Osmosis and osmotic pressure assignment 3rd

osmosis and osmotic pressure assignment

1. Physical Chemistry


Assignment no 3
“Osmosis & Osmotic
Pressure”


BS Chemistry 3
rd
The University of Lahore

2. Osmosis & Osmotic
Pressure:

Definition of Osmosis:
“The passage of solvent into solution or from more dilute to concentrated
solution when the two are separated from each other by a semipermeable
membrane is known as osmosis.”
Diffusion of water through the semi permeable membrane from a solution
of lower concentration towards a solution of higher concentration




Solvent Molecule

3. Osmotic Pressure:
“Osmotic pressure is the minimum pressure which needs to be applied to a
solution to prevent interior flow of water across a semipermeable membrane.”

 The pressure required to stop osmosis.

Osmosis & Osmotic Pressure:

4. Determination Of Osmotic Pressure:
 Pfeffer’s Method
 Berkely and Harthey’s Method
 A Modern Osmometer.

Important Terms Of Osmosis & Osmotic
Pressure:
Isotonic:
Solutions have equal concentration of solute, and so
equal osmotic pressure.




Hypertonic:
Solution with higher concentration of solute.
Solvent moves toward the solute’s higher concentration.

5. Hypotonic:
Solution with lower concentration of solute. Water from
such concentration moves outward towards higher
concentration.


Law of Osmotic Pressure:
 Boyle-van’t Hoff law for solutions
 Charles’- Van’t Hoff law for solution
Combination of two law we get Van’t Hoff law for solution we get


Calculating osmotic Pressure:
The ideal gas law states PV = nRT
But n/V = M and so

6.  Where is the molar concentration of particles and is the osmotic pressure, is
Van’t Hoff factor.

Relationship Between osmotic pressure and
colligative properties:
ΔT
i =
(RT
i )
2
ΔH
i
×
n
2
n
1+ n
2


=
(RT
i )
2
ΔH
i
× ??????
2

 ΔT
i
is the elevation in the boiling or depression in the freezing point.
 T
i
is the boiling or freezing point of the solvent.
 ΔH
i
is the enthalpy change during phase change.
 ??????
2
is the mole fraction of solute in solution.


Applications of osmotic pressure:
 Osmotic pressure effects normally move solvent molecules from a dilute to a
concentrated solution. In water desalination a large “external” pressure is used
to push solvent molecules (water) from sea water through a membrane to
produce drinking water. The process is shown below.

7. Importance of osmosis & osmotic pressure:
 Oncotic pressure of blood plasma
 Formation of tissue fluid
 Regulation of cell volume