Non-Ideal Solutions
Many solutions are far from ideal because the interaction energy between molecules is NOT negligible as it would be for an idela solution.  Moreover these energies are complex functions of molecular properties and relative molecular orientations.

You have already discussed the phase properties of liquid crystals, which seem somehow 'modern' and novel.  Some of the properties of amphiphilic molecules have been known for centuries such as the effect of soap an solubility.


We understand much of the dissolution phenmomenon through its energetics (thermodynamics)

The energetics of the dissolution of Ionic Salts to for Electrolytes is particularly interesting because the LATTICE energy and HYDRATION energies are both very high, but sometimes almost exactly cancel out.



A saturated solution has the same rate precipitation and dissolution.  This means a dynamic chemical equilibrium.  The equilibrium constant for, say, a binary salt MX is sometimes called the solubility product, because the pure solvent and pure solid salt do not enter into the equilibrium expression.

KSP = [M+ (aq)]e[X-(aq)]e

The temperature dependence of the solubility product is that of any other equilibrium constant, and depends on the sign and magnitude of the enthalpy change for the transformation.
 

The Gibb's Helmholtz eqn :
 
 

\The van't Hoff eqn:
 
 
 

Gases dissolve in liquids (and solids), but have much simpler behavior than eleectrolytes. For example, gases are less soluble at high temperature than at low temperature.  (What does this say about the enthalpy of dissolution of a typical gas in a liquid?)  Does a gas dissolved in a liquid behave as an ideal mixture?


 


The saturated concentration of a gas dissolved in a liquid depends on its partial pressure of the solute above the solution.

This is a 'special case' of Henry's Law, an empiricle relation that is best applied to dilute solutions.

pi = kH Xi

Where kH is a constant with units of pressure


When the solution is very concentrated, or alternatively when the vapor pressure of the solvent is considered, another similar rlation holds.  The rate of evaporation depends on the available surface area

So Raoult' Law says:


Impurities in a substance cause a change in its phase diagram by making the liquid region bigger.

The addition of solute RAISES the boiling point of a solvent

The addition of solute LOWERS the freezing point of a solvent

(Why molality??  Because it really should be mole fraction, but Molarity depends too much upon the change in volume upon mixing)


OSMOSIS is the movement of solvent through a membrane to equalize the concentration on both sides.

The pressure required to allow for no transport of solvent across the membrane is called the OSMOTIC pressure and obeys the relation:

Osmotic pressure has a great effect on living CELLS, because their walls are a semipermeable membrane.

(a) crenation is caused by water movement out of a cell in a hypertonic solution.
(b) hemolysis is caused by water movement into a cell in a hypotonic solution.