Why is salt spread on the roads during winter?

Ch 18 Solutions  Properties of Solutions  Concentrations of Solutions  Colligative Properties of Solutions  Calculations Involving Colligative Properties

Ch 18.1 Properties of Solutions  Solution Formation  Solubility  Factors Affecting Solubility

Solution Formation  What is a solution?  A homogeneous mixture

Solution Formation  What factors affect the formation rate of a solution?  Stirring (Agitation)  Temperature  Surface Area – Particle Size

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

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

Miscible  Two liquids are completely soluble in each other in all proportions

Factors Affecting Solubility  Temperature – solubility usually increases as temperature increases  Gases are more soluble in cold water than in hot water

Factors Affecting Solubility  Pressure – gas solubility increases as pressure increases

Chapter 18.2  How do you determine the concentration of a solute in a solvent?

Molarity  Molarity (M) = moles of solute liters of solution

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

Making Dilutions  Increase the amount of solvent, but keep the amount of solute the same  M 1 x V 1 = M 2 x V 2

Making Dilutions  How many mL of stock solution of 2.00M MgSO 4 would you need to prepare 100.0mL of 0.400M MgSO 4 ?  M 1 x V 1 = M 2 x V 2  2.00M x V 1 = 0.400M x 100.0mL  V 1 = 20.0mL  So add 20.0mL stock solution and 80mL of water to make 100mL

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

Chapter 18.3 Colligative Properties of Solutions  Decrease in Vapor Pressure  Boiling Point Elevation  Freezing Point Depression

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

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

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

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

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

Chapter 18.4 Calculations  Molality and Mole Fraction  Boiling Point Depression and Freezing Point Depression  Molar Mass

Molality  Molality = moles of solute kilogram of solvent 1000g of water = 1000mL

Mole Fraction

Boiling Point Elevation  ΔT b = K b m  ΔT b = change in boiling point temperature  K b = molal boiling point elevation constant ( o C/m)  m = molality  For ionics – multiply the number of ions formed times the m

Freezing Point Depression  ΔT f = K f m  ΔT f = change in freezing point temperature  K f = molal freezing point depression constant ( o C/m)  m = molality  For ionics – multiply the number of ions formed times the m