This document discusses osmosis and osmotic pressure. It defines osmosis as the passage of solvent through a semipermeable membrane from a lower concentration solution to a higher concentration solution. It defines osmotic pressure as the minimum pressure needed to prevent this flow of water. It discusses methods to determine osmotic pressure and important terms like isotonic, hypertonic, and hypotonic solutions. It also covers the relationship between osmotic pressure and colligative properties, applications of osmotic pressure including water desalination, and the importance of osmosis and osmotic pressure.

1. Physical Chemistry
Assignment no 3
“Osmosis & Osmotic
Pressure”
BS Chemistry 3rd
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 waterthrough thesemipermeable membranefroma solution
of lower concentrationtowardsa solution of higher concentration
SolventMolecule

3. Osmotic Pressure:
“Osmotic pressure is the minimum pressure which needs to be applied to a
solution topreventinterior flow of water across a semipermeable membrane.”
 The pressurerequired to stoposmosis.
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 haveequalconcentration of solute, and so
equal osmotic pressure.
Hypertonic:
Solution with higher concentration ofsolute.
Solventmoves toward thesolute’shigher concentration.

5. Hypotonic:
Solution with lower concentration ofsolute. Water from
such concentration moves outward towards higher
concentration.
Law of Osmotic Pressure:
 Boyle-van’tHoff law forsolutions
 Charles’- Van’tHoff law forsolution
Combination of two law wegetVan’t Hoff law forsolution weget
Calculating osmotic Pressure:
The ideal gas law statesPV=nRT
But n/V = M and so

6.  Whereis the molar concentration of particles and is the osmotic pressure, is
Van’t Hoff factor.
Relationship Between osmotic pressure and
colligative properties:
ΔTi =
(RTi )2
ΔHi
×
n2
n1+ n2
=
(RTi )2
ΔHi
× 𝒳2
 ΔTi is the elevation in the boiling or depression in the freezing point.
 Ti is the boiling or freezing pointof thesolvent.
 ΔHiis the enthalpy changeduring phasechange.
 𝒳2is the mole fraction of soluteinsolution.
Applications of osmotic pressure:
 Osmotic pressureeffectsnormally movesolventmolecules froma diluteto a
concentrated solution. In waterdesalination a large“external”pressureis used
to push solventmolecules (water) fromsea water through a membraneto
produce drinking water. Theprocessis shown below.

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