Osmosis and Colloids

Osmotic Pressure  Another colligative property  A solution and a pure solvent are separated by a semipermeable membrane - membrane allows solvent but not solute to pass through  As time passes, the volume of the solution increases while the volume of the solvent decreases - stops when equilibrium is reached

 Flow of solvent through the semipermeable membrane is called osmosis  Since the liquid levels are different at equilibrium, there is a different fluid pressure  The excess pressure on the solution is called osmotic pressure  The greater the concentration of the solution the greater the osmotic pressure

Reverse Osmosis

Colloids  Small particles can be suspended, without dissolving, in a liquid – don’t settle to the bottom  Can detect these particles by shining an beam of light through the suspension  If the beam is visible from the side, then there are suspended particles scattering light  Called the Tyndall Effect

 Suspension of tiny particles is called a colloid  Suspended particles range in size from 1 to 1000nm  They are classified according to the states of the dispersed phase and the dispersing medium  Pg. 550

 If heat or an electrolyte is added to a colloid, particles may clump together (called coagulation) and fall to the bottom