Directions
Osmosis involves the selective passage of certain components of a solution through a semipermeable membrane, with exclusion of other components. This membrane is permeable to water, but impermeable to the solute. The membrane at the bottom of the U-tube separates the pure water on the left from the aqueous solution on the right. Water will 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 Π. Osmotic pressure 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 cX/M. An osmotic pressure of 10-3 atm would cause a rise of 1.033 cm for the solution in the tube.
Details
For dilute solutions, the osmotic pressure, in atm, is well approximated by the van 't Hoff equation Π = i[X]RT, where [X] is the solute concentration (mol/L), R = 0.8206 (L atm)/(K mol), T = temperature (K). The van 't Hoff factor i represents the number of ions per molecule for a dissociated solute. For NaCl, i = 2. The other solutes in this simulation are undissociated with i = 1.
About
This simulation was created in the Department of Chemical and Biological Engineering at University of Colorado Boulder for LearnChemE.com by John L. Falconer using Claude AI. It is a JavaScript/HTML5 implementation of a Mathematica simulation by S.M. Blinder. It was prepared with financial support from the National Science Foundation (DUE 2336987 and 2336988). Address any questions or comments to LearnChemE@gmail.com.