Properties of Solutions or Colligative Properties Properties of pure substances are based on strength of IMF Properties of solutions are based on # solute particles in solution # solute particles ~ i x concentration These solution properties include: I.Vapor Pressure II.Boiling Point III.Freezing and Melting Points IV.Osmotic Pressure

I. Vapor Pressure “Vapor Pressure Lowering” Presence of a solute decreases the vapor pressure of a solvent More Solute = lower vapor pressure v.p. solution < v.p. solvent P solution =  solvent P  solvent Where: P solution = vapor pressure of the solution P  solvent = vapor pressure of the pure solvent  solvent = mole fraction of solvent molecular solute:  solvent = mol solv. / (mol solute + mol solv.) ionic solute:  solvent = mol solv. / (mol cation + mol anion + mol solv.)

II. Boiling Points “Boiling Point Elevation” Presence of a solute increases the boiling point of a solvent More Solute = higher b.p. b.p. solution > b.p. solvent (typo corrected) b.p. solution = b.p. solvent +  T b  T b = i k b m Where: i = van’t hoff (# solute particles formed when dissolved) k b = boiling pt elevation constant (based on solvent,  C/m) m = molality of solute (moles solute / Kg solvent)

III. Freezing/Melting Points “Freezing Point Depression” Presence of a solute lowers the freezing/melting point of a solvent More Solute = lower f.p./m.p. f.p./m.p. solution < f.p./m.p. solvent f.p./m.p. solution = f.p./m.p. solvent –  T f  T f = i k f m Where: i = van’t hoff (# solute particles formed when dissolved) k f = freezing pt depression constant (based on solvent,  C/m) m = molality of solute (moles solute / Kg solvent)

IV. Osmotic Pressure Presence of a solute creates osmotic pressure More Solute = higher osmotic pressure o.p. solution > o.p. solvent  = i R T M Where:  = osmotic pressure in atm (1 atm = 760 torr) i = van’t hoff (# solute particles formed when dissolved) R = gas constant, (L ATM) / (mol K) T = temperature in Kelvin ( T K = T  C ) M = molarity of solute (moles solute / L solution)

Osmosis is the flow of solvent from a solution of low solute concentration into a solution of high solute concentration. The solutions may be separated by a semipermeable membrane. A semipermeable membrane allows solvent, but not solute, to flow through it. Osmosis occurs because of the difference in vapor pressure on the two sides (lower v.p. for solution) Osmosis

An isosmotic or isotonic solution has the same osmotic pressure as the solution inside the cell; as a result, there is no net flow of water into or out of the cell. Osmotic Pressure and Cells

A hyperosmotic or hyper tonic solution has a higher osmotic pressure than the solution inside the cell There is a net flow of water out of the cell, causing it to shrivel. Osmotic Pressure and Cells

A hyposmotic or hypotonic solution has a lower osmotic pressure than the solution inside the cell There is a net flow of water into the cell, causing it to swell. Osmotic Pressure and Cells

Calculations involving Solution Properties Two primary types of calculations A.Given concentration: Determine the solution property B.Given a solution property: Determine the molar mass of the solute

A. Determine the Solution Property i.Identify the solvent and solute ii.Identify the solution property needed (v.p. / b.p. / m.p. / f.p. / o.p.) iii.Write the equation for the property iv.Convert the concentration unit as needed v.Plug in numbers with correct units vi.Calculate

B. Determine the Molar Mass of Solute i.Identify the solvent and solute ii.Identify the solution property given to you (v.p. / b.p. / m.p. / f.p. / o.p.) iii.Write the equation for the solution property iv.Plug in numbers with correct units v.Solve for the concentration (m or M) vi.Use concentration definition to find moles solute (M = moles / L soln) or (m = moles / Kg solv) vii. Molar Mass = g solute / moles solute (note that g solute will be given)