molality and mole fraction

• % by mass of solute

  100% of solution = mass of solute / mass of solution
• Molarity


  Moles of solute / Liters of solution
• In dilute aqueous solutions molarity and molality are nearly equal
• Molality


  Moles of solute / Kilograms of solvent
• Calculate molarity and molality of 10.0% glucose solution

  1. Density of solution is 1.04 g/mL

  2. 1 mol C6H12O6 = 180 g
• Calculate molality of solution with 7.25 g benzoic acid in 2.00 x 10^2 mL benzene

  1. Density of benzene is 0.879 g/mL

  2. 1 mol C6H5COOH = 122 g
• Mole fraction


  Number of moles of one component / Total moles of all components
• The sum of all mole fractions must equal 1.00
• Colligative properties


  • Properties of solutions that depend solely on the number of particles dissolved, not the kind of particles
  • Physical properties of solutions
  • do not depend on the kinds of particles dissolved.
• Types of colligative properties

  • Vapor pressure lowering
  • Freezing point depression
  • Boiling point elevation
  • Osmotic pressure
• Vapor pressure lowering is the key to all four colligative properties
• In a two component solution, the mole fraction of one component, A, has the symbol XA.
• The mole fraction of component B - XB
• Addition of a nonvolatile solute to a solution lowers the vapor pressure of the solution.
• Raoult’s Law models this effect in ideal solutions.
• Distillation is a technique used to separate solutions that have two or more volatile components with differing boiling points.
• A simple distillation has a single distilling column.

  • Simple distillations give reasonable separations.
• A fractional distillation gives increased separations because of the increased surface area.
• Addition of a nonvolatile solute to a solution raises the boiling point of the solution above that of the pure solvent.
• Electrolytes have larger effects on boiling point elevation and freezing point depression than nonelectrolytes.
• One mole of sugar dissolves in water to produce one mole of aqueous sugar molecules.
• One mole of NaCl dissolves in water to produce two moles of aqueous ions: 1 mole of Na+ and 1 mole of Cl- ions
• The osmotic pressure is the pressure exerted by a column of the solvent in an osmosis experiment.
• Osmosis is a rate controlled phenomenon.