Why is salt spread on the roads during winter?

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Why is salt spread on the roads during winter?
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Ch 18 Solutions

• Properties of Solutions
• Concentrations of Solutions
• Colligative Properties of Solutions
• Calculations Involving Colligative Properties

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Ch 18.1 Properties of Solutions

• Solution Formation
• Solubility
• Factors Affecting Solubility

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Solution Formation

• What is a solution?
• A homogeneous mixture

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Solution Formation

• What factors affect the formation rate of a
  solution?
• Stirring (Agitation)
• Temperature
• Surface Area Particle Size

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Solubility

• Open to table G of your reference table
• The amount of solute that can dissolve in a given
  amount of solvent

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Types Of Solutions

• Saturated contains the maximum amount of a
  solute in a given solvent
• Unsaturated contains less solute than it has
  the capacity to dissolve
• Supersaturated contains more than the maximum
  amount of a solute in a given solvent

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Miscible

• Two liquids are completely soluble in each other
  in all proportions

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Factors Affecting Solubility

• Temperature solubility usually increases as
  temperature increases
• Gases are more soluble in cold water than in hot
  water

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Factors Affecting Solubility

• Pressure gas solubility increases as pressure
  increases

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Chapter 18.2

• How do you determine the concentration of a
  solute in a solvent?

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Molarity

• Molarity (M) moles of solute
• liters of solution

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Concentration

• Measure of the amount of solute dissolved in a
  given quantity of solvent
• Dilute (low concentration) vs. Concentrated (High
  concentration)

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Making Dilutions

• Increase the amount of solvent, but keep the
  amount of solute the same
• M1 x V1 M2 x V2

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Making Dilutions

• How many mL of stock solution of 2.00M MgSO4
  would you need to prepare 100.0mL of 0.400M
  MgSO4?
• M1 x V1 M2 x V2
• 2.00M x V1 0.400M x 100.0mL
• V1 20.0mL
• So add 20.0mL stock solution and 80mL of water to
  make 100mL

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Percent Solutions

• Percent by Volume Volume of Solute x 100
• Solution Volume
• Percent (mass/volume) mass of solute (g) x100
• solution volume (mL)

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Chapter 18.3 Colligative Properties of Solutions

• Decrease in Vapor Pressure
• Boiling Point Elevation
• Freezing Point Depression

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Colligative Properties

• Properties that depend only on the number of
  particles dissolved in a given mass of solvent

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Vapor Pressure

• Vapor Pressure pressure exerted by a vapor that
  is in dynamic equilibrium with its liquid in a
  closed system

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Decrease in Vapor Pressure

• A solution with a solute that is not easily
  vaporized (nonvolatile) will always have a vapor
  pressure lower than that of a pure solvent
• The more solute particles dissolved, that more
  the vapor pressure is lowered

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Boiling Point Elevation

• When a solute is added to a solvent, the vapor
  pressure decreases. Therefore more KE is needed
  to turn the liquid into a gas.
• The Boiling Point will be higher

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Freezing Point Depression

• When a substance freezes, the particles form an
  orderly pattern.
• The presence of a solute disrupts the formation
  of the orderly pattern
• The more dissolved particles, the lower the
  freezing point

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Chapter 18.4 Calculations

• Molality and Mole Fraction
• Boiling Point Depression and Freezing Point
  Depression
• Molar Mass

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Molality

• Molality moles of solute
• kilogram of solvent
• 1000g of water 1000mL

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Mole Fraction
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Boiling Point Elevation

• ?Tb Kb m
• ?Tb change in boiling point temperature
• Kb molal boiling point elevation constant
  (oC/m)
• m molality
• For ionics multiply the number of ions formed
  times the m

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Freezing Point Depression

• ?Tf Kf m
• ?Tf change in freezing point temperature
• Kf molal freezing point depression constant
  (oC/m)
• m molality
• For ionics multiply the number of ions formed
  times the m

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