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CH 11: Properties of Solutions. Describing Solutions – concentration units Energetics of solution formation Factors impacting solubility – P and T Colligative Properties of solutions BP elevation FP depression Osmotic pressure Vapor Pressure. Terms. Solution – homogeneous mixture

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ch 11 properties of solutions
CH 11: Properties of Solutions
  • Describing Solutions – concentration units
  • Energetics of solution formation
  • Factors impacting solubility – P and T
  • Colligative Properties of solutions
    • BP elevation
    • FP depression
    • Osmotic pressure
    • Vapor Pressure
terms
Terms
  • Solution – homogeneous mixture
  • Solvent – generally the larger component of the solution
    • Determines the physical state of the solution
  • Solute – generally the smaller component of the solution
    • Solute is dispersed in the solvent
solution composition
Solution Composition
  • Concentrated solution – relatively large amount of solute
  • Dilute solution – relatively small amount of solute
solution composition1
Solution Composition
  • Unsaturated solution –solution with less than the maximum amount of solute that will normally dissolve at a given temperature
  • Saturated solution - solution with maximum amount of solute that will normally dissolve at a given temperature
solution composition2
Solution Composition
  • Super-saturated solution - solution with more than the maximum amount of solute that will normally dissolve at a given temperature
concentration units
Concentration Units

Molarity (M) = moles solute/Liters solution

Molality (m) = moles solute/kg solvent

Mass % = Mass solute/mass solution x100%

Mole fraction (cA) = moles A/total moles

normality
Normality

Normality (N) = # gram equivalent wt./L solution

  • Gew = mass of an acid or base that produces 1 mole of H+ or OH -1

Normality = Molarity x (# H+ or OH -1 /mol)

  • 1 M HCl = 1 N HCl
  • 1 M H2SO4 = 2 N H2SO4

For acid base titrations:

(NAcid) (VAcid) = (NBase) (VBase)

practice
Practice!
  • Start by writing definitions for the concentration units

M =

m =

Mass % =

Mole fraction =

starting with molarity
Starting with Molarity

Solution:

  • 3.75 M H2SO4 solution with a density of 1.23 g/mL

Calculate:

  • Mass %
  • Molality
  • mole fraction of H2SO4
starting with masses
Starting with Masses

Solution:

  • A solution is made by combining 66.0 grams of acetone (C3H6 O) with 146.0 grams of water.
  • Solution has a density of 0.926 g/mL

Calculate:

  • Molarity – need volume of solution
  • Mass %
  • Molality
  • Mole fraction of acetone
starting with mass
Starting with Mass %

Solution:

  • 35.4 % H3PO4
  • Density of 1.20 g/mL

Calculate:

  • Molarity
  • Molality
  • Mole fraction of H3PO4
starting with molality
Starting with Molality

Solution:

  • 2.50 m HClsolution
  • Density of 1.15 g/mL

Calculate:

  • Molarity – need _______
  • Mass %
  • Mole fraction of HCl
solution formation
Solution Formation

Formation of a solution involves 3 steps

  • Separate the solute particles
    • expand the solute
  • Separate the solvent particles
    • Expand the solvent
  • Form the solution
    • Solute and solvent interact
solution formation1
Solution Formation
  • Each step of solution formation involves energy and has a DH.

DH1 = energy needed to separate the solute

DH2 = energy needed to separate the solvent

DH3 = energy released when solution forms

solution formation2
Solution Formation

DHsolution = DH1 +DH2 +DH3

Solutions form when the DHsolution is a small value – see page 504

factors impacting solubility
Factors Impacting Solubility
  • Structure – like dissolves like
    • #44 on page 533
factors impacting solubility1
Factors Impacting Solubility
  • Pressure
    • Pressure has little impact on the solubility of liquids and solids
    • Pressure has a significant impact on the solubility of gases in a liquid
      • The higher the pressure of gaseous solute above a liquid the higher the concentration of the gas in the solution
henry s law
Henry’s Law
  • Henry’s Law: C = kP

C = Concentration of dissolved gas

k = solution specific constant

P = partial P of the solute gas above

the solution

  • What does Henry’s Law mean?
    • No calculations required.

Page 506

temperature and solubility
Temperature and Solubility
  • Temperature has variable effects on the amount of solid that will dissolve in an aqueous solution!
    • See figure 11.6 page 508
  • Solutes will dissolve more rapidly at higher temperatures
temperature and solubility1
Temperature and Solubility
  • The solubility of a gas in water decreases as temperature increases.
    • See figure 11.7 on page 508
    • Thermal pollution – read the story on page 510 when you get a chance
vapor pressure of solutions
Vapor Pressure of Solutions
  • See Raoult’s Law on page 510
  • Psolution= csolvent P0solvent
colligative properties
Colligative Properties
  • Colligative properties
    • properties of a solution that depend upon the amount of dissolved solute, not the identity of the solute.
      • Freezing point depression
      • Boiling point elevation
      • Osmotic Pressure
      • Note: I will be weaving section 11.7 and the van’t Hoff factor (i) into my consideration of these properties and not consider it separately.
colligative properties1
Colligative Properties
  • FP = Kf m i
  • BP = Kb m i

See page 517 for needed constants

slide24
Calculating the bp or fp of a solution
  • Calculating the molar mass of a solute from fp or bp data
osmotic pressure
Osmotic Pressure
  • Osmotic Pressure (P) is often used to determine the molar mass of large biological molecules

P = MRTi

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