Colligative Properties - PowerPoint PPT Presentation

About This Presentation
Title:

Colligative Properties

Description:

How do properties of solutions differ from properties of the solute and solvent? ... torr. Ptoluene = 22 torr. Answer: 1 mol C6H6 , 1 mol C7H8, 37.5 torr C6H6, ... – PowerPoint PPT presentation

Number of Views:255
Avg rating:3.0/5.0
Slides: 33
Provided by: tenafl
Category:

less

Transcript and Presenter's Notes

Title: Colligative Properties


1
Colligative Properties
  • Honors ChemistryMrs. Coyle

2
How do you get from this
3
to this?
4
Add an ionic compound!
5
How do properties of solutions differ from
properties of the solute and solvent?
  • We will examine four properties called
    colligative properties
  • Vapor Pressure
  • Freezing Point
  • Boiling Point
  • Osmotic Pressure

6
Colligative Properties
  • Depend on the number of solute particles
    (concentration) and not the type of solute
    particles.
  • Ionic solutes have a greater effect on
    colligative properties since they dissociate and
    produce a higher number of particles.

7
Part I
  • Vapor Pressure Depression

8
Vapor Pressure Depression
  • The vapor pressure of a solution is lower than
    the that of the pure liquid.
  • Nonvolatile solute particles inhibit the movement
    of solvent particles into the vapor phase, since
    there is less solvent per unit volume, and so
    reduce the vapor pressure.

9
Phase Diagram of Water (Black Line) and Solution
(Pink Line)
http//www.chemguide.co.uk/physical/phaseeqia/pdso
lution3.gif
10
Raoults Law
  • Psolution xsolventPsolvent
  • The vapor pressure of a solution varies directly
    as the mole fraction of the solvent particles.
  • Tutorial Link
  • http//www.wwnorton.com/college/chemistry/gilbert/
    overview/ch9.htmvapor_pressure

11
(No Transcript)
12
Ideal Solution
  • A liquid-liquid solution that obeys Raoults Law.

13
Example 1 Nonvolatile Solute
  • Find the vapor pressure of a solution
    containing 63.0 g of glycerine(C3H8O3) in 500.0 g
    of water at 55oC. The vapor pressure of water at
    25oC is 3.2 kPa.(Hint Find the vapor pressure at
    55oC. Psolution xsolventPsolvent
  • Answer 0.685mol C3H8O3 , 27.8 mol H2O,
    Psolvent3.52kPa, Psolution 3.44kPa

14
Vapor Pressure Depression
  • ?P Psolvent-Psolution

15
Example 2 Solution of two volatile substances
(Hint Use Daltons Law of Partial Pressures)
  • Find the vapor pressure of a solution
    containing a mixture of 78.0g benzene(C6H6) and
    92.0g toluene (C7H8) at 20oC.
  • Pbenzene 75 torr
  • Ptoluene 22 torr
  • Answer 1 mol C6H6 , 1 mol C7H8, 37.5 torr C6H6,
    11.0 torr C7H8, PT 48.5 torr

16
Example 3 Ionic Solute
  • Calculate the vapor pressure of a solution
    containing 95.3g MgCl2 and 180g water at 25oC.
    The vapor pressure of pure water at 25oC is
    3.2kPa. (Hint Each formula unit of MgCl2
    produces 3 particles when dissolved) Psolution
    xsolventPsolvent
  • Answer 3 mol of MgCl2 particles, 2.46kPa

17
Part II
  • Freezing Point Depression
  • Boiling Point Elevation

18
Freezing and Boiling Point
  • When a non volatile solute is added to a solvent
    the result is usually
  • Boiling Point Elevation
  • Freezing Point Depression

19
Boiling Point Elevation
Addition of a nonvolatile solute lowers the
vapor pressure of the solvent and therefore
raises the boiling point.
20
Phase Diagram of Water (Black Line) and Solution
(Pink Line)
http//www.chemguide.co.uk/physical/phaseeqia/pdso
lution3.gif
21
Boiling Point Elevation
  • ?Tb m. kb
  • Tsolution Tb ?T
  • kb molal boiling point constant
  • m molality of the solute particles
  • For water kb 0.512oC/m

22
Note
  • If the solute is ionic, dissociation occurs.
  • More particles in solution.
  • Ionic solutions have greater effect on
    colligative properties.

23
Freezing Point Depression
  • Addition of a nonvolatile solute reduces the
  • vapor pressure of ice and therefore reduces the
  • freezing point.

24
Freezing Point Depression
25
Phase Diagram of Water (Black Line) and Solution
(Pink Line)
http//www.chemguide.co.uk/physical/phaseeqia/pdso
lution3.gif
26
Example
  • Salt in water to melt ice by reducing the
    freezing point of ice.

27
Example
  • Addition of ethylene glycol C2H6O2 (antifreeze)
    to the water in the radiator of a car allows the
    radiator to have a broader range of operation by
    raising the boiling point and lowering the
    freezing point.

28
Freezing Point Depression
  • ?Tf m. kf
  • Tsolution Tf - ?T
  • Kf molal freezing point constant
  • m molality of the solute particles
  • Example for water kf 1.86oC/m

29
Example 4
  • Find the boiling point of a solution containing
  • 57.0 g of sugar (MM 342g/mol) dissolved in
  • 50.0 g of water.
  • Answer101.7oC

30
Example 5
  • What is the freezing point of a solution
    containing 100. g of glucose in 150. g of water?
  • Answer-6.88oC

31
Example 6 Ionic Solute
  • What is the freezing point of a solution
    containing 30.0 g of magnesium chloride in 100. g
    of water?
  • Answer-17.6oC

32
Example 7 Calculate Molar Mass of Solute
  • 500g of a molecular solute were dissolved in
    250g of water. This resulted in a boiling point
    elevation of 2 K. Calculate the molar mass of the
    solute substance. (kb water 0.51 K kg/mol)
  • Answer 510g/mol
Write a Comment
User Comments (0)
About PowerShow.com