CH 11: Properties of Solutions

1
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

2
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

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Solution Composition

• Concentrated solution relatively large amount
  of solute
• Dilute solution relatively small amount of
  solute

4
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

5
Solution Composition

• Super-saturated solution - solution with more
  than the maximum amount of solute that will
  normally dissolve at a given temperature

6
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

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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)

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Practice!

• Start by writing definitions for the
  concentration units
• M
• m
• Mass
• Mole fraction

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Starting with Molarity

• Solution
• 3.75 M H2SO4 solution with a density of 1.23 g/mL
• Calculate
• Mass
• Molality
• mole fraction of H2SO4

10
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

11
Starting with Mass

• Solution
• 35.4 H3PO4
• Density of 1.20 g/mL
• Calculate
• Molarity
• Molality
• Mole fraction of H3PO4

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Starting with Molality

• Solution
• 2.50 m HCl solution
• Density of 1.15 g/mL
• Calculate
• Molarity need _______
• Mass
• Mole fraction of HCl

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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

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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

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Solution Formation

• DHsolution DH1 DH2 DH3
• Solutions form when the DHsolution is a small
  value see page 504

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Factors Impacting Solubility

• Structure like dissolves like
• 44 on page 533

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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

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Henrys Law

• Henrys Law C kP
• C Concentration of dissolved gas
• k solution specific constant
• P partial P of the solute gas above
• the solution
• What does Henrys Law mean?
• No calculations required.
• Page 506

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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

20
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

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Vapor Pressure of Solutions

• See Raoults Law on page 510
• Psolution csolvent P0 solvent

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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
  vant Hoff factor (i) into my consideration of
  these properties and not consider it separately.

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Colligative Properties

• FP Kf m i
• BP Kb m i
• See page 517 for needed constants

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1. Calculating the bp or fp of a solution
2. Calculating the molar mass of a solute from fp or
   bp data

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Osmotic Pressure

• Osmotic Pressure (P) is often used to determine
  the molar mass of large biological molecules
• P MRTi