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Lecture Comments (3)

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Post by Richard Meador on August 17, 2013

In calculating the molar mass on the "molar mass from depression and elevation" slide, the numerator of the equation has 2.9x10^3 g/M multiplied by 10^3 g/kg.  The 10^3 g/kg is incorrect and should be deleted. The answer of 2.5 x 10^2 g/mol is correct.

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Post by Marian Iskandar on April 29, 2013

My values are completely different from what the professor has. I have 3.9x10^-2, not -4 for my m (molality), which essentially throws off the rest of the calculation. Does anyone else get the same answer? Just wanting to double check, thanks!

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Post by John Leffingwell on February 12, 2012

What is the difference between "van der Waals alpha factor" and the "van't Hoff factor"? When I Google "van der Waals alpha factor", I can't find anything, but when I Google "van't Hoff factor", I find TONS of pages describing the "alpha factor" you presented in this video.

Colligative Properties, Colloids, Surfactants

  • Colligative properties of solutions – properties depending on number of particles (ions, molecules) dissolved

  • Raoult’s Law of vapor pressure lowering: vp = vpo(mol. frac. solvent)

  • Elevation of b.p. and depression of f.p. similar: DT = K(molality)

  • Use these to determine molar masses of solutes

  • V der W’s alpha: anomalous results due to ionic dissociation

  • Osmosis: flow of solvent across semipermeable membranes; example – red blood cells

  • Osmotic Pressure, PV =nRT where R is usual gas constant

  • Use osmotic pressure to determine molar masses of large molecules like proteins

  • Colloids: particles larger than ions/molecules but not large enough to settle

  • Tyndall effect: colloids scatter light

  • Soaps and surfactants: hydrophilic head and hydrophobic tail

Colligative Properties, Colloids, Surfactants

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Colligative Properties and Raoult's Law 0:43
    • Colligative (Collective)
    • Raoult's Law
    • Uses of Raoult's Law (Mole Fraction and Molar Mass)
  • Boiling Point Elevation, Freezing Point Depression 5:47
    • Pure Water and Solution in Water
    • Lower Vapor Pressure
    • Higher Boiling Point (Elevation)
    • Lower Freezing Point (Depression)
    • Example: Antifreeze
    • Change in Boiling Point (Molality)
  • Molar Mass from Elevation and Depression 12:49
    • Example: Water and Cystine
  • Van der Waals' Alpha Factor 18:59
    • Alpha Factor Equation
    • Example: Salt Ions
  • Osmosis 23:02
    • Blood (Isotonic, Hypertonic, Hypotonic)
  • Osmotic Pressure 27:40
    • Osmotic Pressure Definition (Pi)
    • Van der Waals'
  • Molar Mass from Osmotic Pressure 33:29
    • Example: Peptide in Water
  • Colloids and the Tyndall Effect 38:33
    • Light Beam (Solution and Colloidal Suspension)
  • Surfactants 44:11
    • Example: Sodium Stearate (Soap)
  • Soaps and Detergents 49:24
    • Ordinary Soaps Problem
    • Synthetic Soaps
  • Additional Example 1
  • Additional Example 2