Title: IV. Colligative Properties of Solutions
1IV. Colligative Properties of Solutions
- Ch. 16 Mixtures Solutions
2A. Definition
- Colligative Property
- property that depends on the number of solute
particles, not their identity in an ideal
solution
3B. 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
4B. Types
Freezing Point Depression
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5B. Types
Boiling Point Elevation
Solute particles weaken IMF in the solvent
6B. Types
- Applications
- salting icy roads
- making ice cream
- antifreeze
- cars (-64C to 136C)
- fish insects
7C. Calculations
?t k m n
- ?t change in temperature (C)
- k constant based on the solvent (Ckg/mol)
- m molality (m)
- n of particles
8C. 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)
9C. Calculations
- of Particles
- Nonelectrolytes (covalent)
- remain intact when dissolved
- 1 particle
- Electrolytes (ionic)
- dissociate into ions when dissolved
- 2 or more particles
10C. Calculations
- At what temperature will a solution that is
composed of 0.73 moles of glucose in 225 g of
phenol boil?
GIVEN
WORK
11C. 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
12C. Calculations
- Find the freezing point of a saturated solution
of NaCl containing 28 g NaCl in 100. mL water.
GIVEN
WORK
13C. 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
14C. 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
15C. 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
16C. Calculations
- i VHF
- Examples
- CaCl2
- Ethanol C2H5OH
- Al2(SO4)3
- Methane CH4
17C. 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
18C. 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
19C. 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
20C. 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
21D. 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
22D. Osmotic Pressure
- Net transfer of solvent
- molecules into the
- solution until the
- hydrostatic pressure
- equalizes the solvent flow
- in both directions
23D. 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
24D. Osmotic Pressure
Osmotic Pressure Minimum Pressure required to
stop flow of solvent into the solution
25D. Osmotic Pressure
Osmosis at Equilibrium
26E. 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
27E. 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
28D. Osmotic Pressure
- Colligative Properties useful for
- characterizing the nature of a solute after it is
dissolved in a solvent - determining molar masses of substances
29F. Reverse Osmosis
- If the external pressure is larger than the
osmotic pressure, reverse osmosis occurs - One application is desalination of seawater
30F. Reverse Osmosis
- Net flow of solvent
- from the solution to
- the solvent
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