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SOLUTIONS AND THEIR PHYSICAL PROPERTIES

SOLUTIONS AND THEIR PHYSICAL PROPERTIES. TYPES OF SOLUTIONS. Solution : A homogenous mixture whos properties are uniform and which contains two or more substances that can be varied

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SOLUTIONS AND THEIR PHYSICAL PROPERTIES

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  1. SOLUTIONS AND THEIR PHYSICAL PROPERTIES

  2. TYPES OF SOLUTIONS Solution: A homogenous mixture whos properties are uniform and which contains two or more substances that can be varied Solvent:The component that is present in the greatest quantity or that determines the state of matter in which the solution exists. Solute:A solution component that is present in a solution in lesser quantity than the solvent. Concentrated solution: Solutions containing a relatively high concentrations of solute. Diluted solution:Solution containing a relatively low concentrations of solute. Solubility: The max. amount of the solute that will dissolve in a definite amount of the solvent and produce a stable system at a specified temperature Saturated solution: When dissolving and precipitation occur at the same rate, the quantity of dissolved solute remains constant with time and the solution is said to be saturated. Supersaturated solution: The solution in which the concentration of solute is higher than that of a saturated solution. Alloy: Solid solutions with a metal as the solvent ; e.g. brass (Cu-Zn), solder (Sn-Pb)

  3. Some Common Solutions

  4. Mass percentage % (m/m) = msolute/msolution If we dissolve 5,00 g NaCl, in 95 g water , we get 100 g of a solution that is % 5,00 NaCl . % Volume (V/V) = Vsolute/Vsolution 25,0 mL methyl alcohol and 75,0 mL water is an antifreeze solution that is % 25,0 CH3OH by volume. Mass/Volume % (m/V) = msolute/Vsolution An aqueous solution with 0,9 g NaCl in 100 mL of solution is said to be % 0,9 (mass/volume). Solution Concentration A measure of the quantity of the solute present in a given quantity of solvent is called concentration . Concentration can be explained in many ways using expressions such as saturated, unsaturated, supersaturated, diluted or concentrated solution. Besides, it can be expressed also with some terms of quantity such as, molarity, ppt, ppm ve ppb, molality, normality. In addition, some other definition such as mole fraction, mole percentage can be used. Mass Percent, Volume Percent, and Mass/Volume Percent

  5. Mole Fraction and Mole Percent Amount of component (in moles) Mol fraction Total amount of all solution components( in moles) Mole percent Molarity ve Molality Amount of solute (in moles) Molarity Volume of solution (L) Amount of solute (in moles) Molality Mass of solvent ( Kg ) Solution Concentration

  6. Illustrative Examples a) b) The concentration of a solution in different units: An ethanol-water solution is prepared by dissolving 10,00 mL of C2H5OH (d=0,789 g/mL) in a sufficient volume of water to produce 100 mL of a solution with a density 0,982 g/mL. What is the concentration of ethanol in this solution as (a) volume percent (b) mass percent (c) Mass/Volume percent (d) mole fraction(e) mole percent(f) molarity(g) molality?

  7. Illustrative Examples c) d) Convert the mass of ethanol from part b) to an amount in moles Mole Fraction of Ethanol If 100,0 mL solution weighs 98,2 g ; 98,2 - 7,89 = 90,3gwater.

  8. e) Mole Percent of Ethanol = f) g) “Molality of Ethanol” m: molality (mol/kg) SOLUTION CONCENTRATION

  9. INTERMOLECULAR FORCES AND THE SOLUTION PROCESS II. aşama III. aşama I. aşama In this section we focus on the behaviour of molecules in solution, specifically on intermolecular forces Enthalpy ΔHsoln= 0 Pure solvent seperated solvent molecules ΔHa >0 Pure solute seperated solute molecules ΔHb >0 Seperated solvent and solid molecules solution ΔHc <0 ΔHsoln= ΔHa+ ΔHb + ΔHc

  10. INTERMOLECULAR FORCES IN MIXTURES ThevaluesΔHa, ΔHb, and ΔHcdepend on thestrengths of intermolecularforces of attraction Ifallintermolecularforces of attractionare of aboutequalstrength, a random of intermingling of moleculesoccurs. A homogenousmixtureorsolutionresultsandthis is called as ideal solutions. ΔHa + ΔHb ~-ΔHcΔHsoln ~ 0, Intermolecular forces between: ΔHa = solvent molecules A ΔHb = solute molecules B , ΔHc = solvent molecules A and solute molecules B (A-B)

  11. IDEAL SOLUTIONS Substances with similar molecular structures have similar intermolecular forces of attraction. Example: The solution of the liquid hydrocarbons (Benzene- Toluene mixture). ΔHsoln ~ 0 .

  12. NONIDEAL SOLUTIONS • If forces of attraction between same molecules, A-A or B-B (molecules between solvent or solute),are SMALLER, than forces of attraction of unlike molecules A-B, (forces between solute and solvent), a solution is formed but its properties can not be predicted. These are identified as non-ideal solutions. Interactions between solute and solvent(ΔHc) release more heat than the heat absorbed to seperate the solvent and solute molecules (ΔHa + ΔHb). The work of solubility is an exothermic reaction (ΔHsoln < 0). A-A < A-B OR B-B < A-B CHCl3 Chloroform -- (CH3)2CO Acetone

  13. NONIDEAL SOLUTIONS • If forces of attraction between same molecules, A-A or B-B (molecules between solvent or solute),are ONLY A LITTLE GREATER, than forces of attraction of unlike molecules A-B, (forces between solute and solvent), a NON-IDEAL solution is formed as a complete mixture. The solution has a higher enthalpy(ΔHc) than the pure componentsΔHa+ ΔHb); so the solution process is endothermic(ΔHsoln > 0). A-A > A-B veya B-B > A-B (CH3)2CO Acetone ----- CS2 Carbon disulfide(Polar-Non polar solution)

  14. NONIDEAL SOLUTIONS • If forces of attraction between same molecules, A-A or B-B (molecules between solvent or solute),are MUCH GREATER, than forces of attraction of unlike molecules A-B, (forces between solute and solvent), dissolving does not occur to any siginificant extent. The components remain segregated in a heterogenous mixture. In a mixture of water and octane( a constituent of gasoline) strong hydrogen bonds hold water molecules together in clusters. The non-polar octane molecules are not able to exert a strong attractive force on the water molecules, and two liquids do not mix. A-A >> A-B or B-B >> A-B Water molecules Strong H bonds Octane molecules

  15. IONIC SOLUTIONS KCl(s) K+(g) + Cl-(g) ΔH1=(- lattice energy of KCl)=701,2 kJ K+(g) + Cl-(g) K+(aq) + Cl-(aq) ΔH2= - 684,1 kJ ΔHf= ΔH1 + ΔH2= 17,1 kJ • If the ion-dipole forces of attraction are strong enough to overcome the interionic forces of attraction in the crystal, dissolving will occur. An ion surrounded by a cluster of water molecules is said to be hydrated.

  16. SOLUTION FORMATION AND EQUILIBRIUM • When the solute and the solvent are mixed up; • a) First dissolving occur, • b) Then precipitation starts and increases with time • c) After a while the dissociation and precipitation rates become equal.The quantity of dissolved solid remains constant with time a)Diluted b)Concentrated c)Saturated • These solutions are called as saturated solutions • The concentration of the saturated solution is called the solubility of the solute in the given solvent . It can be expressed as Molarity or Mass Percent • Solubility varies with temperature.

  17. SOLUTION FORMATION AND EQUILIBRIUM • If in preparing a solution we start with less solute than would be present in the saturated solution, the solution is unsaturated. • The precipitation occurs when a saturated solution is cooled. • Occasionally all the solute may remain in the solution(as at that temperature the solvent dissolves a greater amount of solute than that in the saturated solution) We identify these solutions as supersaturated solutions. • KNO3 dissolves in 100 g water and 30oC at an amount of ~32g .This solution is saturated. At the same temp., if 30g KNO3 are dissolved, it is unsaturated, 35g KNO3 are dissolved, it is supersaturated. Solubility Curve for various substances

  18. SOLUTION FORMATION AND EQUILIBRIUM • Thesolubilities of ionicsubstancesincreasewithincreasingtemperatureExceptionstothisgeneralizationare:SO32-, SO42-, SeO42-, AsO43-, PO43-. • WhenHsoln > 0, raisingthetemperatureincreasesthesolubility. • When, Hsoln < 0, thesolubilitydecreaseswithincreasingtemperature. • We prepare a concentrated solution at a high temperature. Then we let the solution cool. At lower temperatures the solution becomes saturated in the desired compound. The excess compound crystallizes from solution and the impurities remain in solution. This method of purifying a solid called fractional crystallisation.

  19. SOLUBILITY OF GASES Solubility: The amount of gas which is able to dissolve at 0oC and 1 atm pressure in 1 L water. • Effect of Temperature In a gas, the molecules are much farther apart than they will be in the solution(solid-liquid mixtures). Hence, the gas must condense to a liquid before it dissolves in another liquid. Condensation is an exothermic reaction and “The solubilities of gases decrease with increased temperature”. Ex: Beverages which contain CO2 are consumed cold. Fish require cold water since there is not enough dissolved air(oxygen) in hot water • Effect of Pressure The solubility of a gas increases as the gas pressure is increased.This is called Henry’s law. C = solubility of gas mL/L k = proportionality constant If the gas pressure increases, the solubility rises Henry’s Law fails for gases at high pressures and it also fails if the gas ionizes in water or reacts with water. We only expect Henry’s law to apply to equilibrium between molecules of a gas and the same molecules in solution

  20. SOLUBILITY OF GASES Example: At 0oC and 1 atm pressure N2 gas has the solubility of 23,54 mL N2/L. in order to reach a solubility of 100,0 mL N2 per liter, what pressure must be exerted at 0oC? Example: At 0oC and O2 pressure of 1,00 atm, the aqueous solubility of O2(g) is 48,9 mL O2/L. What is the molarity of O2 in a saturated water solution when the O2 is under its normal partial pressure in air (0,2095 atm)? Molarity of O2 at 0oC and 1 atm

  21. Fractional Distillation Raoult’s Law: VAPOR PRESSURES OF SOLUTIONS We find the vapor pressures of solutions to be important when we want devise a method of seperating volatile liquid mixtures by distillation. Also, boiling point and osmotic pressure play an important role in the fractional distillation. In 1880, the French chemist Raoult found that a dissolved solid lowers the vapor pressure of the solvent. The partial pressure exerted by solvent vapor above an ideal solution, PA, is the vapor pressure of the pure solvent at the given temperature PAo, multiplied by the mole fraction of the solvent in the solution, XA

  22. Composition of solution Composition of vapor VAPOR PRESSURES OF SOLUTIONS Predicting Vapor Pressures of Ideal Solutions: The vapor pressures of pure benzene and toluene at 25 oC are 95,1 ve 28,4 mmHg. A solution is prepared in which the mole fractions of benzene and toluene are both 0,500. What are the partial pressures of benzene and toluene in this solution? What is the total pressure? What is the composition of the vapor of benzene-toluene at equilibrium ?

  23. LIQUID-VAPOR EQUILIBRIUM: IDEAL SOLUTIONS Composition of Solution Comp. of Vapor Comp. of Vapor The line combining the 3 - 4 points is called “tie line”. The vapor ends of these ties lines can be joined by the green curve. From the relative placement of the liquid-vapor curves we see for ideal solutions of two components, the vapor phase is richer in the more volatile component than is the liquid phase. When this solution is again vaporized; The process of re-vaporisation and condensation can be continiued. This is called fractional distillation.

  24. LIQUID- VAPOR EQUILIBRIUM:NONIDEAL SOLUTIONS In nonideal solutions, if the departures from ideal solution behaviour are sufficiently great, certain solutions may vaporize to produce a vapor that has the same composition as the liquid. These solutions, called azeotropes boil at a constant temperature and because the liquid and vapor have the same composition, they can not be seperated by fractional distillation LIQUID-VAPOR CURVES IN AZEOTROPE MIXTURES Propanol-Water Azeotrope Mixture contains 71,69% propanol and 28,31% water. Ethyl alcohol-water azetrope mixture has the boling point of 78,2˚C with the composition 95.6% ethyl alc. and 4.4% water

  25. Freezing point depression Boiling point elevation Freezing Point Depression and Boiling Point Elevation of Nonelectrolyte Solutions The properties such as Vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure whose values depend only on the concentration of solute particles in solution and not on what the solute is, are calledcolligative properties. Pressure ΔTFP ΔTBP fp fp0 bp0 bp Temperature

  26. Freezing Point Depression and Boiling Point Elevation of Nonelectrolyte Solutions Establishing a molecular formula with freezing point data:Nicotine, extracted from tobacco leaves, is a liquid completely miscible with water at temperatures below 60 oC . (a)What is the molality of nicotine in an aqueous solution that starts to freeze at -0,450 oC ? (b) If the solution is obtained by dissolving 1,921 g of nicotine in 48,92 g of water, what must be the molar mass of nicotine? KFP=1,86 oC/m a) b)

  27. OSMOTIC PRESSURE An aqueous sucrose(sugar) solution in a long glass tube is seperated from pure water by a semipermeable membrane(permeable to water only). Water molecules can pass through the membrane in either direction. But because the concentration of water molecules is greater in the pure water than in the solution, there is a net flow from the pure water into the solution. This net flow called osmosis, causes the solution to rise up the tube. Applying a pressure to the sucrose solution slows down the net flow of water into the solution. The necesssary pressure to stop osmotic flow is called the osmotic pressure and represented by the symbol p. This pressure is 15 atm for a 20% sucrose solution. Osmotic pressure is a colligative property because its magnitude depends only on the number of solute particles per unit volume of solution Osmotic Pressure (p) R(gas constant) = 0,08206 L atm/(mol K) c = Molarity of the solution

  28. OSMOTIC PRESSURE Calculating osmotic pressure: What is the osmotic pressure at 25 oC of an aqueous solution that is 0,0010 M C12H22O11 (sucrose)? Establishing a molar mass from a measurement of osmotic pressure:A 50,00 mL sample of an aqueous solution is prepared containing 1,08 g. of a blood plasma protein, human serum albumin. The solution has an osmotic pressure of 5,85 mmHg at 298 K. What is the molar mass of the albumin?

  29. Freezing Point Depression and Boiling Point Elevation of Electrolyte Solutions Some solutes produce a greater effect on colligative properties. For example consider a 0,0100 m aqueous solution. The predicted freezing point depression of this solution is If the 0,0100 m solution is urea, the measured freezing point is just -0,0186, if the solution is 0,0100 m NaCl (electrolyte), the measured freezing point is -0,0361. The ratio of the measured value of a colligative property to the expected value, if the solute were electrolyte is calledVan’t Hoff factor (i) . Van’t Hoff factor Equations of Colligative Properties for some electrolytes For a non-electrolyte i = 1 NaCl i = 2 MgCl2 i = 3

  30. Freezing Point Depression and Boiling Point Elevation of Nonelectrolyte Solutions Predicting Colligative Properties for electrolyte solutions: Predict the freezing point of aqueous 0,00145 m MgCl2 . KFP = 1,86 oC/m MgCl2(aq) Mg2+(aq) + 2Cl-(aq) Van’t Hoff factor, i = 3

  31. REVERSE OSMOSIS-DESALINATION In this case, the membran is only permeable for the water molecules. Under normal conditions in the event of OSMOSIS , there is a net flow from the pure water to the salty water. When a pressure is applied on side B (P> Pos), a net flow of water from salty water to the pure water occurs. This is called REVERSE OSMOSIS . By means of DESALINATION, pure water can be obtained from seawater and other waste water can be reused by this way .

  32. Practical Applications -FP lowering Salt can be used to deice roads. Automobile antifreeze ethylene glycol (C2H4(OH)2)

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