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March 27, 2017

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A 1.00% by mass MgSO4(aq) solution has a freezing point of -0.192°C. Water has a kf of 1.86 (K·kg)/mol.
(a) Estimate the van't Hoff i factor from the data.


(b) Determine the total molality of all solute species.

I can probably figure out the second part of the question once I learn how to do the first. I am confused about how to determine what the van't Hoff i factor is. I thought it would be either 6--assuming there were 6 particles in MgSO4...since htat was wrong my next guess was 3. But clearly I'm approaching this the wrong way....

  • Chemistry - ,

    delta T = i*Kf*molality
    You know delta T, Kf, convert 1.00% by mass to molality. Solve for i, the van't Hoff factor.
    By the way, did you get the FeCl3 problem cleared up. You had calculated molality of FeCl3. Multiply by 3 to obtain molality of Cl^- which is what the problem asked for.

  • Chemistry - ,

    I am confused by the 1% by mass part...I don't understand what it really even means or if I am multiplying something by 1% or what? I did eventually realize I had to multiply by 3--I have never seen a problem like that before so I was slow to catch on.

    Thanks for your help

  • Chemistry - ,

    And when solving for molality do I need to use the formula dT=Kf*molality? Or do I find it independently of this equation?

  • Chemistry - ,

    nevermind--after 50 hours of pulling my hair out I finally arrived at the answer :)

  • Chemistry - ,

    How do you convert from mass percentage to molality? I get 0.084 m but that is incorrect.

  • Chemistry --to Bob - ,

    You should not post piggy back on another post; usually these posts get lost in the shuffle. For your question, however, you give an answer but no problem. Please go to the top of the page and click on post a new question and someone will take care of you.

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