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How volatile impurity affects boiling point of a liquid?

  1. Jan 13, 2017 #1
    I know that non volatile impurities increases the boiling point of a liquid.

    Does volatile impurity decreases the boiling point? How?
     
  2. jcsd
  3. Jan 13, 2017 #2

    Borek

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    Staff: Mentor

    In general more volatile things boil first, don't they?

    What is the definition of the boiling point? Why does the presence of non-volatile impurity increase the BP temperature? (hint: Raoult's law). Can you extend this line of thinking?
     
  4. Jan 13, 2017 #3
    Because the presence of impurities will block more molecules to jump to gaseous state so the vapore pressure will decrease, hence more energy is needed to elevate vapore pressure to environment pressure and higher boiling point is resulted.

    So, does presense of volatile impurity will cause higher vapore pressure? Because it vaporizes it by itself

    [sorry if my English is bad]
     
  5. Jan 13, 2017 #4

    Borek

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    Staff: Mentor

    OK

    It is not exactly about energy (although in a way you are right, you need energy to heat up the mixture), more like you need a higher temperature so that the partial pressure of the solvent becomes equal to the external pressure. But in general you are on the right track. Note that is pretty easy to show using Raoult's law (try!).

    Yes.

    Actually it is not just bad, it is atrocious :wink: But everyone has to start somewhere.
     
  6. Jan 13, 2017 #5
    Thanks!
    :)

    And I will keep improving my english ;).
     
  7. Jan 13, 2017 #6

    Borek

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    Staff: Mentor

    Popracuj popracuj, warto.
     
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