CHEMISTRY SEMINAR
DILUTE SOLUTION-COLLIGATIVEPROPERTY
Topic: Colligative Properties AND Vant hoff’s factor
Course Code: ED1105
Submitted by:
Name: YASWANTHRAJ G
Roll No.: ED24B1036
Subject Title: THERMODYNAMICS EQUILBRIUM AND
SOLUTIONS
Department: Department of Education (Chemistry)
Submitted to: Mr. S. Detchanamurthy
Faculty of Chemistry
Department of Education
NIT Puducherry, Karaikal
A dilute solutionis a solution that contains a
small amount of solute compared to the solvent.
In such solutions, solute–solute interactions are
negligible, and the properties mainly depend on
the solvent and the number of solute particles.
5.
•⚖️Colligative Properties
• Colligativeproperties are those physical properties of
solutions that depend only on the number of solute particles
present in a given amount of solvent, not on their nature or
chemical type.
• The main colligative properties are:
• Relative lowering of vapour pressure
• Elevation in boiling point
• Depression in freezing point
• Osmotic pressure
5
. Lowering ofVapour Pressure
When a non-volatile solute is added
to a solvent:
The vapour pressure of the solution
is lower than that of the pure
solvent.
This happens because solute
particles occupy some surface area,
reducing the number of solvent
molecules that can escape into the
vapour phase.
Raoult’s Law
For a solution of a non-volatile
solute,
or
Where:
= vapour pressure of pure solvent
= vapour pressure of solution
= mole fraction of solute
This fractional lowering of vapour
pressure is a colligative property
7
8.
️
🌡️2. Elevation inBoiling Point
Adding a non-volatile
solute to a solvent raises
its boiling point.
This is because the vapour
pressure of the solution is
lower, so it must be
heated to a higher
temperature to reach
atmospheric pressure.
Where:
= elevation in boiling point
= molal elevation constant (ebullioscopic constant)
= molality of the solute
8
9.
❄️3. Depression inFreezing Point
Adding a solute lowers the freezing point of
the solvent because solute particles interfere
with the formation of the solid phase
(crystals).
Where:
= depression in freezing point
= molal depression constant (cryoscopic
constant)
= molality of the solute
10.
🧫 4. Osmosisand Osmotic Pressure
o OSMOSIS
o IT IS THE MOVEMENT OF SOLVENT MOLECULES
THROUGH A SEMIPERMEABLE MEMBRANE
FROM A REGION OF LOWER SOLUTE
CONCENTRATION (PURE SOLVENT) TO A
REGION OF HIGHER SOLUTE CONCENTRATION
(SOLUTION) UNTIL EQUILIBRIUM IS REACHED.
o OSMOTIC PRESSURE (Π)
o IT IS THE PRESSURE REQUIRED TO STOP
OSMOSIS.
FOR DILUTE SOLUTIONS, OSMOTIC PRESSURE
FOLLOWS AN EQUATION SIMILAR TO THE IDEAL
GAS LAW:
or
Where:
= osmotic pressure
= molar concentration
of solute
= gas constant
= temperature (in K)
10
11.
11
⚗️Van’t Hoff Factor(i)
For electrolytes that dissociate or solutes that associate in
solution, we use the van’t Hoff factor (i) to correct the
number of particles:
Where = actual number of particles in solution / expected
number of particles.
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