LearnChemE

#### Osmosis and Reverse Osmosis: Interactive Simulations

These simulations were prepared using Mathematica. Download the free Wolfram player, and then download the simulation CDF file (link given below or click on figure to download). Try to predict the behavior when a parameter changes before using a slider to change that parameter. A screencast below explains how to use the second simulation.

##### Simulation: Osmotic Pressure

This simulation was prepared by S. M. Blinder and is located here. Open content licensed under CC BY-NC-SA.

Osmosis involves the selective passage of certain components of a solution through a semipermeable membrane, with exclusion of other components. The membrane is permeable only to water, but impermeable to the solute in a water solution. The membrane, which is represented by a blue disk at the bottom of the U-tube, separates the pure solvent on the left from the solution on the right. Solvent will spontaneously flow through the membrane into the solution, in an attempt to equalize the concentrations on the two sides. This gives rise to an osmotic pressure. Note that for NaCl, the mole fraction used in the osmotic pressure equation is the mole fraction of ions, which is twice the mole fraction of NaCl. The other solutes in this simulation are undissociated. Osmotic measurements provide a sensitive method for determining molecular weights M, particularly for polymers. For a solute concentration of Cx g/L, the molar concentration [X] is equal to Cx/M.

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

1. Will sucrose or NaCl have a larger osmotic pressure if they each have a concentration of 20 mg/L? Why?
2. When the temperature increases, does the osmotic pressure increase, decrease, or not change? Why?