1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculating Freezing and Boiling Points

  1. Dec 10, 2007 #1
    1. The problem statement, all variables and given/known data
    Calculate the freezing point and boiling point of each of the following solutions using the observed van't Hoff factors in Table 11.6.

    (a) 0.070 m MgCl2
    Temp Freezing?

    Temp Boiling?

    (b) 0.020 m FeCl3
    Temp Freezing?

    Temp Boiling?

    2. Relevant equations
    Change in T= imK
    i=Van't Hoff factor
    K=freezing point depression or boiling point elevation

    3. The attempt at a solution
    I don't know what the change in temp is so I can't solve for K.
    Tf MgCl2- Change in T= (3)(.07)K Don't know K or T
  2. jcsd
  3. Dec 11, 2007 #2
    ∆Tb=New boiling point-Boiling point of pure solvent
    ∆Tf=Freezing point of pure solvent-New freezing point,
    now knowing boiling/freezing point of the pure solvent, i, m and K(which will be given) you can find the new boiling/ freezing point.
  4. Dec 11, 2007 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    K is a property of the solvent. It has a specific value for every solvent, and can be looked up in your textbook, or a handbook, or on the web.

    See the tables on this page: http://dbhs.wvusd.k12.ca.us/webdocs/Solutions/BP-Elev-and-FP-Lower.html [Broken]
    Last edited by a moderator: May 3, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook