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Homework Help: Molality Question

  1. Sep 24, 2009 #1
    Is molality equal to moles of solute / kg of solvent

    or is it equal to mole of particles of solute / kg of solvent?

    example: is the molality of 0.5 mol of NaCl dissolved in 1 kg of water 0.5 m or 1 m?
  2. jcsd
  3. Sep 24, 2009 #2
    If you're concerned about NaCl it would be 0.5 m NaCl.

    You would treat it as 0.5m Na+ + 0.5m Cl- if you're trying to calculate boiling point elevation or freezing point depression of the water, though. (Because you're interested in the fraction of ions/molecules that aren't solvent)
  4. Sep 25, 2009 #3
    The first one is molality; the second one is osmolality.
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