Osmotic Pressure

Osmosis is the spontaneous flow of the solvent molecules from a less concentrated solution (dilute) to a more concentrated solution through a semi-permeable membrane. The driving force of osmosis is called osmotic pressure. Osmotic pressure may be defined as "the minimum excess pressure that has to be applied on the solution to prevent the osmosis (entry of the solvent into the solution through the semi permeable membrane)".

According to Van't Hoff, for dilute solution,

Osmotic pressure of a solution  molar concentration of solute in that solution
 

C	where,	R = Gas constant = 0.0821 lit atm K-1 mole-1
CRT		T = Temperature
=		C = Molar concentration
=		C =
		WB = wt. of solute
		MB = molar wt. of solute d = density of solution

Isotonic Solution

Two solutions having same osmotic pressure are called isotonic solutions. For isotonic solutions,

₁ = ₂
 

or	C1 = C2
or

Note: (i) In all numerical problems on osmotic pressure, percentage means weight/volume unless density of the solution is given. (ii) If a number of solutes are present in the solution the total osmotic pressure becomes sum of partial osmotic pressures. P = P1 + P2 + P3 + ........... .