Non-volatile vs volatile solutes?

Discussion in 'MCAT Study Question Q&A' started by unsung, Jun 17, 2008.

  1. unsung

    Joined:
    Mar 12, 2007
    Messages:
    1,356
    Likes Received:
    13
    Status:
    Resident [Any Field]
    How do we know if a solute is volatile or non-volatile? I guess salt NaCl is non-volatile because it lowers vapor pressure of the solution and raises Bpt. But what else?
     
  2. Thread continues after this sponsor message. SDN Members do not see this ad.

  3. Kaustikos

    Kaustikos Archerize It

    Joined:
    Jan 18, 2008
    Messages:
    12,216
    Likes Received:
    4,153
    Yeah, I think that's pretty much how I remembered it. If something is a volatile solute it competes for the vapor pressure owned by the solvent. Basically because it has its own vapor pressure as well. Thus, a volatile solute will decrease the vapor pressure for the solvent like you said.
    If you're asking how will we know on the MCAT, truth be told, I don't. I think that the MCAT always tells you this in the passage or question (ie: You add 0.1M of volatile pentene in aqeous alcohol...). I've never had them NOT specify the compound in question as volatile/non-volatile.
    Correct me if I'm wrong, but dont' volatile solutes also affect the boiling point of their solvent different than non-volatile?
     
  4. TJames

    Joined:
    Feb 18, 2008
    Messages:
    11
    Likes Received:
    0
    Status:
    Post Doc
    A volatile solute is something that is itself volatile. When it is in solution it will have a non-zero vapor pressure.

    Also, adding a volatile solute to a solvent will not necessarily raise the boiling point. Adding a very low-boiling solvent such as diethyl ether to a very high-boiling solvent such as DMSO will lower the boiling point.
     

Share This Page