Physical Properties of Solutions

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Physical Properties of Solutions
Chapter 13
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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.
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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
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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.
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• 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
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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(??) Hydration is one kind of
Solvation
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Concentration Units
The concentration of a solution is the amount of
solute present in a given quantity of solvent or
solution.
Percent by Mass
by mass
Mole Fraction (X)
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Concentration Units Continued
Molarity (M)
Molality (m)
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What is the molality of a 5.86 M ethanol (C2H5OH)
solution whose density is 0.927 g/mL?
Assume 1 L of solution 5.86 moles ethanol 270
g ethanol 927 g of solution (1000 mL x 0.927 g/mL)
mass of solvent mass of solution mass of
solute
927 g 270 g 657 g 0.657 kg
8.92 m
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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
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Temperature and Solubility
Solid solubility and temperature
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Fractional crystallization(????)
Ex 90 g KNO3 mixed with 10g NaCl, when cooled to
0oC, (90-12) g78g KNO3 can be obtained
from mixed solution
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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.
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Pressure and Solubility of Gases
The solubility of a gas in a liquid is
proportional to the pressure of the gas over the
solution (Henrys 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/Latm) that
depends only on temperature
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Henrys law

• Henrys 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 Henrys law, however, some
  gas is
• excluded. EX
• Some reaction make the solubility much
  higher
• 1. NH3 H2O?NH4 OH-
• 2. CO2H2O? H2CO3
• 3. Hb4O2? Hb(O2)4

CO2 gas from soda
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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.

1. The solution concentration is lt 0.2 M
2. Vapor-Pressure Lowering
3. Boiling-Point Elevation
4. Freezing-Point Depression
5. Osmotic Pressure

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Vapor-Pressure Lowering
(?????)
X1 mole fraction of the solvent
Raoults law
???????? ??????X ??????
If the solution contains only one solute
X1 1 X2
X2 mole fraction of the solute
??????????????
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Volatile solution(both A and B are volatile)
PT PA PB
Ideal solution
0
DHsoln
???
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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 than
these between A or B molecular.
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Application Fractional distillation (???? or ??)
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Boiling-Point Elevation
T b is the boiling point of the solution
DTb gt 0
m is the molality of the solution
Kb is the molal boiling-point elevation
constant (0C/m) for a given solvent
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Freezing-Point Depression
T f is the freezing point of the solution
DTf gt 0
m is the molality of the solution
Kf is the molal freezing-point depression
constant (0C/m) for a given solvent
EX ?????? EG ??????
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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.
??
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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 62.01 g.
DTf Kf m
Kf water 1.86 oC/m
2.41 m
DTf Kf m
1.86 oC/m x 2.41 m 4.48 oC
0.00 oC 4.48 oC -4.48 oC
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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
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Osmotic Pressure (p)
time
solution
solvent
High P
Low P
p MRT
Ex 1.??????????, ?????? 2.?????????(????)
M is the molarity of the solution
R is the gas constant
T is the temperature (in K)
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A cell in an
isotonic solution
hypotonic solution
hypertonic solution
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??????
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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.
?????????????????(m or M)
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Free ions v.s bounded ion pair
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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
i should be
nonelectrolytes
1
NaCl
2
CaCl2
3
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Colligative Properties of Electrolyte Solutions
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Colloids (??) Between homogenous solution and
Nonhomogenous solution. A colloid is a
dispersion of particles of one substance
throughout a dispersing medium made of another
Substance.
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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.
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• Hydrophilic and Hydrophobic Colloids
• Hydrophilic water-loving
• Hydrophobic water-fearing

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E.g ?????????????
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A long hydrocarbon tail that is nonpolar.
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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 100.0 mmHg at 26.1C. 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 0.010 M solutions of CaCl2
and urea at 25C are 0.605 atm and 0.245 atm,
respectively. Calculate the van't Hoff factor for
the CaCl2 solution.