1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Biology: Solutions equilibrium

  1. May 1, 2007 #1
    1. The problem statement, all variables and given/known data
    The solutions in the arms of a U-tube are separated at the bottom of the tube by a differentially permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 molar glucose and 0.5 molar sodium chloride (NaCl) and side B is filled with a solution containing 0.8 molar glucose and 0.4 molar sodium chloride. Initially the volume in both arms is the same. If you examine side A after three days, you should find...?

    3. The attempt at a solution
    The solution is: a decrease in the concentration of NaCl, an increase in the concentration of glucose and a decrease in the water level.

    However, since the membrane is not permeable to glucose, why does the glucose level change? Why does the water level decrease?

    Thanks!
     
  2. jcsd
  3. May 1, 2007 #2

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You didn't mention which arm of the U tube would see a decrease in level.

    I would think that since the membrane is permeable to NaCl that the concentration of NaCl in both sides of the U tube would equilibrate and there would be no osmotic pressure from that component. The glucose side would exert an osmotic pressure since it cannot cross the membrane but it is not clear, from the answer you gave, if the glucose side would see an increase in level or a decrease in level. You can figure that out, I'm sure.
     
  4. May 1, 2007 #3
    All the changes are in side A..
     
  5. May 2, 2007 #4

    Borek

    User Avatar

    Staff: Mentor

    You have either changes of the solution level on both sides or on none. This is simple mass preservation.
     
  6. May 4, 2007 #5

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Let's try backing up a step in the thought process and see if these questions help you answer the above questions. Besides NaCl, what else in the tube can move through the membrane? And, how does that "other" substance moving through the membrane change if concentrations of either NaCl or glucose differ on either side of the membrane?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?