สมบัติของสารละลาย (Colligative properties) ว30231 ปริมาณสัมพันธ์ สถานะของสาร และเคมีไฟฟ้า สมบัติของสารละลาย (Colligative properties) นายศราวุทธ แสงอุไร ครูวิชาการสาขาเคมี โรงเรียนมหิดลวิทยานุสรณ์ วันที่ 13 พฤศจิกายน 2552 Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

สมบัติของสารละลาย (Colligative properties) Vapor and osmotic pressures, bp, and mp are colligative properties Depend on relative of solute and solvent particles Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

For Examples: Vapor Pressure Reduction Freezing Point Depression Related to boiling point Freezing Point Depression Salt on the road Anti-freeze in your radiator Boiling Point Elevation Osmotic Pressure Membrane diffusion The Great Sugar Fountain! Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Vapor pressure of soln lower than pure solvent vapor pressure Remember: Equilibrium vapor pressure Pressure of vapor when liq and vapor in equilibrium at specific temp Vapor pressure of soln lower than pure solvent vapor pressure Vapor pressure of solvent  relative # of solvent molecules in soln i.e., solvent vapor pressure  solvent mole fraction Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Vapor Pressure At equilibrium, the rate of evaporation (liquid to gas) equals the rate of condensation (gas to liquid). The amount of gas is the “vapor pressure” P T = K P = atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Vapor Pressure At equilibrium, the rate of evaporation (liquid to gas) equals the rate of condensation (gas to liquid). The amount of gas is the “vapor pressure” P T = K P = atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Vapor Pressure At equilibrium, the rate of evaporation (liquid to gas) equals the rate of condensation (gas to liquid). The amount of gas is the “vapor pressure” P T = K P = atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Vapor pressure of solvent (Psolvent) = 75% of P°solvent Raoult’s Law Psolution = Xsolvent  P°solvent So if 75% of molecules in soln are solvent molecules (0.75 = Xsolvent) Vapor pressure of solvent (Psolvent) = 75% of P°solvent Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Colligative Properties of Nonelectrolyte Solutions P1 = X1 P 1 P 1 = vapor pressure of pure solvent X1 = mole fraction of the solvent Raoult’s law If the solution contains only one solute: X1 = 1 – X2 X2 = mole fraction of the solute P 1 - P1 = DP = X2 Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

PA = XA P A Ideal Solution PB = XB P B PT = PA + PB PT = XA P A Ideal Solution PB = XB P B PT = PA + PB PT = XA P A + XB P B Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

< & > & PT is greater than predicted by Raoults’s law PT is less than predicted by Raoults’s law Force A-B A-A B-B < & Force A-B A-A B-B > & Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Calculate the vapor pressure of acetone above the resulting solution. Problem The vapor pressure of pure acetone (CH3COCH3) at 30°C is 0.3270 atm. Suppose 15.0 g of benzophenone, C13H10O (MW = 182.217 g/mol), is dissolved in 50.0 g of acetone (MW = 58.09 g/mol). Calculate the vapor pressure of acetone above the resulting solution. Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Solution Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Determine the molecular formula of rhombic sulfur. Problem The vapor pressure of pure liquid CS2 is 0.3914 atm at 20°C. When 40.0 g of rhombic sulfur (a naturally occurring form of sulfur) is dissolved in 1.00 kg of CS2, the vapor pressure falls to 0.3868 atm. Determine the molecular formula of rhombic sulfur. Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Boiling Pt. Elevation Freezing Pt. Depression ΔTb = T boiling, solution – T boiling, pure solvent = Kb m ΔTf = T freezing, solution – T freezing, pure solvent = - Kf m m = molality of the solution Kb = boiling constant Kf = cryoscopic constant Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Freezing is a dynamic equilibrium between melting and freezing. P T = K P = atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Freezing is a dynamic equilibrium between melting and freezing. P T = 0 oC P = 1atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Boiling Point Elevation At equilibrium, the rate of evaporation (liquid to gas) equals the rate of condensation (gas to liquid) P T = 100 oC P = 1 atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Boiling Point Elevation T = 100 oC P = 1 atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Boiling Point Elevation T = K P = atm Surface of liquid Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Boiling-Point Elevation DTb = Tb – T b T b is the boiling point of the pure solvent T b is the boiling point of the solution Tb > T b DTb > 0 DTb = Kb m m is the molality of the solution Kb is the molal boiling-point elevation constant (0C/m) Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Freezing-Point Depression DTf = T f – Tf T f is the freezing point of the pure solvent T f is the freezing point of the solution T f > Tf DTf > 0 DTf = Kf m m is the molality of the solution Kf is the molal freezing-point depression constant (0C/m) Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Boiling Pt. Elevation Freezing Pt. Depression ΔTb = T boiling, solution – T boiling, pure solvent = Kb m ΔTf = T freezing, solution – T freezing, pure solvent = - Kf m m = molality of the solution Kb = boiling constant Kf = cryoscopic constant Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

DTf = Kf m Kf water = 1.86 0C/m DTf = Kf m What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is 62.01 g. DTf = Kf m Kf water = 1.86 0C/m = 3.202 kg solvent 478 g x 1 mol 62.01 g m = moles of solute mass of solvent (kg) = 2.41 m DTf = Kf m = 1.86 0C/m x 2.41 m = 4.48 0C DTf = T f – Tf Tf = T f – DTf = 0.00 0C – 4.48 0C = -4.48 0C Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Vapor-Pressure Lowering P1 = X1 P 1 Boiling-Point Elevation DTb = Kb m Freezing-Point Depression DTf = Kf m Osmotic Pressure (p) p = MRT Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

How many grams of sucrose (C12H22O11) are needed to lower the freezing point of 100 g of water by 3° C? Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

We want to decrease the freezing point by 3°C ΔTf = - Kf m We want to decrease the freezing point by 3°C -3° C = -(1.86 °C/molal) m m=1.61 molal = 1.61 moles solute/kg solvent NOTE: Kf is the WATER cryoscopic constant Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

0.161 moles sucrose x 342 g sucrose = 55.1 g sucros 1 mole sucrose 1.61 moles solute = x moles solute 1 kg solvent 0.100 kg water 0.161 moles sucrose x 342 g sucrose = 55.1 g sucros 1 mole sucrose 342 g/mol = 11*12.01 g/mol + 22x1.008 g/mol + 11x16 g/mol Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

How many grams of NaCl are needed to lower the freezing point of 100 g of water by 3 °C? Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

We want to decrease the freezing point by 3°C The Answer ΔTf = = - Kf m We want to decrease the freezing point by 3°C -3° C = -(1.86 °C/molal) m m=1.61 molal = 1.61 moles solute/kg solvent NOTE: Kf is the WATER cryoscopic constant Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

1.61 moles solute * 0.100 kg water = 0.161 moles solute 1 kg solvent Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

It’s all about the of particles 1.61 moles solute * 0.100 kg water = 0.161 moles solute 1 kg solvent BUT NaCl is an electrolyte: NaCl Na+ + Cl- You get 2 moles of solute per mole NaCl 0.161 moles solute * 1 mol NaCl * 58.45 g NaCl = 4.7 g NaCl 2 mol solute 1 mole NaCl Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Colligative Properties of Electrolyte Solutions 0.1 m NaCl solution 0.1 m Na+ ions & 0.1 m Cl- ions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 0.1 m NaCl solution 0.2 m ions in solution van’t Hoff factor (i) = actual number of particles in soln after dissociation number of formula units initially dissolved in soln i should be nonelectrolytes 1 NaCl 2 3 CaCl2 Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Colligative Properties of Electrolyte Solutions Boiling-Point Elevation DTb = i Kb m Freezing-Point Depression DTf = i Kf m Osmotic Pressure (p) p = iMRT Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Freezing Point Depression At what temperature will a 5.4 molal solution of NaCl freeze? Solution ∆TFP = Kf • m • i ∆TFP = (1.86 oC/molal) • 5.4 m • 2 ∆TFP = 20.1 oC FP = 0 – 20.1 = -20.1 oC Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Osmotic Pressure Osmotic pressure is the “funky” colligative property, but it is very important biologically Osmotic pressure is the pressure required to overcome the natural pressure exerted by a solution by virtue of having a concentration. Osmotic pressure looks just like the ideal gas law: ΠV = nRT where Π is osmotic pressure Π= (n/V) RT = M RT Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

What Happens? 1 M NaCl 4 M NaCl Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

The water moves from the 1 M side to the 4 M side. Why? 1 M NaCl 4 M NaCl  Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

On the 1 M side, the pressure is: OSMOTIC PRESSURE Π= M RT On the 1 M side, the pressure is: Π= M RT = 1 M (0.0821 Latm/mol K)(298 K) Π=24.4 atm On the 4 M side, the pressure is: Π= M RT = 4 M (0.0821 Latm/mol K) (298 K) Π= 97.9 atm Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Both solutions “push” on the membrane The bigger push wins! 1 M NaCl 4 M NaCl 24.4 atm 97.9 m 73.5 atm  Note the direction of the arrows. Osmotic pressure is pushing AGAINST the solution. Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Osmotic Pressure (p) more concentrated dilute Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one. A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules. Osmotic pressure (p) is the pressure required to stop osmosis. more concentrated dilute Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

p = MRT Osmotic Pressure (p) in air High P Low P M is the molarity of the solution R is the gas constant T is the temperature (in K) Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

A cell in an: isotonic solution hypotonic solution hypertonic solution Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

Chemistry In Action: Desalination Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร

แหล่งอ้างอิง Martin S. Silberberg, Chemistry: The Molecular Nature of Matter and Change, McGraw-Hill Higher Education, 2004 Raymond Chang, Chemistry, Williams College, McGraw-Hill Higher Education, 2002 Colligative properties ผู้สอน: อ.ศราวุทธ แสงอุไร