Chapter 12 Physical Properties of Solutions 12.1 Types of Solutions 12.2 Concentration Units 12.4 The Effect of Temperature on Solubility 12.5 The Effect of Pressure on the Solubility of Gases 12.6 Colligative Properties of Nonelectrolyte Solutions 12.1 Types of Solutions Solution: homogeneous mixture of two or more substances 6 types of solutions are (i) Gas + Gas Gas solution (Air) (ii) Liquid + Liquid Liquid solution (Soda water) (iii) Gas + Solid Solid solution (H2 gas in Palladium) (iv) Liquid + Liquid Liquid solution (Ethanol in Water) (v) Solid + Liquid Liquid solution (NaCl in water) (vi) Solid + Solid Solid solution (Cu / Zn Brass) Saturated solution Unsaturated solution Supersaturated solution Contains the maximum Contains less solute than it Contains more solute than amount of a solute that will has the capacity to dissolve is present in a saturated dissolve in a given solvent solution at a specific temperature Crystallization..the process in which dissolved solute comes out of solution and forms crystal. 12.3 Concentration Units Concentration… The amount of solute present in a given quantity of solvent or solution. (i) Percent by Mass of solute Percent by Mass of solvent massofsolute x100% (massofsolute massofsolvent ) massofsolvent x100% (massofsolute massofsolvent ) mass of solution = (mass of solute + mass of solvent) (ii) Mole Fraction (X A) X A Mole Fraction (XB) molesofA sumofmolesofallcomponents X B molesofB sumofmolesofallcomponents (iii) Molarity (M) M molesofsolute litersofso lution (iv) Molality (m) m molesofsolute massofsolvent (kg) 12.4 The Effect of Temperature on Solubility (a) Solid Solubility and Temperature (b) Gas Solubility and Temperature (a) Solid Solubility and Temperature solubility In most cases solubility of solid substance increases with temperature (g solute/100g H2O) Temperature(‘C) Fractional Crystallization…separation of a mixture of substances into pure components on the basis of their differing solubilities (b) Gas Solubility and Temperature Solubility of gases in water usually decreases with increasing temperature Solubility (g solute/100g H2O) Temperature (‘C) 12.5 The Effect of Pressure on the Solubility of Gases Henry’s Law The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution: cP i.e c = kP (c = molar concentration (mol/L) P = pressure in atm(gas over the solution) k = constant (mol/L.atm) (Ex: soft drink when the cap of the bottle is removed) Before cap is sealed (pressurized with a mixture of air & CO2 ) Example 12.6 .The solubility of nitrogen gas at 25’C and 1 atm is 6.8x10 -4 mol/L.What is the concentration of nitrogen dissolved in water under atmospheric conditions?The partial pressure of nitrogen gas in the atmosphere is 0.78 atm. c (solubility) = 6.8 x 10 -4 mol/L p (partial pressure) = 0.78 atm Apply Henry’s Law equation c = kp and find constant k = 6.8 x10 -4 mol/L.atm Then find the solubility of nitrogen gas in water where c = (6.8 x 10 -4 mol/L.atm)(0.78 atm) = 5.3 x 10 -4 M (ANSWER) 12.6 Colligative properties of Nonelectrolyte Solutions Colligative properties..properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Types of colligative properties are.. (i) Vapor-Pressure Lowering (ii) Boling-Point Elevation (iii) Freezing-Point Depression (iv) Osmotic Pressure (i) Vapor-Pressure Lowering Case (i) The vapor pressure of solution with nonvolatile solute (no measureable vapor pressure) is always less than that of pure solvent. Raoult’s Law The partial pressure of a solvent over a solution (P1) is equal to the vapor pressure of the pure solvent ( P10) times the mole fraction of the solvent in te solution X1. P1 = X1 . P10 Ref: mole fraction…X1 = 1- X2 (X2 = mole fraction of the solute) P1 = (1 – X2) P10 P1 = P10 – X2 P10 P10 – P1 = ∆ P = X2P10 THEREFORE DECREASE IN THE VAPOR PRESSURE ∆ P, IS DIRECTLY PROPORTIONAL TO THE SOLUTE CONCENTRATION (MEASURED IN MOLE FRACTION) Example 12.7 Explain Question..Why is the vapor pressure of a solution less than that of the pure solvent? Vaporization increases the disorder of a system because molecules in a vapor have less order than those in a liquid. Solution is more disordered than a pure solvent due to that reason difference in disorder between a solution and a vapor is less than that between a pure solvent and a vapor. Therefore solvent molecules have less tendency to leave a solution than to leave the pure solvent to become vapor. That is the reason the vapor pressure of a solution is less than that of the solvent. Case (ii) If both components of solution are volatile (measurable vapor pressure), the vapor pressure of the solution is the sum of the individual partial pressures. Raoult’s Law can be expressed as… PA = XA PA0 PB = XB PB0 PT = PA + PB THEREFORE PT = XAPA0 + XBPB0 Ideal solution..Any solution that obeys Raoult’s law and the heat of solution ∆ Hsoln = 0 (ii) & (iii) Boiling – Point Elevation & Freezing –Point Depression Boiling Point…of a solution is the temperature at which its vapor pressure equals the external atmospheric pressure. ∆Tb = Tb – Tb0 (+ quantity) ∆Tb = Kbm / / ∆Tf = Tf0 – Tf (+ quantity) ∆Tf = Kfm Kb & Kf = molal boiling –point elevation constant (or) molal freezing-point depression constant (‘C /m) m = molality (mol/kg of solvent) (iii) Osmotic pressure (∏) Osmosis…phenomenon which allows free passage of solvent molecules to pass through a porous membrane from a dilute solution to a more concentrated one. Semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules. Osmotic pressure…( ∏ ) the pressure required to stop osmosis. ∏ = MRT ( M = molarity of the solution mol/L)