Title 5.SURFACE CHEMISTRY FINAL 4-3-2014.pdf ✅

SURFACE CHEMISTRY 184 NISHITH Multimedia India (Pvt.) Ltd., JEE ADVANCED - VOL - VI NISHITH Multimedia India (Pvt.) Ltd., SURFACE CHEMISTRY SYNOPSIS  ADSORPTION:  Adsorption from Solution: Apart from adsorption of the gases, solids have also the capacity to adsorb substances present in solutions. For example, if we place a piece of charcoal in a litmus solution taken in a test tube and shake, the solution becomes colourless. It is because of adsorption of the litmus which is in fact a dye, by the charcoal. Similarly, animal charcoal decolorizes impure sugar solution by adsorbing colouring dye. The actual mechanism of adsorption from the solution is not definite. However, it is believed that it continues till a unimolecular layer is built up on the surface of the adsorbent. The Freundlich dsorption isotherm as well as Langmuir adsorption isotherm are applicable to the adsorption from the solutions in the same way as from the gases. The effect of temperature is also similar. However, equilibrium concentration (C) is used in place of equilibrium pressure and the mathematical expressions for the two types of isotherms are: x 1/ n k C m   (Freundlich Adsorption Isotherm) or x aC m 1 bC   (Langmuir Adsorption Isotherm) Competing Adsorption: When more than one type of the adsorbate species are in contact with a particular adsorbent, there is a competition between their molecules or particles to be adsorbed on the solid surface. This depends upon their nature. However, the one which can form stronger bonds is adsorbed more in preference to the other. This is known as competing adsorption and it also happens in the reverse process also i.e. desorption. In this case, the species which is weakly adsorbed are dislodged first from the solid surface. It may be noted that the adsorption chromatography is based upon this principle of adsorption. Determination of surface area of adsorbent:  If V litre of gas is adsorbed at temperature T and Pressure P then the number of gas molecules adsorbed = PVNA RT  surface area of adsorbent = number of molecules x Area of cross section of molecule( 2  r )  Applications of adsorption: 1. In dyeing of cloth: Mordants such as alums are used in dying of cloth. They adsorb the dye particles which, otherwise, do not stick to the cloth. 2. In ion-exchange resins: The organic polymer containing groups like –COOH, –SO3H, –NH2 etc., possess the property of selective adsorption of ions from solutions. These are quite useful in the softening of water and also in the separation of the elements of the Lanthanide series (also called rare earths). 3. Softening of hard water:The hard water is made to pass through a column packed with zeolite. 2 2 Ca Mg ,   ions which are responsible for hardness get adsorbed on zeolite 4. Surfactants: Surfactants will act as emulsifier (which work on the principle of adsorption) in the manufacture of emulsions  Colloids: Coagulation of lyophobic sol: Following are some general methods used for coagulation of sols. a) General methods: 1. By heating: Coagulation of butter 2. By cooling: Coagulation of milk, fat floats over 3. By exposure to light 4. By mechanical agitation 5. By persistent dialysis b) Mutual coagulation: A deep red +ve sol of Fe(OH)3 , on mixing with bright yellow –ve sol of As2 S3 shows mutual coagulation of both leading
NISHITH Multimedia India (Pvt.) Ltd., 185 JEE MAINS - CW - VOL - I JEE ADVANCED - VOL - VI NISHITH Multimedia India (Pvt.) Ltd., SURFACE CHEMISTRY to a colourless solution with precipitate settled down due to neutralization of charges by each other. The coagulation of sols by electrolytes has been dealt in terms of Hardy-Schulze rule. According to this rule:  One of the ions furnished by an electrolyte, carrying charge opposite to that of sol particles is responsible for coagulation of sols and is known as effective ion or counter ion.  The greater is the valency of the counter-ions, the greater will be its coagulating power. For example, in coagulating, a negatively charged sol (e.g., As2 S3 sol) the order of efficiency of coagulating ions will be Ti4+ > Fe3+ > Ca2+ > Na+ . Similarly, for a positively charged sol say Fe(OH)3 sol, the order will be [Fe(CN)6 ] 4– > [Fe(CN)6 ] 3– > SO4 2– > Cl– .  More is the coagulating power, lesser is coagulation or flocculation value (i.e., the minimum amount of electrolyte required to coagulate a definite amount of (sol). Usually, the flocculating value of these ions are quantitatively described as 6 1 (x) where x is the valency of the coagulating ion. For example, for mono-, di-, tri- and tetravalent ions, the ratio in the flocculation value will be         6 6 6 6 1 1 1 1 : : : 1 2 3 4 1.00 :1.56 : 0.137 : 0.025 or  Surfactants: These are the substances which are preferentially adsorbed at the interfaces like oil -water , air- water etc. and Surfactants are responsible for micellisation. Types of surfactants:  cationic surfactants: substances on ionisation giving a cation with hydrophilic & hydrophobic group. Ex: 1. Cetyl trimethyl ammonium chloride [ 16 33 3 3 C H CH N Cl ( )   ] 2. Octa decyl ammonium chloride 18 37 3 [ ] C H NH Cl    Anionic surfactants: Substances giving anion which acts as surfactant Ex: 1.Sodium palmitate 15 31 [ ] C H COONa 2.Sodium oleate 17 35 [ ] C H COONa  Non ionogenic Surfactants: Substances not Ionisable in aqueous medium but have hydrophobic and hydrophillic end. Micelle or Associated colloid:  The minimum concentration of surfactant at which micelle formation starts is Critical Micelle Concentration (CMC)  The formation of micelle takes place above a particular temparature called Kraft temperature (Tk )  Lesser the CMC of surfactant, more is its surface activity  After CMC, the rate of increase of conductivity is slower than the rate at which it increases bellow CMC.  After CMC the rate of increase of turbidity with concentration becomes more than at CMC  After CMC the colligative properties such as osmotic pressure shows a slow rate of increase than the rate at which they increase below CMC  The surface tension of solution shows a sharp decrease after CMC  Process of micellisation is exothermic, but CMC decreases or increases with Temperature LEVEL-V SINGLE ANSWER QUESTIONS 1. Cottrell precipitator acts on which of the following principle A) Hardy-Schulze rule B) Distribution law C) Le-chatlier Principle D) Neutralization of charge on the colloidal particles 2. Gold number is associated with A) Electrophoresis B) Purple of cassius C) Protective colloid D) Amt of pure gold
SURFACE CHEMISTRY 186 NISHITH Multimedia India (Pvt.) Ltd., JEE ADVANCED - VOL - VI NISHITH Multimedia India (Pvt.) Ltd., 3. The no.of moles of lead nitrate needed to coagulate 2 moles of colloidal (AgI) is A) 2 B) 1 C) 1/2 D)2/3 4. Lyophilic sols are (IIT 2008) A) Irreversible sols B) Prepared from inorganic compounds C) Coagulated by adding elctrolytes D) Self-Stabilising 5. Emulsions of polyvinyl acetate are used in A) Medicines B) Latex paints C) fire works D) rayonEL-I 6. The blue colour of the water of the sea is due to A) reflection of blue light by salt present in water B) scattering of blue light by sol particles C) refraction of of blue coloured light by the impurties present in sea water D) absorption of radiation of different colours except blue light 7. Graph between log x m and log P is a straight line inclined at an angle  = 45°. When pressure of 0.5 atm and log k = 0.699, the amount of solute adsorbed per g of adsorbent will be A) 1 g/g adsorbent B) 1.5 g/g adsorbent C) 2.5 g/g adsorbent D) 0.25 g/g adsorbent 8. 3.6 gram of oxygen is adsorbed on 1.2 g of metal powder. What volume of oxygen adsorbed per gram of the adsorbent at STP ? A) 0.19 L B) 1 L C) 2.1 L D) 3.1 L 9. 100 ml of 0.6 M acetic acid is shaken with 2 g activated carbon. The final conc. of the solution after adsorption is 0.5 M. What is the amount of acetic acid adsorbed per gram of carbon ? A) 0.6 g B) 0.3 g C) 1.2 g D) 1.8 g 10. In which of the following conditions, on adding AgNO3 solution to KI solution, a negatively charged colloidal sol will be formed ? A.100mL of 0.1M AgNO3+100mL of 0.1M KI B.100 mL of 0.1 M AgNO3+50 mL of 0.2 M KI C.100mLof 0.2 M AgNO3+100 mL of 0.1M KI D.100mL of 0.1M AgNO3+100mL of 0.15M KI 11. Which of the following is true in respect of adsorption ? A)       G S H 0; 0; 0 B)       G S H 0; 0; 0 C)       G S H 0; 0; 0 D)       G S H 0; 0; 0 12. Among the following, the surfactant that will form micelles in aqueous solution at the lowest molar concetration at ambient conditions, is (IIT 2010) A) 3 2 15 CH CH N Br ( )   B) 3 2 11 3 CH CH OSO Na ( )   C) 3 2 6 CH CH COO Na ( )   D) 3 2 11 3 3 CH CH N CH Br ( ) ( )   13. Cleaning action of soap occurs because A) non-polar tails of soap molecules dissolve in grease B) Oil and grease dissolve into hydrophilic centres of soap micelles and washed away C) Hydrophilic head dissolve in grease D) Grease encapsulate by hydrophilic part 14. Select incorrect statement A) Gold sol is multimolecular colloid B) Large number of atoms of a substance aggregate together and form multimolecular colloids C) Metal sulphides are lyophobic colloids D) Sulphur sol is multimolecular colloid and hydrophilic in nature
NISHITH Multimedia India (Pvt.) Ltd., 187 JEE MAINS - CW - VOL - I JEE ADVANCED - VOL - VI NISHITH Multimedia India (Pvt.) Ltd., SURFACE CHEMISTRY 19. Point out the true statement A)Brownian motion and Tyndall effect are shown by colloidal systems B) The colloidal solution of a liquid in liquid is called emulsion C) Hardy-Schulze law is related with coagulation 20. A poisonous gas is adsorbed at activated charcoal. Which among the following is true: A) Activated charcoal is absorber B) Activated charcoal is adsorbate C) Activated charcoal has a porus surface D) Activated charcoal is adsorbent 21. Which of the following is the application of adsorption? A) Deionization of water B) Gas masks C) Hygroscopic nature of CaCl2 D) Heterogeneous catalysis 22. Isoelectric point is the H P at which colloidal particles A) Coagulate B) become electrically neutral C) cannot move toward either electrode D) moves faster towards opposite electrodes 23. Crystalloid and colloid differ with respect to A) Tyndall effect B) Particle size C) Diffusion through animal or vegetable membrane D) No.of particles per unit volume of solution 24. Tyndall effect is applicable when A) the diameter of the dispersed particles is not much smaller than the wavelength of the light used B) the diameter of the dispersed particles is much smaller than the wavelength of the light used C) the refractive indices of the dispersed phase and the dispersion medium must be same D) the refractive indices of the dispersed phase and the dispersion medium must differ greatly in magnitude 15. During electro-osmosis of   3 Fe OH sol A) Sol particles move towards anode B) Sol particles move towards cathode of a sol. D) Higher is the gold number, greater will be the protective power of a lyophilic colloid C) The dispersion medium moves towards anode D) The dispersion medium moves towards cathode MULTIPLE ANSWER QUESTIONS 16. The correct statements(s) pertaining to the adsorption of a gas on a solid surface is (are) (IIT 2012) A) Adsorption is always exothermic B) Physisorption may transform into chemisorption at high temperature C) Physisorption increases with increasing temperature but chemisorption decreases with increasing temperature. D) Chemisorption is more exothermic than physisorption, however it is very slow due to higher energy of activation 17. Select the correct statement (s) : A)Physisorption is favoured by low temperature B) Chemisorption is favoured by very high temperature because the process is endothermic C) Chemisorption increases with increase in temperature owing to high activation energy D) Oxygen adsorbed by charcoal can be desorbed by lowering pressure and temperature. 18. ‘X’ is the amount of a gas adsorbed by a fixed amount of a solid. If monolayer adsorption is supposed to occur, then which of the following statements is correct? A) At low pressures, x increases more than proportionately to the gas pressure B) At low pressure, x increases proportionately to gas pressure C) At moderate pressures, x increases less than proportionately to gas pressure D) At high pressures, x becomes independent of gas pressure.