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lecture over solutions, solubility, and colligative properties

lecture over solutions, solubility, and colligative properties



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Solutions Solutions Presentation Transcript

  • Solutions Test on Friday March 4
  • What is a solution ?
    • A homogeneous mixture
    • Composed of a solute dissolved in a solvent
    Solute Solvent
  • How is a solution formed?
    • Through the process of
    • Solute particles separate from each other and mix with the solvent
    • particles
    • Solvent particles
    • surround the solute
    • particles and pull
    • them away from other
    • solute particles
    solvation View slide
  • Solute and Solvent
    • Solvent
      • Does the dissolving
      • Greater quantity (usually)
    • Solute
      • What is dissolved
      • Lesser quantity (usually)
    View slide
  • Like dissolves like
    • Baking soda will dissolve in water, but not in oil…..why?
    • “ Like dissolves like” refers to the bonding and polarity of the particles in the solute and solvent
    • Polar means a substance
    • has a positive and a
    • negative end
    • Ionic compounds
  • Ionic compounds in solution Cl - Na + Cl - Na + Na + Cl - Cl -
  • Solubility
    • Only a certain amount of solute can dissolve in a solvent under a certain set of conditions
    • When too much solute is added to a solution at that temperature, the excess solute will crystallize
    • and fall out of solution
    • Solubility is the maximum
    • amount of a solute that
    • dissolves in a solvent at
    • a given temperature
  • Saturation
    • A saturated solution
      • contains the maximum amount of dissolved solute
      • for a given amount of solvent
      • at a specific temperature and pressure
  • Supersaturation
    • A supersaturated solution
      • contains more dissolved solute than a saturated solution
      • at the same temperature.
  • Solubility Curves Shows how much solute will dissolve in 100 g of water at a certain temperature The line represents the saturated amount of solute Underneath the line represents an unsaturated amount Above the line represents a supersaturated amount
    • Which substance is most soluble at 40°C?
    • How many grams of NH 4 Cl will dissolve at 50°C?
    • What two substances have the same solubility at 24°C?
    • If you place 70 grams of KBr into 100g of water at 60°C, what
    type of solution have you made?
    • How many grams of NaNO 3 will dissolve in 300.0g of water at
    10.0°C? NaNO 3 ~ 50 grams Yb 2 (SO 4 ) 3 KNO 3 unsaturated ~ 240 grams (80 x 3)
  • Increasing Solubility - Solids
    • Increase the temperature
      • Why? Increases the amount of solute-solvent collisions and increases speed and energy of particles
    • Agitate the solution (stir)
      • Why? Brings more
      • solvent particles closer to
      • the solute
    • Decrease the particle size
      • Increases the surface area
      • of the solute, making it
      • easier for solvent particles to
      • surround the solute
  • Increasing Solubility – Gases
    • Decrease the temperature
    • Increase the pressure
    • If you increase the pressure,
    • think of pressing the gas
    • particles into the liquid.
    • Increasing pressure always
    • increases the amount of
    • gas that can be dissolved
    • in a liquid.
  • Rate of Solvation
    • Greater solubility = Faster solvation
    • The same factors that increase solubility, increase the rate of solvation
  • Concentration
    • The larger the ratio of solute to solvent becomes, the more concentrated the solution is.
    • Concentrated – large ratio of solute to solvent
    • Dilute – small ratio of solute to solvent
  • Rates of Reaction
    • Concentration affects the rate of reaction
    • Concentrated solutions react faster than dilute solutions
  • Molarity
    • Most commonly used in chemistry
    • Abbreviated as M
    • Moles of solute in per liter of solution
    M = moles of solute Liters of solution
  • Electrolytes
    • Electrolyte – ionic compound whose aqueous solution conducts an electric current
    • – electrolyte
    • – non-electrolyte
    NaCl Sugar How many moles of ions are produced by dissolving 1 mole of NaCl in water?
  • Colligative Properties
    • Colligative - depending on the collection
    • Properties dependent on concentration , number of particles present
  • Boiling Point Elevation
    • When vapor pressure equals atmospheric pressure, water boils
    • More particles = lower vapor pressure
    • Lower vapor pressure = higher boiling point
    • More particles = higher boiling point
    Which raises boiling point more, 1 mole of NaCl in water, or 1 mole of sugar in water?
  • Freezing Point Depression
    • Solute particles interfere with attraction between solvent particles
    • More particles = lower freezing point
  • Osmosis
    • Osmosis – diffusion of solvent across a semi-permeable barrier
    • Solvent goes from:
      • Area of more solvent -> Area of less solvent
  • Osmosis Semi-permeable barrier Pure Solvent Solution
  • Osmosis and Concentration
    • Higher concentration = more osmotic pressure
  • Osmosis and you
  • Colligative Properties Review Atmosphere Vapor Pressure
  • Miscible and Immiscible
    • Substances that are miscible will dissolve in each other.
      • Example: alchohol and water
    • Substances that are immiscible will mix but immediately separate.
      • Example: oil and vinegar