline 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. 8)
You don't have to call me "sir"  :P.
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

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