Honors Notes: Solutions Characteristics of Solutions

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Honors Notes SolutionsCharacteristics of
Solutions

• Insoluble solid that will not dissolve
• Immiscible liquid that will not dissolve in a
  liquid
• Miscible liquid that will dissolve in a liquid

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Solvation (a.k.a solubility)

• When a solid solute is placed in a solvent, the
  solvent particles completely surround the surface
  of the solid solute.
• If attractive forces between the solute particles
  and the solvent are greater than the attractive
  forces holding the the solute particles together,
  the solvent particles pull the solute particles
  apart and surround them.

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H2O H O

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NaCl Na Cl

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Heat of Solution

• Endothermic- takes in heat
• Solute and solvent particles break attractive
  forces holding them together
• Exothermic- gives off heat
• When solute and solvent particles mix, particles
  now attract each other

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Concentration many ways to measure

• How much solute is dissolved in a specific amount
  of solvent
• Percent by mass
• Percent by volume
• Molarity moles/Liter
• Molality moles solute/kilograms solvent

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Molarity

• moles of solute / 1 Liter of solution
• Calculate the molarity of 1.60 L of a solution
  containing 1.55 g of dissolved KBr?
• First change grams to moles of KBr

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Moles calculations

• How many moles are in 1.55 grams of KBr?
• Xmoles 1.55g ( 1 mole)/(39.1 79.9)
• Xmoles 1.55g (1 mole)/119)
• Xmoles 1.55/119
• Xmoles .0130
• .0130moles/1.60L Xmoles/1 liter (Molarity)
• .0130/1.60 .00814..
• Molarity is .00814M

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Molarity cont

• How many grams of CaCl2 would be dissolved in 1.0
  L of a 0.10M solution of CaCl2?
• First change 0.10M of CaCl2 to grams

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Moles calculations

• Xg 0.10moles CaCl2 (111.1g CaCl2 )/1mole
• Ca Cl Cl 40.1 35.5 35.5 111.1
• Xg 0.10 x 111.1
• Xg 11.1g
• Therefore, 11.1 g CaCl2 of would be dissolved in
  1 liter of 0.10 solution

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Diluting Solutions

• M1V1 M2V2
• What volume of a 3.00 M KI stock solution would
  you use to make 0.300 L of a 1.25 M KI solution?
• First set up the equation

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Molarity calculations

• M1 1.25 M and V1 0.300 L
• M2 3.00 M and V2 X L
• (1.25 M)(0.300 L) (3.00M)(X)
• X 0.125L

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Colligative properties of Solns

• Physical properties of solutions that are
  affected by the concentration of dissolved solute
  particles but not the type of dissolved solute
  particles
• Vapor Pressure Lowering
• Boiling point elevation
• Freezing point depression
• Rate of diffusion through a membrane

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Vapor Point Depression

• Vapor pressure equilibrium of a liquid is
  achieved when the of molecules leaving a liquid
  becoming a gas and the of gas molecules
  returning to the liquid are equal
• The presence of nonvolatile solute particles like
  sugar or salt) partially blocks the escape of
  solvent molecules from the liquid and thus lowers
  the vapor pressure of the solvent.
• Example summer coolant in car radiators

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Boiling Point Elevation

• The boiling point of a liquid is the temp at
  which the vapor pressure of the liquid equals the
  atmospheric pressure.
• The presence of nonvolatile solute particles
  (sugar or salt, for example) in a solution make
  it harder to put enough solvent particles into
  the vapor phase to equal the atmospheric
  pressure. The boiling point is therefore higher
  in a solution than the pure solvent.
• Examaple antifreeze in car radiators

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Freezing Point Depression

• Freezing point is the temp at which the vapor
  pressure of a solid and liquid are equal.
• Because the addition of solute particles lowers
  the vapor pressure of the liquid, the vapor
  pressure of the solid and liquid will be equal at
  a lower temp
• Examples salt in an ice cream maker salt on the
  highways.

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Osmosis

• Rate of diffusion through a semi-permeable
  membrane is called osmosis
• Of great importance to living organisms as this
  is how cells take in water
• Solute particles can not pass through membrane,
  but water molecules can
• Water moves through membrane to equalize
  concentration of solute particles on either side
  of membrane.

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Osmosis Examples

• Isotonic IV solutions so red blood cells dont
  burst or shrivel
• Pickles cukes in brine cuke looses water thru
  osmosis and shrivels to a pickle
• Fruit preservation with sugar bacteria shrivel
  and die
• Meat preservation with salt bacteria shrivel and
  die
• Water from soil to plant roots