What mass of calcium chloride must be added to 100 grams of water to make it fre

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What mass of calcium chloride must be added to 100 grams of water to make it freeze at 269 K?

May 19th, 2015

Hello!  Hope this helps:

The equation you will use is Blagden's Law:

deltaTf=Kf*b*i

deltaTf=freezing point depression=Tf(water)-Tf(solution)

Tf(water)=273K, Tf(solution)=269K

Kf=cryoscopic constant = 1.853K*kg/mol for water

b=mol CaCl2/kg of water=mol CaCl2/.1kg water

i=number of ion particles per individual molecule of solute(CaCl2) = 3

deltaTf=Kf*b*i

273-269=(1.853)*(mol CaCl2 / .1)*3

4=55.59*mol CaCl2

mol CaCl2 = .072 mol

Now use the molar mass of CaCl2, which units are in grams per mole, then multiply by moles to get answer in grams of CaCl2.

CaCl2: 110.98g/mol * .072mol = 8grams (approximately)

Let me know if you have any questions.  Please give me a rating so I know how I'm doing.  Best of luck to you :).

May 19th, 2015

What calculations gave us .072 mol?

May 19th, 2015

4 / 55.59

May 19th, 2015

ur good thanks!

May 19th, 2015

You're welcome!  Give me a good rating if you get the chance :).  Good luck with everything else!!!

May 19th, 2015

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May 19th, 2015
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May 19th, 2015
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