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Homework Help: Cause of melting point depression

  1. Jul 6, 2009 #1
    1. The problem statement, all variables and given/known data

    An unknown compound gave a melting point of 230C. When the molten liquid solidified the melting point was determined to be 131C. Give a possible explanation for this discrepancy.

    2. Relevant equations

    3. The attempt at a solution

    I understand that melting point depression arises from impurities within the lattice of the crystallized sample. But, I cannot seem to find why re-melting a "used" MP sample would lead to a MP depression. Most likely the sample was not cooled quickly, but slowly sitting at room temperature, which should allow the crystal lattice to recombine without any impurities within the capillary tube. Any ideas?
  2. jcsd
  3. Jul 7, 2009 #2


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    Staff: Mentor

    Have you ever seen what happens to sucrose when it is heated to melting?
  4. Jul 7, 2009 #3


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    Science Advisor
    Homework Helper
    Gold Member

    Have you heard of polymorphism?
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