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Surface Chemsitry, , Surface Chemistry, The branch of Chemistry, which deals with properties of surface, is called surface chemistry., , ADSORPTION, The phenomenon of attracting and retaining the molecules of substance on the surface of liquid/solid resulting, a higher concentration of that substance on the surface is called adsorption., *, , It occur due to unbalanced force on the surface., , *, , The substance on the surface of which adsorption take place is called adsorbent. It is usually liquid or solid., , *, , The substance which is adsorbed on the surface of adsorbent is called adsorbate ., Ex. – When a gas adsorbed on charcoal, gas is adsorbate and charcoal is adsorbent., , (Absorbent), , *, *, *, , (Absorbate), , The adsorption of a gas on the surface of metal is called Occlusion. Ex. adsorption of H2 on the, surface of Pd., The process of removal of an adsorbed substance from the surface on which it is adsorbed called, desorption. It can be brought about by heating or by reducing the pressure., Adsorption is of two types –, (i), Positive adsorption &, Concentration more at the surface. It is more common., (ii), Negative adsorption & Concentration less at the surface. It is rare., , CHARACTERS OF ADSORPTION, i., ii., , It is a sponteneous process i.e. G = – ve, Adsorption take place until the G of system will become zero. In this situation, an equillibrium will, be established where rate of adsorption become equal to rate of desorption., iii., In adsorption, randomness will decrease i.e. S = –ve, iv., Adsroption is a exothermic process i.e. H = –ve, * The change in enthalpy during the adsorption, is called adsorption enthalpy., * Heat evolved during adsorption of one mole adsorbate is called heat of adsorption., DIFFERENCE BETWEEN ADSORPTION & ABSORPTION, *, Adsorption is a surface phenomenon while absorption is a bulk phenomenon., , GCI, , *, , In absorption molecules of a substance are uniformaly distributed throughout a body., , Ex., , Water vapour absorbed by anhydrous CaCl2 while adsorbed by the silica gel, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 1

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Surface Chemsitry, , Amount of adsorption, , v., , At constant temp, , P, (Isotherm), , i., ii., iii., , iv., v., vi., vii., viii., ix., , GCI, , ABSORPTION, It is a bulk phenomenon., Uniform concentration throughout the body of material., It is a slow process., Uniform rate., , i., ii., iii., iv., v., , Adsorption isotherm–, Amount of absorption, , i., ii., iii., iv., , ADSORPTION, It is a surface phenomenon., Concentration is more on the surface., It is a Fast process., Initially more rate and slows down near, the equillibrum., Adsorption isotherm–, , At constant, temp, , P, (Isotherm), , *, When adsorption and absorption take place simultaneously it is called sorption., TYPES OF ADSORPTION, On the basis of force of attraction between adsorbate and adsorbent, adsorption is of two types–, 1., Physical adsorption / Vander Waal adsorption :–, * In this adsorption, the force of attraction between adsorbate and adsorbent is Vander Waal force., * The adsorption take place without formation of any real chemical bond., Ex.:–Adsorption of CH4 , CO on the surface of charcoal., * It is more common., 2., Chemical Adsorption –, * The adsorption take place by formation of chemical bond between adsorbate and adsorbent., Ex.:- Adsorption of H2 on Ni, Physical adsorption, Chemical adsorption, It is due to Weak vanderwaal forces, i., It is due to strong chemical bond., Low heat of adsorption (less then 40 KJ/mole ), ii., High heat of adsorption (40 & 400 KJ/mole .)., It is not specific in nature i.e. evergy gas will get, iii., It is specific in nature, only take place when, adsorbed on any solid to a lesser or greater extenet., adsorbate and adsorbent can form chemical, bond., Reversible process, It can be reversed by heating iv., Irreversible process, cannot be easily reversed., and reducing pressure., In it multimolecular layers are formed., v., In it unimolecular layers are formed., No activation energy is involved., vi., Activation energy is involved., Rapid process., vii., Slow process., Take place more at low temperature and high, viii., Take place more at high temperature and high, pressure., pressure., Adsorption isobar–, ix., Adsorption isobar–, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 2

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Amount, , Amount, , Surface Chemsitry, , Isobar, , Isobar, , FACTOR AFFECTING ADSORPTION :*, , Adsorption of gases by a solid depends on the following factors., , 1., , Nature of adsorbate, *, , During physical adsorption evergy gas will get adsorbed on any solid to a lesser or greater, extent., , *, , Amount of adsorption  Inter molecular attraction force Ease of liquefication., , *, , Easily liquefiable gases like SO3, CO2, HCl, NH3. etc. are adsorbed greater extent than not, easily liquefiable like H2, N2, O2, etc., , *, , More critical temperature (T C) and more Vander-waal constant (a) containing gases show, more adsorption., , 2., , *, , Order of adsorption of inert gases He < Ne < Ar < Kr < Xe < Rn, , *, , Chemical adsorption is not depend on nature of liquefication of gases., , Nature of adsorbent, *, , More surface area of adsorbent provide more amount of adsorption., , *, , Due to this reason, porous structure containing and finely divided adsorbents become, good adsorbent., Ex., , Due to porous structure of silica gel and powderd form of charcoal, these are, excellent adsorbent., , *, 3., , Due to more surface area colloid Pd is good adsorbent then Pd., , Temperature -, , , Adsorption, , gas + solid, , gas adsorbed on solid, H = –ve, , Desorption, , *, 4., , According to Le Chatelier's principle, temperature should be lower for greater adsorption., This is ture for physical adsorption only., , Pressure, , , Adsorption, , gas + solid, , gas adsorbed on solid, , Desorption, , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 3

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Surface Chemsitry, *, *, , When a gas is adsorbed, then volume get reduced. Therefore, according to Le Chatelier's principle,, adsorption will increase on increasing pressure., After a particular pressure (saturated pressure) no adsorption take place due to estiblishment of, equilibrium., , Adsorption Isotherm –, , Am ount of adsorption, , A plot between amount of adsorption and pressure at constant temperature is called adsorption isotherm., *, It is experimentally observed as–, , B, , C, , A, , o, , PS, , P, , *, , To explain isotherm following isotherms was proposed, , 1., , Freundlich Adsorption Isotherm, *, , It is applicable only for physical adsorption., , *, , Freundlich give following equation –, x, 1/n, ––– = KP, m, where n is a constant for which 0  1/n  1, x = amount of adsorbate that adsorbed on the m gram adsorbent, x/m = relative amount of adsorption, P = pressure of gas, K = constant, , *, Case - I, , Freundlich proposed three situation for explaination of experimental adsorption isotherm., At low pressure :- 1/n = 1, , so, , x/m = KP, , i.e. x/m  P, , In this case graph of x/m vs P will be a straight line (OA part of the above adsorption isotherm)., Case -II, , At high pressure :- 1/n = 0, , , , x/m = KPº = constant, , In this case graph of x/m vs P will be a straight line parallel to pressure axis (BC part of the above, adsorption isotherm)., Case - III, , At moderate pressure :-0 < 1/n < 1 , , x/m = KP1/n  x/m  P1/n, , In this case graph of x/m vs P will be AB part of the above adsorption isotherm., *, , The value of K and n can be calculated by plotting following graph – –, Taking logrithium of Fraeundlich equation –, , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 4

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Surface Chemsitry, x, 1, log ––= log K + –– log P, m, n, , log x/m, Slope = 1/n, , x, log –– vs log P, m, , On plotting, , Intercept = log K, log P, , *, , Freundlich equation for solutions is–, x, 1/n, –– = KC, m, , 2., , where C = concentration of solution, , Langmuir Adsorption Isotherm, *, , It is applicable only for chemical adsorption., , *, , He postulated for this –, i. Gases form unimolecular layer on the surface of adsorbent., ii. Gases undergo adsorption behave idealy., iii. Adjacent adsorbed molecules do not interact i.e. adsorption of gas molecule at a particular site, is independent wheather the neighbouring sites are adsorbed or not i.e.each adsorption site has, equal adsorption capacity., iv. Two opposite process adsorbtion and desorption take place simulateneusly on the surface of, adsorbent., v. Rate of adsorption depends on the fraction of surface area available and pressure of gas on, the surface of adsorbent. Rate of desorption is directly proportional to the fraction of surface area, of adsobed adsorbent., , *, , On the basis of above postulates Langmuir proposes following equation–, x, aP, –– = –––––, m, 1 + bP, where a and b called Langmuir parameter, , *, , This equation can be modified in following two cases –, , Case - I, , when pressure is very low : bp << 1  1+ bP ~ 1, , thus, , x/m = aP, , Case - II, , when pressure very High : bp >> 1  1 + bP ~ bP, , thus x/m = aP/bP = a/b = constant, , here a and b are Langmuir Parameter which can be calculated as–, x, aP, –– = ––––––, m, 1 + bP, or, , GCI, , x, ––– (1 + bP) = aP, m, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 5

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Surface Chemsitry, P, 1, –––– = –– +, x/m, a, , or, , ( ), , b, –– P, a, , P, –– vs P graph, x/m, , on plotting, , Slope = b/a, , P, ––––, x/m, , Intercept = 1/a, P, , *, , Thus by calculating slope and intercept value of b and a can be caluclated, , *, , For solution, Langmuir equation is–, x, aC, –– = –––––, m, 1 + bC, , where C = concentration of solution, , Applications of adsorption, 1., , To production of high vacuum, A bulb of charcoal cooled in liquid air is connected to a vessel which has already been exhausted as far as, possible by a vacuum pump. The remaining traces of air are adsorbed by the charcoal. This results in a very high, vacuum., , 2., , In Gas Masks, Gas mask is a device which consists of activated charcoal or a mixture of adsorbents. This apparatus is used to, adsorb poisonous gases and thus purify the air for breathing., , 3., , To Humidity control, Silica and aluminium gels are use as adsorbents for removing moisture. These gels are use for controlling humidity, of rooms. Silica gel is also used in desicators., , 4., , Removal of colouring matter from solution, Animal charcoal removes colours of solutions by adsorbing coloured impurities. Animal charcoal is used as, decolouriser in the manufacture of cane sugar., , 5., , Heterogeneous catalyst based on adsorption, , 6., , Separation of inert gases, Due to the difference in degree of adsorption of gases by charcoal, a mixture of inert gases can be separated by, adsorption on coconut charcoal at different low temperatures., , 7., , Softening of hard water, The hard water is made to pass through a column packed with zeolite (sodium aluminium silicate). Ca2+ and Mg2+, ions, which are responsible for hardness, get adsorbed on zeolite, exchanging sodium ions., Na2Al2Si2O8 ——————— CaAl2Si2O8 + 2 NaCl, The exhausted zeolite is regenerated with 10% of sodium chloride solution., CaAl2Si2O8 + 2NaCl ———— Na2Al2Si2O8 + CaCl2, , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 6

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Surface Chemsitry, 9., 10., , In curing diseases, A number of drugs are adsorbed on the germs and kill them or these are adsorbed on the tissues and heat them., Cleaning agents, Soaps and detergents get adsorbed on the interface and thus reduce the surface tension between dirt and cloth,, subsequently the dirt is removed from the cloth., , 11., , Chromatographic method of purification and sepration is based on the adsorption., , 12., , Froth floatation process also based on adsorption., , 13., , Indicator like fluorscein based on the adsorption of indicator by sol., , 14., , Dyes are also based on adsorption., , COLLOIDAL STATE, *, , Foundation of colloid chemistry given by & Thomas Graham (1861), , *, , It is observed that crystalloids and colloids are not the type of matter because same substance in some times, behave as colloids while some time behave as crystalloids. For example NaCl in water behave like a crystalloid, but in benzene it behave like a colloid. Thus we can say that crystalloids and colloid are the phase of substances, which depending on the particle size in a solvent., , *, , Size of colloidal particle, 10 Å - 1000 Å or 10–7 cm - 10–5 cm or 10–9 m - 10–7 m or 1 nm - 100 nm, , *, , When a solute dissolved in a solvent then according to the size of solute particle in the solution, solution, can be divided into following types –, , Solution, , *, , True Solution, , – Solute particle size < 10 Å, , Colloidal Solution, , – Solute particle size = 10 Å - 1000 Å, , Suspension, , – Solute particle size > 1000 Å, , By increasing size of solute particles true solution can we converted into colloidal solution and by increasing, size of colloidal particle suspension can be formed., , *, , Colloidal state may be regarded as intermediate of true solution and suspension., , *, , Colloidal state can be achived by every substance by a suitable method., , *, , Substances, which get rapidly diffused through a semi permeable membrane are called crystalloids and which, do not filter are called colloids., Crystalloids - solutions of urea, sugar, etc., acids and inorganic substances., Colloids - gelatin, starch, gum, protein, salicylic acid, etc., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 7

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Surface Chemsitry, Colloidal System, *, , It consists of two phases which are as follows., , (i) Dispersion medium :, The medium or solvent in which colloidal particles are dispersed., (ii) Dispersed phase :, It consist of colloidal particles dissolve in a solvent., *, , Generally colloidal system also contain a third component called stabilizing agent which provides stability., , Some colloidal solution itself act as stabilizing agent., , Property, , Suspension, , Colloidal solution, , True solution, , 1., , Nature, , Heterogeneous, , Heterogeneous, , Homogeneous, , 2., , Visibility, , Visible through naked eye, , Visible under, , Not visible, , ultra-microscope, 3., , Diffusion of particles, , Does not diffuse, , Diffuses slowly, , Diffuses rapidly, , 4., , Separation by, (i) Ordinary filtration, , Possible, , Not possible, , Not possible, , (ii) Ultra-filtration, , Possible, , Possible, , Not possible, , 5., , Tyndall effect, , Not, , Shows, , Does not Show, , 6., , Brownian movement, , Not, , Shows, , Negligible, , 7., , Appearance, , Opaque, , Generally transparent, , Transparent, , 8., , Electro phoresis, , Not, , Observed, , Not, , 9., , Setting of particles, , Settle under gravity, , Settle only on centrifugation, , Do not settle, , 10., , Number of phases, , Two, , Two, , One, , Note : Due to association of solute particles colligative properties of colloidal solution are fairly small and observed, molecular weight is quite large., , Classsification of Colloidal system, [A], , On the basis of nature of dispersed phase, Depending upon the type of the particles of the dispersed phase, the colloids are classified in three parts :, 1., Multimolecular colloids, *, When on dissolution, atoms or smaller molecules of substances (having dimension less than, colloidal dimension) aggregate together to form particles of colloidal dimensions. the particles, thus formed are called multimolecular colloids., *, , GCI, , For example. sols of gold atoms and sulphur (S8) molecules., , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 8

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Surface Chemsitry, , –, , But a concentration above CMC hydrocarbon part pulled into the bulk and aggreagate in, –, , spherical form where hydrocarbon chains pointing towards the centre and COO part, remaining out ward on the surface forming ionic micelles., , Water, , Water, Water, , Water, , *, , In micelle formation polar part of surfactant remains outside whereas nonpolar part remains inside., , [B], , On the basis of physical state of the dispersed phase and dispersion medium, , Eight types of colloidal systems are possibles., Dispersion of gas in a gas forms homogeneous mixture so it is not considered as colloidal solution, it forms a, true solution., SN. Dispersed, 1., , Dispersion, , phase, , medium, , Gas, , Liquid, , Name of colloid, , Example, , system, Foam, , Soda water, shaving cream, whipped cream, foams of, cocacola, soap leather., , 2., , Gas, , Solid, , Solid foam, , Lava, bread, corck, foam rubber., , 3., , Liquid, , Gas, , Liquid aerosol or aerosol, , Cloud, fogs, mists, insecticide sprays, , 4., , Liquid, , Liquid, , Emulsion, , Milk, water-oil mixture, cold cream medicines., , 5., , Liquid, , Solid, , Gel, , Curd,cheese, gelatin, ointment, Boot polish., , 6., , Solid, , Gas, , Solid aerosol, , Smoke, Dust storm, , 7., , Solid, , Liquid, , Sol, , Ink, colour, Gum, Starch, Blood, , 8., , Solid, , Solid, , Solid sol, , Ruby glass, diamond, precious stones, alloys, pearls, , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 10

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Surface Chemsitry, DIFFERENT TYPES AS COMMON COLLOIDAL SYSTEMS, [A] Sol :, *, When a solid is dispersed in liquid medium then formed colloid system is known as sol., *, It is most common type of colloid system so generally colloidal solutions are considered sols., *, On the basis of nature of dispersion phase these are many types., Water –––– Hydrosol/aquasol,, Alcohol –––– Alcosol, Benzene –––– Benzosol, *, On the basis of nature of interaction between dispersed phase and medium, sols are two types., (a), Lyophilic colloids, *, "The colloidal solutions in which the particles of the dispersed phase have a great affinity, for the dispersion medium, are called lyophilic colloids.", *, They are prepared by simply mixing and shaking of components., *, In these the sol particles are generally organic in nature., *, These are also known as solvent loving colloid or emulsoids., *, They are reversible in nature i.e. after evaporation these may be converted into the colloid, state by simply shaking with medium., *, If water is used then it is called hydrophilic colloid., Ex. Gum, Gelatin, Starch, Protein, Polymer, Rubber, Egg albumin etc., (b), Lyophobic colloids, *, "The colloidal solutions in which there is no affinity between particles of the dispersed, phase and the dispersion medium are called lyophobic colloids.", *, They are prepared by special methods., *, The particle are generally inorganic in nature., *, These are also known as solvent hating colloid or suspensoid., *, They are irreversible in nature, if sol is evaporated, then it does not form easily., Ex. Sol of metal hydroxide and sulphide sol, Sol of phosphours, sulphur sol etc., Difference Between Lyophilic Colloids and Lyophobic Colloids., S.No. Properties, Lyophilic Colloids, Lyophobic Colloids, (1), Preparation, easily formed, special method are used, (2), Stability, more Stable, less, (3), Reversibility, Reversible, Irreversible colloids, (4), Charge on particles, No charge on particles, Positive or negative charge on particles, (5), Electrophoresis, No, Yes, (6), Coagulation, Coagulated on adding an, Coagulated on adding small amounts of, electrolyte in large amounts, electrolyte, (7), Brownian motion, Low, High, (8), Tyndall effect, Do not exhibit, Exhibit, (9), Solvation of solute, High, Low, *, Surface tension and viscocity in lyophobic cooloids is equal to pure liquid solvent whereas in lyophilic sol viscosity, is high then pure liquid and surface tension in low., *, Reason of more stability of lyophilic sol is assumed as high solvation and charge less sol particles., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 11

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Surface Chemsitry, Preparation of Sols, *, A., , The lyophilic colloids but for prepartion of lyophobic colloids special methods are used which are :, Dispersion methods, In these methods, larger particles of a substance (suspensions) are broken into smaller particles. The following, methods are empolyed., 1. Mechanical dispersion –, *, In this method, the substance is first finely grounded by usual methods. It is then mixed with dispersion, medium and introduced into the colloidal mill, to get colloidal size particle., *, Colloidal solutions of black ink, paints, varnishes, dyes etc. are obtained by this method., *, In this method a third component called stabilizing agent is also used., *, For preparation of colloidal graphite, tannin is used as stabilizing agent and for preparation of printing, ink, gum arabic is used as stabilizing agent., 2. Electrical dispersion or Bredig's arc method, *, *, , *, *, *, , This method is used to prepare sols of Pt, Ag, Cu, Au etc., Two metal rods are dipped in suitable dispersion medium and electric arc is produced. The intense, heat of the arc vapourises some of the metal which condenses under cold water to obtain colloidal, size particle., This method is not applicable for s-block metals., This method is not suitable for organic substances as they itself can burn., This method involes both dispersion and condensation., , Metal, rod, , Ice, , Solvent, , 3., , 4., , Arc, , Ultrasonic dispersion : *, , In this method suspension particles are broken by ultrasonic wave., , *, , Mercury, sulphur, sulphide and oxide sols are made by this method., , Peptisation : *, , It is reverse process of coagulation., , *, , In this process a freshly prepared ppt. is converted into colloidal solution by addition of small amount of, electrolyte into suitable dispersion medium, used electrolyte is called peptising agent., , *, , Peptising agent is generally electrolyte containing common ion., , *, , In this process precipitate adsorbs a common ion from peptising agent on its surface, so that uniform charge (+, ve or –ve) developes on surface, after adsorption due to repulsion between deposited common ions, precipitate, splits and colloidial particles are obtained., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 12

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Surface Chemsitry, *, , By this method, mixing small quantity of electrolyte into precipitate collodial solution of Fe(OH)3, AgCl, cdS can, be obtained., , Ex - By mixing FeCl3 in freshly precipitated Fe(OH)3, colloidial solution of Fe(OH)3 is obtained., Fe(OH)3, , +, , FeCl3 , , Precipitate, , peptising agent, , [Fe(OH)3]Fe3+, (positively charged sol particle), , 3Cl–, , +, , (in dispersion medium), , Condensation method :, , B., , *, , In these method, particles of molecular size combine to form large particles of colloidal dimensions. These, methods are, , (i) By exchange of solvent In this method a true solution is added in such a solvent in which solute is soluble or partially soluble but both solvent are, mutually soluble., In this process due to decrease in solubility of solute particles they recombine to get colloidial size., Ex. If solution of S or P prepared in alcohol is poured into water then due to less solubility of S or P in water then alcohol,, collodial solution is formed., (ii) By condensation of vapourised element in dispersion medium In this method colloidial solution is obtained by passing vapours of an element into cold solvent., , C., , Chemical methods - Sol is prepared by using chemical reactions, –, , By oxidation, Br2 + H2S  2HBr + sulphur sol, , –, , By reduction, 2AuCl3 + SnCl2  Gold sol, AgNO3 + Glucose  Silver sol, , –, , By hydrolysis, , FeCl3 + 3H2O —— Fe (OH)3 sol, , –, , By double decomposition, AgNO3 + KI  KNO3 + AgI (sol), As2O3 + 3H2S  As2S3 (sol), , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 13

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Surface Chemsitry, , Purification of colloidal solution, Colloidial solution contains electrolyte or other impurities which are crystalloid in nature, which make colloidial, solution unstable., The following are main methods for separating them Dialysis : *, , In this method impure sol is taken in a special bag of parchment paper or animal membrane., , *, , Sol particles cannot diffuse through membrane but impurities diffuses away., , *, , In presence of electrolyte impurities, to make dialysis faster electric field is applied, in this condition it is called electrodialysis., , *, , Blood purifies in kidney by this method., , (ii) Ultra filtration : *, , Impurities can not be separated by ordinary filter paper, but if pores of ordinary filter paper are partially closed then, impurities can be separated., , *, , For reducing size of pores collodian or gelatine solution in acetic acid can be used., Colloidian is colloidial solution of cellulose nitrate in alcohol., , Properties of collodial solution : The main characteristic properties of colloidial solution are following :, (1) Brownian movement :, *, , It was first observed by Robert Brown., , *, , Collodial particles continously move at random in zig-zag path in dispersion medium of colloidial solution. This irregular, motion is called brownian movement., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 14

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Surface Chemsitry, *, , This motion arises due to collison of solute particles with dispersion medium particles i.e. this motion happen due to effect, of dispersion medium on colloidal particles., , *, , Brownian movement is greater in smaller colloidal particles., , *, , Brownian movement is not observed in suspension and true solution., , *, , It does not depend on nature of colloidal particles but depends on size of particles and viscosity of medium., , *, , It helps particles by not allowing them to settle in bottom, i.e. this motion is responsible for stability of colloidal solution., , *, , It is observed only by ultramicroscope, it proves kinetic theory of gases., , (2) Tyndall effect :, *, , When light passes through colloidal solution, its bright path becomes visible. This effect is called tyndall effect., , *, , This effect is due to scattering of light by colloidal particles., , Tyndall cone of, scattered light, Source, of light, , Lens, Colloidal suspension, , *, , Intensity of scattered light is maximum at perpendicular path., , *, , Due to this effect path of light beam illuminates by this effect. It is assumed due to adsorption of light by particles and, scattering of it in all directions., , *, , Due to scattering of light by colloidal particles path of light becomes illuminated cone, known as colloidal cone., , *, , This effect is observed when size of sol particles is of the order of wavelength of light used and refractive index of both, phases are different., , *, , It is more observed in lyphobic sol then lyophilic sol., , *, , It is not observed in true solution and suspension., , *, , Colloidal solution can be differentiated easily by this effect from true solution or suspension., , *, , Tyndall effect is more easier method for identification of colloidal solution then brownian movement., , *, , This effect confirm hetrogenous nature of sol., , *, , Ultramicroscope given by zigmondy is based on this effect., , *, , Blue colour of sky and sea water, visibility of tail of comet, twinkling of stars, illumination during projection of picture in, cinema hall are based on this effect., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 15

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Surface Chemsitry, (3) Charge on colloidal particles :, *, , Sol particles are assumed generally as charged particles, , *, , Uniform charge (positive or negative) is found at lyphobic colloidal particles., , *, , Sol particles do not settle down because due to similar charge repulsion force acts between them. So this charge is, responsible for their stability., , *, , Medium always acquires opposite charge, so that solution is electrically neutral., , *, , Sol particles can acquire this charge due to following reasons -, , (i) Presence of acidic or basic medium : *, , In this condition sol particles acquire charge either by accepting proton or donating proton., Ex - Protein sol has +ve or –ve charge, depending on pH of medium., +, Acidic medium NH, 3 CH2 COOH, , NH2CH2COOH, , Basic medium, , NH2CH2COO, , (ii) Due to self dissociation : - Colloidal particles of soaps and detergent form colloidal solution by dissolution in water and, ionising further., C15H31COONa  C15H31COO– + Na+, (iii) Due to friction between dispersed phase and dispersion medium., (iv) Due to capturing of electron by sol particles in metal sol formation by electric dispersion method., (v) Due to selective adsorption of ions : *, , When more then one type of ions are present in dispersion medium, then sol particles becomes +ve or –ve charge by, adsorbing one of these ions generally common ion. In this way colloidal particles acquire charge., Ex - When FeCl3 is added to hot aqueous solution of Fe(OH)3 then due to adsorption of Fe+3 ions positive charged sol, Fe(OH)3/Fe+3 is obtained., , *, , When H2S is added to hot aqueous solution of AS2S3 then due to adsorption of S–2 ions negatively charged sol AS2S3/S–2 will, be obtained., , Electrical double layer *, , Colloidal particles due to selective adsorption of ions around then form first layer, by which positive or negative charge, developes on particles. This layer of adsorbed ions on colloidal particles is called fixed layer. This layer attracts opposite, ions of medium which forms second layer. It is known as diffused layer., , *, , The combination of these layer is called Helmhotz double layer., , *, , Potential developed between a fixed layer and diffused layer is called electro kinetic potential or zeta potential., + + + + + fixed layer, – – – – – diffused layer, , Fe(OH)3|Fe+3|Cl–, , fixed diffused, , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 16

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Surface Chemsitry, Some positive sol : (i), , Protein sol in acidic medium., , (ii) Hydroxide sols like Fe(OH)3, Al(OH)3, Cr(OH)3., (iii) TiO2 sol, (iv) Basic dyes e.g. sol of methylene blue and haemoglobin., Negative sol., (i), , All metal sol, ex : Ag, Au, Cu, Pt etc., , (ii) All sulphide sol ex : As2s3, Sb2S3, Cds Sol., (iii) Sol of starch, gums, gelatine, soil, blood and charcoal., (iv) Acidic dyes like sol of congored., (v) Protein sol in basic medium., (4) Coagulation or Flocculation : *, , The phenomenon of precipitation of sol particles from a sol is called coagulation., , *, , During coagulation sol particles becomes heavier and settles down due to gravitation., , *, , Following methods are generally used for coagulation., , (i) By boiling : - By boiling kinetic energy of particles increases, due to which probability of aggregation of particle increases, overcoming repulsion between particles., (ii) By electrophoresis : - In this process particles lost their charge by moving on opposite charged electrode and particles, combine to form precipitate., (iii) By mixing two opposite sols together, sols are coagulated., Eg. - By mixing positive charged sol Fe(OH)3 with negatively charged sol As2S3, both sols are coagulated., (iv) By adding suitable solvent : - Lyophilic sol are generally coagulated by mixing suitable solvent because particles are, chargeless., Eg. - When acetone is mixed in lyophilic sol, it coagulates., (v) By adding electrolyte : When an electrolyte is added to colloidal solution then opposite charged ions to sol deposit on sol particles and neutralise, their charge. In this condition formed heavy particles settle down in bottom of container., Eg. - If BaCl2 is mixed in colloidal solution of [Fe(OH)3/Fe3+] then Cl– ions neutralise charge of sol particles and sol particles, settle down in bottom., Hardy - Schulze rule : In coagulation of colloidal particles by electrolyte according to hardy - Schulze, "Greater the valency of opposite charge ion, to sol present in electrolyte, greater will be its coagulating power (proportional to fourth power), , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 17

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Surface Chemsitry, Eg. (i) Order of coagulation power of different cation for negatively charged sol As2S3 is Sn+4 > Al+3 > Mg+2 > Na+, (ii) Order of coagulation power of different anions for positive charged sol like metal hydroxide is [Fe(CN)6]4– > PO4–3 > SO4–2 > Cl–, Qus. Coagulation power of used electrolyte in coagulation of a lyophobic sol depends on (1) Sign of charges of ions present in electrolyte., (2) Magnitude of charges of ions present in electrolyte., (3) Both sign and magnitude of charges of ions prsent in electrolyte., (4) None of these, , (3), , Qus. Most suitable electrolyte for coagulation of ferric hydroxide sol (1) Na3PO4, , (2) MgCl2, , (3) Al2(SO4)3, , (4) K4[Fe(CN)6], , (4), , (4) K4[Fe(CN)6], , (3), , Qus. Most suitable electrolyte for coagulation of Arsenic sulphide sol (1) Na3Po4, , (2) MgCl2, , (3) Al2(SO4)2, , Coagulation or flocculation value : *, , The minimum concentration of an electrolyte in millimole/litre which is required for coagulation of a sol is known as, coagulation value., , *, , Higher coagulation value of an electrolyte means lower coagulation power., Coagulation power , , 1, coagulation value, , Qus. For blood sol which have higher flocculation value (1) AuCl3, , (2) AlCl3, , (3) FeCl3, , (4) Nacl, , (4), , (4) MgSO4, , (3), , Qus. For metal sol which has lower coagulation value (1) NaCl, , (2) CaCl2, , (3) AlCl3, , Qus. For coagulation of 10 litre sol in two hours 0.585 gm NaCl is required, then coagulation value of NaCl is Ans. 1, Protective colloid and gold number : *, , Lyophilic sol are more stable then lyophobic sol, so coagulation of lyophobic can be prevented by adding lypphilic sol., , *, , Lyophobic sol can be easily precipitated by adding small amount of electrolyte. If lyophilic sol like starch, gelatine or babool, gum is already added to a lyophobic sol before adding electrolyte, then these provide a layer which protect it from effect, of electrolyte, due to this layer colloidal particles do not precipitate. Here used lyophilic sol is called protective colloid for, lyophobic sol., , *, , Zigmondy introduced gold number for expressing protective power of protective colloid., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 18

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Surface Chemsitry, Gold number : "Gold number of a protective colloid is minimum quantity of it in milligram. Which is sufficient for preventation of precipitation, of 10 ml gold sol when 1 ml 10% NaCl solution is added to it.", Smaller gold number  greater protective power, Ex. Gold number of gelative = 0.005 – 0.01 (minimum)  Good protective colloid., Gold number of potato starch = 20 – 25 (maximum)  bad protective colloid., , Q., , On addition of one ml solution of 10% NaCl to 10 ml gold sol in the presence of 0.25 gm of starch, the, coagulation is just prevented. Starch has the following gold number., Ans. 250, Q., The gold number of starch, gum arabic, gelatin & haemoglobin are 20 , 15 , 0.005 ,0.7 respectively., Which has highest protection power ?, Ans. Gelatin., Congo rubin no., *, , Ostwald introduced congo rubin number., , *, , The minimum quantity of protective colloidial in mg. which prevent colour change (coagulation) of 100 ml 0.01% congo, rubin dye on adding 0.16 g equivalent KCl, is called congo rubin no. of colloid., , (5), *, *, *, *, , COLOUR, Colloidal solution are coloured due to adsorption and scattering of light., The colour of solution depends on the wave-length of scattered light., Wave-length of scattered light depends on the nature of colloidal particles and their size., Different colour of same sol is due to different size of the sol particles., –5, Ex. Colour of Ag sol, –, Yellow, diameter = 6 × 10 mm, –5, Red, diameter = 9 × 10 mm, –5, Voilet, diameter = 15 × 10 mm, , (6) Electrophoresis : *, , When an electric field is applied in a colloidal solution using two electrodes then colloidal particle move towards oppositely, charged electrodes due to charge present on them. This phenomenon is called electrophoresis., , *, , In electric field positive charge particles move towards cathode and negatively charged particles move towards anode., , *, , This effect on positive charged particles and negative charged particles is called cataphoresis and anaphoresis., , *, , This effect comfirms charge on particles., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 19

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Surface Chemsitry, *, , Due to this effect at end sol particles are coagulated at opposite cahrge electrode, in this phenomenon a potential is, developed which is called sedimentation potential., , *, , if such an arrangement is made so that only dispersion medium moves in electric field, then this phenonmenon is known, as electrosmosis., , *, , In electrosmosis two opposite dipoles are formed and potnetial develop between them is called streaming potential., Isoelectric point of colloid : -, , *, , The H+ ion concentration or pH at which colloidal particles are neither positively charged nor negatively charged i.e. does, not show electrophoresis is called isoelectric point of colloid., , Qus. The pH at which the colloidal solution of amino acid does not migrate in electric field is called (1) Isoelectric point, , (2) Neutralisation point, , (3) End point, , (4) Critical point, , (1), , (B) Emulsion : *, , Emulsion are colloidal system in which dispersed phase and dispersion medium both are liquid., , *, , Two mutually immiscible or partially immiscible liquid from emulsion., , *, , It is formed by brisk shaking of two immiscible or partially miscible liquids, it is known as emulization., , *, , Emulsion are generally unstable, both liquids mutually separate on standing emulsion for some time so to make stable, emulsion a third substance is added during emulsion formation known as emulsifier., Eg. Gum, Soap, Detergent, Gelatine, Albumin, higher alcohols are emulsifier., , *, , Soaps and detergents are excellent emulsifier., Role of emulsifier : -, , *, , The main function of emulsifier is to reduce interfacial tension between liquids forming emulsion, so that both can come in, contact with each other. e.g. soap is a emulsifier in emulsion formation of oil and water., , *, , Emulsifier are generally long chain non polar hydrocarbon species, which also contain a polar group, which can be, represented as -, , Polar Head, , Non Polar tail (Hydrocarbon part), , (Hydrophilic part), , Hydrophobic part, , *, , In emulsifier polar head is water soluble whereas non polar tail is oil soluble., , *, , When some oil drops are added to water then due to soap it mixes in water. Soap forms a layer on oildroplets and prevents, them to meet each other, making emulsion stable., Water, , Water, , Water, Oil, , Water, , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 20

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Surface Chemsitry, Types of emulsion : (1) O/W type or water emulsion : - In this small quantity of oil in dispersed in water., Eg. - Milk, Vanashing cream etc., (2) W/O type or oil emulsion : - In this small quantity of water is dispersed in oil., Eg. - Butter, Cod liver oil, Cold cream etc., *, , Elbumin acts as emulsifier in butter., , *, , In milk oily fat is dispersed in water in which caesin (protein) acts as emulsifier., , *, , Separation of emulsion into its liquid component is called deemulsification. In deemulsification boiling, freezing, centrifugation, different methods are used., Identification of emulsion : -, , *, , Dye test – In this method a dye soluble in oil is mixed in emulsion. If total surface of emulsion becomes coloured then it, is considered as W/O type, if only coloured droplets are observed then emulsion is of O/W type., , *, , Dilution test : - If it is possible to dilute emulsion by water, then it shows that water is dispersion medium and emulsion, is of O/W type. If by adding water in emulsion a separate layer in formed, then emulsion is of W/O type., Application of emulsion : -, , (1) Cleaning action of soaps and detergents –, These contain polar head and non polar tail. Generally dirt particles are oily (fat or greese) substance, which sticks on, clothes. When clothes are soaked in aqueous soap solution then soap and dirt particles come in contact of each other. Non, polar part of soap dissolves in dirt whereas polar head remains towards water. In this way many charged heads develop, around every oil droplet. Due to repulsion oildrops split into small drops and form emulsion in water and oily substance, removes from cloth., (2) Different cosmetics, cold cream, body lotions are emulsion., (3) Pine oil forms emulsion in froth flotation in Process of metallurgy., (4) Digestion of fat in human body occurs by emulsion formation., (C) Gel : * These are colloidal system like jelly in which a liquid is dispersed in solid medium. Process of gel formation is called, gelation., * Process of cementisation is an example of gel., Propertion of gel : * If gel is shaked fast then it converts into sol. If sol in kept for same time then it reconverts into gel, this is known as sol-gel, transformation., * When gel is kept for long time then water dispersed phase comes out, this is known as syneresis or weeping of gel., , Application of Colloid Chemistry, 1., , In food, Many food material like milk, butter, icecream, fruit jelly, whipped cream are colloidal in nature., , 2., , Colloidal Medicines, Many colloidal system are used as medicine. Colloidal medicines are more effective due to adsorption., (i) Colloidal sulphur acts as a germicide., (ii) Antibiotics such as penicillin and streptomycin are in colloidal state., (iii) Colloidal gold, manganese, calcium, iron, copper, are used as health tonics., (iv) Colloidal solutions of silver, argirol and protargirol are used as eye ointment., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 21

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Surface Chemsitry, 3., , Purification of Blood, Blood is a colloidal solution, in which many poisonous substances like urea, uric acid, etc., are present. The substances, can pass through the semipermeable membranes in the kidney, but haemoglobin cannot. Dialysis process stops when, kidney fails., , 4., , Blue colour of Sky, Atmosphere is also a colloidal system of dust and water, which disperse the blue light and adsrob the remaining, colours., , 5., , Origin of Delta in Rivers, River water forms colloidal solution with soil particles. Soil particles are negatively charge which coagulated by NaCl, present in sea water forming delta at junction of river and sea., , 6., , Clotting of Blood, To coagulate blood, FeCl3 solution and alum are used, because blood is negative charge colloid, which coagulate by, Fe3+., , 7., , Cleansing action of Soap, , 8., , Purification of Water, Alum is used to purify turbid water (in which soil is present). Becuase Al+3 and K+ ions present in it, coagulate the, negatively charged colloidal particles of soil and they get settled down., , 9., , Precipitation of Smoke, Smoke released from industries contain poisnous particles on passeing through two opposite charge plates which, adsorb charge particles and makes smoke non-poisnous., , 10., , Rubber Industry, Rubber is emulsion of negatively charged particles which is covered by protective protein layer, rubber gets coagulated, in the presence of salts. Sulphur is added to this precipitated rubber forming vulcanised rubber, which is marketed., , 11., , Refining of Leather, Leather consists of positively charged protein particles. Leather is dipped in colloidal solution of tannin, which is, negatively charged. Due to coagulation leather becomes hard., , 12., , In Rains, Artificial rain can be done by spraying electrolyte (usually AgI)., , 13., , Sewage Disposal, Sewage water consists of negatively charged colloidal particles of soil and dirt, after separating by electrophoresis., Precipitate obtained is used in the form of fertiliser and water is used in irrigation., , 14., , Paints, All type of paints are colloidal solution of solid dye in liquid., , 15., , TiO2 is released during war in atmosphere. In prsence of this nothing can be seen., , 16., , Inductrial products, Paint, ink, synthethic plastic, graphite lubricant are colloidal solution., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 22

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Surface Chemsitry, , CATALYSIS, The substance which changes the rate of chemical reaction, but itself remains unchanged with respect to, weight and constituents till the end of the reaction, is called a catalyst and the phenomenon is called catalysis., *, , First proposed by  Berzelius (1835), , (First Noble prize was given in catalysis), , *, , They change the reaction rate by changing the activation energy of the reaction., , *, , They are of two types–, , (i) Positive catalyst :*, , They increase the rate of reaction., , *, , They decrease the activation energy., Ex, , 2KClO3 –––––––––– 2KCl + 3O2 ,, , Positive catalyst = MnO2, , N2 + 3H2 –––––––– 2NH3 ,, , Positive catalyst = Fe, , H2O2, , Positive catalyst = Pt, , ––––––––––– H2O + ½O2 ,, , (ii) Negative catalyst or Inhibitor :–, *, , They decrease the rate of reaction., , *, , They increase the activation energy., 4CHCl3 + 3O2 –––– 4COCl2 + 2H2O + 2Cl2, Negative catalyst = C2H5OH, , Ex., , C6H5CHO + ½O2––––– C6H5COOH,, , Negative catalyst = Diphenyl amine, , Na2 SO3 + ½O2 ––––– Na2SO4,, , Negative catalyst = C2H5OH, , *, , In the knocing of petrol tetraethyl lead (TEL) act as negative catalyst., , *, , In the H2O2 decomposition H3PO4, Glycerol or Acetanilide act as negative catalyst., , Promoter or activators, *, , Such substances which increase the efficiency of a catalysts are called catalytic promoters., , *, , Catalytic promoter is adsorbed in the interstitial space of crystal lattice of the catalyst and increases, the number of active centres. Thus, catalytic efficiency is increased., Ex., , In Habor Process, N2 + 3H2 ––––––––––– 2NH3, , Mo  activator , Fe - catalyst, , Anti catalyst or catalytic poison, *, , Substances, which decrease the efficiency of a catalyst, are called catalytic poison., , *, , Reactivity of catalysts gets destroyed due to adsorption of these substances on active centres of, catalyst., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 23

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Surface Chemsitry, Ex., , –, , H2S decrease the efficiency of Fe in Haber method., , –, , Compounds of As decrease the efficiency of Pt catalyst in contact process., , –, , Decomposition of platinum catalysed by H2O2 is poisoned by HCN., , –, , In the reaction of hydrogen with ethylene, CO2 deactivates the copper catalyst., , Type of catalytic reactions, 1. Homogeneous Catalysis :–, *, , Catalytic reactions in which the catalyst, reactants and the product are in same phase., , Ex., , NO(g), SO2 (g) + O2 (g) –––––– 2SO3 (g) (Lead Chamber Process), H+ (l), C12H22O11 (l) + H2O(l) –––––– Glucose (l) + Fructose (l) (Inversion of Sucrose), H+ (l), CH3COOC2H5(l) + H2O (l) –––––– CH3COOH (l) + C2H5OH (l) (Hydrolysis of Esters), , 2. Heterogeneous Catalysis:–, *, , Catalytic reactions in which the catalyst, reactants and the product are in different phases., , Ex., , Fe(s), N2(g) + 3H2(g) –––––– 2NH3(g), 2H2O2 (l), , Pt(s), –––––– 2H2O (l) + O2 (g), , AlCl3(s), C6H6 (l) + CH3COCl (l) –––––– C6H5COCH3(l) + HCl(l), 3. Auto Catalysis :–, *, , Catalysed reaction in which one of the products it self acts as a catalyst, then it is called auto catalysis., , Ex., , CH3COOC2H5 + H2O ––––––– C2H5OH + CH3COOH, auto catalyst = CH3COOH, 2 AsH3, , –––––––––––––––– 2 As + 3H2, auto catalyst = As, , KMnO4 + H2C2O4 + H2SO4 ––– K2SO4 + MnSO4 + CO2 + H2O, auto catalyst = Mn+2 ion, *, , Initial stages the reaction is slow but as soon as the products come into existance, the reaction rate increases., , 4. Induced Catalysis :–, *, , When one reaction influences the rate of other reaction, which does not occur under ordinary, condition, the phenomenon is known as inducesed catalysis., , Ex., , Na2SO3 solution is oxidised by air but Na3AsO3 solution is not oxidised by air sepreately. If mixture, of both is taken, both pf them undergo simultaneous oxidation. The oxidation of Na 2SO3 induce the, oxidation of Na3AsO3., , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 24

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Surface Chemsitry, O2, Na2 SO3 ––––––– Na 2SO4, O2, Na 3AsO3 ––––––– Na3AsO4, General Characters of Catalyst, *, , Catalyst remains unchanged in mass and chemical composition at the and of reaction.Physical state and, colour may change., , *, , The catalyst generally can not initiate the reaction., , *, , The catalyst in generally specific in nature i.e particular substance can act as a catalyst only in a particular, reaction and not in other., , *, , Catalyst has maximum activity at optimum temperature., , *, , They not change heat of reaction (H), , *, , Catalyst provides a new path by reducing activation energy of reaction. Due to this, the rate of reaction, increases., Absence of, catalyst, , Activation energy high, Reaction slow, , , , *, , E, , Activation energy low,, Reaction fast, , Presence of, catalyst, , Reaction path , , In catalytic reversible reactions, catalysts affect the rate of forward and backward reaction equally, thereby, equilibrium is established rapidly. But the value of equillbrium constant KC remain constant., , *, , Impurities can change the reactivity of catalyst., , *, , Generally, catalysts do not bring about any change in the products of the reaction. Same product is obtained, even in the absence of the catalyst. AMount of product also unaffected by catalyst., , *, , They more effective in powdered state., , *, , Catalyst can be promoted by promoters and poisoned by anticatalyst., , *, , In the case of colloidal solution acting as catalyst the catalytic activity decreases by increasing temperature, due to coagulation., , Mechanism of Catalysis, There are two theories–, , 1. Intermediate compound theory :&, It is applicable for homogeneous catalysis. According to this theory mechanism of a catalytic reaction given as–, X(g) (catalyst½, A(g) + B(g)  AB(g), , GCI, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 25

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Surface Chemsitry, Step (i) First of all more reactive reactant react with catalyst and formed reactive intermediate., A+ X, , , , AX, , (fast), , Step (ii) This intermediate react with another reactant and form product–, AX + B ––––––––––– AB + X, *, , (slow), , According to kinetics–, Rate  [AX] [B] [A] [B] [X] , , Rate  [X], , So in homogeneous catalysis, the rate of reaction depends on concentration of catalyst., *, , Intermediate theory failed to explain following fact–, (i), , Mechanism of heterogeneous catalysis., , (ii), , Mechanism of promoters and poison., , 2. Adsorption theory %&, *, *, *, *, , It is applicable for heterogeneous catalysis., It is based on chemical adsorption., According to the theory there are free valencies on the surface of catalyst on which reactants can adsorb, easily., According this theory, reaction take place in the following step:–, Step (i) Diffusion & In this step reactant molecules diffuse towards surface catalysis., Step (ii) Adsorption & Therefore, concentration of reactants increase on the surface of catalyst., Due to this number of effective collisions increase between reactants molecules and so the reaction, rate increase. The heat evolved in this adsorption is used to overcome energy barrier involved in, reaction., Step (iii) Formation of activated complex – Adsorbed reactants combine and form activated, complex., Step (iv) Product Formation – Finally unstable activated complex dissociate and give product., , A, A + B + Catalyst, , Adsorption, Fast, , Catalyst, , Activated complex formation, Slow, , B, , Catalyst, , *, , Here formation of activated complex is a rate determining step., , *, , In this catalysis, rate does not depend on the concentration of catalyst., , Fast, , Product + Catalyst, , Rate  [A] [B], , GCI, , *, , This is based on chemical adsorption which explain selectivity., , *, *, *, *, , The surface of catalyst is use angain and again due to alternate adsorption and desorption., Transition metals are good catalyst due to presence of free valencies., More number of free valencies are provide more increase in rate., This theory explain following fact satisfactory–, –, In powder state of catalyst, no. of free valencies are high and thus the catalytic activity is high., –, Promoters combined with catalyst and increase the no. of free valencies and thus the, reactivity of catalyst increases., –, Poison combine with catalyst decrease its valencies., , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 26

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Surface Chemsitry, ENZYME, *, , In living organism most of the chemical reactions are catalysed by complex organic substances, which are called enzymes., , *, , Enzymes are Bio chemical catalys which catalyse bio-chemical reactions., , *, , These formed in Living Cells, can not be synthesised., , *, , Enzymes are nitrogen-containing protein molecules having high molecular weight and which are, found in plants and animals., , *, , Enzymes form colloidal solution with water. When electrolyte is added their activity decrease becuase, they destroyed by coagulation., , *, , Enzymes can be destroyed by ultraviolet rays., , *, , Enzymes behave as heterogeneous catalysts., , *, , In Living organism each reaction associated with a particular enzyme., , *, , They are highly specific in nature., , *, , Enzymes are most active at optimum temperatures. On higher temperature enzyme coagulated thus these, are sensetive about temperautre, , *, , Enzymes show maximum activity at a optimum pH (5 – 7)., , *, , Most of the biochemical reaction occurs at body temperature and pH = 7, , *, , The difference between enzyme and heterogenous catalyst are following–, – Enzyme are not synthesised while Catalyst may synthesised or natural., – Enzyme always required an inorganic compound called co-enzyme but for catalyst it is not always required., , *, , Mechanism :- their mechanism based on Key -lock system., , Enzyme + Substate, , , , E – S –––––––– E + Product, (Intermediate), , Some Important Enzymatic process :Conversion, , GCI, , Enzyme used, , Starch  Maltose,, , Diastase (malt source ½, , Glucose –––––––––– Ethyl alcohol, , Zymase (Yeast source), , Sucrose –––––––––– Glucose + fructose, , Invertase (Yeast source), , Maltose –––––––––– Glucose, , Maltase (Yeast source), , Urea ––––––––––––– NH3 + CO2, , Urease (Soyabeen source), , Ethyl alcohol ––––––– Acetic acid, , Micoderma aceti, , Fat/lipid ––––––––––– Fatty acid + Glycerol, , Lypase, , Protein ––––––––––– Amino acid, , Trypsion, , Protein ––––––––––– Peptide, , Pepsin, , Starch –––––––––––– Sugar, , Ptyalin, , Milk ––––––––––––– Curd (Fermentation of milk), , Lactic bacilli, , GCI (P) Ltd., Jyoti Nagar, Piprali Road, Sikar, Ph. 01572 - 256688, , 28