Kerala Plus Two Chemistry Notes Chapter 5 Surface Chemistry<\/h2>\n
Surface chemistry deals with phenomena that occur at the surfaces or interfaces.<\/p>\n
Adsorption:<\/span> Adsorbate: Adsorbent: Desorption: Difference between Adsorption and Absorption:<\/span> Absorption – Sorption: Mechanism of Adsorption :<\/span> Types of Adsorption:<\/span> Characteristics: 2. Chemical Adsorption (Chemisorption): Characteristics: Sometimes physisorption and chemisorption occur simultaneously and it is not easy to ascertain the type of adsorption. A physisorption at low temperature may pass into chemisorption as the temperature is increased. For example, dihydrogen is first adsorbed on Ni by van der Waals\u2019forces. Molecules of hydrogen then dissociate to form hydrogen atoms which are held on the surface by chemisorption.<\/p>\n Comparison of Physisorption and Chemisorption<\/p>\n Adsorption Isotherms:<\/span> Freundlich Adsorption isotherm:<\/span> Adsorption from Solution Phase: Applications of Adsorption:<\/span> Catalysis :<\/span> Promoters: Poisons: Homogeneous and Heterogeneous Catalysis<\/span> Heterogeneous Catalysis: Important Features of Solid Catalysts b) Selectivity: e.g. CO and H2<\/sub> combine to form different products by using different catalysts. Shape Selective Catalysis by Zeolites:<\/span> Zeolites are good shape-selective catalysts because of their honey comb-like structures. Zeolites are widely used in petrochemical industries for cracking and isomerisation of hydrocarbon. Enzyme Catalysis:<\/span> Characteristics: Mechanism (Lock and key model)<\/span> Catalysts in Industry<\/span><\/p>\n Colloids:<\/span> Classification of Colloids:<\/span> ii) Based on Nature of Interaction between Dispersed Phase and Dispersion Medium:<\/span> 2. Lyophobic (solvent repelling) Colloids: iii) Based on Types of Particle of the Dispersed Phase<\/span> b) Macromolecular Colloids : c) Associated Colloids (Micelles): The formation of micelles take place only above a particular temperature called Kraft temperature (Tk.) and above a particular concentration called Critical Micelle Concentration(CMC).<\/p>\n Mechanism of micelle formation –<\/span> Preparation of Colloids<\/span> b) Electrical Disintegration or Bredig\u2019s Arc Method c) Peptization: Mechanism of peptization –<\/span> Purification of Colloids:<\/span> ii) Electro-dialysis: iii) Ultrafilteration: Properties of Colloids<\/span> 2) Tyndall Effect (Optical Property): Conditions for observing Tyndall effect: 2. The refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude. The ultramicroscope used to observe the light scattered by colloidal particles is based on Tyndall effect.<\/p>\n The colour of the sky can be explained by Tyndall effect. The dust and other colloids present in the atmosphere scatter the light. Only blue light reaches to our eyes.<\/p>\n 3) Colour: 4) Brownian Movement: 5) Charge on Colloidal Particles: Negatively charged sols: Reason for charge: Helmholtz Electrical Double Layer: Electrokinetic Potential or Zeta Potential: Significance of Charge on Colloidal Particles: 6) Electrophoresis: Coagulation\/Flocculation\/Precipitation:<\/span> Coagulation of lyophobic sols can be carried out by the following ways: Addition of electrolytes – Hardy – Schulze Rule: The ion having opposite charge to sol particles (coagulating ion) cause coagulation.<\/p>\n In the coagulation of negative sol, the flocculating power is in the order: Al3+<\/sup> > Ba2+<\/sup> > Na+<\/sup><\/p>\n In the coagulation of positive sol, the flocculating power in the order: Protective Colloids: Emulsions:<\/span> 2) Water dispersed in oil (W\/O type): Emulsifying agent or emulsifier – Emulsifying agents for O\/W emulsions : Emulsifying agents for W\/O emulsions: Colloids Around Us :<\/span> Application of Colloids<\/span> II) In industries : We hope the Plus Two Chemistry Notes Chapter 5 Surface Chemistry help you. If you have any query regarding Plus Two Chemistry Notes Chapter 5 Surface Chemistry, drop a comment below and we will get back to you at the earliest.<\/p>\n","protected":false},"excerpt":{"rendered":" Plus Two Chemistry Notes Chapter 5 Surface Chemistry is part of Plus Two Chemistry Notes. Here we have given Plus Two Chemistry Notes Chapter 5 Surface Chemistry. Board SCERT, Kerala Text Book NCERT Based Class Plus Two Subject Chemistry Notes Chapter Chapter 5 Chapter Name Surface Chemistry Category Plus Two Kerala Kerala Plus Two Chemistry […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[42728],"tags":[],"yoast_head":"\n
\naccumulation of molecular species at the surface rather than in the bulk of a solid or liquid, it is a surface phenomenon, e.g. Moisture gets adsorbed on silica gel.<\/p>\n
\nmolecular species or substance, which accumulates at the surface.<\/p>\n
\nmaterial on the surface of which adsorption takes place, e.g. Charcoal, Silica gel, etc.<\/p>\n
\nprocess of removing adsorbed substance from the surface of adsorbent.<\/p>\n
\nAdsorption –
\nthe substance is concentrated only at the surface and does not penetrate to the bulk of the adsorbent.<\/p>\n
\nthe substance is uniformly distributed throughout the bulk of the solid, e.g. Moisture gets absorbed on anhydrous CaCl2<\/sub> while adsorbed on silical gel.<\/p>\n
\nterm used when both adsorption and absorption take place simultaneously.<\/p>\n
\nThe unbalanced or residual attractive forces are responsible for attracting the adsorbate particle on adsorbent surface. During adsorption energy decreases, therefore adsorption is exothermic process, i.e., \u2206H of adsorption (heat of adsorption) is always negative. The entropy of the system also decreases (\u2206S = – ve).<\/p>\n
\n1. Physical Adsorption (Physisorption):
\nHere the adsorbed molecules are held on the surface of the adsorbent by physical forces such as van der Waals\u2019 forces. It is reversed by reducing pressure or by heating.<\/p>\n
\nLack of specificity, easily liquifiable gases readily adsorbed, reversible in nature, extent of adsorption increases with increase in surface area of adsorbent, enthalpy of adsorption quite low (20 – 40 kJ mol’ ).<\/p>\n
\nthe forces of interaction between the adsorbent and adsorbate are chemical in nature. It cannot be easily reversed.<\/p>\n
\nHigh specificity, irreversibility, increases with increase in surface area, enthalpy of adsorption is high (80 -240 kJ mol”1).<\/p>\n\n\n
\n Physisorption<\/td>\n Chemisorption<\/td>\n<\/tr>\n \n 1) Arises because of van der Waals\u2019 force<\/td>\n 1) Caused by chemical bond formation<\/td>\n<\/tr>\n \n 2) Not specific<\/td>\n 2) Highly specific<\/td>\n<\/tr>\n \n 3) Reversable<\/td>\n 3) Irreversible<\/td>\n<\/tr>\n \n 4) More easily liquefiable gases are adsorbed readily.<\/td>\n 4) Gases which can react with the adsorbent show chemisorption.<\/td>\n<\/tr>\n \n 5) Enthalpy of adsorption is low (20-40 kJ mol’1)<\/td>\n 5) Enthalpy of adsorption is high (80-240 kJ mol-1)<\/td>\n<\/tr>\n \n 6) Low temperature is favourable. It decreases with increase of temperature<\/td>\n 6) Hig temperature is favourable. It increases with increase of temperature<\/td>\n<\/tr>\n \n 7) No appreciable activation energy is needed.<\/td>\n 7) High activation energy is sometimes needed.<\/td>\n<\/tr>\n \n 8) Increases with an increase of surface area.<\/td>\n 8) Increases with an increase of surface area.<\/td>\n<\/tr>\n \n 9) Results into multimolecular layers on adsorbent surface under high pressure.<\/td>\n 9) Results into unimolecular layer<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\nThe variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature can be expressed by means of a curve termed as adsorption isotherm.<\/p>\n
\nempirical relation between the quantity of gas adsorbed by unit mass of the solid adsorbant and pressure at a particular temperature.
\nx\/m = k.P1\/n<\/sup> (n > 1)
\nx \u2192 mass of the gas adsorbed
\nm \u2192 mass of adsorbent
\n\u2018k\u2019 and \u2018n\u2019 are constants which depend on the nature of the adsorbent and the gas at a particular temperature.
\nOR log x\/m = log k + \\(\\frac{1}{n}\\) log P
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-1.png\")
<\/p>\n
\nFreundlich’s equation approximately describes the behaviour of adsorption from solution.
\n\\(\\frac{x}{m}\\) = k.C1\/n<\/sup> m
\nC – equilibrium concentration
\nlog x\/m = log k + \\(\\frac{1}{n}\\) log C
\nPlotting log x\/m vs log C a straight line is obtained<\/p>\n
\nProduction of high vacuum, in Gas masks – activated charcoal is filled in gas mask to adsorb poisonous gases, for removal of colouring matter from solution in heterogeneous catalysis, in chromatographies analysis, in froth floatation process.<\/p>\n
\nThe process of altering the rate of chemical reaction by the addition of a foreign substance (catalyst) is called catalysis, e.g. MnO2<\/sub> acts as a catalyst in the thermal decomposition of KClO3<\/sub>.<\/p>\n
\nsubstances that enhance the activity of a catalyst, e.g. In Haber\u2019s process, iron is used as catalyst and molybdenum acts as a promoter.
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-2.png\")
<\/p>\n
\nsubstances which decrease the activity of a catalyst.<\/p>\n
\na) Homogeneous Catalysis:
\nWhen the reactants and catalyst are in the same phase, the process is said to be homogeneous catalysis.
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-3.png\")
\nHere both the reactants and the catalyst are in the liquid phase.<\/p>\n
\nIf the reactants and the catalyst are in different phase, the catalysis known as heterogeneous catalysis.
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-4.png\")
\nHere reactants are gaseous state while the catalysts are in the solid state.<\/p>\n
\na) Activity:
\nability of catalysts to accelerate a chemical reaction.
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-5.png\")
\nBut pure mixture of H2<\/sub> and O2<\/sub> does not react at all in the absence of a catalyst.<\/p>\n
\nability of a catalyst to direct a reaction to yield a particular product.<\/p>\n
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-6.png\")
<\/p>\n
\nThe catalytic reaction depends upon the pore structure of the catalyst and size of the reactant and the product molecules.<\/p>\n
\ne.g. ZSM – 5 – which convert alcohols into petrol.<\/p>\n
\nEnzymes are biological catalysts. They catalyse biological reaction in animals and plants to maintain life. e.g.<\/p>\n\n
\nHighly efficient, highly specific in nature, highly active under optimum temperature, highly active under optimum pH<\/p>\n
\nThe molecules of the reactant (substrate), which have complementary shape, fit into the cavities on the surface of enzyme particles just like a key fits into a lock. The enzyme catalysed reactions proceeds in two steps:
\nStep -1 :
\nBinding of enzyme to sutbstrate to form an activated complex.
\nE + S \u2192 ES*
\nStep-2 :
\nDecomposition of the activated complex to form product.
\nES* \u2192 E + P<\/p>\n\n
\nThe heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium, e.g. Starch, Gelatin. In colloids the particle size (diameter) is between 1nm and 1000 nm.<\/p>\n
\ni) Based on physical state of dispersed phase and dispersion medium:
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-7.png\")
\n<\/span><\/p>\n
\n1. Lyophilic (solvent attracting) Colloids:
\nthere is strong interaction between the dispersed phase and dispersion medium. They are reversible sols. e.g. Starch, gelatin, albumin etc.<\/p>\n
\nthere is little or no interaction between the dispersed phase and dispersion medium. They are also irreversible colloids and are not stable.<\/p>\n
\na) Multimolecular Colloids :
\nthe individual particles consist of an aggregate of atoms or small molecules with molecular size less than 1 nm, the particles are held together by van der Waals\u2019 forces, e.g. Sulphur sol, Gold sol etc.<\/p>\n
\nthe particles of dispersed phase are sufficiently big in size, maybe in the colloidal range, e.g. Starch, cellulose, proteins.<\/p>\n
\ncolloids which behave as normal strong electrolytes at low concentration but get associated at higher concentrations and behaves as colloidal solutions. The associated particle formed are called micelles.
\ne.g. Soap, detergents etc.<\/p>\n
\nIn soaps, the RCOO–<\/sup> ions are present on the surface with their COO–<\/sup> groups in water and R staying away from it and remain at the surface. At CMC, the anions are pulled into the bulk of the solution and aggregate to form \u2018ionic micelle’ having spherical shape with R pointing towards the centre of the sphere and COO–<\/sup> part remaining outward on the surface of the sphere.<\/p>\n
\na) Chemical Methods
\nSome examples:
\n![\"Plus](\"https:\/\/www.aplustopper.com\/wp-content\/uploads\/2019\/02\/Plus-Two-Chemistry-Notes-Chapter-5-Surface-Chemistry-8.png\")
<\/p>\n
\nMetallic sols can be prepared by striking an arc between two electrodes of the metal, immersed in the dispersion medium. The metal is vapourised by the arc which then condenses to form particles of colloidal size. e.g. Gold sol, Platinum sol, Silver sol etc.<\/p>\n
\nprocess of converting a precipitate into colloidal sol by shaking it with dispersion medium in the presence of small amount of electrolyte (peptizing agent), e.g. Freshly prepared Fe(OH)3 is peptized by adding small quantity of FeCI3 solution (peptizing agent).<\/p>\n
\nDuring peptization, the precipitate adsorbs one of the ions of the electrolyte on its surface. This causes the development of positive or negative charge on precipitates, which ultimately break up into smaller particles of the size of a colloid.<\/p>\n
\nprocess of reducing the amount of impurities to a requisite minimum from the colloids.
\ni) Dialysis:
\nprocess of removing a dissolved substance from a colloid by means of diffusion through a suitable membrane.<\/p>\n
\nprocess of dialysis in presence of an applied electric field. It is faster and is applicable if the dissolved substance in the impure colloid is only an electrolyte. The ions present in the colloid migrate out to the oppositely charged electrodes.<\/p>\n
\nprocess of separating the colloidal particles from the solvent and soluble solutes present in the colloid by ultra filters. The ultra filter paper is prepared by soaking the filter paper in a colloidion solution (4% solution of nitro cellulose in a mixture of alcohol and ether). It is then hardened by formaldehyde and finally dried.<\/p>\n
\n1) Colligative Properties:
\nvalues of colligative properties as smaller due to smaller number of particles.<\/p>\n
\nphenomenon of the scattering of light by colloidal particles.<\/p>\n
\n1. The diameter of the dispersed particles is not much smaller than the wavelength of the light used; and<\/p>\n
\nIt depends on the wavelength of lighty scattered by the dispersed particles which in turn depends on the size and nature of the particles and changes with the manner in which the observer receives the light, e.g. a mixture of milk and water appears blue when viewed by the reflected light and red when viewed by transmitted light.<\/p>\n
\nThe constant zig-zag movement of the colloidal particles. It is due to the unbalanced bombardment of the particles by the molecules of the dispersion medium. It does not permit the particles to settle and is responsible for the stability of sols. ,<\/p>\n
\nColloidal particles carry an electric charge.
\nPositive charged sols: Al2<\/sub>O3<\/sub>. xH2<\/sub>O, CrO3<\/sub>.xH2<\/sub>0, basic dye stuffs, blood (Haemoglobin) etc.<\/p>\n
\nMetal sols (Cu, Ag, Au), metallic sulphides, acid dyes stuffs, starch, gelatin.<\/p>\n
\nIt is due to
\ni) electron capture by sol particles during electrodispersion of metals,
\nii) preferential adsorption of ions from solution and\/ or
\niii) formulation of electrical double layer.<\/p>\n
\ncombination of two layers of opposite charges around the colloidal particle. The first layer of ions is firmly held and is termed fixed layer while the second layer is mobile which is termed as diffused layer.<\/p>\n
\nIt is the potential difference between the fixed layer and the diffused layer of opposite changes in the electrical ‘ double layer.<\/p>\n
\nprovides stability to the colloid because the repulsive forces between charged particles having same charge prevent them from coalescing or aggregating when they come closer to one another.<\/p>\n
\nlled anaphoresis and that of cathode is called cataphoresis.<\/p>\n
\nprocess of settling of colloidal particles by the addition of electrolyte.<\/p>\n
\nElectrophoresis, mutual coagulation (mixing two oppositely charged sols), boiling, persistent dialysis, addition of electrolytes, etc.<\/p>\n
\nColloids interact with ion carrying charge opposite to that present on themselves. This causes neutralisation leading to their coagulation.<\/p>\n
\nthe greater the valence of the flocculating ion added, the greater is its power to cause precipitation.<\/p>\n
\n[Fe(CN)6<\/sub>]4-<\/sup> > PO4<\/sub>3-<\/sup> > SO4<\/sub>2-<\/sup>> Cl–<\/sup><\/p>\n
\nthe lyophilic sol used for protection of lyophobic sol.<\/p>\n
\nliquidin liquid colloidal systems i.e., the dispersion of finely divided droplets in another liquid. There are two types of emulsions.
\n1) Oil dispersed in water (O\/W type):
\nwater acts as dispersion medium, e.g. Milk, Vanishing cream.<\/p>\n
\noil, acts as dispersion medium.e.g. Butter, Creams, Cod liveroil Emulsification – process of making an emulsion. Emulsion may be obtained by vigourously agitating a mixture of both liquids.<\/p>\n
\nsubstance used to stabilise an emulsion. It forms an interfacial film between suspended particles and the medium, e.g.<\/p>\n
\nProteins, gums, natural and synthetic soaps etc.<\/p>\n
\nHeavy metal salts of fatty acids, long chain alcohols, lampblack etc.<\/p>\n
\nFog, mist and rain; food materials, blood, soils, formation of delta.<\/p>\n
\nI) In Medicine:
\nColloidal medicines are more effective because they have large surface area and are, therefore, easily assimilated, e.g. Colloidal silver (Argyrol) – as eye lotion, Colloidal antimony – in curing Kalaazar, Colloidal gold – for intramuscular injection. Milk of magnesia – in stomach disorder.<\/p>\n
\nElectrical precipitation of smoke – by Cottrell smoke precipitator, purification of water, tanning, cleansing action of soaps and detergents (micelle formation), photographic plates and films, rubber industry and Industrial products.<\/p>\n