Students can go through TS Inter 2nd Year Chemistry Notes 4th Lesson Surface Chemistry will help students in revising the entire concepts quickly.
TS Inter 2nd Year Chemistry Notes 4th Lesson Surface Chemistry
→ The phenomenon of attraction and conse-quent accumulation or adherence of mole-cules of a substance on the surface of a liquid or solid is called adsorption.
→ The phenomenon of concentration of mole-cules of a gas or a liquid on a surface of solid or liquid is called absorption.
→ The substance adsorbed on the surface of a liquid or solid is called adsorbate.
→ The substance on whose surface the adsorption occurs is called adsorbent. Eg. in the adsorption of acetic acid on charcoal adsor-bate is acetic acid and charcoal is adsorbent.
→ Adsorption is two types Physical adsorption and Chemical adsorption.
→ The adsorption due to physical forces or – van der Waals’ forces is known as physical adsorption. This is also known as van der Waals’ adsorption.
→ If the adsorption is due to chemical attractive forces, it is known as chemical adsorption.
→ The amount of a gas adsorbed on metal surface or a solid depends on
- surface area of the adsorbent
- nature of gas
- pressure of gas
- temperature.
→ The graph showing relation to pressure (p) and the ratio of masses of adsorbate (x) and adsorbent (m) at a constant temperature is called adsorption isotherm.
→ Freundlich adsorption isotherm is \(\frac{x}{m}\) = Kp1/n which indicates that at any given temperature the amount of gas (x) adsorbed by unit mass of the adsorbent (m) is related to this adsorption equilibrium pressure (p).
→ The graph showing the relation between x/m and temperature at constant pressure is called as adsorption isobar.
→ The substances which accelerates the rate of a reaction is known as positive catalyst. Positive catalyst increase the rate of reac-tion by lowering the activation energy.
→ Substances which decreases the rate of a reaction or retard the reaction are called negative catalyst or inhibitors.
→ Substance which itself has no catalytic acti-vity but will increase the activity of catalyst is called promoter or activator. A promotor thus be regarded as a catalyst for catalyst e.g. Al2O3 K2O, MO powder act as promoter to iron catalyst in Haber process for the manufacture of ammonia.
→ The substances which reduces or even com-pletely destroy the activity of a catalyst are known as catalytic poisons or anticatalysts.
→ If one of the products or intermediate formed in a reaction acts as catalyst for the same reaction it is known as autocatalyst and the phenomenon is known as autocatalysis.
→ If the catalyst and reactants are not in the same phase, then it is known as heterogen-eous catalysis. Generally the catalyst is solid while the reactants are liquids or gases. Most of the solid catalysts are either transition metals or their compounds.
→ Zeolites can act as molecular seives which allow certain molecules which are smaller than the pore size to pass through them while the molecules bigger than the pore size cannot pass through them.
→ Enzymes are protein molecules which are complex nitogeneous organic compounds which are present in the living plants and animals.
→ Metal ions such as Na+, Mn2+, Co2+, Cu2+ etc which activate the enzyme catalysis are called activators.
→ If the particle size of the solute in the binary system is in the range of 1 μ to 1 mμ a colloidal solution is formed.
→ In the colloids the phase constituting the colloidal particles is called dispersion phase while the medium in which the colloidal particles are distributed is called dispersion medium. The dispersion medium or disper¬sion phase may be solid or liquid.
→ The dispersion medium in a colloid is named as lyo. Colloidal solutions in which the parti¬cles of the dispersed phase have great affinity for the dispersion medium are called lyophilic colloids. The colloidal solutions in which particles of the dispersed phase have no affinity for the dispersion medium are called lyophobic colloids.
→ If water is dispersion medium lyophilic colloids are called hydrophilic colloids while lyophobic colloids are called hydrophobic colloids.
→ The process of transferring back a preci-pitate into colloidal form is called peptisation. It is the reverse of coagulation.
→ When a beam of light is made to fall on a colloidal solution, the path of the beam of light is illuminated by a bluish light. The luminosity by the path of beam is known Tyndall effect. It is due to the scattering of light from the surface of the colloidal par¬ticles. The scattering of light due to the absorption of light energy and then scatter the light of shorter wavelength.
→ The constant rapid zig-zag of colloidal particles in a collodial solution is known as Brownian movement named after its discoverer.
→ The migration of electrically charged sol particles under an applied electric field is called electrophoresis strictly cataphoresis or anaphoresis according to the electrode to which the particles move.
→ The potential difference between the fixed layer and the diffused layer having oppo-site charge is called the electro kinetic potenital or zeta potential and the double layer is called electrical double layer.
→ At a particular pH the sol particles become neutral and exhibit no movement in an ele-ctric field and this pH is called isoelectric point.
→ When electrophoresis of dispersed particles is prevented by suitable means the medium can be made to move under the influence of an applied potential. This phenomenon is referred to as electro osmosis.
→ Coagulation or flocculation is the process of breaking up of a colloidal solution by which colloidal particle come close and result in the precipitation of the dispersed phase.
→ If a colloidal solution is stored for longer periods smaller particles dissolved and crystallise out on the larger particles causing the coagulation of colloid. This is known as ageing.
→ The minimum concentration of an electrolyte which is able to cause coagulation or flocculation of sol is termed as flocculation value.
→ The coagulation of lyophilic colloid by adding salt solutions of high concentrations is called ‘salting out’. This may be due to the removal of solvent layer around the lyophilic colloid by the salt.
→ The process by which the sol particles are prevented from coagulation by electrolyte due to the previous addition of some lyophilic sol is called protectioii of colloid.
→ The number of milligrams of protective colloid which just prevents the coagulation of 10 ml of given gold sol when 1 mL of 10% solution of NaCl is added to it is called gold number.
→ A colloidal system involving one liquid dispersed in another is known as emulsion.
→ The substances that stabilises an emulsion are called emulsifier or emulsifying agent.
→ Emulsions are two types
- oil in water (0/w)
- water in oil (w/o) depending on the dispersion medium and dispersion phase.