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Effects of solute on solvent

Effects of solute on solvent. 12.5-12.6. Homework Check. 39-57 4 sheets. Vapor Pressure. Define: The pressure of the vapor created by the solution evaporating. Must be volatile solution Evaporates easily. Effect of Nonvolatile Solute. Causes vapor pressure to decrease

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Effects of solute on solvent

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  1. Effects of solute on solvent 12.5-12.6

  2. Homework Check • 39-57 • 4 sheets

  3. Vapor Pressure • Define: • The pressure of the vapor created by the solution evaporating. • Must be volatile solution • Evaporates easily

  4. Effect of Nonvolatile Solute • Causes vapor pressure to decrease • Concentration volatile solvent decrease • Less ability to evaporate

  5. Partial PressureRaoult’s law • Colligative property • Dependent on mole fraction Psoln = PopureXpure

  6. Vapor Pressure Lowering • Subtract • Pressurepuresolvent - Pressuresolution • Vapor Pressure Lowering Formula DP = PopureXsolute

  7. EX. Calculate the vapor-pressure lowering of water when 5.67 g of glucose is dissolved in 25.2 g of water at 25oC. The vapor pressure of water at 25oC is 23.8 mmHg. What is the vapor pressure of the solution?

  8. Naphthalene, C10H8 is used to make mothballs. Suppose a solution is made by dissolving 0.515 g of naphthalene in60.8 g of chloroform, CHCl3. Calculate the vapor-pressure lowering of chloroform at 20oC from the naphthalene. The vapor pressure of chloroform at 20oC is 156 mmHg. Naphthalene can be assumed to be nonvolatile compared with chloroform. What is the vapor pressure of the solution?

  9. You need to boil a water-based solution at a temperature lower than 100oC. What kind of liquid could you add to the water to make this happen?

  10. Boiling Point Elevation • The addition of a nonvolatile solute to a liquid reduces its vapor pressure; therefore, the temperature must be increased in order to achieve a set vapor pressure in order to boil. Hence Bp elevation.

  11. Boiling point elevation, • Tb is a colligative property of a solution equal to the boiling point of the solution minus the boiling point of the pure solvent. (p 523) Tb = KbCm • Kb = boiling point constant listed on p523 • Cm = molal concentration

  12. Freezing point depression • Tf, is a colligative property of a solution equal to the freezing point of the pure solvent minus the freezing point of the solution. Tf = KfCm (Kf = Fp constant p 523)

  13. EX. An aqueous solution (dissolved in H2O) is 0.0222 m glucose. What are the boiling point and the freezing point of this solution?

  14. Calculation Molar Mass • From the freezing point lowering, you can calculate the molal concentration and from the molality, you can obtain the molecular weight. • Find moles solute (gsolvent X molality) • gsolute / moles = MM

  15. EX. A solution is prepared by dissolving 0.131 g of a substance in 25.4 g of water. The molality of the solution is determined by freezing point depression to be 0.056 m. What is the molecular weight of the substance?

  16. EX. Camphor melts at 179.5oC. Its freezing point constant is 40oC/m. A 1.07 mg sample of a compound was dissolved in 78.1 mg of camphor. The solution melted at 176.0oC. What is the molecular weight of the compound? If the empirical formula of the compound is CH, what is the molecular formula?

  17. Homework Page: 545 Q: 59-67

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