Solutions

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Solutions

• Chapter 12

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Types of solutions

• Suspensions largest particle size
• gt 1000nm
• Blood, paint, aerosols, muddy water
• Colloids mid sized particles
• 2-1000nm
• Milk, fog, butter
• Solution smallest particles
• lt2nm
• Air, seawater, gasoline

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Types of colloids
Aerosol liquid in gas
Solid Aerosol solid in gas
Sol -- solid in liquid like protein particles in
milk
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Emulsion liquid in liquid like oil droplets in
mayonnaise.
Foams gases in liquids like whipped cream
Solid emulsion liquid in a solid like milk in
butter
Gel a solid emulsion which is soft but holds
its shape like Jell-O
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Key terms

• Solution - A general term for a solute dissolved
  in a solvent. A homogeneous mixture of 2 or more
  components in which particles intermingle at the
  molecular level.
• Solvent - The component of a solution that is the
  greater quantity.
• Solute - The component of a solution that is the
  lesser quantity.

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Solution Types

• Gas in gas
• Gas in liquid
• Gas in solid
• Liquid in liquid
• Miscible - refers to 2 or more liquids that are
  infinitely soluble in one another.
• Immiscible - refers to 2 liquids that are not
  soluble in one another and if mixed separate into
  2 layers.
• Liquid in solid
• Solid in liquid
• Solid in solid

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Dissolving process

• solute particles are surrounded by solvent
  particles and begin go move through the solution
  in a solvent cage.
• Ions surrounded by water molecules are called
  hydrated ions.

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Energetics of Dissolving Process

• ?G ?H - T?S
• ?H can be either or -, it depends on
• the enthalpy to break the crystal apart
• the enthalpy of disrupting solvent structure
• the enthalpy change for hydrating solute.
• ?S is generally positive.

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Energetics of Dissolving Process
Costs energy to disrupt solvent and solute
structure. ?H
Formation of solvent-solute interactions releases
energy. ?H -
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• 1.36 g of MgCl2 are dissolved in 47.46 g of water
  to give a solution with a final volume of 50.00
  mL. Calculate the concentration of the solution
  in mass , ppm, mole fraction, molarity, and
  molality.

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• Hydrochloric acid is sold as a concentrated
  aqueous solution. The concentration of
  commercial HCl is 11.7 M and its density is 1.18
  g/mL. Calculate the mass percent of HCl in the
  solution. Calculate the molality of the
  solution.

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• Concentrated sulfuric acid has a density of 1.84
  g/mL and is 18 M. What is the mass H2SO4 in
  the solution? What is the molality of H2SO4 in
  the solution?

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• Solubility - the maximum amount of solute than
  can dissolve in 100 g of solvent at a given
  temperature.
• Saturated solution - a solution that contains the
  maximum amount of dissolved solute that will
  dissolve at a given temperature.
• Unsaturated solution - a solution that contains
  less solute than can be dissolved at a given
  temperature.
• Supersaturated solution - a solution that
  contains more dissolved solute than will
  ordinarily dissolve at a given temperature.

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Factors Affecting Solubility
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Temperature

• For gases, solubility decreases as temperature
  increases.
• For liquids and solids solubility generally
  increases as temperature increases.

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Pressure

• Pressure has very little effect on the solubility
  of liquids and solids.
• Pressure is very important to the solubility of
  gases however.

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Henrys Law

• The solubility of a gas is directly proportional
  to its partial pressure above the solution.
• Or Solubility kP
• where k henrys law constant

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• The solubility of pure N2 (g) at 25oC and 1.00
  atm pressure is 6.8 x 10-4 mol/L. What is the
  solubility of N2 under atmospheric conditions if
  the partial pressure of N2 is 0.78 atm?

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• The solubility of pure N2 (g) at 25oC and 1.00
  atm pressure is 6.8 x 10-4 mol/L. What is the
  solubility of N2 under atmospheric conditions if
  the partial pressure of N2 is 0.78 atm?

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Colligative Properties
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Vapor pressure lowering

• The vapor pressure of a solution is always lower
  than the vapor pressure of the corresponding pure
  solvent.
• Raoults Law
• P solution (P solvent )(X solvent)

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• What is the vapor pressure of a solution made of
  10.0 g of glucose and 100.0 g water at 37.0oC?
  (Vapor pressure of water at 37oC is 47.1 torr.)

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Why is vapor pressure lowered in solutions?

• ?Gvap ?Hvap - T?Svap

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Solutions with a volatile solute

• P total PA PB
• PA (XA)(PAo)
• PB (XB)(PBo)
• PAo is the vapor pressure of the pure solvent.

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Boiling point elevation

• A non-volatile solute raises the boiling point of
  a solvent.
• ?Tb Kb ? m where
• ?Tb boiling point elevation
• Kb a constant
• m molality

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Freezing point depression

• A non-volatile solute depresses the freezing
  point of a solvent.
• ?Tf Kf ? m where
• ?Tf freezing point depression
• Kf a constant
• m molality

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• Calculate the FP and BP of a solution containing
  100 g of ethylene glycol (C2H6O2) in 900 g H2O.
• For water Kb 0.52 oC/m
• Kf 1.86 oC/m

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• Tartaric acid can be produced from crystalline
  residues found in wine vats. It is used in
  baking powders and as an additive in foods.
  Analysis show that it is 32.3C, 3.97 H, and the
  remainder O. When 1.161 g tartaric acid is
  dissolved in 11.23 g water, the solution freezes
  at 1.26oC. Determine the empirical and
  molecular formula for tartaric acid.

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Osmotic Pressure
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Osmotic Pressure

• p MRT where
• p osmotic pressure
• M molarity
• R ideal gas constant
• T temperature in K

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• For a solution containing 3.00 g of pepsin in
  10.0 mL of solution p 0.213 atm at 25oC. What
  is the molecular mass of pepsin?

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Colligative properties of electrolytes

• Colligative properties depend on the number of
  particles in solution.
• Vant Hoff factor

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New equations

• ?Tb iKb ? m
• ?Tf iKf ? m
• p iMRT

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• The freezing point depression constants for the
  solvents cyclohexane and naphthalene are 20.1oC/m
  and 6.94oC/m respectively. Which would give a
  more accurate determination by freezing point
  depression of the molar mass of a substance that
  is soluble in either solvent? Why?