States of Matter Lesson 4.9

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States of MatterLesson 4.9
CHEMISTRY 2 HONORS
Jeff VenablesNorthwestern High School
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• 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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• Eventually the pressure difference between the
  arms stops osmosis.

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• Osmotic pressure, ?, is the pressure required to
  stop osmosis
• Isotonic solutions two solutions with the same ?
  separated by a semipermeable membrane.

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• 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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• 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

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• 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.

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• Cucumber placed in NaCl solution loses water to
  shrivel up and become a pickle.
• 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).

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• Active transport is the movement of nutrients and
  waste material through a biological system.
• Active transport is not spontaneous.

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• Example
• What is the osmotic pressure of a solution of
  7.95 g of NaCl in 50.0 mL of an aqueous solution
  at 75C?
• 155 atm
• 118,000 mm Hg

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• One major application of vapor pressure lowering
  and colligative properties is in molar mass
  problems
• 1. An aqueous solution contains 1.00 g/L of a
  detergent. The osmotic pressure of this solution
  at 25C is 17.8 torr. What is the molar mass of
  the detergent?

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• 1.008 g of a compound was dissolved in 11.38 mL
  of benzene (d0.879 g/mL) and the solution froze
  at 4.37C. What is the molar mass of the
  compound?
• Tf(benzene) 5.48C
• Kf(benzene) 5.12C/molal

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• 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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• 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
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• 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.