# AP Inter 2nd Year Chemistry Notes Chapter 4 Surface Chemistry

Students can go through AP Inter 2nd Year Chemistry Notes 4th Lesson Surface Chemistry will help students in revising the entire concepts quickly.

## AP Inter 2nd Year Chemistry Notes 4th Lesson Surface Chemistry

→ Adsorption : The accumulation (or) concentration of a substance on the surface rather than in the bulk of solid (or) liquid is known as adsorption.
Eg.: Adsorption of gases like O2, H2, Cl2 etc., on charcoal.

→ Absorption : The uniform distribution of a substance through out the bulk of the solid substance is known as absorption.

→ Desorption : The process of removing an adsorbed substance from a surface on which it is adsorbed is called desorption.

→ In case of some substances both adsorption and absorption takes place. This phenomenon is called sorption.

→ Adsorption of a gas on solids is influenced by the following factors.
a) Surface area of the adsorbent
b) Nature of the gas
d) Temperature.

→ Higher the critical temperature, greater is the case of liquefaction of a gas. Then the extent of adsorption will be high.

→ Adsorption Isotherm : The variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature can be expressed by means of a curve known as adsorption isotherm.
Freundlich adsorption isotherm equation is $$\frac{x}{m}$$ = k, P1/n
x = mass of the gas adsorbed,
m = mass of the adsorbent,
P, k and n are constants.

→ Catalysis : A substance which alters the rate of a chemical reaction without itself being consumed in the process, is Called a catalyst.
The action of catalyst in altering the rate of a chemical reaction is called catalysis.
Types of catalysis : Catalysis is classified into two types as
a) Homogeneous catalysis and
b) Heterogeneous catalysis

Homogeneous catalysis : The catalytic process in which the catalyst is present in the same phase as that, of reactants, is known as homogeneous catalysis.
Heterogeneous catalysis : The catalytic process in which the catalyst is present in a phase different from that of the reactants is known as heterogeneous catalysis.

→ Enzymes are complex nitrogenous organic compounds which are produced by living plants and animals.

• These act as specific catalysts in biological reactions.
• These catalyse the numerous reactions that occur in the bodies of animals and plants to maintain the life process.

→ A heterogeneous system in which one substance is dispersed as large particles in another substance is called colloidal solution.

• In colloidal solution the particle size of the dispersed phase is of the order of 1 mg -1 p.
• Where as in true solution the particle size of the solute are the order of mg or less.
• Colloidal solution is a heterogeneous binary system. Where as true solution is a homogeneous binary system.

→ Lyophilic colloid : The colloidal solution in which the dispersed phase has great affinity to the, dispersion medium is called a Lyophilic colloid or Lyophilic solution.
Ex : Starch solution.
Lyophobic colloid : The colloidal solution in which there exists not much affinity between the dispersed phase and dispersion medium, it is called a Lyophobic colloid or Lyophobic solution.
Ex : Gold solution.

→ Micelles : Some substances which at low concentrations behave as normal strong electrolytes, but at high concentrations exhibit colloidal behaviour due to formation of aggregates. The aggregated particles thus formed are called micelles.

→ Peptization : The process of converting a precipitate into colloidal sol by shaking it with the dispersion medium in the presence of a small amount of electrolyte is called Peptization.

→ Dialysis : The process of removing a dissolved substance from a colloidal solution using a suitable membrane is called dialysis.
Dialysis is made faster by applying an Emf. This is known as Electrodialysis.

→ Collodion solution : Collodion is a 4% solution of nitro cellulose in a mixture of alcohol and ether.

→ Tyndall effect: When light enters a colloidal solution, it is scattered by the large sized colloidal dispersed phase particles. Therefore when light passes through a solution we will be able to see the path of the light as a luminous beam. This is called Tyndall effect.

→ Brownian movement : When a colloidal solution is examined by ultramicroscope, the colloidal particles are seem to be moving in a rapid zig – zag motion. This rapid motion of colloidal particles is called Brownian movement.

→ In a colloidal sol the charges of opposite signs on the fixed and diffused parts of the double layer results in a difference in potential between these layers. The potential difference between the fixed layer and the diffused layer of opposite charge is called electro kinetic potential (or) zeta potential. .

→ When electric potential is applied across two platinum electrodes dipping in a colloidal solution, the colloidal particles move towards one or the other electrode. The movement of colloidal particles under an applied emf is called “electrophoresis”.

→ If the movement of colloidal particles is arrested by some suitable means, the dispersion medium moves in opposite direction. This phenomenon is termed “electro osmosis”.

→ Greater the valence of the coagulating ion added, the greater is its power to cause coagulation. This is known as Hardy-Schulze rule.

→ Emulsion : The colloidal system in which a dispersion of finely divided droplets of a liquid in another liquid medium is called emulsion.
Eg. : Milk, Vanishing cream, Cold cream.

→ Emulsifying agent: The third substance which is added in small amounts to an emulsion to stabilize the emulsion is called emulsifying agent.

→ Demulsification : The separation of an emulsion into constituent liquids is known as demulsification.

→ Artificial rain is produced by throwing electrified sand (or) spraying a sol carrying charge opposite to the one on clouds from an aeroplane.