F       How to do diffusion problems (Rules)  -- The ANSWERS

         1     FACTS TO REMEMBER IN SOLVING THESE PROBLEMS

                  a    Smaller molecules diffuse faster than larger ones.  Due to its small size,  which of
                     the above four molecules diffuses first?   _ WATER _

                b     Molecules diffuse from regions of _ GREATER_ conc. to ones of _ LESSER_ conc.

         2     STEPS IN DIAGRAMMING THE PROBLEM

                a     Draw & label all stated information on a set-up diagram (one of the two formats
                        in section E above).

                b     Change known solute concentrations into equivalent solvent (water) concentrations
                        (If you have 3% sugar (the solute) dissolved in water (the solvent), then the solvent
                         concentration is (100%-3%)  _ 97 I hope_  % water.

                c     Draw a thick arrow showing the direction of water diffusion (osmosis) 
                       Why does the water & not the solute move first and faster than the solvent?
                       __ It is smaller than any of the possible solute molecules  __

                d     Locate where in the diagram water is first gained and place a “G” in this location.
                        This location varies from problem to problem. 

                e      Draw a thin arrow showing the direction of diffusion of the solute (sugar or salt)
                       The solute (sugar or salt) is also diffusing in the direction  O P P O S I T E to that
                       of the water solvent.  The solute is moving at a  S L O W rate compared to the
                       water.

                        (Bio H only)  After a very long time, the water diffusion will  R E V E R S E    
                        D I R E C T I O N   and the water will eventually be  E Q U A L  in
                        concentration on both sides of the membrane. 

         

 

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