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Chapter 2 Solutions, , Solution is @ homogeneous mixture of two or more substances in sare or different physical, phases. The substances forming the solution are called components of the solution. On the basis of, number of components a solution of two components Is called binary solution., , Solute and Solvent, In a binary solution, solvent is the component which is present in large quantity while the other, component is known as solute., Classification of Solutions, , {A) Following types of solutions are seen on the basis of physical state of solute and salvent., , , , , , 1 Salle Satin Alioys, 2. Laud ‘Solid bydrated sats. insane, a Gas Solid Dissolved gases in mineral ‘, Liquid sotons ', 4 Satie ciquid——-Saltsugar soluton in water, 5 Liqud Liaw eohot an ater, 6 Gas ‘Liquid ated mks, In yale, Gaseous solutions ~ - NK 1h Yh, 4 Solid Gas Iodine vapeur av, 8 us |sas Water vapour In ai, 9 Gas Gas Ait (0, + Np), , [if water is used as 2 solvent, thé solution is called aqueous solution and if not, the solution is, called non-aqueous solution], {B) Deperiding upon the amount of solute dissolved in a solvent we have the following types of, solutions:, (i) Unsaturated solution A, solution in which more solute can be dissolved without raising temperature Is called an, unsaturated solution., (ii) Saturated solution A, solution in which no solute can be dissolved further at a given temperature Is called a saturated, solution., ji) Supersaturated solution A, , , , solution which contains more solute than that would be necessary to saturate it at a gi, , , , temperature Is called @ supersaturated solution,, Solubility, , ‘The maximum amount of a solute that can be dissolved in a given amount of solvent (generally, 100 g) at a given temperature Is termed as its solubility at that temperature,, The solubility cf a solute in a liquid depends upon the following factors:, (i) Nature of the solute, (ii) Nature of the solvent, (il) Temperature of the solution, (iv) Pressure (In case of gases), , Henry's Law, , Scanned with Cases

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The most commonly used form of Henry"s faw states “the partial pressure (P) of the gas in vapour, phase is proportional to the mole fraction (x) of the gas in the solution” and is expressed as, paky.x, , Greater the value of Kj. higher the solubility of the gas. The value of Ky decreases with Increase in, the temperature. Thus, aquatic species are more comfortable in cold water [more dissolved Op], , rather than Warm water., , , , , , Applications, 1. In manufacture of sott drinks and soda water, CG is passed at high pressure to increas, solubliity., , 2. To minimise the painful effects (bends) accompanying the decompression of deap sea divers., , Oxdiluted with less soluble, He gas is used as breathing gas., 3. At high altitudes, the partial pressure of Oz is less then that at the ground level. This leads to low, concentrations of O» in the blood of climbers which causes ,anoxia®, Concentration of Solutions, The concentration of a solution is defined as the relative amount of solute present in a solution. On, the basis of concentration of solution there are two types of solutions., (i) Dijute solution, (i) Concentrated solution, Methods of Expressing Concentration of Solutions, Various expression for the concentrations of solutions can be summarised as, () Percentage by weight, (w J w %) It Is defined as the amount of solute present in 100 g of solution., w/w % = weight of solute / weight of solution +100, Percentage by volume, , , , (w/ V%) Itis defined as the weight 01 solute presentin 100 mt of solution,, w/V % = weight of Solute / weight cf solution * 100, or the volume of solute present In 100 mL of solution., u/V % = Volume of Solute / volume of solution * 100, ) Male fraction, , (x) It is defined as the ratio of the number of moles of a component to the total number of moles of, , , , all the components. For a binary solution, if the number of moles of A and B are ng and rg, respectively, the mole fraction of A will be, oa, na tng, Similarly, tee —"B— > ta ttp=1, . . na trp, (iv) Parts per mittion, (ppm) Itis defined as the parts of a component per million parts (10°) of the solution. Itis widely, used when a solute is present in trace quantities., ppm = number of parts of the component / total rumber of parts of all the components * 108 (v), Molarity (M) itis the number of moles of solute present in 1L(ém3) of the solution., , M-= number of moies of solute / volume of solution (L), , M-= mass of salute (in gram) * 1000 / mol. wt. of solute x volume of solution (in mL), Molarity varies with temperature due to change in volume of solution., , [When molarity of a solution is 1M, itis called a motar solution. 0.1 M solution is called a, decimolar solution while 0.5 M solution is known as semi molar solution], , Molarity = Percent by mass * density * 10 / molecular weight, , Dilution fav, My Va = Mz V2 (for dilution from volume Vy to V2), , For reaction between two reactants, My V; /1n1 = Mz V2 / np where, ny and np arc stoichiometric, coefficient in balanced equation., , (vi) Molality (m) It is the number of moles of solute per kilogram of the solvent., , Molallty = mass of solute in gram * 1000 / mol. wt. of solute * mass of solvent (in 9), Molality is independent of temperature., , [When solvent used is water, a molar (1 M) solution is more concentrated than a molal (2M), solution.J, , (vii) Normality (N) The number of gram equivalents of solute present in 1 L of solution., Normality = number of grams - equivalent of solute / volume of solution in L, , Number of gram-equivelents of solute = mass of solute in gram / equivalent weight, [Relationship between normality and molarity N x Eq. weight = M x mol. weight ], , If two solutions of the same solute having volumes and molarities 4, My and V2, Mz are mixed,, , the molarity of the resulting solution is, , Scanned with Cases

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Vp +Vo, Similarly, Normality (N) =< NM ¥2Vo, Vi+Ve, , To dilute V) mL of a solution having molarity M to molarity Mz up to the final volume Vp mL, the, , volume of water adde, , , , Similarly, mW =(MEXa) Y, ,, , , , (viii) Formality (F) itis the number of formula weights of solute present per litre of the solution., Formality = moles of substance added to solution / volume of solution (in L)), (ix) Mass fraction Mass fraction of any component in the solution Is the mass of that component, divided by the total mass of the solution., Molallty, mole fraction and mass fraction are preferred over molarity, normality, etc., because, former involve weights which da not change with temperature., (x) Demal (0) It represents one mole of solute present in 1L of solution at OC., , Raoult’s Law, The Raoult"s law states “For a solution of two volatile liquids, the vapour pressure of each liquid in, the solution is less than the respective vapour pressure of the pure liquids and the equilibrium, partial vapour pressure of the liquid Is directly proportional to its mole fraction., For a solution contai, , , , ids A and B, the partial vapour pressure of liquid Ais, Pa=ta OF PAs hyy, , n, 5 ee, where, 14 =———4— = mole fraction of liquid A, (ng + Np), The proportionality constant is obtained by considering the pure liquid whenya= 1 then k = P*a,, , the vapour pressure of pure liquid, hence, , Pa PA Xa, , similarly, Pa = Pate, , ‘The total vapour pressure of the solution,, Pr = Pa + Pp = PA Xa + Pata, , = PA +(P5- PadXe, Konowaloff Rule, , , , At any fixed temperature, the vapour phase is always, , , , icher in the more volatile component as, compared to the solution phase. In other words, mole fraction of the more volatile component is, always greater in the vapour phase than In the solution phase., The composition of vapour phase in equilibrium with the solution is determined by the partial, pressure of components. If Y; and Y2 are the, component 1 and 2 respectively in the vapour phase then. using Dalton"s jaw of partial pressure,, pl =yl* total, p2 = y2*Ftotal, , Ideal Solutions, Those solutions in which solute-solute (B-B) and solvent-solvent (A-A) interactions are almost, similar to solvent solute (A-B) interactions are called ideal solutions. These solutions satisfy the, following conditions :, , , , , , =1, foro, , , , (i) Solution must obey Raoult"s faw, Le,,, , Pa = PALA» Pa= PaXe, , (ii) Hmix = 0 (No energy evolved or absorbed), , Scanned with Cases

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)) AVmix = 0 (No expansian or contraction on mixing), Some solutions behave like nearly ideal solutions, e.g., benzene + toluene, n-hexane + nheptane,, ethyl iodide + ethyl bromide, chlorobenzene + bromobenczene., , Non-ideal Solutions, Those solutions which shows deviation from Raouit*s law is called non-ideal solution., For such solutions,, Amix # 0, AVmix * 0, , (a) Non-ideal solutions showing positive deviation, In such a case, the A - B interactions are weaker than A - Aor B - B interactions and the observed, vapour pressure of each component and the total vapour pressure are greater than that predicted, by Raoult”s law., , Pa > Pa%a» Pa> Poke, Prat > Paka + Pike, , For such solutions, , AH niz> 0, AV: > 0, , , , Xa=1 Mole fraction a=0, yo=0 21, , Examples : Ethanol + water, CS, + 2cotone, CCl, + CHty, CC, +CH,CH,. ethanal + cyelohexane. CCL + CHC. if, , (b) Non-ideal solution showing negative deviation, , In such a case, the A - B interactions are stronger than A - A or 8 - B interactions and the observed, vapour pressure of each component and the total vapour pressure are lesser than that predicted, by Raoult"s taw., , Pa < PaXa» Pa< PaXE, , Protat < PAXA + PBXB, For such solutions,, , AH gig <0, AVeriz< 0, , , , 2421 -Mole fraction 14 50, 1=0 a=, Non-ideal solution showing negative deviation, , Examples : CHCI, +CH,COCH,,CHCI, +C,H,, H,O+ HCl,, H,0+HNO,, methanol + acetic acid., Azeotropic Mixture, A mixture of two liquids which bolls at a particular temperature lke 2 pure liquid and distils over in, the same composition is known as constant boiling mixtures. These are formed by nonideal, solutions., () Minimum boiling azeotropes, , , , are formed by those liquid pairs which show positive deviation from ideal behaviour. Such, , azeotropes have boiling points lower than either of the components, e.g., CZHSOH (95.57%) +, , , , Scanned with Cases

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H20 (4.43%)(by mass}., Gi) Maximum boiling azeotropes, are formed by those liquid pain; which show negative deviation from ideal behaviour. Such, azeotropes have boiling points higher than either of the components. e.9., H20(20.220%)+ HCI, (79.78%] by mass., Colligative Properties, , , , IColligatille : from Latin. = Co mean .together’; ligare means .to bind” ], Colligative properties are those properties which depends only upon the number of solute particies, In a solution irrespective of their nature., , Relative Lowering of Vapour Pressure, tis the ratio of lowering in vapour pressure to vapour pressure of pure solvent. The relative, , lowering in vapour pressure of solution containing a nonvolatile solute is equal to the mole fraction, , of solute in the solution., , PA- Pay,, PA, o " ., where, PAPA ~ relative lowering of vapiuir pressure, , PA, , Pi-Py __ Np, ph nating, , for dilute solutions, ng<<n,. Hence,, , PAR Pa _ Mp, PMA, or Pat Pa Wax Ma, pa My xW,, My = "2 xM,x—24—, UZ) (Di - Pa), , Above expressian is used to find the molecular weight of an unknown solute dissolved in 2 given, , solvent. Where, We and Wa = mass of Solute and solvent respectively. Mz and Ma = molecular, , weight of solute and solvent respectively., , Ostwald and Walker method Is used to determine the relative lowering of vapour pressure., Elevation in Boiling Point (ATp), , Boiling point of a liquid is the temperature at which its vapour pressure becomes equal to the, , atmospheric pressure. As the vapour pressure of a solution containing a nonvolatile solute is lower, , than that of the pure solvent, it boiling point will be higher than that of the pure solvent as shown, , in figure. The increase in bolling point is known as elevation in bolting point, AT,, , , , , , , , iatm, , g, , 3, , R, , g, , &, , 3, a ! ATgt, > no, Ty oT), , Temperature —>, ATb = Th ~ T*p ATp = Kp m (where; m = molality), Kp is molal elevation constant or ebullioscopic constant. Molecular mass of solute can be, , calculated as, , Ky: Wz 1000, gl RIO, at, Max Wa, =x, Mp, 1000, Ma= Ky * an,, , where, Wg and Wa = mass of solute and solvent respectively., , Kp has uni, , , , of K/ mor K kg mot, for water, K, = 0.52 K kg mot?, The boiling point elevation of a solution is determined by, (i) Landsberger*s method, , ) Cottrell"s method, , Nenraccian in Fraazina Dnint (ATA, , Scanned with Cases