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Solutions

Solutions. . . . the components of a mixture are uniformly intermingled (the mixture is homogeneous ). Solution Composition. 1. Molarity ( M ) = 2. Mass (weight) percent = 3. Mole fraction (  A ) = 4. Molality ( m ) =. Steps in Solution Formation.

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Solutions

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  1. Solutions • . . . the components of a mixture are uniformly intermingled (the mixture is homogeneous).

  2. Solution Composition • 1. Molarity (M) = • 2. Mass (weight) percent = • 3. Mole fraction (A) = • 4. Molality (m) =

  3. Steps in Solution Formation • Step 1 - Expanding the solute (endothermic) • Step 2 - Expanding the solvent (endothermic) • Step 3 - Allowing the solute and solvent to interact to form a solution (exothermic) • Hsoln = Hstep 1 + Hstep 2 + Hstep 3

  4. Henry’s Law The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution. • P = kC • P = partial pressure of gaseous solute above the solution • C = concentration of dissolved gas • k = a constant

  5. Raoult’s Law • Psoln= solventPsolvent • Psoln= vapor pressure of the solution • solvent = mole fraction of the solvent • Psolvent= vapor pressure of the pure solvent The presence of a nonvolatile solute lowers the vapor pressure of a solvent.

  6. Vapor Pressure • . . . is the pressure of the vapor present at equilibrium. • . . . is determined principally by the size of the intermolecular forces in the liquid. • . . . increases significantly with temperature. • Volatile liquids have high vapor pressures.

  7. Boiling Point • Constant temperature when added energy is used to vaporize the liquid. • vapor pressure of liquid = pressure of surrounding atmosphere

  8. Melting Point • Molecules break loose from lattice points and solid changes to liquid. (Temperature is constant as melting occurs.) • vapor pressure of solid = vapor pressure of liquid

  9. Phase Diagram • Represents phases as a function of temperature and pressure. • critical temperature: temperature above which the vapor can not be liquefied. • critical pressure: pressure required to liquefy AT the critical temperature. • critical point: critical temperature and pressure (for water, Tc = 374°C and 218 atm).

  10. Colligative Properties • Depend only on the number, not on the identity, of the solute particles in an ideal solution. • Boiling point elevation • Freezing point depression • Osmotic pressure

  11. Boiling Point Elevation • A nonvolatile solute elevates the boiling point of the solvent. • T = Kbmsolute • Kb = molal boiling point elevation constant • m = molality of the solute

  12. Freezing Point Depression • A nonvolatile solute depresses the freezing point of the solvent. • T = Kfmsolute • Kf= molal freezing point depression constant • m = molality of the solute

  13. Osmotic Pressure • Osmosis: The flow of solvent into the solution through the semipermeable membrane. • Osmotic Pressure: The excess hydrostatic pressure on the solution compared to the pure solvent.

  14. If the external pressure is larger than the osmotic pressure, reverse osmosis occurs. • One application is desalination of seawater.

  15. Colligative Properties of Electrolyte Solutions • T = imK •  = iMRT van’t Hoff factor, “i”, relates to the number of ions per formula unit. NaCl = 2, K2SO4 = 3

  16. Colloids • Colloidal Dispersion (colloid): A suspension of tiny particles in some medium. • aerosols, foams, emulsions, sols • Coagulation: The addition of an electrolyte, causing destruction of a colloid.

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