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Homework Help: Is water a solvent in this problem?

  1. Feb 22, 2009 #1
    The problem statement, all variables and given/known data
    Determine the molality of a solution of water dissolved in methanol for which the mole fraction of water is 0.25.

    Hi all,
    I just want to ask if water in this problem is a solvent or a solute!? Is water always a solvent even though they say "a solution of water dissolved in methanol" in the problem? Please help me clear it up.
  2. jcsd
  3. Feb 22, 2009 #2
    It appears you've answered your own question. Also, note the mole fraction of water in the solution.
  4. Feb 22, 2009 #3
    Thanks!!! Yes, and that's how it get me confused. A solvent is what we have more of, and a solute is what we have less. This appears violating the common rule. I think this is an exception right? what do you think?
    Last edited: Feb 23, 2009
  5. Feb 23, 2009 #4
    That's basically how you look at it. Consider a typical aqueous solution, say 1M HCl. That means there's one mole of HCl in one liter of water. But water is at roughly ~55M so there's quite a bit more of it. In this case, we're told that a water/methanol solution has water at 0.25 mole fraction. By extension we know that methanol has to be 1 - 0.25 = 0.75 which of course is greater than 0.25 so we can only conclude that methanol is the solvent here.
  6. Feb 23, 2009 #5
    Yes, that makes sense to me! Thank so much!
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