1. Physical Properties of Solutions
Chapter 13
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2. Chapter 13: Physical Properties of Solutions
Types of Solutions
Colligative Properties
Vapor Pressure Lowering
Mole fraction, Xa
Boiling Point Elevation
molality, m
Freezing Point Depression
Osmostic Pressure
Molarity, M

3. Chapter 13: Physical Properties of Solutions
Factors in Forming a Solution
Dissolution Process
Temperature & Solubility
Solids
Gases
Pressure and Gas Solubility
Colloids

4. A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount
12.1

5. A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.
An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.
A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.
12.1

6. IDEAL SOLUTIONS -Henry’s Law
The solubility of a gas is directly proportional to the gas pressure
Sg= khPg
When the partial pressure of the solute above a solution drops, the solubility of the gas in the solution drops as well to maintain the equilibrium.
This can be used to calculate the molar solubility of a gas.
What is the concentration of O2 in a fresh water stream in equilibrium with air at 25oC and 1.0 atm. (Hint there is 21% O2 in the air)

7. IDEAL SOLUTIONS(contd.) Vapor Pressure (Raoult’s Law))-
Vapor pressure at a given temperature is the pressure that the vapor exerts when the rate of molecules leaving the surface is equal to the rate of them re-condensing.
But what happens when something is now dissolved in the solvent.
2 things- 1. less solvent molecules at the surface. 2. different sets of attractive forces

8. RAOULT’S LAW
Less solvent molecules at the surface. Therefore less chance the water leaves, the vapor pressure is lowered.
This makes sense based on Henry’s law. The vapor pressure of the solvent will be proportional to the mole fraction in the liquid.
Psolvent= XsolventK
If we also look at a pure solvent Po,
then Po= XsolventK, Therefore Psolvent= Xsolvent Po
This is Raoult’s Law

9. Colligative Properties of Solutions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
Vapor Pressure Lowering
Boiling Point Elevation
Freezing Point Depression
Osmotic Pressure

10. Colligative Properties of Nonelectrolyte Solutions
Vapor-Pressure Lowering; The vapor pressure of a
Solution is lower than pure solute.
P1 = X1 P 1
P 1
= vapor pressure of pure solvent
X1 = mole fraction of the solvent
Raoult’s law
Mole Fraction (X1)
X1 =
moles of 1
sum of moles of all components
12.6

11. If the solution contains only one solute:
X1 + X2 =1
X1 = 1 – X2
X2 = mole fraction of the solute
X1 = mole fraction of the solvent
P1 = X1 P 1
P1 = (1-X2) P 1
P1 = P01-P01X2
P 1
- P1 = DP = X2
12.6

12. Lowering the Pressure Above the Solution (by opening bottle) Decreases Gas Solubility

13. Boiling-Point Elevation of Nonelectrolyte Solutions
DTb = Tb – T b
T b is the boiling point of
the pure solvent
T b is the boiling point of
the solution
Tb > T b
DTb > 0
DTb = Kb m
m is the molality of the solution
Kb is the molal boiling-point
elevation constant (0C/m)
12.6

14. Concentration Units Molarity (M) moles of solute M =
liters of solution
Molality (m)
m =
moles of solute
mass of solvent (kg)
12.3

15. 5.86 moles ethanol = 270 g ethanol
What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is g/mL?
m =
moles of solute
mass of solvent (kg)
M =
moles of solute
liters of solution
Assume 1 L of solution:
5.86 moles ethanol = 270 g ethanol
927 g of solution (1000 mL x g/mL)
mass of solvent = mass of solution – mass of solute
= 927 g – 270 g = 657 g = kg
m =
moles of solute
mass of solvent (kg) =
5.86 moles C2H5OH
0.657 kg solvent
= 8.92 m
12.3

16. 12.6

17. Freezing-Point Depression of Nonelectrolyte Solutions
DTf = T f – Tf
T f is the freezing point of
the pure solvent
T f is the freezing point of
the solution
T f > Tf
DTf > 0
DTf = Kf m
m is the molality of the solution
Kf is the molal freezing-point
depression constant (0C/m)
12.6

18. De-icing of Airplanes is Based on Freezing-Point Depression

19. DTf = Kf m Kf water = 1.86 0C/m DTf = Kf m
What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is g.
DTf = Kf m
Kf water = C/m =
3.202 kg solvent
478 g x
1 mol
62.01 g
m =
moles of solute
mass of solvent (kg)
= 2.41 m
DTf = Kf m
= C/m x 2.41 m = C
DTf = T f – Tf
Tf = T f – DTf
= C – C = C
12.6

20. Osmotic Pressure (p) of Nonelectrolyte Solutions
Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one.
A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules.
Osmotic pressure (p) is the pressure required to stop osmosis.
more
concentrated
dilute
12.6

21. A cell in an: isotonic hypotonic hypertonic
solution
hypotonic
solution
hypertonic
solution
12.6

22. Colligative Properties of Nonelectrolyte Solutions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
Vapor-Pressure Lowering
P1 = X1 P 1
Boiling-Point Elevation
DTb = Kb m
Freezing-Point Depression
DTf = Kf m
Osmotic Pressure (p)
p = MRT
12.6

23. Colligative Properties of Electrolyte Solutions
0.1 m NaCl solution
0.1 m Na+ ions & 0.1 m Cl- ions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
0.1 m NaCl solution
0.2 m ions in solution
van’t Hoff factor (i) =
actual number of particles in soln after dissociation
number of formula units initially dissolved in soln
i should be
Nonelectrolytes-Sugar 1 2
NaCl 3
CaCl2
AgCl
12.6

24. Colligative Properties of Electrolyte Solutions
Boiling-Point Elevation
DTb = i Kb m
Freezing-Point Depression
DTf = i Kf m
Osmotic Pressure (p)
p = iMRT
12.7

25. Factors in Forming a Solution
Dissolution Process
Temperature & Solubility
Solids
Gases
Pressure and Gas Solubility

26. Three types of interactions in the solution process:
solvent-solvent interaction
solute-solute interaction
solvent-solute interaction
DHsoln = DH1 + DH2 + DH3
12.2

27. “like dissolves like”
Two substances with similar intermolecular forces are likely to be soluble in each other.
non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
polar molecules are soluble in polar solvents
C2H5OH in H2O
ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)
12.2

28. Temperature and Solubility
Solid solubility and temperature
solubility increases with increasing temperature
solubility decreases with increasing temperature
12.4

29. Temperature and Solubility
Gas solubility and temperature
solubility usually decreases with increasing temperature
12.4

30. Pressure and Solubility of Gases
The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).
c is the concentration (M) of the dissolved gas
c = kP
P is the pressure of the gas over the solution
k is a constant (mol/L•atm) that depends only
on temperature
low P
high P
low c
high c
12.5

31. Colloid versus solution
A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.
Colloid versus solution
collodial particles are much larger than solute molecules
collodial suspension is not as homogeneous as a solution
12.8

32. The Cleansing Action of Soap
12.8