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CSC – 1 SURFACE CHEMISTRY Syllabus : Adsorption - Physisorption and chemisorption and their characteristics, factors affecting adsorption of gases on solids - Freundlich and Langmuir adsorption isotherms, adsorption from solution. Catalysis - Homogeneous and heterogeneous, activity and selectivity of solid catalyst, enzyme catalysis and its mechanism. Colloidal state - Distinction among true solutions, colloids and suspensions, classification of colloids - lyophilic, lyophobic; multi molecular, macromolecular and associated colloids (micelles), preparation of colloids - Tyndall effect, Brownian movement, electrophoresis, dialysis, coagulation and flocculation; Emulsions and their characteristics; Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 2 SURFACE CHEMISTRY C1 Colloids : A colloid is a heterogeneous system in which one substance is disprersed (dispersed phase) as very fine particles in another substance called dispersion medium. In a colloid, the dispersed phase may consist of particles of a single macromolecule (such as protein or synthetic polymer) or an aggregate of many atoms, ions or molecules. Colloidal particles are larger than simple molecules but small enough to remain suspended. Difference between a solution and colloid is one of particle size. True Solution : Colloid : 1. Homogeneous mixture & are transparent Heterogeneous mixture are transluscent 2. In as solution, the particles are ions or small molecules and invisible under all circumstances Particles are visible under powerful microscope but scattering effect by the particles can be observed under ultra microscope 3. Particle size is of the order of molecule size i.e. 1mµ or 10Å or < 103 pm or < µmm Size of particle range of diameter between 1 and 1000 nm. 4. True solution passes easily through filter paper as well as animal memberane or parchment membrane Colloidal particles passes easily through filter paper but slowly through parchment membrane 5. Does not scatter light Particle scatter light i.e. Tyndall effect 6. Particle do not settle on ultracentrifugation Particle settle on ultracentrifugation C2 Classification of colloids Colloids are classified on the basis of the following criteria : (a) (a) Physical state of dispersed phase and disperseion medium (b) Nature of interaction between dispersed phase and dispersion medium (c) Type of particles of the dispersed phase Classification based on physical state of dispersed phase and dispersion medium Eight types of colloidal syster are possible : (solute) Dispersed Phase (solvent) Dispersed Medium Type of colloid 1. Solid Solid Solid Sol Coloured glasses, Gemstone, Some alloys, minerals, rock salts. 2. Solid Liquid Sol Paints, cell fluids, starch or protein in water, glue, gold sol, Indian ink, muddy water, milk of magnesia, white of an egg 3. Solid Gas Solid Aerosol Smoke, dust, storm, fumes 4. Liquid Solid Gel (solid emulsion) Cheese, butter, jellies, boot polish, curd, Fe(OH)3, Al(OH)3. 5. Liquid Liquid Emulsion Milk, hair cream, emulsified oils, cod liver oil, medicines. 6. Liquid Gas Liquid Aerosol Fog, mist, cloud, insecticide spray. 7. Gas Solid Solid Foam Styrene foam, rubber, occluded gases, pumice stone, bread 8. Gas Liquid Foam or froth Whipped cream, soap, lather, lemonade froth, beer, shaving cream, beaten egg Einstein Classes, Examples Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 3 If dispersion medium is water, the solution is called aquasol or hydrosal and if the dispersion medium is alcohol, it is called alcosol and so on. (b) Classification based on nature of interaction between dispersed phase and dispersion medium. They are : Lyophilic Colloid Lyophobic Collidal Solution 1. Solvent attracting (If water is the dispersion medium term used in hydrophilic Solvent repelling (same here) i.e. if water is the dispersion medium the term used is hydrophobic 2. The word lyophilic means liquid loving The word lyophobic means liquid hating 3. Collidal sols directly formed by substances like gum, gelatine, starch, rubber etc. on mixing or warming with suitable liquid (dispersion medium). Subtances like metals, their sulphides etc. when mixed simply with dispersion medium do not form colloidal sol. They can be prepared by special method. 4. If dispersion medium is seperated from dispersed phase by evaporation, the sol can be reconstituted by simply remixing with the dispersion medium These sols are readily precipitated or coagulated on the addition on the addition of small amount of electrolytes by heating or by shaking and hence are not stable 5. Thus these sols are reversible sols Once they precipitate they do not give back the collidal sol by simple addition of the dispersion medium. These sols are Irreversible. Viscosity is much higher than dispersion medium whereas Lyophobic sol have of same as of dispersion medium. Lyophobic sols need stablising agent for their preservation. (c) Classification based on type of particles of the Dispersed Phase : They are 1. Multimolecular colloid 2. Macromolecular colloid 3. Associated colloid 1. Multimolecular Colloid : When on dissolution, a large number of atoms or smaller molecules of a substance aggragate together to form species having size (with diameter less than 1 nm) e.g. Gold sol may contain particles of various sizes having many atoms. Sulphur sol consists of particles containing a thousand or more of S8 sulphur molecules. 2. Macromolecular Colloid : Macro molecules have large molecular masses. These on dissolution in a suitable solvent form a solution in which the size of the macromolecules may be in the collidal range. Such systems are called macro-molecular colloid. These colloids are quite stable and resemble true solution in many respect. e.g. naturally occuring macromolecules are strach, collulose, proteins, and enzymes. Examples of man-made macromolecules are polythene, nylon, polystyrene, synethetic rubber etc. 3. Associated Colloids (Micelles) : These are some substance which at low concentrations hehave as normal, strong electrolytes but at higher concentrations exhibit colloidal behaviour due to formation of aggregated particles. The aggregated particles thus formed are called micelles. These are known as associated colloid. The formation of micelles takes place only above a particular temperature called “Kraft Temperature” (Tk) and above particular concentration called “Critical Micelle concentration (CMC)”. On dilution, these colloids revert back to individual ions. e.g. surface active agents soaps, detergents belong to this class. For soaps CMC is ~ 10–4 to 10–3 mol L–1. These colloid have both lyophilic and lyophobic part. Micelles may contain as many as 100 molecules or more Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 4 Mechanism of Formation of Micelle e.g. let us take example of soap solution i.e. RCOO–Na+ (soap is sodium salt of high fatty acids e.g. sodium stearate) i.e. CH3(CH2)16COO–Na+ or sodium Lauryl Sulphate CH3(CH2)11SO4Na+ In Polar part is water loving whereas non-polar part water repelling. Thus RCOO– present with COO– part in water and R staying away from it and remain on surface. With higher concentration they are pulled in water. An aggregrate thus formed called ionic micelle. C3 Prepration of collidal solution : 1. Preparation of Lyophobic solutions : (a) Condensation method (b) Dispersion method (a) Condensation Method : 1. Chemical Method 2. Physical Method (i) Exchange of solvent (ii) Excessive cooling 1. Chemical Method : Colloidal solutions can be prepared by chemical reactions leading to formation of molecules by double decomposition, oxidation, reduction and hydrolysis. These molecules then aggregate leading to formation of sols, provided a suitable stabliser is present. (i) Oxidation : A colloidal solution of sulphur can be obtained by bubbling oxygen or any other oxidising agent like HNO3, Br2 etc. through a solution of hydrogen sulphide in water 2H2S + O2 2H2O + 2S (ii) By reduction : A number of metals, such as silver, gold and platinum have been obtained in colloidal state by treating the aqueous solution of their salts with a suitable reducing agent, such as formaldehyde, hydrazine, H2O2, SnCl2 etc. 2AuCl3 + 3SnCl2 3SnCl4 + 2Au (iii) By hydrolysis : Many salt solutions are easily hydrolysed by boiling dilute solutions of their salts. e.g. Fe(OH)3 and Al(OH)3 sol are obtained by boiling solutions of corresponding chlorides. FeCl3 + 3H2O Fe(OH)3 + 3HCl (iv) By double decomposition : A solution of arsenic sulphide is obtained by passing H2S through a cold solution of arsenious oxide in water. As2O3 + 3H2S As2S3 + 3H2O (b) Dispersion Method : In these methods the coarser particles are broken to smaller particles of colloidal size in the presence of dispersion medium. These are stabilized by adding suitable stabilizer. (i) Mechanical Dispersion : In this method, the coarse suspension of the substance is brought into colloidal state in the dispersion medium by grinding in a colloid mill. (ii) Electrical dispersion or Bredig’s Arc method : This process involve dispersion as well as condensation. If an electric arc is struck between two electrodes of a metal like gold, silver, platinum or copper in water having traces of an alkali, the metal is found to be converted into colloidal solution. Alkali Act as stabliser. Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 5 (iii) Peptization : The process of converting precipitate into colloidal solution by shaking it with dispersion medium in the presence of (small amount of) electrolyte. The electrolyte used for this purpose is called peptizing agent or stablizing agent. During peptization, the precipitate absorbs one of the ions of the electrolyte on its surface.The ion absorbed on the surface is common either with the anion or cation of the electrolyte. This causes the development of positive or negative charge on precipitates which ultimately break-up into small particles having the dimensions of colloids. e.g. Freshly prepared Fe(OH)3 can be converted into colloidal state by shaking it with H2O containing FeCl3 or NH4OH Fe(OH)3 + FeCl3 [Fe(OH)3Fe]3+ + 3Cl– Stable solution of stannic oxide collodial is obtained by adding small amount of dilute HCl to stannic oxide precipitate. Similarly colloidal solution Al(OH)3 and AgCl are obtained by treating corresponding ppt. with dilute HCl and AgNO3 or KCl respectively. Gelatin stablised colloidal state of ice-cream. Lamp black is peptised by gums to form indian ink. C4A Purification of Colloidal Solution : 1. Dialysis : Dialysis may be defined as the process of seperating a crystalloid from a colloid by diffusion or filtration through a fine memberane, the memberane (or appratus) used for this purpose is called Dialyser. The process of dialysis can be quickened by using hot water or by applying electric feild (electrodialysis). 2. Ultra filtration : Solution particles pass directly through the ordinary filter paper because their pores are larger (more than 1 µ or 1000 mµ) then the size of solution particles (less than 200 mµ). But if the pores of ordinary filter paper made smaller by soaking the filter paper in a solution of gelatin and subsequently hardened by soaking in formaldehyde, the filter paper may retain colloidal particles and allow true solution particle to escape. Such filter is known as ultrafilter paper. 3. Ultra-Centrifugation : In this method, the colloidal solution is taken in a tube which is place in a ultra-centrifuge on rotation the colloid particle settle down at the bottom of the tube. C4B Properties of Colloidal System : (i) Heterogeneous character : As it contain two phases i.e. dispersed phase and dispersion medium. (ii) Non-Setting : Colloidal solutions are stable systems. (iii) Filterability : Colloidal particles readily pass through ordinary filter paper. However they can be retained by special filters known as ultrafilters. (iv) Visibility : not visible under most powerful microscope. (v) Colour : Colour of a colloidal solution depends on the size and shape of particle. (vi) Colligative Properties : Colloidal solutions shows colligative properties i.e. relative lowering in V.P., somotic property, elevation in B.pt., Depression in fz. pt. However due to high molecular masses of colloidal particles, mole fraction of the dispersed phase is very low. Thus value of colligative properties determined experimentally are colligative properties determined experimentally is very low. Only osmotic pressure measument is used to determine the molecular mass of polymer. (vii) Tyndall Effect (optical property) : Tyndall in 1869, observed that when a beam of light is passed through a true solution is can not be seen. When a same light is passed through a colloidal solution it become visible as a bright streak. This phenomenon is called Tyndall effect and illuminated path (streak of light) is known as Tyndall cone. The appearance of dust particles in a semidarkened room when a sun beam enters or when a light is thrown from a projector in cinema hall are well known example of Tyndall effect. The dust particles are large enough to scatter light which renders the path of light visible. (viii) Brownian Movement : Robert Brown, observed that pollen grain in aqueous suspension were in constant motion. When colloidal solutions are observed in ultramicroscope, the particles are in constant, random or zig-zag motion, not following the definite path called as Brownian motion. Brownian movement is due to collision of colloidal particles with dispersion medium which are in constant motion. Since colloidal particles are heavier than dispension medium molecules their movement is considerably slower than that of medium molecules. The mass of particle of ordinary suspension is so large that the bombardment of molecules of the dispersion medium produces little effect and thus ordinary suspension do not exhibit brownian movement. Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 6 (ix) Electrical Property : Colloidal particles are electrically charged. All the particles of a colloidal system carry the same charge while the dispersion medium has an equal but opposite charge with the result the system as a whole is electrically natural. Colloidal particles having similar charge, repel each other, and do not combine to form bigger particles and thus solution is stable and particles do not settle down. When an electric current is passed through a colloidal solution the solid particles and the liquid medium being oppositely charged move in opposite direction. In case the experiment is so arranged that only the particles can move and no liquid medium, the phenomenon is known as Cataphoresis or Electrophoresis. When only the medium is allowed to migrate and not the particles, then is known as electrosmosis. Distance travelled by colloidal particles in one second under a potential gradient of 1 volt per cm is called electrophoretic mobility of colloidal particles. (x) Origin of the charge on colloidal particles : The origin of the charge on the sol particles in most cases is due to the preferential of either positive or negative ions on their surface. When two or more ions are present in the dispersion medium differential adsorption of common to the colloidal particle usually takes place. e.g. Fe(OH)3 sol prepared by the hydrolysis of ferric chloride has positive charge because of the preferential adsorption of ferric ions i.e. Fe3+ on the surface of the ferric hydroxide particles. Fe(OH)3 + Fe3+ Fe(OH)3 . Fe3+ Some other positively charged colloidal sols are Al(OH)3, Heamoglobin, basic dyes etc. Similarly, the negative charge on the arsenic sulphide sol is found to be due to preferential adsorption of sulphide ions, produced by the ionization of H2S. Other negatively charged sol are starch acidic dyes etc. C5 Co-agulation of colloidal solutions : As stability of the colloidal state is due to existance of electrical charge on the particles. If charge is lowered to a certain critical value or neutralised, the particles approach close enough to coalesce to form bigger particles of the suspension range. This phenomenon of change of colloidal state to suspension state is known as coagulation or flocculation of colloidal solution. It is generally brought about by following treatments : (i) By the mutual action of sols (mutual precipitation) : When the two oppositely charged sols e.g. As2S3 and Fe(OH)3 sols are mixed in approximately equal proportions, the charge of one sol is neutralised by the opposite charge on the other sol with the result the dispersed phase of both the sols are precipitated out. (ii) By the addition of electrolytes : Although traces of an electrolyte are essential for stablising the sols, presence of large amounts causing their coagulation or flocculation. As colloidal particles carry opposite charge ions, they take up oppositely charged ions from electrolytes with the result the charge on the sol particles is neutralised and thus these are precipitated. The ion carry opposite charge is called Flocculating ion. e.g. The amount of electrolyte required to coagulate a fixed amount of a sol depends upon the valency of the flocculating ion. In general, greater the valency of the flocculating ion the higher is its power to cause precipitation. This is known as Hardy - Schulze rule. Flocculation power of the various ions follows the following order : Cations : Al3+ > Mg2+ > Na+ Anions : [Fe(CN)6]4– > PO43– > SO42– > Cl– Flocculating cations and anions cause coagulation (floculation) of the negatively and positively charged colloids respectively. The minimum concentration required to cause flocculation is known as Flocculation value, which is generally expressed in milli mol per litre. C6 Protective colloids : Lyophilic sol added to a lyophobic colloid prevent from precipitation by electrolyte, the lyophilic sol added to a lyophobic sol, provide envelop to the particles of lyophobic sol, and thus protect is from the action of electrolytes. This lyophilic colloids used for such purposes are known as protective colloids. e.g. addition of gelatin (lyophilic colloid) to a gold sol (lyophobic sol) protects the latter by the action of limited amount of NaCl. The lyophilic colloids differ in their protective powers. Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 7 Gold Number : is used to measure the protective power of different colloids. It is defined as weight in milligrams of a protective colloid which checks the co-agulation of 10mL of a given gold solution of adding 1 mL of a 10% solution of sodium chloride. Thus smaller the gold no. of a lyophilic colloid greater is the protective power. Q. 0.025 g of starch sol. is required to prevent coagulation of 10mL gol sol when 1 ml of 10% NaCl solution is present. What is the gold number. Solution : By def. amount of protective sol. in mg is required to prevent the coagulation of 10 mL gold sol when 10% NaCl solution is added. Thus amount of starch required is 0.025 g i.e. 25 mg thus gold number is 25. There is another term called “Rubin number” which is defined as the amount of protective colloid in milligrams which prevents the colour change in 100 mL of 0.01% congo rubic dye to which 0.16 gm equivalent of KCl is added. C7 Emulsions : Emulsions are those colloidal systems in which the dispersed phase is liquid normally. The two common examples are : Milk : Which consists of particles of liquid fat dispersed in water. Cod Liver Oil : in which particles of water are dispersed in oil. Particles of dispersed phase are generally bigger then those in sols and are sometime visible in microscope. Emulsions, particles carry a negative charge and are sensitive to addition of electrolytes. They show Tyndall effect and Bownian movement. In most of emulsions the two liquid phases are oil and water and thus emulsions may be of following two types. 1. Oil in water emulsion : In these emulsions, oil is the dispersed phase and water is dispersion medium milk and vanishing cream are two important examples. 2. Water in oil emulsion : Water is dispersed phase and oil is dispersion medium e.g. Butter and Cold Cream. FOAM : are colloidal dispersions of gas in liquid, which is stabilized by soap or other surface active agents. Industrial application of foam : (i) in ore floatation (ii) in detergency (iii) in fire fighting etc. C8A ADSORPTION Adsorption is defined as phenomenon of attracting & retaining the molecules on the surface of a liquid or a solid resulting into a higher concentration of the molecules on the surface is called adsorption. Process of removal of adsorbed particle called as desorption. The susbtance which is adsorbed on surface is called adsorbate. The substance on which adsorption takes place is adsorbent e.g. charcoal, silica gel, alumina gel, clay etc. are very good adsorbent Absorbtion : The molecule of substance are uniformly distributed througout the body of a solid or a liquid. In certain cases both absorption & adsorption takes place simultaneously called as sorption. Adsorption is of two types : Physisorption Chemisorption H adsorption is low 20 kJ/mol H adsorption is high ~ 200 kJ/mol Molecule of adsorpate & adsorbent are Held by chemical bonds held by weak vander wall forces Take place at low temperature & decreases Take place at high temperature with T Not very specific Very specific Multimolecular layer formed Usually monomolecular layer is formed. C8B Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 8 1. Freundlich Adsorption Isotherm (at temp. T) x Amount of Adsorbate m Amount of Adsorbant kP1/n, n > 1, P Pressure of gas adsorbed k, n are parameter depend on nature of gas and solid. x kP 1 / n m log x 1 log k log P m n value of k & n can be find out. 2. Langmuir Adsorption Isotherm : Applicable to chemisorption x ap m 1 bP a, b Langmuir Parameter By reversing equation : m 1 bP b 1 1 . x aP a a P a, b can be calculated Einstein Classes, x ap m 1 bP At. low pressure bp < < 1, thus x aP m At high pressure pb > > 1, thus x aP a (constant) m bP b Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 9 E X E R C I S E (OBJECTIVE) 1. 2. 3. 4. 5. 6. 7. Which requires catalyst (a) X is threshold energy level (a) S + O2 SO2 (b) (b) 2SO2 + O2 2SO3 (c) C + O2 CO2 Y and Z are energy of activation for forward and backward reaction respectively (d) All (c) Q is heat of reaction and reaction is exothermic (d) All During hydrogenation of oils catalyst commonly used is 8. The catalyst used in the contact process of sulphuric acid is (a) Pd or CuCl2 (b) Finely divided Ni (a) Copper (c) Fe (b) Iron (d) V2O5 (c) Vanadium pentoxide or Pt (asbestos) (d) Ni Which is used in the Haber’s process for the manufacture of NH3 (a) Al2O3 (b) Fe + Mo (c) CuO (d) Pt 9. Which explains the effect of a catalyst on the rate of a versible reaction (a) It provides a new reaction pathway with a lower activation energy Which is not correct for heterogeneous catalysis (a) The catalyst decreases the energy of activation (b) It moves the equilibrium position to the right (b) The surface of catalyst plays an important role (c) It increases the kinetic energy of the reacting molecules (c) The catalyst actually forms a compound with reactants (d) It decreases the rate of the reverse reaction (d) There is no change in the energy of activation 10. For absorption of gas on solid surface, the plots of log x/m vs log P is linear with a slope equal to Catalytic poisoners act by (a) K (a) Coagulating the catalyst (b) log K (b) Getting absorbed on the active centres on the surface of catalyst (c) lnK (d) 1 / n (n being integer) (c) Chemical combination with any one of the reactants (d) None 11. Protons accelerate the hydrolysis of esters. This is an example of (a) A heterogeneous catalysis (b) An acid-base catalysis (c) A promoter (d) A negative catalyst Mark the correct statement about given graph Einstein Classes, 12. Which statement about enzymes is not correct (a) Enzymes are in collodial state (b) Enzymes are catalysts (c) Enzymes can catalyse any reaction (d) Urease is an enzyme Which is not true in case of catalyst (a) The catalyst is unchanged chemistry at the end of a reaction (b) The catalyst accelerates the reaction (c) In a reversible reaction, the catalyst alters the equilibrium position (d) A small amount of catalyst is often sufficient to bring about a large change in reaction Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 10 13. 14. 15. 16. 17. 18. 19. Which type of metals form effective catalyst 20. (a) Alkali metals The minimum energy level necessary to permit a reaction to occur is (b) Transition metals (a) Internal energy (c) Alkaline earth metals (b) Threshold energy (d) Radioactive metals (c) Activation energy (d) Free energy A catalyst increases the rate of reaction because it (a) Increases the activation energy (b) Decreases the energy barrier for reaction (c) Decreases the collision diameter (d) Increase the temperature coefficient 21. Which is wrong in case of enzyme catalysis (a) Enzymes work best at an optimum temperature (b) Enzymes work at an optimum pH (c) Enzymes are highly specific for substrates (d) An enzyme raises activation energy Air can oxidise sodium sulphite in aqueous solution but cannot do so in the case of sodium arsenite. If however, air is passed through a solution containing both sodium sulphite and sodium arsenite then both are oxidised. This is an example of (a) Positive catalysis (b) Negative catalysis (c) Induced catalysis (d) Auto-catalysis 22. 23. 24. The oxidation of oxalic acid by acidified KMnO4 becomes fast as the reaction progresses due to According to Langmuir absorption isotherm the amount of gas absorbed at very high pressure (a) Reaches a constant limiting value (b) Goes on increasing with pressure (c) Goes on decreasing with pressure (d) Increases first and decreases later with pressure Which of the following type of catalysis can be explained by the absorption theory (a) Homogenous catalysis (b) Acid-Base catalysis (c) Heterogeneous catalysis (d) Enzyme catalysis The reaction rate at a given temperature is slower when (a) The energy of activation is higher (b) The energy of activation is lower (c) Entropy changes (d) Initial concentration of the reactant remains constant Which is not correct for catalyst. If (a) Enhances the rate of reaction in both directions (a) Auto catalysis by Mn2+ (b) Changes enthalpy of reaction (b) Presence of SO42— (c) Reduces activation energy of reaction (c) Presence of K+ (d) Specific in nature (d) Presence of MnO4— 25. Which process does not involve a catalyst Which is universally correct for the catalyst (a) Haber’s process (a) Initiates reaction (b) Thermite process (b) Does not initiate reactions (c) Ostwald’s process (c) Does not alter the nature of products (d) Contact process (d) Is not specific in nature The catalyst iron, employed in the Haber’s process, contains molybdenum, the function of which is (a) To increase the rate of combination of gases (b) To counterbalance for the presence of impurities in the gases (c) To act as a catalyst promoter and increase activity of catalyst (d) To make up for the adverse temperature and pressure conditions Einstein Classes, 26. Which plot is the absorption isobar for chemisorption where X is the amount of gas absorbed on mass m (at constant pressure) at temperature T. (a) Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 11 30. (b) 31. (c) 32. (d) 27. 28. 33. In the titration between oxalic acid and acidified potassium permanganate, the manganous salt formed during the reaction catalyses the reaction. The manganous salt acts as (a) A promoter (b) A positive catalyst (c) An auto-catalyst (d) None of the above Which equation represents Freundlisch absorbtion isotherm (physical adsorption is basis of this theory) (a) x K (P )1/ n where x is amount of gas m 34. 35. 36. absorbed on mass ‘m’ at pressure P x 1 log K log P m n (b) log (c) x x KP at low pressure and K m m at high pressure (d) 29. All The function of negative catalyst is (a) To remove the active intermediate from the reaction (b) To terminate the chain reaction Einstein Classes, 37. (c) Both (a) and (b) (d) None Zeolites (a) Are microporous aluminosilicates (b) Have general formula Mx/n [(AlO2)x (SiO2)4].mH2O (c) Have pore sizes between 260 pm to 740 pm (d) All The phenomenon in which absorption and absorption takes place simultaneously is called (a) Desorption (b) (c) Both (a) and (b) (d) Sorption None The extend of absorption of a gas on a solid depends on (a) A nature of gas (b) Pressure of gas (c) Temperature of the system (d) All An increase in the concentration of absorbate at the surface relative to its concentration in bulk phase is called (a) Adsorption (b) Enthalpy (c) Absorption (d) None On adding few drops of dil. HCl or FeCl3 to freshly precipitated ferric hydroxide, a red coloured collodial solution is obtained. This phenomenon is known as (a) Preptization (b) Dialysis (c) Protection (d) Dissolution Which is not shown by sols (a) Adsorption (c) Flocculation (d) Paramagnetism (b) Tyndall effect The arsenious sulphide sol has negative charge. The maximum coagulating power for precipitating it is of (a) 0.1 N Zn (NO3)2 (b) 0.1 N Na3PO4 (c) 0.1 N ZnSO4 0.1 N AlCl3 (d) Lyophilic sols are more stable than lyophobic sols because (a) The collodial particles have positive charge (b) The collodial particles have no charge (c) The collodial particles are solvated (d) There are strong electrostatic repulsions between the negatively charged collodial particles. Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 12 38. 39. 40. Which forms a collodial solution in water (c) 10–7 cm to 10–10 cm (a) NaCl (b) Glucose (d) 10–1 cm to 10–2 cm (c) Starch (d) Barium nitrate Collodial solution of arsenious sulphide can be prepared by The separation of collodial particles (or purification of sol) from particles of molecular dimensions is known as (a) Electrodispersion method (a) Photolysis (b) Dialysis (b) Peptization (c) Pyrolysis (d) Peptization (c) Double decomposition (d) Hydrolysis 42. (a) The amount of gold present in the colloid (b) The amount of gold required to break the colloid (c) The amount of gold required to protect the colloid (a) To prevent the formation of a colloid (b) To stabilize the colloid and prevent crystal growth (c) To cause the mixture of solidify (d) To improve the flavour Preptization is a process of Precipitating colloidal particles None of the above (b) Purifying colloidal particles Collodial solutions are not purified by (c) Dispersing the precipitate into colloidal state (d) None (a) Dialysis (b) Electrodialysis (c) Electrophoresis (d) Ultrafiltration 48. Gold number : (b) (c) (d) 44. 47. Gelatin is often used as an ingredient in the manufacture of ice-cream. The reason for this is (a) (a) 43. 46. Gold number gives (d) 41. 45. May be defined as the milligram of the dry material of which the hydrophilic sol is prepared and which when added to 10 mL of red gold sol, will prevent it from coagulation on the addition of 1 mL of 10 per cent sodium chloride solution 49. May be defined as the milligram of the dry material of which the hydrophilic sol is prepared and which when added to 1 mL of red gold sol, will prevent it from coagulation on the addition of 10 mL of 10 per cent sodium chloride solution May be defined as the milligram of the dry material of which the hydrophilic sol is prepared and which when added to 1 mL of red gold sol, will prevent it from coagulation on the addition of 1 mL of 1 per cent sodium chloride solution 50. None of the above 51. A liquid aerosol is a colloidal system of (a) A liquid dispersed in a solid (b) A liquid dispersed in a gas (c) A gas dispersed in a liquid (d) A solid dispersed in a gas Gold number of a lyophilic sol refers that (a) Larger is its value, the greater is the peptizing power (b) Lower is its value, the greater is the peptizing power (c) Lower is its value, the greater is the protecting power (d) Larger is its value, the greater is the protecting power Gold number is minimum in case of (a) Gelatin (b) Egg albumin (c) Gum arabic (d) Starch (a) Electro deposition When dilute aqueous solution of AgNO3 (excess) is added to KI solution, positively charged sol particles of AgI are formed due to absorption of ion (b) Electrodialysis (a) K+ (b) Ag+ (c) — (d) NO3— The movement of sol particles under an applied electric field is called (c) Electro-osmosis (d) Electrophoresis The average size of the colloids is of the order (a) 10–4 cm to 10–2 cm (b) 10–5 cm to 10–7 cm Einstein Classes, 52. I The charge on As2S3 sol is due to the absorption of (a) H+ (b) OH— (c) O 2— (d) S2— Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 13 53. The Rubin number which was proposed by Ostwald as an alternative to the Gold number in order to measure the protective efficiency of a lyophilic colloid may be defined as the (a) (b) (c) (d) 54. 55. 56. 57. 58. Mass is milligram of a colloid per 100 mL of solution which just prevents the colour change of standard sol of dye Congo-Rubin from red to violet when 0.16 g eq. KCl is added to it Mass in gram of a colloid per 100 mL of solution which just prevents the colour change of standard sol of dye Congo-Rubin from red to violet when 0.1 M KCl is added to it 59. 60. 61. Mass in gram of a colloid per 100 mL of solution which just prevents the colour changed of standard sol of dye Congo-Rubin from red to violet when 0.2 M KCl is added to it Mass in gram of a colloid per 100 mL of solution which just prevents the colour change of standard sol of dye Congo-Rubin from red to violet when 1 M KCl is added to it 62. If dispersion medium is water, the colloidal system is called (a) Sol (b) Aerosol (c) Organosol (d) Aquasol 63. The property of colloidal suspension used to determine the nature of charge on the particles is (a) Dialysis (b) Electrophoresis (c) Sedimentation (d) Ultrafiltration Which reaction gives colloidal solution (a) Cu + HgCl 2 CuCl2 + Hg (b) 2HNO3 + 3H2S 3S + 4H2O + 2NO (c) 2Mg + CO2 2MgO + C (d) Cu + CuCl2 Cu2Cl2 The correct statement in case of milk (a) Milk is an emulsion of fat in water (b) Milk in an emulsion of protein in water (c) Milk is stabilized by protein (d) Milk is stabilized by fat When a colloidal solution is observed under a microscope, we see (a) Light scatered by colloidal particles (b) Sol particles (c) Shape of the particle (d) None The coagulation of sol particles or sol destruction may be brought in by Lyophobic colloids are (a) Cataphoresis (a) Reversible colloids (b) Adding oppositively charged sol (b) Irreversible colloids (c) Adding electrolyte (c) Protencitve colloids (d) All (d) Gum, proteins 64. Foam is a colloidal solution of Which is not related with colloids (a) Gaseous particles dispersed in gas (a) Brownian movement (b) Gaseous particles dispersed in a liquid (b) Dialysis (c) Solid particle dispersed in a liquid (c) Ultrafiltration (d) Solid particles dispersed in gas (d) Wavelength 65. Gold number is the index for Flocculation value is expressed in terms of (a) Protective power of lyophilic colloid (a) Millimole per litre (b) Purity of gold (b) Mol per litre (c) Metallic gold (c) Gram per litre (d) Electroplated gold (d) Mol per millilitre 66. (a) Liquid particles dispersed in gas Cane sugar (b) Gaseous particles dispersed in a liquid Blood (c) Solid particles dispersed in a liquid (d) Solid particles dispersed in gas Which one is a colloid (a) (c) Urea (b) Sodium chloride (d) Einstein Classes, Fog is a colloidal solution of Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111 CSC – 14 67. 68. 69. 70. 71. 72. 73. 74. 75. At CMC, the surfactant molecules undergoes A N S W E R S (OBJECTIVE) (a) Association (b) Aggregation (c) Micelle formation (d) All In emulsion the dispersed phase and dispersion medium are 1. b 31. b 61. a 2. b 32. b 62. a 3. b 33. a 63. d (a) Both solids (b) Both liquids 4. d 34. a 64. b (c) A solid and liquid 5. b 35. d 65. a (d) A liquid and solid 6. b 36. d 66. a 7. d 37. c 67. d 8. c 38. c 68. b A liquid which markedly scatters a beam of light (visible in dark room) but leaves no residue when passed through a filter paper is best described as 9. a 39. c 69. c 10. d 40. d 70. b (a) A suspension (b) Sol 11. c 41. c 71. a (c) True solution (d) None 12. c 42. a 72. a 13. b 43. d 73. b 14. b 44. b 74. c 15. d 45. b 75. c 16. c 46. b 17. a 47. c 18. b 48. b 19. c 49. c 20. b 50. a 21. a 51. b Cod liver oil is 22. c 52. d (a) Fat dispersed in water 23. a (b) Water dispersed in fat 53. a (c) Water dispersed in oil 24. b 54. d (d) Fat dispersed in fat 25. b 55. b 26. c 56. d 27. c 57. a 28. d 58. d 29. c 59. b 30. d 60. b Brownian motion of sol particle is the......property of sol (a) Electrical (b) Optical (c) Kinetic (d) Colligative Surface tension of lyophilic sols is (a) Lower than H2O(b) More than H2O (c) Equal to H2O None (d) A colloidal system in which gas is dispersed in a liquid to form bubble is known as (a) Foam (b) Sol (c) Aerosol (d) Emulsion The outcome of internal liquid of gels on shear is called (a) Synerisis (b) Thixotropy (c) Swelling (d) None Which is not lyophilic colloid (a) Milk (b) Gum (c) Fog (d) Blood Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi – 110 018, Ph. : 9312629035, 8527112111