Ch 11 properties of solutions
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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



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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