Pure Liquid with solute. Pure Liquid

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1 Colligative properties are physical properties of solutions that arise because of the number of solute molecules dissolved in solution and not on the kind of solute particles dissolved in solution. Pure Liquid Pure Liquid with solute

2 Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. The Four-Colligative Properties Vapor-Pressure Lowering Boiling-Point Elevation Freezing-Point Depression Osmotic Pressure (π) P solution = X solvent P solvent ΔT b = K b msolution ΔT f = -K f msolution π = MRT

3 Osmosis is the selective passage of solvent molecules through a semipermeable membrane from a dilute solution to a more concentrated one. dilute more concentrated

4 Osmosis is the diffusion of a solvent (frequently water) through a semi-permeable membrane, from a solution of low solute concentration (high water potential) to a solution with high solute concentration (low water potential), up a solute concentration gradient. pure solvent semipermeable membrane solution osmotic pressure An applied pressure is needed to prevent volume increase; this pressure is the osmotic pressure!

5 An pressure difference results from the net movement of solvent from a less-solute concentrated (hypotonic) to the more-solute concentrated (hypertonic) solution. For dilute solutions of electrolytes the osmotic pressure is given by: π = n V R T π = M R T Δπ = ΔM R T M is the molarity of the solution R is the gas constant T is the temperature (in Kelvin) Remember: The driving force is due to the difference in concentration of the solutions on each side of the membrane.

6 Cell membranes are semi-permeable membranes that are susceptable to diffusion of water and a some ions. No Osmotic Pressure Concentrations Are the Same Movement of solvent (water) from dilute to concentrated side! isotonic solution hypotonic solution hypertonic solution

7 Calculate molarity of a aqueous solution at 300K which is found to have an osmostic pressure of 3.00 atm. M = π R T = π = M R T 3.00 atm L atm mol 1 K K = M A solution prepared by dissolving 20.0 mg of insulin in water and diluting to a volume of 5.00 ml gives an osmotic pressure of 12.5 torr at 300K. What is the molecular mass of the insulin? M = 12.5 torr 1 atm 760 torr L atm mol 1 K K = mol insulin L 4 mol insulin moles = L 0.005L = mol MolarMass = grams/mole = g/ mol = 5988 g/mol =

8 Suppose we have a molar solution of table sugar (sucrose) and a semi-permeable membrane not permeable to sucrose. What osmotic pressure in mm Hg and to what height could this pressure support a column of water (density Hg =13.6 g/ml and water = 1g/mL? π = M R T π = 0.02 M x L atm/mol K x 298K π =.49 atm x 760 torr/1 atm π = 371 mm Hg x 13.6 = 5.0 meters!

9 Now this is wild: Anology to Osmosis In a closed container the solution with the highest vapor pressure will completely transfer to the container of lower vapor pressure until the mole fractions of solvent are equal in both! Cool... Pure High Vapor Pressure Low Vapor Pressure

10 Dialysis and Osmosis Pres Memb Pure Water Water With High concentration of dissolved solute

11 Biochemists have discovered more than 400 mutant varieties of hemoglobin (Hb), the blood protein that carries oxygen throughout the body. A physician studying a form of Hb associated with a fatal disease first finds its molar mass (M). She dissolves 21.5 mg of the protein in water at 5.0 o C to make 1.50 ml of solution and measures an osmotic pressure of 3.61 torr. What is the molar mass of this Hb mutant? PLAN: We know Π as well as R and T. Convert Π to atm and T to Kelvin. Use the Π equation to find the molarity M and then the amount and volume of the sample to calculate M. SOLUTION: # mol = g/m M = Π RT 2.08 x 10-4 mol L 21.5 mg x x g 10 3 mg = 3.61 torr x atm 760 torr ( L. atm/mol. K)( K) L 1.50 ml x = 3.12 x 10-7 mol 10 3 ml x x 10-7 mol = 2.08 x 10-4 M = 6.89 x 10 4 g/mol

12 Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. The Four-Colligative Properties Vapor-Pressure Lowering P 1 = X 1 P 1 Boiling-Point Elevation Freezing-Point Depression Osmotic Pressure (π) ΔT b = K b m ΔT f = -K f m π = MRT

13 Ionic solutes affect colligative properties differently than non-ionic solutes. 0.1 m nonelectrolytes solution 0.1 m in solution 0.1 m NaCl solution 0.2 m ions in solution 0.1 m CaCl2 solution 0.3 m ions in solution We modify the non-ionic colligative equations by multiplying by the van t Hoff factor, i Boiling-Point Elevation Freezing-Point Depression Osmotic Pressure ΔT b = i K b m ΔT f = i K f m π = i M R T

14 Calculation of Molar mass We can calculate the Molar Mass of a substance using any four of the colligative properties solutions. We use the freezing point depression and osmotic pressure normally as both have much larger changes (easier to measure). If you measure the change in colligative properties for a 1.25 molal sucrose osmotic pressure and freezing point show the largest change and are easiest to measure (especially osmotic pressure).

15 van t Hoff Factors are listed in handbooks van t Hoff Factors

16 Colloids are dispersions of particles of submicrometer dimensions, suspended in a solvent. suspended colloidal particles are much larger than solute molecules---1 micron Much of living matter form sols and emulsions and dispersions (starches, proteins, smog) Colloids appear milky or cloudy-- particulate phase colloidal suspension is not homogeneous as a solution

17 Suspension (left) vs Colloid (right)

18 Colloids and the large particles scatter light in a process called the Tyndall Effect. Particles in solution that are have dimensions on the order of the wavelength of visible light scatter light that can be observed by the eye. Dust particles, pollution particles, smoke, fog, solid solute particles in water all scatter light.

19 Colloids can be formed by combining any two or more phases of matter.