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Colligative Properties of Solutions

Colligative Properties of Solutions. Concentration. Molarity (M) = moles of solute liter of solution Dilutions: M 1 V 1 = M 2 V 2 Percent by volume (%(v/v)) = volume of solute x 100% volume of solution

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Colligative Properties of Solutions

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  1. Colligative Properties of Solutions

  2. Concentration Molarity (M) = moles of solute liter of solution Dilutions: M1V1= M2V2 Percent by volume (%(v/v)) = volume of solute x 100% volume of solution Percent by mass (%(m/m)) = mass of solute x 100% mass of solution

  3. Concentration Mole Fraction: the ratio of the moles of the solute to the total number of moles of solvent and solute. XA= nA___ XB= nB___ nA + nB nA + nB XA= mole fraction of A nA= moles of A nB= moles of B • Look in your book on page 492.

  4. Colligative Properties • Colligative Property: A property that depends only upon the number of solute particles (concentration), and not upon their identity. • Three Important Colligative Properties of Solutions. • Vapor-pressure lowering • Boiling-point elevation • Freezing-point depression

  5. Vapor-Pressure Lowering • Vapor pressure: is the pressure exerted by a vapor that is in dynamic equilibrium with its liquid in a closed system. • A solution that contains a solute that is nonvolatile (not easily vaporized) always has a lower vapor pressure that the pure solvent. • This is true because in a solution, solute particles reduce the number of free solvent particles able to escape the liquid.

  6. Vapor-Pressure Lowering • The decrease in a solution’s vapor pressure is proportional to the number of particles the solute makes in solution.

  7. Freezing-Point Depression • Freezing-Point Depression: The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent (water). • The presence of a solute in water disrupts the formation of the orderly pattern of ice. Therefore more kinetic energy must be withdrawn from a solution than from the pure solvent to cause the solution to solidify.

  8. Freezing-Point Depression • The freezing point of a solution is lower than the freezing point of the pure solvent. • Phase Diagrams are mentioned on pages 402-403 and 494.

  9. Freezing-Point Depression • The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity. • Which would be a better salt for putting on icy roads, NaCl or CaCl2?

  10. Boiling-Point Elevation • Boiling Point: The temperature at which the vapor pressure of the liquid phase equals atmospheric pressure. • Because of the decrease in vapor pressure, additional kinetic energy must be added to raise the vapor pressure of the liquid phase of the solution to atmospheric pressure to initiate boiling.

  11. Boiling-Point Elevation • Boiling-Point Elevation: The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent. • The boiling point of a solution is higher than the boiling point of the pure solvent.

  12. Boiling-Point Elevation • The magnitude of the boiling-point elevation is proportional to the number of solute particles dissolved in the solvent. • It takes additional kinetic energy for the solvent particles to overcome the attractive forces that keep them in the liquid.

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