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Osmolarity question

  1. Sep 6, 2004 #1
    hello guys!

    i am stucked at this one. i hope you can help me out. i have to make this solution;

    41g/l NaCl
    Hepes-buffer 10mM
    Osm. 960 mOsm

    i know how to prepare all the components, EXCEPT for 960mOsm. i wonder ;
    1. how do i know that i have 960mOsm?
    2. how to adjust the Osm, if the value is not correct.

    and lastly, what is so important with mOsm?

    thank you all for your time and sharing!
  2. jcsd
  3. Sep 6, 2004 #2


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    I think this is also one of Biology's concerns, but let me contribute to the topic as a chemist.

    I have no knowledge about osmolarity, but osmotic pressure is a known issue, easily calculated by a variation of the known gas equation, Pi*V=n*R*T, where Pi is osmotic pressure, V is volume, n is number of moles, R is a constant and T is the temperature.

    However, we may speculate that osmolarity is the concentration of the compound undergoing osmosis, but calculation is the same though; Cosm=nosm/Vosm

    I am sure you know this; osmotic pressure is caused by a membrane. So you are probably using a membrane and causing something to diffuse the other side from the membrane. Maybe this approach helps you a bit.

  4. Sep 7, 2004 #3


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    Actually, osmolarity is calculated as the the product of the molarity and the number of ions in solution per formula unit of the molecule.

    Sometimes, the normality is used instead of molarity - I'm not sure which is the standard convention.
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