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Colligative Properties

Colligative Properties. Colligative Properties of Solutions. Colligative properties of a solution depend only on the concentration of solute particles, and not on the nature of the solute. Non-colligative properties: color, odor, viscosity, toxicity, reactivity, etc.

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Colligative Properties

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  1. Colligative Properties

  2. Colligative Properties of Solutions • Colligative propertiesof a solution depend only on the concentration of solute particles, and not on the nature of the solute. • Non-colligative properties: color, odor, viscosity, toxicity, reactivity, etc. • We will examine two colligative properties: • Freezing point depression • Boiling point elevation

  3. Vapor Pressure of a Solution • The vapor pressure of solvent above a solution is less than the vapor pressure above the pure solvent.

  4. Vapor Pressure LoweringBy A Nonvolatile Solute At all temperatures, the vapor pressure (curve) from a solution (nonvolatile solute) is lower than… This means that the solid-liquid curve must also shift to the left. …the vapor pressure from the pure solvent. Consequences: the boiling point of the solution increases by DTb … …and the freezing point decreases by DTf .

  5. Freezing Point Depression and Boiling Point Elevation DTf= Kfm DTb= Kbm

  6. Practice 1 • Glycerol, C3H8O3, (molecular weight 92 g/mol) , is essentially a nonvolatile liquid that is very soluble in water.  A solution is made by dissolving 46.0 g of glycerol in 250 g of water.  Calculate the boiling point of the solution at an atmospheric pressure of 1 atm. (Kb=0.512)

  7. Practice 2 • A solution of 14 g of an unknown (molecular) compound in 1 kg of benzene boiled at 81.7oC.  Calculate the formula weight of the unknown. (bp = 80.1⁰C, Kb= 2.53)

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