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IV. Colligative Properties of Solutions

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Title: IV. Colligative Properties of Solutions


1
IV. Colligative Properties of Solutions
  • Ch. 16 Mixtures Solutions

2
A. Definition
  • Colligative Property
  • property that depends on the number of solute
    particles, not their identity in an ideal
    solution

3
B. Types
  • Freezing Point Depression (?Tf)
  • f.p. of a solution is lower than f.p. of the pure
    solvent
  • Boiling Point Elevation (?Tb)
  • b.p. of a solution is higher than b.p. of the
    pure solvent

4
B. Types
Freezing Point Depression
View Flash animation
5
B. Types
Boiling Point Elevation
Solute particles weaken IMF in the solvent
6
B. Types
  • Applications
  • salting icy roads
  • making ice cream
  • antifreeze
  • cars (-64C to 136C)
  • fish insects

7
C. Calculations
?t k m n
  • ?t change in temperature (C)
  • k constant based on the solvent (Ckg/mol)
  • m molality (m)
  • n of particles

8
C. Calculations
?T i m K
  • ? T change in temperature (C)
  • i Vant Hoff Factor (VHF), the number of
    particles into which the solute dissociates
  • m molality (m)
  • K constant based on the solvent (Ckg/mol) or
    (C/m)

9
C. Calculations
  • of Particles
  • Nonelectrolytes (covalent)
  • remain intact when dissolved
  • 1 particle
  • Electrolytes (ionic)
  • dissociate into ions when dissolved
  • 2 or more particles

10
C. Calculations
  • At what temperature will a solution that is
    composed of 0.73 moles of glucose in 225 g of
    phenol boil?

GIVEN
WORK
11
C. Calculations
  • At what temperature will a solution that is
    composed of 0.73 moles of glucose in 225 g of
    phenol boil?

GIVEN b.p. ? ?tb ? kb 3.04Ckg/mol
WORK m 0.73mol 0.225kg
?tb (3.04Ckg/mol)(3.2m)(1) ?tb 9.7C b.p.
181.8C 9.7C b.p. 192C
m 3.2m n 1 ?tb kb m n
12
C. Calculations
  • Find the freezing point of a saturated solution
    of NaCl containing 28 g NaCl in 100. mL water.

GIVEN
WORK
13
C. Calculations
  • Find the freezing point of a saturated solution
    of NaCl containing 28 g NaCl in 100. mL water.

GIVEN f.p. ? ?tf ? kf 1.86Ckg/mol
WORK m 0.48mol 0.100kg
?tf (1.86Ckg/mol)(4.8m)(2) ?tf 18C f.p.
0.00C - 18C f.p. -18C
m 4.8m n 2 ?tf kf m n
14
C. Calculations
  • ? T
  • Change in temperature
  • Not actual freezing point or boiling point
  • Change from FP or BP of pure solvent
  • Freezing Point (FP)
  • ? TF is always subtracted from FP of pure solvent
  • Boiling Point (BP)
  • ? TB is always added to BP of pure solvent

15
C. Calculations
  • i VHF
  • Nonelectrolytes (covalent)
  • remain intact when dissolved
  • 1 particle
  • Electrolytes (ionic)
  • dissociate into ions when dissolved
  • number of ions per formula unit
  • 2 or more particles

16
C. Calculations
  • i VHF
  • Examples
  • CaCl2
  • Ethanol C2H5OH
  • Al2(SO4)3
  • Methane CH4
  • i
  • 3
  • 1
  • 5
  • 1

17
C. Calculations
  • K molal constant
  • KF molal freezing point constant
  • Changes for every solvent
  • 1.86 Ckg/mol (or C/m) for water
  • KB molal boiling point constant
  • Changes for every solvent
  • 0.512 Ckg/mol (or C/m) for water

18
C. Calculations Recap!
?T i m K
  • ? T subtract from F.P.
  • add to B.P.
  • i VHF covalent 1
  • ionic gt 2
  • K KF water 1.86 Ckg/mol
  • KB water 0.512 Ckg/mol

19
C. Calculations
  • At what temperature will a solution that is
    composed of 0.730 moles of glucose in 225 g of
    water boil?

GIVEN b.p. ? ?TB ? i 1
WORK m 0.730 mol 0.225 kg
100 ?Tb
?TB (1)(3.24m)(0.512C/m) ?TB 1.66C b.p.
100.00C 1.66C b.p. 101.66C
m 3.24m KB 0.512C/m ?TB i m KB
20
C. Calculations
  • Find the freezing point of a saturated solution
    of NaCl containing 28 g NaCl in 100. mL water.

GIVEN f.p. ? ?TF ?
WORK m 0.48mol 0.100kg
0 ?TF
?TF (2)(4.8m)(1.86C/m) ?TF 18C f.p.
0.00C 18C f.p. -18C
i 2 m 4.8m KF 1.86C/m ?TF i m KF
21
D. Osmotic Pressure
  • Osmosis The flow of solvent into a solution
    through a semipermeable membrane
  • Semipermeable Membrane membrane that allows
    solvent to pass through but not solute

22
D. Osmotic Pressure
  • Net transfer of solvent
  • molecules into the
  • solution until the
  • hydrostatic pressure
  • equalizes the solvent flow
  • in both directions

23
D. Osmotic Pressure
  • Because the liquid level for the solution is
    higher, there is greater hydrostatic pressure on
    the solution than on the pure solvent
  • Osmotic Pressure
  • The excess hydrostatic pressure on the solution
    compared to the pure solvent

24
D. Osmotic Pressure
Osmotic Pressure Minimum Pressure required to
stop flow of solvent into the solution
25
D. Osmotic Pressure
Osmosis at Equilibrium
26
E. Osmotic Pressure Calculations
  • ? i M R T
  • where
  • p osmotic pressure (atm)
  • i VHF
  • M Molarity (moles/L)
  • R Gas Law Constant
  • T Temperature (Kelvin)

0.08206 L atm/mol K
27
E. Osmotic Pressure Calculations
  • Calculate the osmotic pressure (in torr) at 25oC
    of aqueous solution containing 1.0g/L of a
    protein with a molar mass of 9.0 x 104 g/mol.

GIVEN ? ?
WORK M 1.0 g prot.
1 mol prot.

1 L soln
9.0 x 104 g
i 1 M 1.11 x 10-5 M R 0.08206 L atm/mol K T
25oC 298 K
1.11 x 10-5 M ? (1)(1.11x10-5)(.08206)(298)
? 2.714 x 10-4 atm ? 0.21 torr
28
D. Osmotic Pressure
  • Colligative Properties useful for
  • characterizing the nature of a solute after it is
    dissolved in a solvent
  • determining molar masses of substances

29
F. Reverse Osmosis
  • If the external pressure is larger than the
    osmotic pressure, reverse osmosis occurs
  • One application is desalination of seawater

30
F. Reverse Osmosis
  • Net flow of solvent
  • from the solution to
  • the solvent

31
  • Carli Elizabeth Oster and Ayzsa Fulani Tannis are
    the most fantastic people in the whole wide
    world.
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