Asked by Hannah

I have to find the calculation of Van't Hoff factor "i" for NaCl and sucrose. The directions say to use the equation

delta Tf = kf X m X i
and to use Kf for water = -1.86C/m

So I have the molality of NaCl and sucrose as well as delta Tf so for NaCl I plugged the numbers into the equation.

2.5C = -1.86C/m X 0.6697mol/kg X "i"

2.5 = -1.2456 X i
i=-2

Did I do this correctly? Thank you for your help!!
Answered by DrBob222
If you have the right m, yes.
Answered by Hannah
Is it ok that "i" is negative?
Answered by DrBob222
No, i is not negative, ever.
Forget the - sign for 1.86 unless you are going to be consistent and place a - sign for 2.5. Wasn't that 2.5 C BELOW the normal freezing point. That's why I don't worry about the signs. You KNOW m is positive you KNOW Kf is negative, you KNOW delta T is a depression. Usually you go through all this to calculate m and you KNOW molality is +.
Answered by Hannah
Ok and for sucrose I did
-4.5C = -1.86C/m X 0.1004 mol X i
-4.5 = -0.1867i

i =24

Can i be a big number like this?
Answered by Hannah
Nevermind, I made a mistake im sorry. Disregard the question.
Answered by DrBob222
I don't believe 24. i should be 1 for sucrose.
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