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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

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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.)

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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 = vant 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)

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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 = vant 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)

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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 = vant hoff (# solute particles formed when dissolved) R = gas constant, 0.08206 (L ATM) / (mol K) T = temperature in Kelvin ( T K = T C + 273.15) M = molarity of solute (moles solute / L solution)

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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

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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

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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

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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

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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

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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

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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)