1. Physical Properties of Solutions
Chapter 13

2. 1. Most chemical reaction occurs when ions and molecular
Interaction within solution phase
2. In Ch5 and Ch11, we mentioned the gas, liquid and solid
properties.
3. In this chapter, we will focus on the molecular interaction
in solution phase.

3. 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

4. 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.
Crystallization
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.

5. Molecular view of the formation of solution
Three types of interactions in the solution process:
solvent-solvent interaction
solute-solute interaction
solvent-solute interaction
Molecular view of the formation of solution
DHsoln = DH1 + DH2 + DH3

6. Solvation(溶合): Hydration is one kind of Solvation
“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)
Solvation(溶合): Hydration is one kind of Solvation

7. Concentration Units
The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.
Percent by Mass
x 100%
mass of solute
mass of solute + mass of solvent
% by mass = =
x 100%
mass of solute
mass of solution
Mole Fraction (X)
XA =
moles of A
sum of moles of all components

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

9. What is the molality of a 5
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

10. Selection of the concentration unit
Mole fraction: used to calculate the partial pressure of gas or
the vapor pressure of a solution.
Molarity : Ease for preparing the solution
Molality : When consider the temperature effect on solution
using Molality will be better
e.g.: 1.0 M solution prepared at 25 oC will change to
0.97M when temperature upto 45oC

11. Temperature and Solubility
Solid solubility and temperature
solubility increases with increasing temperature
solubility decreases with increasing temperature

12. Fractional crystallization(分項結晶)
Ex: 90 g KNO3 mixed with 10g NaCl, when cooled to 0oC,
(90-12) g=78g KNO3 can be obtained from mixed solution

13. Temperature and Solubility
O2 gas solubility and temperature
solubility usually decreases with increasing temperature
Heat west will strongly effect the environment due to the low solubility
of O2 in water.

14. 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 for each gas (mol/L•atm) that depends only on temperature
low P
high P
low c
high c

16. Henry’s law
Henry’s Law can be explained as the impact frequency between gas molecular and liquid surface
The kinetic equilibrium: Vapor rate v.s Solubility
Most gas will follow Henry’s law, however, some gas is
excluded. EX:
Some reaction make the solubility much higher:
1. NH3 + H2ONH4+ + OH-
2. CO2+H2O H2CO3
3. Hb+4O2 Hb(O2)4
CO2 gas from soda

17. Colligative Properties
依數性質
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
The solution concentration is < 0.2 M
Vapor-Pressure Lowering
Boiling-Point Elevation
Freezing-Point Depression
Osmotic Pressure

18. 溶液中之溶劑分壓= 純溶劑蒸氣壓X 溶劑莫耳分率
Vapor-Pressure Lowering
(蒸氣壓下降)
P1 = X1 P 1
P 1
= vapor pressure of pure solvent
Raoult’s law
X1 = mole fraction of the solvent
溶液中之溶劑分壓= 純溶劑蒸氣壓X 溶劑莫耳分率
If the solution contains only one solute:
X1 = 1 – X2
P 1
- P1 = DP = X2
X2 = mole fraction of the solute
蒸氣壓下降與溶質莫耳數成正比

19. Volatile solution(both A and B are volatile)
PA = XA P A
PB = XB P B
Ideal Solution
PT = PA + PB
PT = XA P A
+ XB P B
Ideal solution:
DHsoln =0
溶解熱

20. Nonideal gas:
Case 1: The intermolecular forces between A and B are weaker
than these between A or B molecular.
Case 2: The intermolecular forces between A and B are stronger

21. Application: Fractional distillation (分餾結晶 or 蒸餾)

22. Boiling-Point Elevation
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)
for a given solvent

23. Freezing-Point Depression
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)
for a given solvent
EX: 灑鹽讓雪融化
EG 乙二醇抗凍劑

24. How to explain the freezing-point depression:
A transition from the disordered state to the order state. For
This to happen, more energy needs to be removed from the
System. Because solution has greater disorder than the solvent,
More energy need to removed. 亂度

26. DTf = Kf m Kf water = 1.86 oC/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 = 1.86 oC/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
= 1.86 oC/m x 2.41 m = 4.48 oC
DTf = T f – Tf
Tf = T f – DTf
= 0.00 oC – 4.48 oC = oC

27. Osmotic Pressure (p)
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

28. Osmotic Pressure (p) p = MRT High P Low P Ex: 1.紅血球放在低滲溶液中, 使血球爆破。
time
solvent
solution
High P
Low P
p = MRT
Ex: 1.紅血球放在低滲溶液中,
使血球爆破。
2.用大量糖保存食物。(高滲溶液)
M is the molarity of the solution
R is the gas constant
T is the temperature (in K)

29. A cell in an:
isotonic
solution
hypotonic
solution
hypertonic
solution

30. 海水淡化科技

32. Colligative Properties
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
一般可由實驗方式量測溶液的待測濃度(m or M)

33. Free ions v.s bounded ion pair

34. Colligative Properties of Electrolyte Solutions
考慮電解質的依數性質
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 1
NaCl 2
CaCl2 3

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

36. Colloids (膠體)
Between homogenous solution and Nonhomogenous solution.
A colloid is a dispersion of particles of one substance throughout
a dispersing medium made of another Substance.

37. How to identify the solution and colloid?
One way to distinguish a solution from
A colloid is be the Tyndall effect.
When a beam of light passes through
A colloid, it is scattered by the dispersed
Phase.

38. Hydrophilic and Hydrophobic Colloids
Hydrophilic: water-loving
Hydrophobic: water-fearing

39. E.g: 河流道出海口形成淤泥的現象

40. A long hydrocarbon tail that is nonpolar.

42. HW CH13
13.17 Calculate the molalities of these aqueous solutions: (a) 1.22 M sugar (C12H22O11) solution (density of solution = 1.12 g/mL), (b) 0.87 M NaOH solution (density of solution = 1.04 g/mL), (c) 5.24 M NaHCO3 solution (density of solution = 1.19 g/mL).
13.49 The vapor pressure of benzene is mmHg at 26.1°C. Calculate the vapor pressure of a solution containing 24.6 g of camphor (C10H16O) dissolved in 98.5 g of benzene. (Camphor is a low-volatility solid.)
13.75 The osmotic pressure of M solutions of CaCl2 and urea at 25°C are atm and atm, respectively. Calculate the van't Hoff factor for the CaCl2 solution.