C1-Allens Made Chemistry Theory {PART-1}

SOLVED SUBJECTIVE PROBLEMSEx .1For the non-equilibrium process, A + B  Products, the rate is first order with respect to A and second orderwith respect to B. If 1.0 mol each of A and B are introduced into a 1 litre vessel, and the initial rate were1.0 × 10 mol/litre-sec, calculate the rate when half of the reactants have been used.–2Sol.Rate = k [A] [B]1210 = k [1] [1]–22ork = 10 litre mol sec–22–2–1NowRate = 10 × 0.5 × (0.5)II–22orNew rate = 1.2 × 10 mol/litre-sec–3Ex .2The energy of activation for a certain reaction is 100 kJ/mol. Presence of catalyst lowers the energy ofactivation by 75%. What will be effect on rate of reaction at 25°C, other things being equal ?Sol.k = A ea ERT , k = A e1100RT , k = A e225RT 12kk=100RT25RTee=75RTeloge21kk= log e75RT e log 21kk=75RT=375 108.314 29821kk= 1.4020 × 10 , As r = k(conc)13 n21rr=21kk= 1.4020 × 1013Ex .3Show that for a first order reaction, time required for 99% completion is twice for the time required for thecompletion of 90% of the reaction.Sol.t99% = 2.303k log 10100100 – 99.....(1)( a = 100; x = 99)t = 90%2.303k log 10100100 – 90.... (2)( a = 100; x = 90)By Eqs. (1) and (2),99%90%tt = 1010log 100log10 = 2t99% = 2 × t90%Ex .4For the reaction, A + B  C, the following data were obtained. In the first experiment, when the initialconcentrations of both A and B are 0.1 M, the observed initial rate of formation of C is 1 × 10 mol–4 litre minute . In second experiment when the initial concentrations of (A) and (B) are 0.1 M and–1 –10.3 M, the initial rate is 3.0 × 10 mollitre minute . In the third experiment, when the initial concen-–4 –1 –1trations of both A and B are 0.3 M, the initial rate is 2.7 × 10 mol litre minute .–3 –1 –1(a)Write rate law for this reaction.(b)Calculate the value of specific rate constant for this reaction.

Sol.Let, Rate = k[A] [B]x yr = 1 × 10 = k(0.1) (0.1)1–4 x y...(1)r = 3 × 10 = k(0.1) (0.3)2–4 x y...(2)r = 2.7 × 10 = k(0.3) (0.3)3–3 x y...(3)By Eqs. (1) and (2), 12rr=441 103 10=y13    y = 1By Eqs. (2) and (3),23rr=443 1027 10=x13    x = 2 Rate = k[A] [B]2 1Also, 1 × 10 = k (0.1) (0.1)–4 2 1 k = 10 = 0.1 L mol min–1 2 –1 –1Ex .5The chemical reaction, 2O 3 3O proceeds as follows :2O 3 O + O2.... (Fast)O + O 3 2O2.... (Slow)The rate law expression should be[A] r = k[O ]32[B] r = k[O ] [O ]322–1[C] r = k[O ][O ]32[D] UnpredictableSol.Rate of reaction (r) = k [O] [O ]3The rate of formation if [O] depends on first stepSince K = eq23[O ][O][O ][O] = Keq32[O ][O ]orr = kkeq332[O ][O ][O ] = k . [O ] [O ]322–1Ex .6Disintegration of radium takes place at an average rate of 1.42 × 1013 -particles per minute. Each-particle takes up 2 electrons from the air and becomes a neutral helium atom. After 420 days, the Hegas collected was 0.5 × 10 L measured at 300 K and 750 mm of mercury pressure. From the above–3 data, calculate Avogadro's number.Sol.No. of -particles (or) He formed = 1.42 × 10 min13 –1 No. of He particles formed in 420 days = 1.42 × 1013 × 420 × 1440 = 8.588 × 1018Also at 27°C and 750 mm ; He = 0.5 mLUsing PV = nRT750760 × 0.51000 = n × 0.0821 × 300n = 2.0 × 10 moles–5 2.0 × 10 moles of He = 8.588 × 10 particles of He–5 18  1 mole of He= 1858.588 102.0 10 4.294 × 10 particles22  Avogadro's number = 4.294 × 10 particles/mol22

Ex .7The optical rotations of sucrose in 0.5 N HCl at 35°C at various time intervals are given below. Showthat the reaction is of first order :Time (minutes) 0 10 20 30 40Rotation (degrees)+32.4+28.8+25.5+22.4+19.6–11.1Sol.The inversion of sucrose will be first order reaction if the above data confirm to the equation,k =12.303tlog0trrrrwhere r , r and r represent optical rotations initially, at the commencement of the0treaction after time t and at the completion of the reaction respectively.In this case, a = r – r = +32.4 – (–11.1) = +43.500The value of k at different times is calculated as follows :Ti mer tr – rt k10 min+28.839.92.30310log43.539.9 = 0.008625 min–120 min+25.536.62.30320log43.536.6 = 0.008625 min–130 min+22.433.52.30330log43.533.5 = 0.008694 min–140 min+19.630.72.30340log43.530.7 = 0.008717 min–1The constancy of k indicates that the inversion of sucrose is a first order reaction.1Ex .8For A + B  C + D; H = 20 kJ mol ; the activation energy of the forward reaction is 85 kJ/mol. Calculate–1activation energy of the reverse reaction.Sol.H=20kJ85 kJE in kJEa for Backward reaction1H of forward reaction= 20 kJ mol .–1Energy of activation for forward reaction (E )a= 85 kJ mol–1Energy of activation for backward reaction= E – Ha= 85 – 20= 65 kJ mol–1

Ex .9The reaction given below is observed to be first order with rate constant 5.26 × 10 sec . Calculate the–3 –1time required for the total pressure in a system containing A at an initial pressure of 0.1 atm to rise0.145 atm and also find the total pressure after 100 sec.2A (g) 4B (g) + C (g)Sol.2A (g)4B (g)+C(g)Initial P0 0 0At time t P – P'0 2P'P'/2Ptotal = P – P' + 2P' + P'/2 = P +00 3 P'2P' = 23 (0.145 – 0.1) = 0.03 atmk =2.303tlog00PPP ' t = 32.3035.26 10log0.10.07 = 67.82 secAlso, k =2.303tlog00.1PP '5.26 × 10 =–3 2.303100log0.10.1 P ' 0.1 – P' = .059P' = 0.041Ptotal = 0.1 + 32 (0.041) 0.162 atm.Ex. 10 For a reaction 3A  Products, it is found that the rate of reaction doubles if concentration of A is increasedfour times, calculate order of reaction.Sol.Rate = k [Reactant]nif [Reactant] = a; rate = r1r = k[a]1nif [Reactant] = 4a; rate = 2r12r = k[4a]1n12 = n 14   n = 12Ex. 11The amount of C isotope in a piece of wood is found to be one fifth of that present in a fresh146piece of wood. Calculate the age of the piece of wood (half-life of C = 5577 year).146Sol.t =02.303NlogNt =1 / 202.303 tNlog0.693Nt =2.303 55770.693log00NN / 52.303 55770.69890.693= 12.953 yearsEx. 12 In a reaction, 2A  Products, the concentration of A decreases from 0.5 mol litre to 0.4 mol litre in 10–1–1minute. Calculate rate during this interval.Sol.Rate of reaction = 12 × rate of disappearance of A= 12d [A]dt– = 120.5 – 0.410 = 0.005 mol litre minute–1–1

Ex. 13The time required for 10% completion of first order reaction at 298 K is equal to that required for its76% completion at 308 K. If the pre-exponential factor for the reaction is 3.56 × 10 s , calculate its9 –1energy of activation.Sol.For first order reactions,t =2.303klog01NNAt 298 K ; t =2982.303klog10090At 309 k ; t =3082.303klog10076Since time is same2982.303klog10090=3082.303klog10076or 2980.0458k=3080.1191kor 308298kk=0.11912.600.0458According to Arrhenius equation,2.303 log308298kk=a E8.31411298308or 2.303 log 2.60 =a E8.31410298 308 E = 72.93 kJaEx. 14 In a reaction, the decrease in reactant’s concentration is 20% in 20 minute and 40% in 40 minute. Calculateorder of reaction and rate constant.Sol.For zero order reaction : t = xk ork =xtIft = t20% = 20 minute,x = 20Thenk = 2020 = 1 mol litre minute–1–1Ift = t40% = 40 minute,x = 40Thenk = 4040 = 1 mol litre minute ; Thus, reaction is of zero order.–1–1 Ex. 15The rate constant for the decomposition of a certain substance is 2.80 × 10 m–3–1 s at 30°C and –11.38 × 10 m s at 50°C. Evaluate the Arrhenius parameters of the reaction. (R = 8.314 × 10 kJmol K )–1–1 –1–3–1 –1Sol.Energy of activation (E ) and pre-exponential factor A are Arrhenius parameters.ak = 2.80 × 10 m s at 303 K1–3–1–1k = 1.38 × 10 m s at 323 K2–2–1–1As log10 2a1kEkR 2112TTTT    E =a12212.303 R T T(TT ) log1021kk E =a32.303 8.314 10303 323(323 303)log10231.38 102.80 10 = 64.91 kJ mol–1Also, k = A e–Ea/RTorA = k eEa/RT = 2.80 × 10–3 364.91× 10 /8.314 × 303e= 4.34 × 10 s8 –1

Ex. 16 Calculate the order of reaction for which rate becomes half if volume of container having same amount ofreactant is doubled. (Assume gaseous phase reaction)Sol.Rate = k[a]nFor Case I : Let a mole of reactant in vessel of V litrer = k1naV ......(1)For Case II : The volume is doubled, rate becomes half1 r2 = kna2V .....(2)By Eqs. (1) and (2),or2 = (2)nn = 1Ex. 17Rate constant of a first order reaction, A B, is 0.0693 min . Calculate rate (i) at start and (ii) after–120 minutes. Initial concentration of A is 1.0 M.Sol.k = 0.0693 min1 –11120.693tk=0.6930.0693= 10 minSince C = C0n 12   1 / 2tnt n = 20210C = 1 M0  C = 1 × 2 12   = 1M4Rate of the reaction at the start of the reaction = k × C10 = 10 × 0.0693 × 1 = 0.693 M min–1Rate after 30 min. = k C = 0.0693 × 114 = 17.33 × 10 M min–3–1Ex. 18Two reactants A and B separately show two chemical reactions. Both reactions are made with same initialconcentration of each reactant. Reactant A follows first order kinetics whereas reactant B follows secondorder kinetics. If both have same half-lives, compare their rates at the start of reactions.Sol.For A : rate = k [A]A...(i)12(A )A0.693tk...(ii)For B : rate = k [B]B 2...(iii)12(B )B1tka...(iv)Initial rate of Ar = k × aAAInitial rate of Br = k × aBB2AAA2BBBrkakrkaka ...(v)If 1122(A )(B )tt , thenA0.693k=B1kaABkk= 0.693 × aABrr=0.693 aa= 0.693

Ex. 19The rate of a certain reaction depends on concentration according to equationd[A]dt =12k [A]1k [A] What will be the order of reaction when (i) concentration is very high (ii) very low?Sol.Given, d[A]dt =12k [A]1k [A] d[A]dt=12k1k[A](i)When [A] is very high1[A]is very small, and thus negligible d[A]dt=12kconstantkThus, order of reaction is zero.(ii)When [A] is very low[1 + k [A] = k'2  d[A]dt=1k [A]k\"[A]k'Thus, order of reaction is one.Ex. 20Pseudo first order rate for the reaction, A + B Product, when studied in 0.1 M of B is given byd[A]k[A] , where, k = 1.25 × 10 sec , calculate the value of second order rate constant.dt 4 –1Sol.A + B Productd[A]k[A] dt d[A]dt = 1.25 × 10 × [A]4....(i)Assuming the reaction to be of second orderd[A]dt = k' [A] [B]  d[A]dt= k' [A] [0.1]....(ii)Dividing Eq. (i) by (ii), we get1 =41.25 10k ' (0.1) k' = 1.25 × 10 L mol s5–1–1Ex. 21 N O decomposes according to equation, N O 2525 2NO + 212O 2(a) What does25 d[N O ]dtdenote ? (b) What does2 d[O ]dt denote ? (c) What is the units of rate of this reaction?Sol.(a) Rate of decomposition of N O . (b) Rate of formation of O . (c) Unit of rate = mol litre time .252–1–1Ex. 22 A first order reaction takes 69.3 minute for 50% completion. How much time will be needed for 80% completion ?Sol.k = 1/20.693t = 0.69369.3 minute–1( t = 69.3 min) ½k = 2.303t log 100100 – xNowk = 2.303t log 1010020 ; [if a = 100, x = 80 and a – x = 20]0.69369.3 =2.303t log 510;t = 160.97 minute

Ex. 23The half-life of the nucleide 220Rn is 693 s. What mass of radon is equivalent to a 1 millicurie (mci) ?Sol.120.693t120.693t =0.693693 × 10 s–3–11 mci = 3.7 × 10 disintegration s =7 –1 dNdt  dNdt = NN =dN / dt=71313.7 10 s10 s= 3.7 × 1010Mass of 220Rn =10233.7 102206.022 10= 1.35 × 10–11g = 1.06 × 10–14 kgEx. 24For the reaction A  B + CTimetTotal pressure of (B + C)P 2P 3Calculate k.Sol.A B +CAt t = 0P 100At t = tP – x1xxAt t = 0P 1P 12P = P13P =13 P22x = P 2 x =2 P2 P – x =13232PPPP222  k = ln03t321[A]1Plnt[A]t(PP )Ex. 25Derive a relation between 12 t and temperature for an n order reaction where n > 2 ?thSol.lnk = lnA –a ERT(Arrhenius equation)....(i)12 t=n 1n 1021k(n 1)a...(ii) ln 12t= lnn 1n 1021lnk(n 1)a..(iii)From the Eqs. (i) and (iii)ln 12t= lnn 1an 10E21ln ART(n 1)a ln 12t= lnA +ERTwhere A =n 1n 1021(n 1)aAThat is 12 tdecreases with increase in temperature.A plot of 12 t vs 1T gives a straight line with slope E .a

COLLOIDAL STATE :When water soluble substances like sodium chloride, copper sulphate, sugar etc., are put into water theydissolve and a homogeneous solution is obtained. The particles of the solute are not visible and their size ismolecular size. Such mixtures are called molecular solutions or true solutions.Now suppose we take muddy river water or an insoluble substance like lead sulphate or calcium sulphate is putinto water. The particles of the solutes are visible even with the naked eye because their size is large. Onkeeping for some time, particles settle down. These mixtures are called suspension.In between these two extremes, there are particles which are bigger than molecules but are too small to be seeneven by a microscope. The colloidal state can thus be regarded as the intermediate state between moleculesand particles of a coarse suspension.Thomas graham (1861) classified substances into two categories on the basis of their rates of diffusion-Crystalloids : They diffuse rapidly in solution and can rapidly pass through animal or vegetablemembranes, e.g. urea, sugar, salts and other crystalline substances.Colloids : They diffuse very slowly in solution and can not pass through animal or vegetable membranes,e.g. starch, gelatin, silicic acid, proteins etc. Since this class of substances generally exist in amorphousor gelatinous condition and hence the name colloid meaning \"glue form\".Note: Actually every substance irrespective of its nature can be crystalloid or colloid under suitable conditions. Forexample:(i)NaCl though a crystalloid in water behaves like a colloid in benzene.(ii)Soap is a colloid in water, while it behaves like a crystalloid in benzene.Therefore colloidal state now a days may be defined as following \"A substance is said to be in the colloidal state,when it is dispersed in another medium in the form of very small particles having diameter between10 to 10 cm (100 m to 1 m ).–4–7M olecula rs iz e in tru es olu tionC olloida l pa r ticle s iz eC oa rs es u s pens ionpa r ticle s iz e10 to 10 cm–7–810 to 10 cm–5–710 to 10 cm–3–5COLLOIDAL SOLUTIONS :They considered as a heterogeneous system consisting of the following three essential components:(i)A dispersed phase: It is also known as discontinuous or inner phase. It consists of discrete particlessignificantly larger than ordinary molecules and in this small particles of solute is diffused in solvent.(ii)A dispersion medium or continuous phase or the outer phase : It is the medium in whichdispersed phase is present. This consists of continuously interlinked molecules.(iii)A stabilising agent: This is a substance which tends to keep the colloidal particles apart. Some colloidsare self stabilizers.Dispersed phase + Dispersion medium = Dispersion system (Colloidal solution)Each of the two phases constituting a colloidal system may be a gas, a liquid or a solid. For example, in milk, thefat globules are dispersed in water. Hence fat globules form a dispersed phase and water is the dispersion medium.Sol : If dispersion of a solid in a liquid, solid or gaseous medium, the resulting solution is called sol.Colloidal Solution : If dispersion of a solid (dispersed phase) in a liquid (dispersion medium), theresulting solution is called colloidal solution.Solid aerosol: The dispersion of a solid (dispersed phase) in a gas( dispersion medium).Liquid aerosol : If the dispersed phase is a liquid and the dispersion medium is a gas, the resulting solis called a liquid aerosol.Emulsion : When a liquid is dispersed in another liquid the resulting system is called an emulsion.COLLOIDAL STATE & SURFACE CHEMISTRY

Gel : If colloidal system becomes fairly rigid, it is termed as a gel.CLASSIFICATION OF COLLOIDS :There are a number of basis for the classification of colloids.( i )Depending upon the nature of the dispersed phase and that of dispersion medium the colloidal solutions aredivided into the following eight categories:S.No.D is pers ed Pha s eD is pers ionMediumNa m eExa m ple1SolidSolidSolid solColoured glass,gems, alloys2SolidLiquidSolPaints, inks,white of eggsmud3SolidGasAerosolSmoke, dust4LiquidSolidGelCurds,pudding,cheese, jellies5LiquidLiquidEmulsionMilk, Cream, Butter',Oil in water6LiquidGasLiquid AerosolClouds, Mist,fog(water in air)7GasSolidSolid foamCake, bread, lava,pumice stone8GasLiquidFoamSoap lather,froth on beer, whippedcreamSince the two gases are completely miscible with each other, they always form a true solution.(ii)Depending upon the appearance of colloids :On this basis colloids are divided into the following two main categories.( a )Sol : When a colloidal solution appears as fluids, it is termed as sol. Sols are named after dispersionmedium. For example, when dispersion medium is water, they are called hydrosols when the dispersionmedium is alcohol they are called alcosols and so on.( b )Gels : When a colloid has a solid-like appearance, it is termed as gel. The rigidity of gel varies fromsubstance to substance.(iii)Depending upon the interaction of the two phases.According to Perrin and Freundlich, colloids may be classified into lyophobic and lyophilic.( a )Lyphobic or solvent-hating : When the dispersed phase has less affinity for the dispersion medium,the colloids are termed as lyophobic. But when the dispersion medium is water, they are given the namehydrophobic. Substances like metals, etc. which have particles of size bigger than the colloidal particlesor NaCl which has particles of size smaller than the colloidal size, fall in this category. Such substancesare brought into colloidal state with difficulty.( b )Lyophilic or solvent loving : When dispersed phase has a greater affinity for the dispersion medium,the colloids are termed as lyophilic and when the dispersion medium is water, they are given the namehydrophilic. They are also called natural colloids, substances like proteins, starch and rubber etc. aregrouped under this category.

(i v)Depending upon the electrical charge on the dispersed phase :On this basis the colloids may be divided into :( a )Positive Colloids :The dispersed phase carries the positive charge. The particles of Fe(OH) sol in water are positively3charged. Examples of this type are also methylene blue and TiO sols.2( b )Negative Colloids :This dispersed phase carries the negative charge. For example the particles of As S sol in water are23negatively charged. The other examples are copper or gold sol and certain dye-stuffs like eosin, congored etc.( v )Depending on the structure of colloid particles :According to Lumiere and others, colloids can also be classified into molecular and micellar colloids. The particlesof molecular colloids are single macromolecules and their structure is similar to that of small molecules. The particlesof micellar colloids are aggregates of many molecules or groups of atoms which are held together by cohesive or vander Waal's forces. The examples of molecular colloids are albumin, silicons, rubber etc. while that of micellar colloidsor sulphur, gold, soap detergents etc.( a )Multimolecular colloids :The multimolecular colloidal particles consists of aggregate of atoms of small molecules with diameterless than 10 m or 1 nm. For example, a sol. of gold contains particles of various sizes having several–9atoms. A sol.of sulphur consists of particles containing a thousand or so S molecules. These particles2are hold together by vandel Waal's forces. These are usually lyophobic sols.( b )Macromolecular colloids :The macromolecular colloidal particles themselves are large molecules. They have very high molecularweights varrying from thousand to millions. These substances are generally polymers. Naturally occurringmacromolecules are such as starch, cellulose and proteins. Artificial macromolecules are such aspolyethylene, nylon, polysyrene, dacron, synthetic rubber, plastics, etc. The size of these molecules arecomparable to those of colloidal particles and therefore, their dispersion known as macromolecularcolloids. Their dispersion also resemble true solutions in some respect.( c )The associated colloids or miscelles :These colloids behave as normal electrolytes at low concentrations but colloids at higher concentrations.This is because at higher concentrations, they form aggregated (associated) particles called miscelles.Soap and synthetic detergents are examples of associated colloids. They furnish ions which may havecolloidal dimensions.RCOONa  RCOO + Na–+Sod. Stearate soap (R = C H )1735The long-chain RCOO ions associates or aggregate at higher concentrations and form miscelles and–behave as colloids. They may contains 100 or more molecules.Sodium stearate C H COONa is an example of an associated colloid. In what it gives Na and sterate,1735+C H COO ions. These ions associate to form miscelles of colloidal size.1735–Note : Sometimes the names Emulsoids and Suspensoids are also used for hydrophilic and hydrophobic colloids respectively.

In general lyophilic sols are more stable than lyophobic sols. The additional stability is due to the presence of anenvelop of the solvent (say water) around the colloidal particle. The process is known as hydration. To coagulatea hydrophilic sol we have to add a dehydrating agent in addition to an electrolyte. Main points of differencesbetween the two types are given in the table:S.No.PropertyLyophilic (Intrins ic s ol.)Lyophobhic (extrins ic s ol.)1PreparationThey are easy to prepare. Only contact with the dispersion medium is needed to stabilise themThey are difficult to prepare. Special methods are used. Addition ofstabilizers is essential for theirstability.2Size of particlesThe particles are just bigger moleculesThe particles are aggregates ofthousands of molecules.3NatureReversible; once precipitated easily pass back into the colloidal state by contact withdispersion mediumIrreversible, once precipitated does not easily pass intocolloidal state 4ConductivityWith lyophilic salts high conductivitiescan generally be measuredOwing to their sensitivity in electrolytes the conductivity oflyophobic sol can rarely bemeasured over a considerablerange of concentration5Tyndall effectLess distinctMore distinct6ViscosityHigher than that of waterAlmost same as that of water7Surface TensionLower than that of waterAlmost same as that of water8HydrationParticles are heavily hydratedParticles are poorly hydrated9StabilityVery stable, coagulated withdifficultyLess stable, coagulated easily1 0ChargeDepends on the pH of the medium. It can be even zero.Have characteristic charge(Positive or negative)1 1Concentration of thedispersed phaseHigher concentrations of dispersedphase are possibleOnly low concentrations of the dispersed phase are possible1 2ExamplesAlbumin, Glycogen, Rubber,Silicic acid etc.Au, Ag, some emulsions etc.PREPARATION OF SOLS :Preparation of lyophilic sols :Many organic substances like gelatin, starch, agar, eggalbumin, glycogen etc. dissolve readily in water either incold or on warming to give colloidal solutions directly. These are the lyophilic colloids. For example, sols of eggalbumin or glycogen can be prepared by dissolving 1-2 g of the finely ground substance in 100 mL of distilledwater and then allowing it to stand for two hours after constant stirring. After two hours, the solutions arefiltered.Gelatin may be regarded as a typical lyophilic linear colloid. If two grams of gelatin are placed in distilled waterand kept there for several hours, it has been observed that unlike egg albumin and glycogen, gelatin does notdissolve in cold water although it does swell. The swellen gelatin may be dissolved by heating with water at80- 90°C. If two grams of gelatin are dissolved in 400 mL of distilled water, a clear sol. is obtained on cooling.Preparation of lyophobic sols: Such sols can be prepared by the two general ways.

(i) By dispersion of coarse particles (Dispersion method). Here we start with bigger particles and break themdown to the colloidal size.(ii) By inducing molecular particles to form large aggregates (condensation method). Here we start with particlesof molecular dimensions and condense them to the colloidal dimensions.DISPERSION METHODS :( a )Mechanical dispersion : Here the substance is first finely powdered and a coarse suspension is made byshaking the powdered substance with the dispersion medium. This suspension is then passed through a colloidmill consisting of two discs, moving in opposite directions at a very high speed (fig.I) The particles of thesuspension are subjected to a great shearing force and break down to the colloidal dimension. The spacebetween the two discs controls the size of the colloidal particles to be obtained. Rubber, ink, paints and varnishesare prepared by this method.A ball mill shown in fig. (II) has been employed to get a colloidal solution from a coarse suspension. Due to ahigh speed rotation of the mill the coarse ball-like particles roll over one another and drop down at a certainposition of the mill, thereby grinding the preliminary wetted mixture. This gives rise to particles of size 6 Å. Ifsome quantity of the dispersion medium is added, it becomes possible to get a colloidal solution.Fig-IFig-II A colloid ball mill( b )Electrical Dispersion- Bredig's arc methods :This is commonly used method for preparing the colloidal solutions of metals. An electric arc is struck betweentwo metallic rods kept under the liquid (dispersion medium). A current of 10 amperes and a voltage of100 to 300 volts is generally employed. The liquid is kept cooled by surrounding it with a cooling mixture. Tinyparticles of the metal break away from the roads and disperse in the liquid. Gold, platinum, silver, copper andsuch other metals can thus be obtained in the colloidal form. (Fig.III)Svedberg modified this method and prepared sols in non-aqueous media like pentane, diethyl ether, by strikingan arc with high frequency alternating current which greatly diminishes the decomposition of the liquid (fig.IV)Svedberg has shown that the electrical methods are suitable not only for preparing the hydro sols of metals likegold, silver, platinum etc., but also for sols of strongly electropositive metals, such as sodium in benzene.Fig-IIIIceCondenserInflammable liquidFig-IV Svedberg's method of preparing metals solsInduction coilMetal in inflammable liquids

(c)Peptization : The process of bringing a precipitated substance back into the colloids state is known as peptization.It is carried out by the addition of an electrolyte. The electrolyte added is termed as peptising or dispersingagent. It involves the adsorption of a suitable ion supplied by the electrolyte added by the particles of theprecipitate. Peptisation may be carried out by the following ways :(i)By electrolyte : Freshly prepared precipitate of Fe(OH) can be changed into colloidal state when precipitate3is treated with a small amount of FeCl solution. The sol thus obtained is positively charged due to the3preferential adsorption of Fe ions (from FeCl ) on sol particles of Fe(OH) as [Fe (OH) ]Fe .+++333+++It should be noted that only freshly prepared precipitates can be peptized.(ii) By washing a precipitate : Peptization sometimes can be brought about by repeated washings of aprecipitate. For example if the precipitate of BaSO is washed continuously, a state is reached when the4washings carry some of the particles of the substances in the form of colloidal solution.Chemical Methods : All chemical changes giving rise to insoluble reaction products can be used for theformation of sols, particularly when suitable, stabilizers are also present.( a ) Oxidation : Sols of some non-metals are obtained by oxidation. For example. Sulphur is obtained incolloidal form by passing H S gas through bromine water of dil. HNO solution.23H S + Br 22 2 HBr + S ColloidalSimilarly, sol. of iodine is obtained by oxidising hydriodic acid with iodic acid as HIO +5HI33 H O+3I ,22It can be made stable by adding a small amount of gelatin.( b ) Reduction : Sols of some metals are obtained by the reduction of their salts. Gold sols are made byreduction of HAuCl solution with reducing agents like tannic acid, HCHO, H O , phosphorus, hydrazine422etc. Carey Lec's silver sole is obtained by reducing solution of AgNO containing alkaline dextrin as stabilizer3with variety of reducing agents. Stabilised colloidal suspension of graphite in water is known as aquadagand one in oil is known as oildag.( c ) Hydrolysis : This method is generally employed for the preparation of sols of number of a hydroxidesand hydrous oxides. Fe(OH) and Al(OH) sols are obtained by boiling solution of the corresponding33chlorides.FeCl + 3 HOH 3 Fe(OH) + 3 HCl3A beautiful red sol of ferric hydroxide is prepared by boiling ferric acetate in a beaker having distilled water(500 mL).(CH COO) Fe + 3H O 332 Fe(OH) + 3CH COOH33The excess of ferric acetate may be removed by electrodialysis because its presence renders the sol unstable.Organic esters of silicon, such as ethyl silicate, will hydrolize in water to form colloidal silicic acid, Si(OH)4and alcohol.( d ) Double decomposition : This is the usual way of forming sols of insoluble salts. If the solutions containingthe component ions of an insoluble substance are mixed, a precipitate will result. If the substance has lowsolubility, the precipitate will be colloidal. Colloidal sol of prussian blue may be prepared by mixing verydilute solutions of FeCl and K Fe(CN) .3463K Fe(CN) + 4 FeCl 463 Fe [Fe(CN) ] + 12 KCl46 3Sols of arsenius sulphide and mercuric sulphide are obtained by passing H S into the saturated solutions of2corresponding soluble salts of their oxides,As O + 3H S 232 As S + 3H O232Hg (CN) + H S 22 HgS + 2 HCN

( e ) Oxidation-reduction methods : Many colloidal sols are prepared by oxidation- reduction reactions. Anexample of this method is the preparation of the colloidal molybdenic oxide which may be prepared by thereduction of ammonium molybdate with hydrogen sulphide. The sol of hydrated MnO can be prepared by2the reduction of 0.01 M KMnO with ammonia. This sol can be made stabilize by adding a definite4quantity of gelatin.PURIFICATION OF SOLS:Excessive quantities of electrolytes and some other soluble impurities remain in a sol as a result of the methodselected for preparation, particularly in chemical condensation methods.( i )Dialysis : This method is based on the fact that colloidal particles are retained by animal membrane or aparchment paper while electrolytes pass through them. The sol is taken in a parchment or cellophane bag,which itself is placed in running water in a trough. Gradually the soluble impurities diffuxe out leaving apure sol behind. Dialysis is a slow process and it takes several hours and sometimes even days for completepurification.Water(b) ElectrodialysisUpperpart of abottle+––+WaterWatermembrane(a) DialysisImpure colloidal solution(ii) Electrodialysis : Dialysis can be fastened by applying an electric field if the substance in true solution isan electrolyte. This process is then called electrodialysis. By means of electrodialysis it is possible to get acolloid in pure state in short time, although the electric current does not affect non-conducting impuritiessuch as alcohol, sugar, etc.+–Water outletsWater inletsWaterSolutionWater(iii) Ultra filtration : This is a method not only for purification of the sol but also for concentrating the sol.The pores of the ordinary filter paper are large enough (1030 m ) for the colloidal particles (203 m ) topass through. But if the pores are made smaller the colloidal particles may be retained on the filter paper.This process is known as ultra filtration.(i v) Electro decantation : This is a method not only for purification of the sol but also for concentrating thesol. If electrodialysis is carried out without stirring the sol, the lower layer becomes more concentratedwhereas the top layer becomes dilute. This process is known as electro decantation and was introduced byPauli.

(v) Ultracentrifuging : The colloidal particles share the motion of the molecules of the dispersion mediumand are in a state of continuous zigzag motion, called Browninan movement. Sol particles are preventedfrom setting by this continuous haphazard zigzag motion. The sol is kept in a high speed centrifugingmachine revolving at a very high speed (about 15,00 revolutions per minute) so that the colloidal particlessettle quickly, the slim can be suspended in water so as to get a sol.PROPERTIES OF COLLOIDS:General properties of colloids may be studied under several heads.( i )Heterogeneous nature : Colloidal solutions are heterogeneous in nature consisting of two distinct phasesviz. the dispersed phase and the dispersion medium. Experiments like dialysis, ultrafiltration and ultracentrifuging,clearly indicate the heterogeneous character of colloidal system.(ii)Non- settling nature : Colloidal solutions are quite stable. The suspended colloidal particles remain suspendedin the dispersion medium indefinitely. In other words there is no effect of gravity on the colloidal particles.(iii)Filtrability : Colloidal particles readily pass through ordinary filter papers. It is because the size of the pores ofthe filter paper is larger than that of the colloidal particles.(i v)Size of the particles of the dispersed phase : Colloidal dispersions generally range in particle size from 1m to 1 in diameter. The properties which distinguish them from true solution are mainly due to their largesize.( v )Diffusibility : Colloidal suspensions unlike true solutions do not readily diffuse through fine membranes andhave a little power of diffusion. This is due to the large size of the colloidal particles as compared to ordinarysolute particles.(v i)Colour : The colour of the sol is not always the same as the colour of the substance in the bulk. The colour ofthe colloidal solution changes as the size and shape of the particles change. It may exhibit different colourswhen seen by reflected and transmitted light. For example diluted milk gives a bluish tinge in reflected light andreddish tinges in transmitted light.(vii)Shape of the colloidal particles : Different sol particles have different shapes, for example, red gold sol,silver sol, platinum sol. As S sol has spherical particles whereas Fe(OH) sol and blue gold sol have disc or233platelet like particles. Rod-like particles appear in V O sol. tungstic acid sol, etc.25(viii) Visibility : Most of the sols appear to be true solutions with a naked eye, but the colloidal particle can be seenthrough an ultramicroscope.(ix)Colligative properties : Sol particles because of their free suspensions amongst the molecules of the medium,share kinetic energy with them in the same manner as molecules of regular solutes do. This gives rise tocolligative properties like osmotic pressure lowering, depression of freezing point and elevation of boilingpoint. Of these, the osmotic pressure alone has measurable values and its measurement has been used forfinding average particle weight in colloidal suspensions. The reason for this may be put as follows:As colloidal particles are not simple molecules and are bigger particles (i.e. physical aggregation of about 1000molecules) their number in the colloidal solutions are comparatively small. As the magnitude of colligativeproperties depends upon the number of solute particles present in the solvent, their values are smaller.( x )Optical properties : Colloidal sols exhibit the following noted optical properties:( a ) Tyndall effect -If a homogeneous solution is observed in the direction of light, it appears clear and whenit is observed from a direction at right angles to the direction of the light beam, it appears perfectly dark.But when a beam of light passes through colloidal solutions, it is scattered, the maximum scattered intensitybeing in the plane at right angles to the path of light. The path beam becomes visible. The effect was firstobserved by Faraday but was studied in detail by Tyndall and the effect is not commonly known as Tyndalleffect.

Scattering also occur in true solutions but the amount of scattering is extremely weak and there is a fundamentaldifference between the two types of scattering. Tyndall effect is characteristic of large particles (Rayleighscattering) and there being no difference between the wavelengths of incident and scattered light, solutionsexhibit Raman scattering which is characteristic of molecules.Vessel containing solBright Tyndall coneDarknessThe randomness of scattering of light by colloidal particles was shown by Tyndall as a bright cone of light. It isknown as Tyndall cone.Explanation : The tyndall effect is due to scattering of light by the colloidal particles. The colloidal particlesfirst absorb light and then a part of the absorbed light is scattered from the surface of the colloidal particles.Maximum scattereo intensity being in a plane at right angles to the plane of incident light, the path becomesvisible when seen from that direction.Application of Tyndall effect : Tyndall effect has been used by Zsigmody and Scidentonpf for making anultramicroscope. Ultramicroscope is a microscope arranged so that light illuminates the object from the sideinstead of from below. In ultramicroscope, incident light does not strike the eye of the observer and thusobserves the scattering produced by the sol particle against a dark back ground. An actual image formation isnot obtained but the presence of particle can be seen.ELECTRICAL PROPERTIES OF COLLOIDS :Electro-kinetic effects : Colloid particles carry an electric charge. When the sols are placed in the electricfield, certain special effects are noticed, which are termed as electro-kinetic effect. Such effects involve therelationship between the movement of one phase with respect to another in the exhibition of some electricalproperties. Such effects are of four types:(i) Electrophoresis or catephoresis(ii) Electro osmosis or Electroendosmosis(iii) Streaming potential(iv) Sedimentation potential or Dorn Effect. Let us discuss these one by one.( i ) Electrophoresis or Cataphoresis : The colloidal particles carry an electric charge. The colloidal solutionis taken in a U- tube and two platinum electrodes are dipped in the sol as shown in the figure. The currentis then switched on. On closing the circuit it is found that colloid particles move to the oppositely chargedelectrode and on reaching that electrode they get discharged. As soon as the charge of the particles isneutralized, they aggregate and settle down. This movement of colloid particles in electric field is known aselectrophoresis in case of the true solutions.CataphoresisWaterCoagulatedsol particles migratingsol particles

Since the current in the colloidal solution must be carried by both positive and negative particles, ions of thediffused layer must be moving in a direction opposite to the direction of the movement of colloid particles. In aFe(OH) sol which is positively charged, the sol particles move to the negative electrode where their charge is3neutralised and they aggregate and finally precipitate out. Thus, the entire colloidal matter settles down at the bottom.Importance : This phenomenon of electrophoresis is made use of in the following ways :(i) Determining the charge on the colloidal particles : direction of movement of the colloidal particles in theelectric field shows the charge on them.(ii) It can also be used to determine the rate at which colloidal particles migrate under the influence of anelectric field.(iii) It is also used in the identification and determination of homogeneity.(iv) It is of great importance for the preparative separations of the colloidal substances.(ii) Electro osmosis : It is also known as electro-endosmosis, in the above experiment, a partition is made byanimal membrane or parchment paper in between two electrodes, so that only the dispersion medium canmove through it and not the colloidal particles. When potential difference is set up between the electrodes,then the dispersion medium is seen to move in a direction opposite to the direction of movement of thecolloidal particles. This movement of the dispersion medium relative to the dispersed phase under theinfluence of the electric field is known as electro-osomosis. This is indicated by the rise of water level in onelimb of the U-tube.+–Measurement of electro-osmosisT'TACBELECTRIC DOUBLE LAYER:The surface of a colloidal particle acquires a positive or a negative charge by selective adsorption of ionscarrying +ve or –ve charges respectively. The charges layer attracts counter ions from the medium which formsa second layer. Thus, an electrical double layer is formed on the surface of the particles i.e., one due toabsorbed ions and the other due to oppositely charged ions forming a diffused layer. This layer consists of ionof both the signs, but its net charge is equal and opposite to those absorbed by the colloidal particles. Theexistence of charges of opposite signs on the fixed and diffused parts of the double layer creates a potentialbetween these layers. This potential difference between the fixed charge layer and diffused layer of oppositechange is called electrolkinetic potential or zeta potential.PROTECTION OF COLLOIDS :Protection : When certain hydrophilic colloids such as gum, gelatin, agar-agar etc. are added to a hydrophobiccolloid, the stability of the latter is markedly increased. Now the addition of the small amounts of electrolytesdoes not cause the precipitation of the hydrophobic colloid. This action of the hydrophilic colloids to preventprecipitation of the hydrophobic colloid by the electrolytes is called protection and the hydrophilic colloid iscalled protective colloid. It is further observed that the protective colloid not only increase the stability of thehydrophobic colloid but the latter can be evaporated to dryness and the dry mass peptised by simply shakingwith water. Thus the protective colloid converse an irreversible (hydrophobic) colloid into a reversible colloid.Protected ParticlesProtected ParticlesFormation of protective colloids

Some examples of protective colloids are :(i) Soluble substance like Ca (PO ) are held as colloids in blood due to protective action of protein in blood.34 2(ii) To prevent clogging in pens; superior pen inks contain some protective colloids(iii) Casein in human milk is better protected than in the cow's milk. It is because of this that cow's milk is moreeasily coagulated.(iv) Protargol and Argyrol powders are the protected forms of colloidal silver.Explanation :The particles of the protected colloid get adsorbed on the particles of the hydrophobic colloid, therebyforming a protective layer around it. The protective layer prevents the precipitating ions from coming incontact with the colloidal particles. According to a recent view the increase in stability of the hydrophobiccolloid is due to the mutual adsorption of the hydrophilic and hydrophobic colloids. It is immaterial whichis adsorbed on which. In fact the smaller particles whether of the protective colloid or of the hydrophobiccolloid are adsorbed on the bigger particles.Preparation of protected colloid : It is possible to get a protected sol by means of protective one. Bymeans of protection, colloid in higher concentration can be obtained. Furthermore, it is important inpreventing the growth of primarily precipitated particles.Protected sol of platinum : Paal and Amberger prepared protected sols of several metals. Theplatinum protected sol was obtained as follows : Chloroplatinic acid is added to sodium lysalbate(decomposition product of protein) taken in excess of water. To this NaOH is added till we get reddish-brown liquid which is then treated with hydrazine where N gas evolved. This solution is kept for 6 to 72hours and then dialysed. The black brittle and lustrous residue so obtained was dissolved in water whichgives a protected platinum sol.Gold Number : The power of the hydrophilic colloid to prevent the precipitation of a lyophobic colloidby addition of an electrolyte depends upon the nature of the substance. The protective character ofvarious hydrophilic substances can be expressed quantitatively by gold number. The gold number accordingto Zsigmondy may be defined as: \"The number of milligrams of the protective colloid which must beadded to 10 cc of a given gold sol so as to just prevent its precipitation by addition of 1 cc of 10% NaClsolution.\"Smaller the gold number, higher the protective power of a colloid. Gold numbers of some protective colloidsare given below :Protective ColloidGold Number Heamoglobin0.03 to 0.07 Starch 15 to 25 Gum Arabic 15 to 25 Gelatin0.005 to 0.1The protective power was also measured by Ostwald in terms of Congo Robin number. It is the amount ofa protective colloid in mg which prevents colour change in 100 mL. of 0.01% congo robin dye solution towhich 0.16 g equivalent of KCl is added when observed after 10-15 minutes.COAGULATION OR FLOCCULATION :The colloidal sols are stable by the presence of electric charges on the colloidal particles. Because of the electricrepulsion the particles do not come close to one another and coalesce. The removal of charge by any meanswill lead to the aggregation of particles and hence precipitation immediately. The process by means of whichthe particles of the dispersed phase in a sol are precipitated is known as coagulation or flocculation.Electric charges on lyophobic particles can be removed by the application of an electric field as is used inelectrophoresis. But a common method of producing precipitation is by the addition of electrolytes.The precipitate after being coagulated is known as coagulum.

Methods for coagulating a sol : There are several methods employed for coagulating a sol. Some of themare noted below :( i )By the addition of electrolytes : In this method large amount of electrolytes are added to the sols whichcause precipitation. This is due to the fact the colloidal particles take up the ion whose charges are opposite tothat on colloidal particles. With the result that the charge on colloidal particles is neutralised and coagulationtakes place. In case of arsenious sulphide sol (negatively charged) coagulation takes place by adding BaCl . It is2due to the fact that negatively charged particles of the arsenious sulphide sol take up barium ions, resultingneutralisation of the charge on the colloidal particles and hence lowering the stability of the sol.It has been observed that generally the greater the valency of the added ion, the greater is its power to causecoagulation. An ion having an opposite charge to that of the particles of the sol is responsible for coagulation.This ion is generally called as active ion. For example calcium chloride is approximately 100 times more activethan NaCl in the coagulation of a silver sol. The particles of a silver sol are stabilised by negative charges andfor the coagulation the valency of the cation is effzective. Similarly for the coagulation of positive sols thevalency of the anion is decisive. Further, the precipitating power of an electrolyte increases very rapidly withincrease in the valency of the cation or anion, the ratios being approximately 1 : 40 : 90 for the ferrichydroxide sol and 1 : 70 : 500 for the arsenious sulphide sol.Thus in the coagulation of ferric hydroxide sol, the coagulating power increases in the order ofCl > SO–4– –> PO4– – – Fe(CN)6– – – –, while in the coagulation of arsenious sulphide sol, the coagulating powerincreases in the order of Na > Ba , Al++++++. This importance of valency was first recognised by Schulze(1882) and more data were obtained latter by Linder, Picton, Hardy and Freundlich. The coagulationvalues of NaCl, BaCl and La(NO ) , for the silver sol prepared by reduction of silver carbonate with tannin23 3are 30, 0.5 and 0.003 milli/mol per/liter respectively. The coagulation or flocculation power can then beexpressed as the reciprocal of these flocculation values i.e.130: 10.5: 10.003i.e. NaCl : BaCl : La (NO ) as 0.033 : 2 : 33. 3 or 1.60 : 1000023 3 (ii)Physical methods : The coagulation of some sols can be carried out by (a) mechanical treatment, (b) heatingor cooling, (c) irradiation, (d) vigorous shaking, (e) treatment with electric current, etc.(iii)By continuous dialysis : We know that traces of electrolytes are present in the colloidal system which arenecessary for the stability. If the sol is subjected to continuous dialyser the colloidal system becomes unstable.(i v)Salting out : Coagulation of lyophilic sol can be made by the addition of sufficient high concentrations ofcertain ions. Thus salting out of lyophilic colloids is due to the tendency of ions to become solvated, causing theremoval of adsorbed water from the dispersed particles.( v )By hydrated ions: Since ions can also differ in the degree of hydration or solvation, this factor also plays animportant role in the precipitation of sols.(v i)By removal of electric charge : Removal of electric charge on lyophobic particles by means of the applicationof electric field results precipitation. This is accomplished by electrophoresis.The coagulating effect of electrolytes on hydrophobic sols was studied by Schulze, Hardy, Linder and Picton.( a )Hardy- Schulze Law : According to them, the greater the valency of the active ion, greater is thepower to cause coagulation. Active ion is responsible for coagulation.Thus, in the case of positively charged sol the coagulation power of anions is in the order of[Fe(CN) ] > [PO ] > [SO ] > [Cl]4–443–4–2–In the case of negatively charged sols, the coagulation power is in order ofAl+++ > Ba > Na+++The coagulation values of NaCl, BaCl and La(NO ) for silver sol are 30, 0.5 and 0.003 millimoles/litre.23 3The reciprocal of coagulation value is regarded as the coagulating power or flucculating power i.e.130: 10.5: 10.003 i.e., 1 : 60 : 1000

ElectrolyteCoagulation valuemilli moles/litreElectrolyteCoagulation value(milli moles/litre)1NaCl52KCl1322KCl51K CrO230.2253BaCl20.69K SO240.214MgSO40.22K Fe(CN)360.0965AlCl30.093K Fe(CN)460.085Ars enious s ulphide s olFerric hydroxide s olS .No.EMULSIONS :Emulsion is a colloidal system consisting of immiscible liquids. e.g. milk is an emulsion in which particles ofliquid fat are dispersed in water. In common occurrence, however, one of the liquids is water and the other, andoily substance insoluble in it. The suspended droplets are larger than the particles of the sols: it is because of thedensity differences between the phases being small. Emulsion droplets can be observed under an ordinarymicroscope and sometimes even with a magnifying lens.An emulsion is a heterogeneous system consisting of more than one immiscible liquids dispersed in one anotherinform of droplets whose diameter, in general, exceeds 0.1 . Such systems possess an extremely small stabilitywhich is made by the addition of surface active agents, finely divided solids, etc.Type of Emulsions : Emulsions are of two types :( i ) Oil in water (o/w) type : In these emulsions oil forms the dispersed phase and water, the dispersionmedium. For example, milk, vanishing cream, etc. These are also called aqueous emulsions.(ii) Water in oil (w/o) type : In these emulsions water is in the dispersed phase and oil in the dispersionmedium. For example, butter, cold cream etc. are also called oil emulsions.In addition to above there is one usual type known as multiple emulsion. As the name indicates, a multipleemulsion is one in which both types of emulsion exists simultaneously. It can be denoted as w/o/w emulsion.Factors determining the type of emulsions : When two liquids, say oil in water are shaken to form anemulsion, the type of emulsion formed, (i.e. oil in water or water in oil) depends upon the following factors:( a ) Relative proportion of the two liquids : As a general rule the liquid present in excess forms thedispersion medium. For example to obtain an emulsion of oil in water, water is taken in excess and toobtain water in oil emulsion, oil is taken in excess.( b ) Surface tension of the two liquids : The liquid with greater tendency to form spherical drops andhence the dispersed phase. Thus, if the surface tension of an oil in is greater than that of water, it will forman oil in water type emulsion.Preparation of emulsions : Emulsions are usually obtained by spraying mixtures of phases through narrownozzles or in counter-rotary agitators. The nature of the emulsifying agent determines the type of the emulsionobtained. According to Boncroft Rule :\"The phase in which the stabilizer is more insoluble becomes the external phase.\"Neutral soaps which are insoluble in hydrocarbons but soluble in water give oil-in water emulsions while acidsoaps which are more soluble in hydrocarbons yield water-in-oil water emulsions. Emulsions can also be preparedby using ultrasonic waves.Emulsion is, however, also possible with stabilizers insoluble in both phases. In these cases the phase whichwets the emulsifier better becomes the outer phase. Clay, glass powder, calcium carbonate, and pyrites areeasily wetted by water and give rise to aqueous emulsion while lamp black, which is more easily wetted by anoil, gives oily emulsion.A condensation method given by Summer has been employed in preparation of concentrated o/w emulsions.

Characteristic of emulsions:(i) Concentration and particles size : In the case of emulsions the amount of one liquid dispersed in anotheris relatively much greater as compared to the soles. The maximum amount of one liquid which can dispersedin another cannot exceed 74% of the total volume available. Emulsions more concentrated than 74% havealso been found. The diameter of droplets in case of emulsions is of the order of 0.001 – 0.05 mm. Recentlystable emulsions having diameter of 0.0001 mm have also been reported.(ii) Optical properties : A relationship between optical properties and particle size and also between lightscattering with the properties of suspensions have been reported. The interfacial areas in emulsions byoptical measurements have been determined by Langlois and other's in 1954.(iii)Viscosity : The property of viscosity (resistance to flow) is quite important both for practical and theoreticalpurposes. It provides some information about the structure of emulsions.(i v) Electrical `Conductivity : This property is useful in distinguishing between o/w and w/o type of emulsions.The emulsion in which water is the dispersion medium possesses high conducitivity than the emulsionhaving oil as dispersion medium.Emulsifiers :In order to prepare stable emulsions, it is important to add a third component known as emulsifier or emulsifyingagent in suitable amounts. Several types of emulsifiers are known.(i) Long chain compounds with polar groups such as soap, sulphonic acid, sulphates etc.(ii) Most of the lyophilic colloids also act as emulsifiers such as glue, gelatin etc.(iii) Certain insoluble powders as clay, lamp, black etc.(iv) Soluble substances like iodine also act as emulsifiers.Role of an emulsifier : An emulsifier may act in two ways :1. It may be more soluble in one liquid than in the other: In this case it will form a sort of protective filmaround the drops of this liquid in which it is less soluble and thus prevents them from coming together (fig-a)] For example neutral soaps which are more soluble in water than in olive oil is water type emulsion [Fig.-b]. Acidic soaps which are more soluble in oils than in water, give water in oil type emulsion [fig-c]2. The emulsifiers may be insoluble in both the liquids but not unequally wetted by the two.Oil Emulsification of oil and water by an acid soapE m u ls i f ie rWaterOilWater Emulsification of oil and water by neutral soapE m u ls i f ie rWaterSoot particlesKerosene Oil Emulsification of water and kerosene by soot particles [Fig-a] [Fig-b] [Fig-c]Importance of Emulsions : Emulsions find manifold applications in various fields.( i ) Medicine - Numerous medicines and pharmaceutical preparations are emulsions. In such forms they havebeen found to be more effective. Cod-liver oil, caster oil, petroleum oil are used in medicines and areemulsions.(ii) Articles of daily use- Milk is an emulsion of fat dispersed in water stabilised by casein. Ice cream is anemulsion. Butter, coffee, fruit jellies etc., are all emulsions in nature.(iii)Cosmetics : The skin penetrating vanishing creams o/w type emulsions and hair creams, cold creams arew/o type emulsions. The lotions, creams and ointments are stabilized by lanoline.(i v) Industry :The latex obtained form the sap of certain trees is an emulsion of negatively charged rubber particlesdispersed in water.

During the concentration of sulphide ores, froth floatation process is employed. In the process, oil emulsion isadded to the finely divided ore and foam produced by passing ore contains most of the particles of the ore.Emulsion of oils and fats have been employed in leather industry for making soft leather and water proof.Asphalt emulsified in water is used for building roads, with the necessity of melting the Asphalt.Emulsions are also employed in oil and fat industry, paints and varnishes, cellulose and paper industry etc.Furthermore, spraying liquids in the form of emulsions are used in agriculture.MICELLIZATIONThe diphilic nature of surfactant molecules, i.e. the presence in them of a polar (hydrophillic) and non-polar(hydrophobic) parts has been a feature of their structure imparting special properties to these molecules. Thediphilic nature was characterized very well by Hartley as a \"split personality\". It has been exactly the diphilicnature of surfactant molecules that underlies their tendency of gathering at phase interfaces, immersing theirhydrophillic part in water, and isolating their hydrophobic part from it. This tendency ascertains their surfaceactivity i.e. their ability to be adsorbed at the water-air interface or a water-oil one, to wet the surface ofhydrophobic bodies, and form structures such as soap films or lipid membranes.With an increase in the asymmetry of the molecules ( a growth in the length of the hydrophobic chain), theirsurface activity grows (Traube's rule) and accordingly, their special behaviour in a solution, different from that ofsimple salts, gets more pronounced. It manifests itself the most appreciably for long-chain surfactants with 10-20 carbon atoms in a chain that get characterized by an optimal balance of hydrophilic and hydrophobicproperties. These substances, which are having many practical applications (for example, as floatation reagents,stabilizers, and detergents) have special properties in solutions that are of considerable interest.At low concentrations these surfactants tend to form true solutions that disperse up to individual molecules (orions). With a growth in the concentration, however, the duality of the properties of the molecules of suchdiphilic substances gives rise to their self-association in the solution. This results in the formation of what arecalled micelles.Micelles may be defined to be aggregates of long- chain diphilic surfactant molecules or ions formed spontaneouslyin their solutions at a definite concentration. The latter depends on the nature of the polar group and especiallyon the length of the molecule chain, Micelles can be characterized by the aggregation number (the number ofmolecules in a micelle) and the micellar mass (the sum of the molecular masses of the molecules forming amicelle).Micelles form by the cooperative binding of monomers to one another at concentrations exceeding a rathernarrow region called the critical micellization concentration (CMC). The latter is the concentration of a surfactantat which a large number of micelles form in its solution that have been in thermodynamic equilibrium with themolecules (ions), and a number of properties of the solution sharply change.This sharp transition to the CMC region for systems with flexible chains could be attributed to the cooperativenature of the self- association process. This makes aggregates containing many monomers considerably morestable than small particles. The CMC has been one of the most easily determined experimentally and usefulquantitative characteristics of solutions of surfactants with flexible chains.IONIC MICELLESAccording to McBain colloidal electrolytes cannot be regarded as macromolecules as they are individual moleculesof giant size in solution. They also differ from lyophobic colloids, because the latter are unstable. Large sizeanions, e.g., C17H . COO , RSO etc. and cations like RH(CH ) , aggregate to form ionic micelles of colloidal33–33 3+dimensions containing number of ions together containing appreciable water molecules. So the ionic micellesare the aggregates formed in solution by colloidal electrolytes.The formation of micelles can also take place from neutral or non-ionic molecules, e.g. polythelene oxide.Ionic micelles of sodium oleate : The formation of micelle by sodium oleate, C H COO Na is a1733–+striking example of colloidal electrolytes. In this case there are two parts, one is tail, i.e. hydrocarbonpart C H , and the other is head COONa. The COONa is an ionisable lyophillic group which tries to1733go in to water resulting into ions. The C H part tends to go away from solution. But if the concentration1733is increased the hydrocarbon part forms the aggregate micelle is therefore that of anions and maycontain hundred or more oleate ions clamped together.

Critical micelle concentration (CMC) : In very dilute solutions, sodium and potassium oleate andother similar substances, remain as individual molecules ionising into positive and negative ions. Accordingto Davies and Bury the concentration at which micelle becomes appreciable, is termed as critical micelleconcentration. At this concentration there is an abrupt change in the properties, it decreases with theincrease of temperature. Every colloidal electrolyte has a definite value of CMC.Type of ionic micelles : McBain suggested the presence of more than one type of ionic micelles in agiven solution of a colloidal electrolyte. Some of them are described below :+++++++++( i )Lamellar micelle :In consists of double leaflet of soap molecules placed end to end and side by side. X-ray study has revealed theexistence of other kind of micelle in which molecules are laid end to end, side by side, as in lameller micelle.The difference from each other and are separated by layer of water, depending upon concentration. Hoffman'sinvestigation has shown that the molecules in the micelle are rotated at an angle of 55°. According to Stuff themolecules are closely packed side by side in an irregular manner as in a liquid crystal. (Fig.1)(ii)Spherical micelle :According to Hartley ionic micelles can be spherical. Although this consent is employed but is open to criticism.(iii)Elleipsoidal or cylindrical micelle :Klevens has suggested that the micelle may also be an elongated ellipsoidal or of cylindrical model.GELS :Colloidal system in which liquids are the dispersed phase and solid act as the dispersion medium are called gels.The common examples are : boot pollishes, jelly, gum arabic, agar agar, processed cheese and silicic acid.When the gels are allowed to stand for a long time, they give out small quantities of trapped liquids withaccumulate on its surface. This action of gels is known as Synresis of Weeping. Some gels such as silica, geltinand ferric hydroxide liquify on shaking and reset on alloweing to stand. This phenomenon of Sol-geltransformation is called thixotropy.Gels are divided into two categories i.e. elastic gels and non elastic gels. The two categories differ from theirbehaviour towards dehydration and rehydration as under,E la s t ic g elsN o n -ela s t ic g els1 They change to solid m ass on dehydration which They change to solid m ass on dehydration which can be changed back to original form by addi-tion of water followed by warm ing. cannot be changed back to original form with water.2 They absorb water placed in it with sim ultaneous sewlling. This phenom enon is called im bibation. They do not exhibit im bibation.

INTRODUCTION : SURFACE CHEMISTRYIt has been known that the surface of a liquid is in a state of strain or unsaturation due to the unbalanced orresidual forces which act along the surface of a liquid. Similar to it, the surface of a solid may also have residualforces or valances. Thus, the surface of a solid has a tendency to attract and to retain molecules of otherspecies (gas or liquids) with which such surfaces come in contact. This phenomenon of surfaces is termed asadsorption.As the molecules remain only at the surface, and do not go deeper into the bulk of the solid, the concentrationof adsorbed gas or liquid is more at the surface than in the bulk. Hence this discussion may follow up by thedefinition of adsorption.\"Adsorption is a technical term coined to denote the taking up (Latin, surbere, to such up) of gas, vapour,liquid by a surface or interface.Differences between Adsorption, Absorption and Sorption. Adsorption is a surface phenomenon whereasabsorption is a bulk phenomenon in which the substance assimilated is uniformly distributed throughout thebody of a solid or liquid to form a solution or a compound. The phenomenon of adsorption and absorption areillustrated in figure.AdsorbateAdsorbed molecule(Surface Concentration)AdsorbentAbsorbed molecule(Uniform Penetration)(Adsorption and absorption)(Sorption)Adsorption should be distinguished carefully from absorption.(i)In absorption, the substance is distributed throughout the body of a solid or a liquid to form a solution or acompound. On the other hand, adsorption only takes place on the surface and not in the body of adsorbent.Thus, adsorption is a surface phenomenon, and absorption is a bulk phenomenon.(ii)In absorption, the concentration of the adsorbed molecules is always found to be greater in the immediatevicinity of the surface (Adsorbent) than in the free phase (Adsorbate). On the contrary, absorption involvesbulk penetration of the molecules into the structure of the solid or liquid by some process of diffusion.(iii)In case of adsorption, the equilibrium is easily attained in a very short time whereas in absorption the equilibriumtakes place slowly.(iv)According to freundlich absorption isotherm 1 / nxk p m 

PxmT=Const.bPsaLog PxmIntercept = log kSlope = 1nLogExamples for adsorption and absorption(i)Water vapour is absorbed by anhydrous calcium chloride while it is adsorbed by silica gel.(ii)Ammonia is adsorbed by charcoal while it is absorbed by water to form ammonium hydroxide.NH + H O 32 NH OH4(iii)Decolourisation of sugar solution by activated charcoal is another example of adsorption. In this example,charcoal adsorbs the colouring material and thus decolourises the solution.(iv)The colour of the lake test for aluminium ions is due to adsorption of dye (litmus) on the freshly precipitatedaluminimum hydroxide.(v)When a hot crucible is allowed to cool in air, a film of moisture is formed at the surface. This is the caseof adsorption of water vapour on the surface of a crucible.(vi)When sponge is put into water, it takes up water. It is example of absorption.Nomenclature used in Adsorption : The material on the surface of which adsorption takes place is calledthe adsorbent and the substance adsorbed is called the adsorbate. The common surface separating two phases,where the adsorbed molecule concentrates is referred to as the interface. The large the surface area of theadsorbent, the more the adsorption. Due to this reason colloids are good adsorbents due to their high surfacearea per unit mass although they have very small dimensions.Adsorption stands for different concentrations of a substance at an interface. If the concentration is more at aninterface, the adsorption is said to be positive; if the concentration is less at an interface, the adsorption is saidto be negative. The reverse process of removal of an adsorbed substance from the surface of a solid is knownas desorption.Example of Adsorbents :( a )Silica gel : It acts as a good adsorbent and is prepared by mixing sodium silicate with 10% hydrochloricacid at 50°C.( b )Metals : Metals act as good adsorbents and are being used for contact catalysis. These are prepared bythe reduction of their oxides or of the salts under suitable experimental conditions. Examples are Ni, Cu,Ag, Pt and Pd.( c )Colloids : As colloids possess high surface per unit mass due to their small size, they act as goodadsorbents.Examples of Adsorbates : There are various gases (He, Ne, O , N ,SO , NH etc.) and substances in2223solution (NaCl, KCl) which can be adsorbed by suitable adsorbents.CHARACTERISTICS OF ADSORPTION :The various characteristics of adsorption are as follows :(i)Adsorption is a spontaneous process and takes place in no time.(ii)The phenomenon of adsorption can occur at all surfaces and five types of interfaces can exist: gas -solid,liquid-solid, liquid-liquid, solid-solid and gas-gas. The gas-solid interface has probably received the mostattention in the literature and is the best understood. The liquid- solid interface is now receiving muchattention because of its importance in many electrochemical and biological systems.(iii)It is accompanied by a decrease in the free energy of the system, i.e., G. The adsorption will continueto such an extent that G continues to be negative.

(iv)As the process of adsorption involves loss of degree of freedom of the gas in passing from the free gasto the adsorbed film there is a decrease in the entropy of the system.It follows from the Gibbs-Helmholtz equationG = H –T S... (i)orH = G + T S... (ii)Where G is the change in free energy, H is the change in heat content, S is the change in entropy, andT is the temperature of the system. As the entropy and free energy decrease in adsorption, the value of Hdecreases. This decrease in heat content ( H) appears as heat. Hence the adsorption process must always beexothermic.SORPTION AND OCCLUSION :In many examples, the initial rapid adsorption is followed by a slow process of absorption of the substance intothe interior of the solid. In these cases, the effect of absorption cannot be distinguished from those of adsorption.Therefore, the two new terms were introduced:( i )Sorption : The process in which both adsorption and absorption take place simultaneously is generally termedas sorption. This term was suggested by Mcbain (1990). Examples are-(a) The uptake of gases by zeolites is a striking example of sorption(b) When hydrogen is taken up by charcoal, it first condenses on its surface. This is adsorption. After sometime,the hydrogen diffuses slowly into the interior of the charcoal forming a true solid solution and hence, this isabsorption. So the charcoal has adsorbed as well as absorbed hydrogen gas. Therefore, it is an example ofsorption.(c) The direct dye-stuff taken up by cotton fibres are also in the adsorbed as well as in the absorbed state.(ii)Occulusion : In 1886 T Graham proposed the term occlusion which possesses a similar significance tosorption. But this term occlusion is restricted to the sorption of gases by metals only.ADSORPTION OF GASES ON SOLIDS :( 1 )Introductory :The study of the gas-solid adsorption process has excited the interest of both academic and industrial scientistsfor many years, and the reactions are not hard to find. Industrially, it is known that this phenomenon plays anessential role in the catalytic process. The ability of surface to selectively accelerate the rates of many chemicalreactions is the basis of much of the heavy-chemical production in the world.It is generally believed that all gases or vapours are adsorbed on the surfaces of all solids with which they are incontact. The phenomenon was first described in 1773 by Scheele, who discovered the uptake of gases bycharcoal.( 2 )Factors on which Adsorption depends :The phenomenon of adsorption of gases by solids depends upon the following factors:( i ) Nature of adsorbent and adsorbate :The amount of the gas adsorbed depends upon the nature of the adsorbent and the gas (adsorbate) whichis to be adsorbed.Gases like SO , NH , HCl and CO which liquefy more easily are adsorbed more readily than the permanent232gases like H , N and O which do not liquefy easily. This is because the easily liquefiable gases have greater222van der waal's or the molecular forces of attraction or cohesive forces.As the critical temperatures of the easily liquefiable gases are more than the permanent gases, it followsthat higher the critical temperature of the gas (adsorbate), the greater the extent of adsorption.

(ii) Surface area of the adsorbent :The extent of adsorption of gases by solids depends upon the exposed surface area of the adsorbent. It iswell known that larger the surface area of the adsorbent, the large will be the extent of adsorption undergiven conditions of temperature and pressure. It is for this reason that silica gel and charcoal obtained fromdifferent animal and vegetable sources become activated because they posses a porous structure andthereby render a larger surface.(iii)The partial pressure of the gas in the phase :For a given gas and a given adsorbent, the extent of adsorption depends on the pressure of the gas.Adsorption of a gas is followed by a decrease of pressure. Therefore, in accordance with Le chatelier'sprinciple, the magnitude of adsorption decreases with the decrease in pressure and vice-versa. The variationof adsorption with pressure at constant temperature is expressed graphically by a curve known as adsorptionisotherm.(i v) Effect of temperature :For a given adsorbate and a adsorbent, the extent of adsorption depends upon the temperature of theexperiment. As discussed earlier, adsorption usually takes place with the evolution of heat. Therefore,according to the Le chatelier's principle, the decrease in temperature will increase the adsorption and vice-versa. An example is that if the temperature of the coconut charcoal is lowered from –29° to –78°C, theamount of nitrogen gas adsorbed increases from 20 to 45 mL. under the same pressure.( 3 )Types of Adsorption of the gases on solids :Based on the nature of forces between the gas and the solid surface, there are two types of adsorption.( 1 ) Physisorption or Physical Adsorption :If the physical forces of attraction hold the gas molecules to the solid, the adsorption is known as physicaladsorption or physisorption. The forces of attraction bringing about physical adsorption are :(i) Permanent dipole moment in the adsorbed molecule.(ii) Polarisation(iii) Dispersion effect(iv) Short range repulsive effectIn case of physisorption, the forces of attraction which hold the gas molecules to the solid are very weak.Therefore it is characterised by a low heat of adsorption, usually of the order of 40 kJ per mole. This valueis of the same order of magnitude as the heat of vaporisation of the adsorbate and lends credence to theconcept of a weak \"physical\" bonding. Physical adsorption is usually observed at low temperature or onrelatively \"inert\" surfaces.Examples of physisorption are as follows:(i) Adsorption of various gases on charcoal(ii) Adsorption of nitrogen on mica( 2 ) Chemisorption or chemical Adsorption :If the chemical forces hold the gas molecules to the surface of the adsorbent, the adsorption is known aschemisorption. In this case the adsorbate undergoes a strong chemical interaction with the unsaturatedsurface and gives rise to a high heat of adsorption, usually of the order of 400 kJ per mole. Chemisorptionis often characterised by taking place at elevated temperatures and is often an activated process. It may bedissociative, non- dissociative or reactive in nature. Some examples of chemisorption are :(a) Ethyl alcohol vapours condensed on the divided nickel.(b) Adsorption of oxygen on tungsten(c) Adsorption of hydrogen on nickel.

(3 ) Distinction between Physisorption and Chemisorption :Exact differentiation between chemical and physical adsorption is often difficult and usually unprofitable. Tothe practising chemist a physically adsorbed species is usually considered to be an adsorbed material thatcan be completely removed from the surface, without decomposition, by prolonged evacuation at roomtemperature or by heating to 120°C. This experimental choice of conditions is completely arbitrary, and thefinal decision is always left with the experimenter. However, the advent of infrared spectroscopy had led toa better means of distinguishing between the two processes.32003000330032003260333(c)cm–1(b)(a)0.20.40.10.202800(Infrared spectra of (a) acetylene in liquid solution, (b) acetylene on porous silica glass (c) acetylene on poroussilica glass coated with palladium)We know that the infrared spectrum of a molecule arises as a result of the vibrations of the atoms within themolecules. If the molecule is physically adsorbed, the infrared spectrum is altered only slightly and smallfrequency shifts, usually less than 1 percent, are observed. During the chemisorption process, the symmetryof the adsorbed molecule is completely different from that of the gaseous molecule. In this case a completelynew infrared spectrum is observed and band shifts and intensities are removed from those of the gaseousabsorbate.Let us illustrate this method by considering the IR spectra of acetylene in solution and adsorbed on silicaand on palladium coated silica. These spectra are shown in figure (a) which represents the infrared spectrumof acetylene in liquid solution, (b) represents of acetylene on porous silica glass, and (c) of acetylene onporous silica glass coated with palladium. The IR spectrum on silica (fig b) is like that in solution (fig-a)except for a small shift to lower frequencies, but the IR spectrum on palladium (fig-c) is completely differentand contains extra new bands. These spectra can be explained by saying that the latter case is a chemisorptionwith formation of new bonds (fig c) whereas the former case (fig b) is a typical physical adsorption.( 4 ) Differences between physisorption and chemisorption :The various differences are as follows:( a ) Specificity :Physisorptions are non-specific. Thus, every gas is adsorbed to a lesser or a greater extent on all solidsurfaces. On the other hand, chemisorptions are more specific in nature. A gas will be chemisorbed onsuch solids only with which it can combine chemically.( b ) Speed :Physisorptions are instantaneous. Chemisorptions may sometimes be quite slow depending upon the natureof chemical reaction involved. A rough estimate is that adsorbable impurities of air are adsorbed by gasmasks in a contact of less than 0.01 second.

(c) Reversibility :Physisorption equilibrium is reversible and is rapidly established. Chemisorption is irreversible. Physicallyadsorbed layer can be removed very easily by changing pressure or concentration. On the other hand theremoval of a chemisorbed layer, however, requires much more rugged conditions such as high temperature,etc.( d ) Heat of adsorption :Physical adsorption is generally characterised by low heats of adsorption which is about 40 kJ/mole orless.Chemisorption is characterised by high heats of adsorption viz. 40 to 400 kJ per mole which indicates thatforces are similar to those involved in chemical reactions. Therefore, it is highly probable that gas moleculesfrom a chemical compound with the surface of the adsorbent.( e ) Nature of adsorbate and adsorbent :Physical adsorption like condensation can occur with any gas-solid system provided only that the conditionsof temperature and pressure are suitable. The chemisorption will take place only if the gas is capable offorming a chemical bond with the surface atoms.( f ) Effect of Pressure :As the pressure of the adsorbate increases, the rate of physical adsorption increases. The rate of chemisorptiondecreases with the increase of pressure of adsorbate.( g ) Effect of temperature :Physical adsorption occurs to an appreciable extent at temperatures close to those required for liquefactionof adsorbed gases. Generally, chemisorption occurs at high temperatures. But certain examples are knownin which it occurs at low temperature. Chemisorption increases at first and then falls off with risingtemperature.A graph drawn between amount adsorbed (x/m) and temperature (T) at a constant equilibrium pressure ofadsorbate gas is called an adsorption isobar. Adsorption isobars of physisorption and chemisorption showon important difference (fig) and this difference is used for experimentally distinguishing chemisorptionfrom physisorption. While the physical adsorption isobar shows a decrease in x/m along the rise intemperature, the chemisorption isobar shows an initial increase with temperature and then the expecteddecreases. The initial increase shows that, like the chemical reactions, chemisorption also needs activationenergy. However, the latter decrease indicates that at higher temperatures desorption does occur inchemisorption process. Frequently during the high temperature desorptions the evolved gas carries with itsome atoms of the adsorbent as well in a chemically bound form.TPhysical adsorptionxmTChemisorptionxm

The various differences between physorption and chemisorption are summarised in table.Phys ica l a ds orptionChem is orption(i)It involves physical forces.It involves transfer of electrons between gas and solid.(ii)Heat of adsorption is generally lessthan 40 kJ/mole Heat of adsorption is 40-400 kJ/mol(iii)It is reversibleIt is not reversible.(iv)It is general phenomenon which will occur with any gas-solid system provided only that the conditions of temperature and pressure are suitable.It will only take place if the gas is capable of forming chemical bond with the surface atoms(v)Multilayers are possible in physicaladsorptionOnly monolayer is formed.(vi)It is appreciable at low temperatureshigh pressuresIt can occur at high temperatures. Therate of chemisorption decreases with the increase of pressure(vii)No appreciable activation energy isinvolved.Chemisorption is an activated phenomenon and involves appreciable activation energy.(viii)It is an instantaneous processIt may be rapid or slow.(ix)Physical adsorption is a function ofcoverage of surfaceIt is adsorbed at fixed sites on the sirface. These sites are known as active centres.(x)Not very specificOften very specificPHYSICAL ADSORPTIONTypes of adsorption curves : As discussed earlier, the magnitude of adsorption depends on the pressure ofthe gas and the temperatures of the experiment for a given gas and a given adsorbent. Hence, the amount ofthe gas adsorbed is a function of temperature and pressure only. Mathematically, it can be expressed asa = f (P.T.)... (i)where a is the amount of gas adsorbed, P is the pressure, and T is the temperature.When equation (i) is represented graphically, three different curves are obtained.( i )Adsorption Isotherm - If the temperature is kept constant and pressure is changed, the curve between a andP is known as adsorption isotherm.a = f(P) if T is constant.(ii)Adsorption Isobar : If pressure is kept constant and temperature is varied, the curve between a and T iscalled the adsorption isobar.a = f(T) if P is constant(iii)Adsorption Isostere : If the amount adsorbed is kept constant, the curve between P and T is known asadsorption isostere.P = f(T) if a is constant.

Types of Adsorption Isotherms (Physical) : Seven types of physical adsorption isotherms have been reported.These are give below in the figure.P(I)aP(II)aBP (III)aP (IV)aP(V)aType I : This type of curve is obtained in such cases where mono-molecular layer is formed on the surface ofthe adsorbent. This curve shows that a saturation state is reached. It means that there is no change in the valueof 'a' (the amount adsorbed) with the increase in pressure onwards. This type of the curve is rare. Example is theadsorption of nitrogen on charcoal at –195° C.Type II : This type of isotherm has a transition point 'B' which represents the pressure at which the formationof monomolecular layer is complete and that of the multi-molecular layer is being started. For many years it wasthe practice to take point B at the knee of the curve as the point of completion of a monolayer, and the surfaceareas obtained by the method are fairly consistent with those found using adsorbates that give type I isotherms.Example is the adsorption of nitrogen on silica gel at –195°C.Type-III : In this type of isotherm there is no transition point. In this the multi-molecular layer formation startseven before the formation of monomolecular layer is complete.Example is the adsorption of bromine or iodine vapours on silica gel at 79°C. Type III This type is relatively rareand a recent example of this is that of the adsorption of nitrogen on ice. This type seems to be characterised bya heat of adsorption equal to or less than the heat of liquefaction of the adsorbate.Type IV : In this case there is a tendency for a saturation state to be reached in the multimolecular region aswell. In fact that can be regarded as a duplication of the II type. Example is the adsorption of benzene vapouron ferric oxide get at 50°C.Type V : This isotherm indicates multimolecular layer formation in the beginning. At higher pressure, there isa tendency for 'a' (amount absorbed) to remain constant. It means that the saturation state has been reached.Example is the adsorption of water vapour on charcoal at 100°C.Type VI and Type VII : There is a need to recognise at least the two additional isotherms shown in fig. Theseare expected for non wetting adsorbate-adsorbent systems.P/P0(VI)001x0xP/P0(VII)x001x0(Two additional types of adsorption isotherms expected for non-wetting adsorbate-adsorbent systems)

VARIOUS ADSORPTION ISOTHERMS :The various types of adsorption isotherms are :(i) Classical Freundlich adsorption isotherm in 1909, Freundlich proposed an empirical equation and was known as Freundlich adsorption isotherm. This equation is as follows:x/m = kp1/n... (i)where x is amount of adsorbate, m is the amount of adsorbent, p is the pressure, k and n are two constantsdepending upon the nature of the adsorbent and adsorbate, and n being less than unity.Equation (i) is applicable to the adsorption of gases on solids.In case of solution, equation (i) takes the formx/m = kc1/n...(ii)where c is the concentration of the solute in gm moles per litre.Equations (i) and (ii) predict the effect of pressure (or concentration) on the adsorption of gases (or solution) atconstant temperature in a quantitative manner.Test of Freundlich's Adsorption Isotherm.Taking logarithms of equations (i) and (ii), we getlog xm= log k + 1nlog p... (iii)and logxm = log k +1nlog c... (iv)If log xm is plotted against log p or log c, a straight line should be obtained as shown in fig. The slope of the linewill give the value of 1nand the intercept on the Y-axis gives the value of log k, i.e.xablog klog Pxmlog}xlog PxmlogIntercept = log kandslope = ba=1nThus by using equations (iii) and (iv), the values of k and n can be calculated from the graph (fig). Analysis of thegraph shows that as p increases xm, also increase and, thus, the Freundlich's equation indicates no limit to thisincrease. But experimental values, when plotted, show some deviations from linearity especially at low pressures.This is seen in fig. If we compare theoretical and experimental curves (fig), the two agree over a certain rangeof pressure only. Thus, Freundlich's equation has a limitation that it is valid over a certain range of pressure only.Limitations of Freundlich's Equation :(1)It is valid over a certain range of pressure only.(2)The constant k and n vary with the temperature.(3)Freundlich adsorption equation is a purely empirical formula without theoretical foundation.

(ii)Langmuir Adsorption Isotherm : It has already been stated that Frenudlich adsorption isotherm holdsgood for a certain range of pressure only. To solve this difficulty, Langmuir (1916) worked out an adsorptionisotherm known as Langmuir's adsorption isotherm The various assumptions are :(a)The adsorbed layer on the solid adsorbent is assumed to be unimolecular in thickness. This view is widelyaccepted for adsorption at low pressure or at moderately high temperature. However, the adsorbedmolecules can hold other gas molecules by van der Waal's forces, so that multimolecular layers arepossible. Such behaviour is apparent only at relatively low temperatures and at pressure approachingthe saturation value. But Langmuir only considered the formation of unimolecular layer while derivingthis relation.(b)The adsorption is taking place on the fixed sites and there is no interaction between the adsorbedmolecules on the surface. One site adsorbs one molecule. When the whole surface is completely coveredby a unimolecular layer of the gas, further adsorption is not possible and indicates a maximum ofsaturation of adsorption.(c)The process of adsorption is a dynamic process which consists of two opposing processes:( i )Condensation Process : It involves the condensation of the molecules of the gas on the surface oftheir solid.(ii)Evaporation Process : It involves evaporation of the molecules of adsorbate from the surface of theadsorbent.When adsorption starts, the whole adsorbent surface remains bare and so the initial rate of condensation ismaximum. As the surface becomes gradually covered, the rate of condensation becomes smaller and smaller.On the contrary, the initial rate of evaporation (desorption) of the condensed molecules is smallest at thebeginning of adsorption, but increases as the surface becomes more and more covered.Ultimately, when the equilibrium is reached, the rate of condensation becomes equal to the rate of evaporation.It means that the number of gas molecules condensing on the given surface is equal to the number of moleculesevaporating away per unit time from the same surface, i.e. the arrangement of the adsorbed molecule on thesurface in unidirectional.(d)Gas behaves ideally.(e) Surface is uniform energetically.Derivation :On the basis of above postulates, Langmuir deduced the equation describing the quantitative relationshipbetween the pressure and the amount of gas adsorbed at constant temperature. Suppose n is the number ofmolecules of the gas striking one square cm of the surface per second. Let be the fraction of the moleculescondensing on the surface. Then n is the total number of molecules which condense on the surface. Thiscondensation is not taking place on the whole surface but it is taking place at only n (1 – ) sq. cm.,where sq.cm. is the fraction of the area already covered by the gas molecules and 1 sq. cm is the total surface area. Rate of condensation of gaseous molecules on the surface= (1 – ) n ... (v)One know that :Rate of evaporation area of surface covered.or Rate of evaporation = kwhere k is the proportionality constant. When equilibrium is set up, the rate of condensation is equal to the rateof evaporation, i.e.k = (1 – ) n ...(vi)ork +  n = n

or =nkn ... (vii)From kinetic theory of gases, it follows that Number of molecules pressure of the gas striking the surfaceorn pn = p... (viii)where is the proportionality constant.Nowknn = kn+ 1... (ix)= kp + 1{From equation (8) p = n}= 11k p+ 1 =111k pk p... (x)Where k = 1k is another constant equation (x) can be written asknn =111k pk p... (xi)or nkn =11k p1k pcomparing equations (vii) and (xi), we obtain =11k p1k p... (xii)If it is supposed that one molecule thick layer of the gas is formed on the surface, thenxm... (xiii)orxm= k2... (xiv)where k is another proportionality constant.2Equation (xiii) implies that amount of gas adsorbed per unit mass of adsorbent is proportional to fraction of thesurface covered. Substituting the value of from equation (xii) into the equation (xiv), we obtainxm =211k k p1k p... (xv)or1x / m= 1211k pk k porpx / m= 121k k+2pk... (xvi)Equation (xvi) is known as Langmuir's adsorption isotherm.A plot of px / magainst p should be a straight line.Another form of equation (xvi) can be obtained by introducing the term V which is equal to the volume ofmadsorbate required to complete a unimolecular layer, i.e, to saturate the surface. The fraction, , of the surfacecovered is then equal to V/V where V is the volume adsorbed at a given pressure p. Hence equation (xii)mbecomes asmVV=11k p1k por pV= 1m1k V+mpV... (xvi A)Equation (xvi A) is another form of the Langmuir equation.

Discussion : Three different cases may arise :Case I : When pressure of the gas is very low, k p is negligible as compared to unity. It implies that , the1fraction covered by adsorption, is quite small. In such a special case, equation (xv) becomes asxm= k k p1 2... (xvii)orxm p... (xviii)Thus, under low pressure, the amount of the gas adsorbed per unit quantity of adsorbent is directly proportionalto the pressure. This has been confirmed by experimental observation.Case II : When pressure is very large, k p becomes larger than unity. In such a special case equation (xv)1becomes as :xm =121k k pk p( k p >> 1) 1orxm= k2... (xix)This equation shows that at high pressure, the amount of adsorbed gas is independent of pressure.Case III : At low pressure, equation (xviii) isxm p or xm = constant × pAt high pressure, equation (xix) is xm = constantTherefore, at moderate pressure, Langmuir adsorption equation becomes asxm = constant × p1/norxm= kp1/n... (xx)Equation (xx) is the Freundlich adsorption equation (i). In equation (xx), 1/n lies between zero and unity. Sometypical shapes of Langmuir's curves are illustrated in figure.v PxAs pressure is increased or temperature is decreased, additional layers are formed. This has let to the modernconcept of multi-molecular adsorption.Test of the Langmuir adsoprtion isothermFrom equation (xvi), we havepx / m=121k k+2pkA plot of px / mversus p should give a straight line. The slope of this is 21kand the intercept on the y-axis gives21k(fig.)p Px/m

In certain cases, the experimental curves are not straight. This may be due to the following reasons:(i)non-uniformity of surfaces.(ii)formation of multiple layers in some cases.(iii)partial adsorption, and(iv)some chemical reaction of the adsorbate with the adsorbent.Successes of the theory :(i)The mechanism of adsorption presented by Langmuir explains chemical adsorption or chemisorption.(ii)Langmuir's theory is more satisfactory than the Feundlich's equation while explaining physical adsorptionof gases on different adsorbent whenever saturation is approached.Limitations : The main limitations are :(i)Langmuir postulated that a saturated value of adsorption is independent of temperature. But experimentshows that it is actually falling off with rising temperatures.(ii)Langmuir assumed that an adsorption film on a plane surface will never be over a molecule thick. Inactual practice, much thicker films have been reported.(iii)This theory cannot explain all the five types of adsorption isotherms.



1 .INTRODUCTIONWhen solution which contain two or more salts in simple molecular proportion are evaporated, crystals of newcompounds separate out.These compounds are called molecular or additon compounds.Ex.K SO + Al (SO ) + 24 H O 2424 32K SO · Al (SO ) 24H O2424 32CuSO + 4NH + H O 432[Cu(NH ) ]SO · H O3 442These addition compounds can be divided into two classes:( a )Those which lose their identity in solutionIn solutions these compounds break down into simpler ions. Such addition compounds which lose their identity insolutions are called double salts .(b)Those which retain their identity in solution.In aqueous solution, these addition compounds do not furnish all simple ions but instead give more complex ionshaving complicated structure .These types of compounds are called complex compounds or co-ordination compounds.Central metal ion Ligandcounter ionCo-ordination sphereML xA2 .LIGANDSAtom/molecule/ ion, which form co-ordinate bond with central metal atom by donating its electron pair knownas ligand. Ligands are electron pair donors so they are Lewis bases.3 .DENTICITYTotal number of lone pair donated by a ligand when it is bonded with metal is called denticity or number of donarsites on a ligand is called denticity.4 .THE FORMATION OF CO-ORDINATION COMPOUNDSIt can be explained by number of theories.(A)Werner's co-ordination theory(B)Sidwick theory or Effective Atomic Number Theory (EAN)(C)Valence bond theory(D)Crystal field theory(A)Werner's co-ordination theory : Werner's co-ordination theory has the first attempt to explain the bonding inco-ordination complex. The main postulates of this theory are:(a)In co-ordination compound metals have two types of valencies :– Primary valency and secondary valency.(b)Primary valencies are normally ionisable and non directional. Secondary valency is normally non ionisableand directional.CO-ORDINATION CHEMISTRY

(c)Every metal has fixed secondary valencies i.e. it has a fixed co-ordination number.(d)Primary linkages (valencies) are satisfied by negative ions while secondary valencies are satisfied by eitherneutral molecules or negative ions. In certain cases, a negative ion may satisfy both type of valencies.P.V. = O.S. of central metal atom.S.V. = Coordination number(B )Sidwick Theory or Effective Atomic Number Concept (EAN)Sidwick proposed effective atomic number theory to explain the stability of the complexes. EAN is definedas the total number of electrons with the metal atoms or ions after gaining electrons from the donoratoms or the ligand. The EAN generally coincides with the atomic number of next inert gas except insome cases.EAN can be calculated by the following relation:EAN = atomic number (Z) of the metal – oxidation state of metal ion + number of electrons gainedby central atom from the donor atoms of the ligands.(C)Valence Bond TheoryThe main features of this theory are -(a)Every metal ion when it forms a complex compound undergoes formation of coordinate covalent bond.(b)During this bond formation, the central metal ion acts as electron pair acceptor. For this the metal ionprovides vacant orbitals.(c)The number of vacant orbitals provided is equal to the coordination number of metal ion.Ex.In the formation of [Fe(NH ) ] , Fe ion provides six vacant orbitals.3 6 3++3In [Cu(NH ) ] , Cu ion provides four vacant orbitals.3 4 2++2(d)The metal provides vacant orbitals only after the process of hybridisation, thus vacant hybrid orbitals areprovided by the metal ion.(e)The vacant hybrid orbitals of metal ion get overlapped by orbitals of ligands containing lone pair ofelectrons.(f)The number of such overlappings is equal to the coordination number of metal ion.(g)The empty 'd' orbitals involved in hybridisation may be inner (n-1)d or outer \"nd\" orbitals and thesecomplexes are called as Inner orbital complexes and Outer orbital complexes respectively.(h)If inner 'd' orbitals are involved in hybridisation, then it is through only the pairing of unpaired electrons inthe 'd' orbitals of metal ion.(i)Then such type of complexes will be diamagnetic or less paramagnetic and will be called as Lowspin complexes.(j)All outer orbital complexes have paramagnetic nature and they are called as High spin complexes.

Some Example : CoordinationHybridisedGeometrical shape ofExamples ofNumberorbitalthe ComplexComplex2spM180°LLinearL3 22[Ag(NH ) ][Ag(CN) ] 3sp2LLL[HgI ]3– 4sp3LLLL109°28'24244423 4[CuCl ][ZnCl ][FeCl ][Ni(CO) ][Zn(NH ) ] 4dsp2LLLL90°90° M90°90°Square plannar242423 423 424[PdCl ][Ni(CN) ][Pt(NH ) ][Cu(NH ) ][PtCl ]The d-orbitalinvolved isdx –y 22 orbital5sp d or dsp33120°90°LMLLLLTrigonal bipyramidalFe(CO)55dsp3LLLLL90°90°35 [Ni(CN) ]6222233232zxyd sp / sp dWhen d orbitalsare(n1)d orbitals(Inner orbital complexes).or sp dW hen d orbitalsare nd orbitals (Outer orbitalcomplexes)In both cases d orbitalsare d and dorbitals90°90°MLLLLOctahedralLL33 63263633 62366[Cr(NH ) ][Ti(H O) ][Fe(CN) ][Co(NH ) ][PtCl ] ,[CoF ]

Drawback of valence bond theory(a)It describes bonding in co-ordination compounds only qualitatively but not account for the relative stabilitiesfor different co-ordination complexes.(b)It does not offer any explanation for optical absorption spectra (coloration) of complexes(c)It does not describe the detailed magnetic properties of co-ordination compounds.( D )Crystal Field Theory : This is a model of electronic structure of transition-metal complexes that considers howthe energies of the d-orbitals of a metal ion are affected by the electric field of the ligand. According to thistheory.(a)The ligands in a transition-metal complex are treated as point charges.(b)A ligand anion becomes simply a point of negative charge. A neutral molecule, with its electron pair thatit donates to the metal atom, is replaced by a negative charge, representing the negative end of themolecular dipole.(c)In the electric field of these negative charges, the five d orbitals of the metal atom no longer have exactlysame energy. Splitting of five degenerate d-orbitals of the metal ion into sets of orbitals having differentenergies is called crystal field splitting.(d)The extent of splitting of metal d-orbitals depends upon the nature and number of ligands surrounding itand the charge on the central metal ion.(e)The extent of splitting of metal d-orbitals determines the magnetic and spectroscopic properties of thecomplexes.5 .STABILITY OF CO-ORDINATION COMPOUNDS IN SOLUTIONThe term stability can be used in a number of different ways.(a)Thermodynamic stability of a complex : It measures the extent to which this complex is formed fromor is transformed into other complex, under certain conditions when the system, has attained equlibrium.(b)The kinetic stability: It referes to the speed with which transformation occurs which leads to theattainment of equilibrium.According to thermodynamic stability, the reaction between a metal ion and the ligands may be considered as aLewis acid base reaction in solution. If the equilibrium constant is high then the complex obtained istheromodynamically stable in solution. The reaction can be written as follows : M + nL [ML ]nThe stability constant K, of the complex [ML ] is given by the relation, K = nnn[ML ][M][L]. The greater the value of K,more stable is the complex.The strength of a complex ion also depends upon –(i)Higher charge of the central metal ion.(ii)Greater base strength of the ligand.(iii)Ring formation (chelation) in structure of complexes.6 .ISOMERISM IN COMPLEXES(a)Compounds which have the same molecular formula, but differ in their properties due to the difference instructure are called as Isomers.(b)Isomerism is commonly considered, to be the characteristic of only organic compounds, it is also found althoughless frequently among inorganic substances.

Classification of isomerismType of isomerismStructural isomerismIonization Hydrate Coordination LinkageLigandStereo isomerismGeometrical OpticalCoordinationpositionNote :General formulaTotal No. of geometrical isomersMabcdef15Ma bcde29Ma b cd226Ma b c22 25Ma bcd34Ma b c323Ma b332Ma bc42Ma b422Ma b5NilMa6NilHere M = central atom. a, b, c, d, e, f = Monodentate ligandsNUMBER OF POSSIBLE ISOMERS FOR SPECIFIC COMPLEXESFormulaNumber of stereoisomersPairs of EnantiomersMa b2 220Ma b3 320Ma bc420Ma bcd351Ma bcde2156Mabcdef3015Ma b c2 2 261Ma b cd2 282Ma b c3 230M(AA)(BC)de105M(AB)(AB)cd115M(AB)(CD)ef2010M(AB)342Note: Uppercase letters represent chelating ligands and lowercase letters represent monodentate ligands.

SOLVED THEORETICAL ILLUSTRATIONINTRODUCTION1 .Why potash alum (K SO .Al (SO ) .24H O) is in the category of double salt ?2424 32Ans.When potash dissolves into water it completely ionise into their constituent ions K , Al , SO++342–.When addition compound which are completely ionises into its constituent ions then it is called double saltso potash alum is in the category of double salt.2 .What type of ions furnishes by potassium ferrocyanide K [Fe(CN) ] dissolve in water ? Is it46a complex compound, if yes then why ?Ans.When potassium ferrocyanide dissolves in water it give two type of ions K & [Fe(CN) ]+6–4K [Fe(CN) ] 462H O–4(aq.)6 (aq.)4K[Fe(CN) ]Yes it is a complex compound because it is not dissociated completely into its contituent ions (K , Fe , CN)++23 .Why K [Fe(CN) ] does not gives the test of CN ion ?46–Ans.When K [Fe(CN) ] potassium ferrocyanide dissolves into water it give two type of ions K & [Fe(CN) ]46+6–4The complex ion [Fe(CN) ] is fairly stable and further dissociation or feebly dissociation is not possible6–4in solution state.Ex. K [Fe(CN) ] 46 4K + [Fe(CN) ]+64– Fe + 6CN (Feebly dissociated)2+–The ferrocyanide ion [Fe(CN) ] is so insignificantly dissociated so that it can be considered as practically64–undissociated and does not give the test of Fe or CN ions2+–DO YOURSELF - I 1.Predict which among the following properties given below belong to double salt and co-ordinationcompounds.( a ) Compounds in which the individual properties of the constituents are usually lost (................).(b) Alum's (................).(c) The blue coloured solution prepared by Cu+2 (aq.) and NH (aq.) (NH OH) does not show the34presense of Cu (................).+2(d) Compounds which are stable in the solid state but break up into its constituents in aqeoussolution (................).(e) Aqueous solution of carnallite (................).(f) The compounds in which central metal ion form dative bonds with species surrounding it(................).(g) Mohrs salt (................).Ans. Hints are given on last page.

IMPORTANT TERMS4 .Define the given terms with respect to complex compounds and represent them by an example ?(i) complex-ion(ii) central metal ion(iii) co-ordination number(iv) ligand(v) co-ordination sphereAns.Cu (HO) Cl26Central metal ion Ligand2Counter ionCo-ordination sphere(i)Complex ion : A complex ion may be defined as an electrically charged radical which is formed bythe combination of a simple cation with one/more neutral molecules or one/more simple anions or insome cases positive group also.(ii)Central ion : The cation to which one or more neutral molecules or anions are attached is called thecentre of co-ordination or central ion. Since, the central ion acts as an acceptor and thus has toaccommodate electron pairs donated by ligands, it must have empty orbitals.(iii)Co-ordination number : The total number of co-ordinate covalent bond form by central metal incomplex called the co-ordination number of the central metal ion .(iv)Ligand : Atom/molecule/ ion, which form co-ordinate bond with central metal atom by donating itselectron pair.(v)Co-ordination sphere : The central atom and the ligands which are directly attached to it areenclosed in square bracket are collectively termed as the co-ordination sphere.5Explain different type of ligands on the basis of denticity and also give example ?Ans.Type of ligands on the basis of denticity :( a )Unidentate ligandsLigands which have only one e donor atom.–X , CN , NO , NH , Pyridine, OH , NO , H O, CO, NO, OH , O , (C H ) P etc.––2–3–3–2––265 3(b)Bidentate ligandsLigands which have two donor atoms and have the ability to link with central metal ion at two positionsare called bidentate ligands. Ex. Symmetrical UnsymmetricalCH 2NH 2CH 2NH 2Ethylenediamine(en)or Ethan-1,2-diamineOOOO C COxalate (ox)2—––OCH CH CH3CAcetyle-acetonate(acac)—–C3ODimethyl glyoxim ion (DMG)—CH C N O3–CH C N OH3NN2, 2'-Dipyridyl (Dipy)NN1, 10-Phenanthroline (O-phen)CH 2NH 2CO –OGlycinato (Gly)—

(c)Tridentate ligandsThe ligands having three donor atoms are called tridentate ligands. Ex.NH 2NH 2HC2CH 2NHHC2CH 2Diethylenetriamine (Dien)NNN2, 2', 2''-Terpyridine (Terpy)(d)Tetradentate ligandsThose ligands possess four donor atoms,Ex. NitriloacetatoCHCOO2–CHCOO2–CHCOO2–NNitriloacetato (nta)3—(e)Pentadentate ligandsThey have five donor atoms.Ex.Ethylenediaminetriacetate ion.CH 2CH 2NNCHCOO2–CHCOO2–HCHCOO2–....(EDTA)–3Ethylenediaminetriacetate ion6 . Define hexadented ligand with explanation ?Ans.Ligand which have six donor atoms.For eg.[Metal with a Hexadented ligand]Ethylenediaminetetraacetate ion (EDTA)–4MO –NNO –CH 2CH 2C OO –O –CH 2C–CH2OCOCH 2CH 2CO

7 .( a )What is chelation?(b)Which type of ligand show chelation and what are they called? give example.Ans.( a )Polydentate ligand when attached with central metal ion forms one or more rings this is known aschelate or chelate ring and the phenomenon is called chelation.(b)Polydentate ligand forms atleast four member rings with central metal ion show chelation. Theseligands are known as chelating ligand.Ex.(i) CH—CH22NH 2NH 2 (ii) 2–24 C O(iii) EDTA4–8 .Why some ligands are called ambidentate ligand? write them.Ans.Ligand which have two doner sites (atoms) but at a time only one site (atom) donates are known as ambidentateligand. They are CNNOSCNCNOS O222NCONOCNSNCOOSOS223Ex.CN can coordinate through either the nitrogen or the carbon atom to a central metal ion.– 9 .What do you mean by flexidentate ligand ?Ans.Ligands which have two or more than two donor sites but sometimes in complex, formation they do notuse all donor sites this type of ligands are called flexidentate ligand.Ex.24 SO, 23 CO.DO YOURSELF - II 1.[Pt(NH ) Cl Br] Cl Now answer the following from above complex.3 32( a )Write the formula of complex sphere ?(b)What is the charge on complex ion ?(c)How many ligands are in complex ?(d)What is the co-ordination number ?(e)What is the oxidation number of central metal ?(f)How many ions are formed on ionisation ?(g)The number of halide ion will be ............(h)Will the aqueous solution of above complex give Cl test ?–(i)Will the above solution give AgBr when treated with AgNO ?3(j)One mole of above complex gives how many moles of AgCl and AgBr when treated withexcess of AgNO ?3(k )Will Pt ion present in aqueous solution or not ?NOTE : Hints are on last page.

NOMENCLATURE1 0 .What are the conventions to write the IUPAC name of co-ordination compounds ?Ans.IUPAC nomenclature of coordination compounds :The main rules of naming of complexes are –(a)Like simple salts, the positive part of the coordination compound is named first.Ex. K [Fe(CN) ] the naming of this complex starts with potassium.46 [Cr(NH ) ]Cl the naming of this complex starts with name of complex ion.3 63(b)Coordination sphere are to be named the ligand first than metal atom or ion(c)The ligands can be neutral, anionic or cationic.(i)The neutral ligands are named as the moleculeEx. C H N pyridine, (C H ) P Triphenyl phosphine, H N — CH —CH —NH ethylene diamine.5565 32222The neutral ligands which are not named as the molecule are CO carbonyl, NO nitrosyl, H O2Aqua, NH ammine.3(ii)Anionic ligands ending with 'ide' are named by replacing the 'ide' with suffix 'O'. Symbol Name as ligandSymbol Name as ligandCl-–Chloro/ChloridoN 3–NitridoBr–Bromo/BromidoO 22–PeroxoCN–CyanoO H2–PerhydroxoO 2–OxoS 2–SulphidoOH –HydroxoNH2–ImidoH –HydridoNH2–AmidoLigands whose names end in 'ite' or 'ate' become 'ito' i.e., by replacing the ending 'e' with 'o' as follows. Symbol Name as ligandSymbol Name as ligandCO32–CarbonatoSO32–SulphitoC O242–OxolatoCH COO3—AcetatoSO42–SulphatoNO2—(bonded through oxygen) nitrito-ONO3–Nitrato(bonded through nitrogen) nitrito-NS O23 –2Thiosulphato(iii)Positive ligands naming ends with 'ium' NH —NH Hydrazinium, NO nitronium, NO23+2+ +nitrosonium(d)If ligands are present more than once, then their repitition is indicated by prefixes like di, tri, tetra etc.However, when the name of the ligand includes a number, Ex. dipyridyl, ethylene diamine, then bis, tris,tetrakis are used in place of di, tri, tetra, etc.(e)If ligand already contains prifix (eg. ethylenediamine) or if it is Polydented ligends the prifixes bis–, tris,tetrakis–, pentakis–, are used instead.Ex. [Pt(en) Cl ]Cl dichlorobis (ethylenediamine) platinum (IV) chloride.222 (f)When more than one type of ligand are present in the complex, then the ligands are named in thealphabetical order.

(g)After naming of ligands the central metal ion is to be named immediately followed by its oxidation statein Roman numbers in brackets. (as per IUPAC)If the central metal comes in anionic complex sphere then the central metal ion is to be named as it is.If the complex provides anionic complex ion then the name of central metal ion ends in 'ate'Ex. (NH ) [CuCl ] Ammonium tetrachlorocuprate(II)4 24(h)After the naming of central metal ion, anion which is in the outer sphere is to be named.The naming of some of the complexes is done as follows – (as per IUPAC)1 1 .Write IUPAC name of following Complex compounds ?(i)K [Fe(CN) ]46 (ii)K [Pt Cl ]26 (iii)[Co (NH ) ] Cl3 6 3(iv)[Cr(H O) Cl ] Cl242 (v)[Pt(NH ) Cl ]3 24 (vi)[Co(NH ) Cl ]3 33 Ans. (i)Potassium hexacyanoferrate(II)(ii)Potassium hexachloroplatinate(IV)(iii)Hexamminecobalt(III) chloride(iv)Tetraaquadichlorochromium(III) chloride(v)Diamminetetrachloroplatinum(IV)(vi)Triamminetrichlorocobalt(III)1 2 .( a ) What are bridging ligands ?(b) How to show bridging ligands in naming, explain with suitable example.Ans.(a)If a complex ion has two or more than two metal atoms then it is termed polynuclear. The ligandwhich connects the two metal ions is called as Bridging ligand or Bridge group.(b)A prefix of Greek letter , is repeated before the name of each different kind of bridging group.OH(HO) Fe24Fe(HO) (SO)244 2NO 2Tetraaquairon(III)-µ-hydroxo-µ-nitrotetraaquairon(III) sulphateDO YOURSELF - III 1.Write IUPAC name of following complex compounds ?(i)K [Co(NO ) ]32 6 (ii)Na [Fe(CN) NO]35(iii)[NiCl4 ]–2(iv)[Ru(NH ) Cl]3 5+2(v)[Fe(en) ]Cl33(vi)[Ni (Gly) ]2

WERNER THEORY1 3 .Deduce the different complex and modern formula for PtCl .nNH where n = 2, 3, 4, 5, 6 also43show the number of ions precipitated when these compounds react with excess of AgNO solution3and also show the number of ions given into aqueous solution ?Ans.ComplexModern formulaNo. of Cl lons precipitated– Total number of ionsPtCl 6NH4 3[Pt(NH ) ]Cl3 6 445PtCl 5NH43[Pt(NH ) Cl]Cl3 5 334PtCl 4NH4 3[Pt(NH ) Cl ]Cl3 4 2223PtCl 3NH4 3[Pt(NH ) Cl ]Cl3 3 3 12PtCl 2NH4 3[Pt(NH ) Cl ]3 2 4 00(non-electrolyte)1 4 .How to draw werner representation of complex compound and represent the following ?(i)Fe(NH ) Cl3 63(ii)Fe(NH ) Cl3 53(iii)Fe(NH ) Cl3 43Ans. Primary valency show by dotted line. P.V. = oxidation state of central metal atomSecondary valency show by solid line (continous line). S.V. = coordination numberLigand which satisfies both secondary and primary valency are attached by solid line with dotted line.(i)Fe(NH ) Cl3 63[Fe(NH ) ]Cl3 63FeClClClNH 3NH 3HN3HN3NH 3HN3P.V. = 3S.V. = 6Both = 0Dotted lines indicate primaryvalency and continuous linesindicate secondary valency of metal ion.(ii)Fe(NH ) Cl3 53[Fe(NH ) Cl]Cl3 52FeClNH 3HN3HN3ClNH S.V. = 63ClHN3P.V. = 3Both = 1In this complex 'Cl' groups act as primaryvalencies and one of the 'Cl' acts as primayas well as secondary valency.(iii)Fe(NH ) Cl3 43FeClNH 3HN3HN3ClHN3ClP.V. = 3S.V. = 6Both = 2[Fe(NH ) Cl ]Cl3 42In this complex 'Cl' groups act as primaryvalency and two of the 'Cl' group act as primaryvalencies as well as secondary valencies.DO YOURSELF - IV 1.Draw werner representation of following complexes ?(i)PtCl .6NH43(ii)PtCl .4NH43(iii)PtCl .2NH23