[CHM 112] Freezing Point Depression Lab Question

[Andrew J. Pounds]

That was for the molar mass lab....


for the freezing point depression lab you know the mass of the solute 
(around 25 g) and the mass of the solute (around 3 grams for the first 
part.   Based on the amount of temperature change ($\Delta T$) between 
the pure solution and the one with the solute in it you can set up the 
equation..

$\Delta T = k_f m$

where $m$ is the molality.  The molality is the moles  of solute divided 
by the kilograms of solvent.

$\Delta T = k_f \frac{n}{\mathrm{mass\ in\ kg\ of\ solvent}}$

So plug in $\Delta T$, $k_f$, and the mass in kilograms of solvent to 
solve for the number of moles.

Then divide the actual mass of the solute by the moles you just 
determined to compute the molar mass.




On 07/01/14 20:19, Andrew J. Pounds wrote:
>
>
> On 07/01/14 20:13, wrote:
>>
>> Dear Professor,
>>
>> I have a question about the one part of the 2nd lab. What is the 
>> molecular weight and how would you calculate the molecular weight, in 
>> terms of this lab?
>>
>> I have asked multiple people about it, but they were confused about 
>> it as well. Could you help by any chance?
>>
>> Thanks a lot, professor.
>>
>> Sincerely,
>>
>>
>
> You use the P, V, T data from the lab to determine the number of moles 
> of volitalized liquid in the flask.  You then divide the mass of the 
> liquid after it cooled by the number of moles -- this should give you 
> the molar mass.  Does that help?
>
>
> -- 
> Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
> Professor of Chemistry and Computer Science
> Mercer University,  Macon, GA 31207   (478) 301-5627
> http://faculty.mercer.edu/pounds_aj


-- 
Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
Professor of Chemistry and Computer Science
Mercer University,  Macon, GA 31207   (478) 301-5627
http://faculty.mercer.edu/pounds_aj

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