Colligative properties depend only on the number of solute particles and not their identity. They include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. The boiling point of a solution is higher than the pure solvent due to lowered vapor pressure when solutes are added. Boiling point elevation is directly proportional to the molal concentration of the solute. Freezing point is also depressed when solutes are added, with freezing point depression directly proportional to molality. Osmosis is the movement of the solvent through a semipermeable membrane from a region of lower to higher solute concentration.

1. COLLIGATIVE PROPERTIES
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2. COLLIGATIVE PROPERTIES
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Colligative properties depend only on the
number of solute particles present, not on the
identity of the solute particles. Among
colligative properties are
Vapor pressure lowering
Boiling point elevation
depression of freezing point of solvent in
solution
Osmotic pressure

3. BOILING POINT ELEVATION
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BOILING POINT
Boiling point is defined as the temperature at
which the vapour pressure of liquid becomes
equal to the atmospheric pressure .
Boiling point is a characteristic property of
liquids and is criterion to check the purity of
liquids.
It increases with in external pressure . Liquids
having grater intermolecular forces have high
boiling point.

4. ELEVATION OF BOILING POINT
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 It is known that a liquid boils only when its
vapour pressure becomes equal
atmospheric pressure. But when
to the
a non-
volatile solute is added to the solvent,the
vapour pressure is lowered.
In order to boil the solution, the temperature
has to be raised further so as to make its
vapour pressure equal to atmospheric
pressure.

5. In the graph shown above, we can see
the change in vapour pressure of a pure
solvent and a solution with the increase in
temperature. Here, we can see that the two
samples, the solvent and the solution, will
attain the condition of boiling when their
vapour pressure becomes equal to the
atmospheric pressure. We can see here,
the pure solvent attains this condition at a
temperature equal to Tb° whereas, for the
solution to attain this pressure, the
temperature of the sample needs to be
increased by a small amount equal to ΔTb,
such that,
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6. Here the value ΔTb is known as the elevation in boiling
point. The value of ΔTb for a solution depends upon the number of
molecules of the non-volatile solute. It has been shown
experimentally that the elevation in boiling point is directly
proportional to the molal concentration of the solute in a solution.
T is the change in boiling point of the solvent,
Kb is the molal boiling point elevation constant, and
m is the molal concentration of the solute in the solution.
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7. Here molarity is the number of moles of solute
dissolved in 1 Kg of solvent and the contast of
proportionality,Kb is called Boiling point
elevation constant .
The unit of Kb is K kg mol-1
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8. FREEZING POINT DEPRESSION
FREEZING POINT
 The temperature at
which liquid state is converts
into a solid state. It is
opposite to melting point.
Pressure increases freezing
point also increases.
Hence freezing point of a
liquid is a temperture at
which the vapour pressure of
soild is equal to the vapour
pressure of liquid.
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9. DEPRESSION OF FREEZING POINT
Freezing point depression is a colligative property
observed in solutions that results from the
introduction of solute molecules to a solvent.
The freezing points of solutions are all lower
than that of the pure solvent and is directly
proportional to the molality of the solute.
ΔTf=Tf°(solvent)−Tf(solution)
ΔTf is the depression in freezing point
Tf° is the freezing point of the solvent,
Tf is the freezing point of the solution
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10. FREEZING POINT DEPRESSION GRAPH
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• The figure below shows the phase diagram
for a pure solvent and how it changes when a
solute is added to it. The solute lowers the
vapor pressure of the solvent resulting in a
lowering of the freezing point of the solution
compared to the solvent. The freezing point
depression is the difference in temperature
between the freezing point of the pure solvent
and that of the solution. On the graph, the
freezing point depression is represented by .

11. • When a pure solvent freezes, its particles
become more ordered as the intermolecular
forces that operate between the molecules
become permanent. In the case of water, the
hydrogen bonds make the hexagonally-shaped
network of molecules that characterizes the
structure of ice. By dissolving a solute into the
liquid solvent, this ordering process is
disrupted.As a result, more energy must be
removed from the solution in order to freeze it,
and the freezing point of the solution is lower
than that of the pure solvent.
• The magnitude of the freezing point depression
is directly proportional to the molality of the
solution. The equation is
ΔTf= Kf m
ΔTf is freezing-point depression
Kf is called the molal freezing-point
depression constant
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12. Depression Of Freezing-point And
Molar Mass Of Solute
Let W2 Grams Of Solute With Molar Mass
M2is Dissolved In W1 Gram Of Solvent , The
Molality (M) Is Given By
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13. OSMOSIS
• Osmosis is the movement of water or other
solvent through a plasma membrane from a
region of low solute concentration to a region
of high solute concentration. Osmosis is
passive transport, meaning it does not require
energy to be applied
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14. • A Technique for purifying water, in which
pressure is applied to force liquid through a
semipermeable membrane in the opposite
direction to that in normal osmosis.
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15. SEMI PERMEABLE MEMBRANE
• A semipermeable membrane is a
barrier that will only allow some
molecules to pass through while
blocking the passage of other
molecules. A semipermeable
barrier essentially acts as a filter.
• Different types of
semipermeable membranes can
block out different sized
molecules. A semipermeable
membrane can be made out of
biological or synthetic material.
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16. OSMOSIS DEMONSTRATION
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19.  Isotonic: Solutions have equal concentration of solute, and so
equal osmotic pressure.
 Hypertonic: Solution with higher concentration of solute.
 Hypotonic: Solution with lower concentration of solute.
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