Osmosis and Reverse Osmosis: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • The osmotic pressure is proportional the molar concentration of solute species (i.e., if a solute molecule dissociates, the molar concentration of ions is used to calculate osmotic pressure).
  • For reverse osmosis, the pressure difference (membrane side with the solute -membrane side with pure solvent) must be higher the osmotic pressure.
  • As pressure on the membrane side with the solute increases, the flux through the membrane during reverse osmosis increases.
  • Concentration polarization decreases the solvent flux through a membrane because the solute concentration near the membrane is higher than its concentration in the bulk.
  • Mixing on the membrane side with a solute can decrease concentration polarization and thus increase solvent flux through the membrane.
From studying this module, you should now be able to:
  • Calculate the osmotic pressure for a liquid mixture.  
  • Calculate molecular weight of a solute given the osmotic pressure of the solute.  
  • Explain how fugacity can be used to calculate the equation for osmotic pressure.  
  • Explain how reverse osmosis works to purify a mixture.
  • Understand how concentration polarization affects permeation through a membrane
Additional Screencasts:
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder