# Chapter 21 - Colligative Properties Explain how solutes effect the properties of a solution. Use Raoult’s Law to calculate vapor pressure of solution.

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Chapter 21 - Colligative Properties Explain how solutes effect the properties of a solution. Use Raoult’s Law to calculate vapor pressure of solution. Explain Fractional Distillation & its uses. Explain how solutes effect boiling & freezing points.

Colligative Properties Properties determined by the number of particles in solution rather than the type of particles. Vapor Pressure Freezing Point Boiling Point Rate of Diffusion

How Vapor Pressure Depression Occurs Solute particles take up space in a solution. Solute particles on surface decrease # of solvent particles on the surface. Less solvent particles can evaporate which lowers the vapor pressure of a liquid.

Vapor Pressures of Pure Water and a Water Solution The vapor pressure of water over pure water is greater than the vapor pressure of water over an aqueous solution containing a nonvolatile solute. Solute particles take up surface area and lower the vapor pressure

Raoult’s Law Vapor pressure of a solution varies directly as the mole fraction of solvent Vapor Pressure Solution = (mole fraction solvent )(Vapor Pressure solvent )

Raoult’s Law (continued) A solution of water and glucose with a mole fraction of 0.5 will have a vapor pressure that is 0.5 times the vapor pressure of water alone.

Ideal Solution All intermolecular attractions are the same. Solute-Solute Solvent-Solvent Solute-Solvent Attractions are the same

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