ADSORPTION

SURFACE TENSION

• “Surface tension is the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area”.

SUFACE TENSION : FACTORS

• EFFECT OF TEMPERATURE:

 Surface tension decreases when the temperature increases because cohesive forces decrease with an increase in molecular thermal activity.

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SURFACE TENSION: FACTORS

• EFFECT OF ADDING SOLUTE:

Surface tension of liquid varies on adding solute. Addition of solute into solvent may lead to an increase in surface tension, such as salt in water and water in alcohol or decrease in surface tension, such as methanol , acetone in water. Such substances which lowers the surface tension of liquid are known as surface active agents or surfactant. Such agents also acts as detergents.

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SURFACE TENSION: MEASUREMENT

• CAPILLARY ACTION: The rise of all liquids in the capillary tube is called capillary action.

SURFACE TENSION: MEASUREMENT

• DOUBLE CAPILLARY RISE METHOD:

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SURFACE TENSION: MEASUREMENT

• STALLGOMETER METHOD: The stallagometric method is a common way to measure the surface tension of a liquid using a stallagometer.

SURFACE ENERGY

• The effect of surface tension is to reduce the surface area to minimum. To increase the area of surface of liquid, we have to perform some work against the force of surface tension.
• The work required to increase the area of surface of liquid by 1cm square is called Surface energy of the liquid .

ADSORPTION : BASIC

The phenomenon of higher concentration of any molecular species at the surface than in the bulk of a solid or liquid is known as adsorption

Or

Adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface is known as Adsorption.

ADSORPTION : BASIC

• ADSORBATE : The substance which is adsorbed on the surface.
• ADSORBENT : The solid that takes up gas, vapour or solute from a solution is known as adsorbent.
• Adsorption is a spontaneous process i.e.

G is negative

• Adsorption is an exothermic process i.e.

G is negative

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ADSORPTION : PRINCIPLE

• Adsorption is a surface phenomenon and consequence of surface energy . The surface of a liquid or solid is in a state of tension, strain or unsaturation which results in unbalanced residual force at the surface. These unbalanced residual forces results in higher surface energy. Consequently, the surface of liquids/solid always have a tendency to attract and retain the molecular species with which it comes in contact. This tendency is responsible for the phenomenon of Adsorption.

LAPLACE EQUATION

• Laplace equation is an equation which correlate the pressure difference with surface tension.
• The Laplace pressure is the pressure difference between the inside and the outside of a curved surface that forms the boundary between two fluid regions. The pressure difference is caused by the surface tension of the interface between liquid and gas, or between two immiscible liquids.

LAPLACE EQUATION

• The Laplace pressure equation is ΔP = 2σ/r, where:
• ΔP: Laplace pressure, which is the pressure difference across a curved interface between two fluids
• σ: Surface tension of the fluid
• r: Radius of curvature of the fluid interface

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KELVIN EQUATION

• Kelvin deduced that vapour pressure of a liquid is greater when it is in the form of small drops than when it has a planar structure.
• The Kelvin equation describes the change in vapour pressure due to a curved liquid–vapour interface, such as the surface of a droplet.
• It shows that smaller droplets have higher vapour pressure.

KELVIN EQUATION

• The Kelvin equation tells us how the vapour pressure depends on the curvature of the liquid.

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BET THEORY

• This theory aims to explain the physical adsorption of the gas molecules on the solid surface and serves as the basis for an important analysis measurement of the specific surface area.

BET THEORY

• The adsorption occurs only on well defined adsorption active sites.
• Adsorption is multilayer.
• Adsorption is physical.
• The upper most layer is in equilibrium with adsorbate molecules.
• The surface area available for nth layer being equal to the coverage of (n-1) layer.

BET EQUATION

• The BET equation describes the relationship between the number of gas molecules adsorbed (X) at a given relative pressure (P/P₀), where C is a second parameter related to the heat of adsorption.

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ELECTROKINETIC EFFECTS

• It is well established that colloid carry an electric charge, when they are placed in electric field. Certain effects are noticed which are termed as electrokinetic effects.

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• Such effects involves the relationship between the movement of one phase w.r.t. the other in the presence of some electrical properties.

ELECTRO OSMOSIS EFFECT

• It is a fundamental electrokinetic effect involving movement of the bulk solution against a charged solid surface under the influence of an electric field.

ELECTRO OSMOSIS EFFECTS

• Electro-osmosis is the movement of a liquid or charged particles in response to an electric field.

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• When an electric field is applied to a charged surface, charged particles move towards the oppositely charged poles. This movement of particles creates a circular flow of fluid in the surrounding area. 

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ELECTROPHORESIS

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• Electrophoresis is the migration of electrically charged molecules under the effect of the electrical field.
• Electrophoresis is a technique used to separate particles such as DNA, RNA, proteins, and carbohydrates based on their charge

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ELECTROPHORESIS

• The colloid solution is taken in U- shaped tube and two platinum are dipped in the colloidal solution and current is switched on.
• The colloidal particles starts moving towards oppositely charged electrode and on reaching the electrode , they gets discharged.
• As soon as their charge is neutralized , they aggregate and settle down.
• This movement of particles under the influence of electric field is known as Electrophoresis.