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Homework Help: Delta T is making my solution come out negative

  1. Sep 10, 2016 #1
    1. The problem statement, all variables and given/known data
    Lauryl alcohol is obtained from coconut oil and is used to make detergents. A solution of 5.00 gram of lauryl alcohol in 0.100Kg of benzene freezes at 4.1 degrees Celsius. What is the molar mass of the lauryl alcohol?
    Kf for benzene = 5.12, Freezing point of benzene is 5.5

    2. Relevant equations
    Molality = mol of solute/kg solvent
    Delta T = (Kf) x (m)

    3. The attempt at a solution
    (4.1 - 5.5) = (5.12) x (m)
    m = -0.27344

    -0.27344 = (5.00g/mm)/0.100Kg
    5/(-0.27344) x (0.100) = mm

    molar mass = -182.855

    So when im doing delta t, its supposed to be final minus initial right? So im doing the new temperature, 4.1, degrees as the final, and the unchanged or natural temperature, 5.5, as the initial. The answer would be the same thing just positive, but im probably doing something wrong to have this negative answer. Is delta T supposed to be absolute value? Maybe its supposed to be 5.5 - 4.1, but that doesnt make sense, why would 5.5 be the final temp?

    edit: I just found out that Delta T can mean different things. So for this formula, delta T is Tf^0 - Tf. So i figured it out
    Last edited: Sep 10, 2016
  2. jcsd
  3. Sep 10, 2016 #2


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    Gold Member

    Way to go.
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