Colligative Properties

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Colligative Properties

• Osmosis
• Semipermeable membrane permits passage of some
  components of a solution. Example cell
  membranes and cellophane.
• Osmosis the movement of a solvent from low
  solute concentration to high solute
  concentration.
• There is movement in both directions across a
  semipermeable membrane.
• As solvent moves across the membrane, the fluid
  levels in the arms becomes uneven.

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Colligative Properties

• Osmosis
• Eventually the pressure difference between the
  arms stops osmosis.

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Colligative Properties

• Osmosis
• Osmotic pressure, ?, is the pressure required to
  stop osmosis

? osmotic pressure M Molarity (mol/L) R
Ideal Gas Constant T Temperature (K)

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Osmotic Pressure is a VERY sensitive measure of
Molarity

• Seawater contains 3.4 g NaCl per liter
• M 3.4 g/58.5 g/L 0.0582 M
• ? (0.0582 mol/L)(0.0821L atm/mol K )(298K)
• ? 1.42 atm
• 1 atm supports column of water 10.34 m length
• (1.42 atm)(10.34 m/atm) 14.68 m
• (14.68 m)(3.28 ft/m) 48 feet

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Pure solvent/solution
48 feet
Seawater
Sea water
Pure Water
Pure Water
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Figure 17.8 Pure H20 solution
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Colligative Properties

• Osmosis
• Osmotic pressure, ?, is the pressure required to
  stop osmosis
• Isotonic solutions two solutions with the same ?
  separated by a semipermeable membrane.
• Hypotonic solutions a solution of lower ? than a
  hypertonic solution.
• Osmosis is spontaneous.
• Red blood cells are surrounded by semipermeable
  membranes.

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Colligative Properties

• Osmosis
• Crenation
• red blood cells placed in hypertonic solution
  (relative to intracellular solution)
• there is a lower solute concentration in the cell
  than the surrounding tissue
• osmosis occurs and water passes through the
  membrane out of the cell.
• The cell shrivels up.

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Colligative Properties

• Osmosis
• Crenation and Hemolysis

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Crenation of Red Blood Cells, Electron Micrograph
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Colligative Properties

• Osmosis
• Hemolysis
• red blood cells placed in a hypotonic solution
• there is a higher solute concentration in the
  cell
• osmosis occurs and water moves into the cell.
• The cell bursts.
• To prevent crenation or hemolysis, IV
  (intravenous) solutions must be isotonic.
• Examples of osmosis
• Cucumber placed in NaCl solution loses water to
  shrivel up and become a pickle.

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Colligative Properties

• Osmosis
• Limp carrot placed in water becomes firm because
  water enters via osmosis.
• Salty food causes retention of water and swelling
  of tissues (edema).
• Water moves into plants through osmosis.
• Salt added to meat or sugar to fruit prevents
  bacterial infection (a bacterium placed on the
  salt will lose water through osmosis and die).
• Active transport is the movement of nutrients and
  waste material through a biological system.
• Active transport is not spontaneous.

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Drinking Seawater will Cause Dehydration of Body
Tissues
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Reverse osmosis
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Reverse Osmosis Water Purification
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Desalination plant
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• The facility is the largest seawater reverse
  osmosis desalination facility in the United
  States. The incoming seawater is pretreated in
  round horizontal media filters. There are two
  sets of filters primary, consisting of sand,
  gravel, and anthracite, and secondary consisting
  of the same media as primary, plus garnet. Next,
  the cartridge filters act as a check to catch any
  material that gets through the primary and
  secondary stages. Then, pumps drive the water at
  800 pounds per square inch (p.s.i.) through
  reverse osmosis membranes that separate the
  dissolved salt from the water. Approximately 45
  of the pressurized seawater goes through
  membranes and becomes drinking water.

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Desalination Schematic
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The Cost of Desalination
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Cost of Water from Freshwater Sources
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Home water purification by reverse osmosis
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Colloids

• Colloids are suspensions in which the suspended
  particles are larger than molecules but too small
  to drop out of the suspension due to gravity.
• Particle size 10 to 2000 Å.
• There are several types of colloid
• aerosol (gas liquid or solid, e.g. fog and
  smoke),
• foam (liquid gas, e.g. whipped cream),
• emulsion (liquid liquid, e.g. milk),
• sol (liquid solid, e.g. paint),
• solid foam (solid gas, e.g. marshmallow),
• solid emulsion (solid liquid, e.g. butter),
• solid sol (solid solid, e.g. ruby glass).

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Colloids

• Tyndall effect ability of a Colloid to scatter
  light. The beam of light can be seen through the
  colloid.

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Colloids

• Hydrophilic and Hydrophobic Colloids
• Focus on colloids in water.
• Water loving colloids hydrophilic.
• Water hating colloids hydrophobic.
• Molecules arrange themselves so that hydrophobic
  portions are oriented towards each other.
• If a large hydrophobic macromolecule (giant
  molecule) needs to exist in water (e.g. in a
  cell), hydrophobic molecules embed themselves
  into the macromolecule leaving the hydrophilic
  ends to interact with water.

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Colloids
Hydrophilic and Hydrophobic Colloids
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Colloids

• Hydrophilic and Hydrophobic Colloids
• Typical hydrophilic groups are polar (containing
  C-O, O-H, N-H bonds) or charged.
• Hydrophobic colloids need to be stabilized in
  water.
• Adsorption when something sticks to a surface we
  say that it is adsorbed.
• If ions are adsorbed onto the surface of a
  colloid, the colloids appears hydrophilic and is
  stabilized in water.
• Consider a small drop of oil in water.
• Add to the water sodium stearate.

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Colloids
Hydrophilic and Hydrophobic Colloids
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Colloids

• Hydrophilic and Hydrophobic Colloids
• Sodium stearate has a long hydrophobic tail
  (CH3(CH2)16-) and a small hydrophobic head
  (-CO2-Na).
• The hydrophobic tail can be absorbed into the oil
  drop, leaving the hydrophilic head on the
  surface.
• The hydrophilic heads then interact with the
  water and the oil drop is stabilized in water.

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Colloids
Hydrophilic and Hydrophobic Colloids
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Colloids

• Hydrophilic and Hydrophobic Colloids
• Most dirt stains on people and clothing are
  oil-based. Soaps are molecules with long
  hydrophobic tails and hydrophilic heads that
  remove dirt by stabilizing the colloid in water.
• Bile excretes substances like sodium stereate
  that forms an emulsion with fats in our small
  intestine.
• Emulsifying agents help form an emulsion.

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Colloids

• Removal of Colloidal Particles
• Colloid particles are too small to be separated
  by physical means (e.g. filtration).
• Colloid particles are coagulated (enlarged) until
  they can be removed by filtration.
• Methods of coagulation
• heating (colloid particles move and are attracted
  to each other when they collide)
• adding an electrolyte (neutralize the surface
  charges on the colloid particles).
• Dialysis using a semipermeable membranes
  separate ions from colloidal particles.

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Coagulation of a Colloid
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Kidney and Dialysis
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Artificial kidney
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A Dialysis Unit
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Principle of Dialysis