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Chapter 12
A
solution is a homogeneous mixture
composed of two or more substances. In such
a mixture, a solute is dissolved in another
substance, known as a solvent. A common
example is a solid, such as salt or sugar,
dissolved in water, a liquid. Gases may
dissolve in liquids, for example, carbon
dioxide or oxygen in water.
A measure often used in Chemistry is parts
per million(ppm) which can refer to mass or
volume. The number of parts per million by
mass is the mass of a solute in milligrams
divided by the mass of solvent in kg.
 The number of parts per million by volume is
the volume of a solute in microliters divided
by the volume of solvent in liters.

 The molar
solubility of a substance is its molar
concentration in a saturated solution. A saturated
solution is one in which the dissolved and
undissolved solute are in dynamic equilibrium
with each other. A saturated solution represents
the limit of a solute’s ability to dissolve in a given
quantity of solvent. Example if we measure the
concentration of glucose in its saturated solution
at 20⁰C we find it to be 6mol/L; so the molar
solubility of glucose in water at 20⁰C is 6mol/L.

Temperature:The solubility of a given solute in a given
solvent often depends on temperature. For around 95% of
solid solutes, the solubility increases with temperature, but
gaseous solutes exhibit more complex behavior. As the
temperature is raised gases usually become less soluble in
water, but more soluble in organic solvents.
 Polarity:
"Like dissolves like" This indicates that a
solute will dissolve best in a solvent that has a
similar polarity to itself. For example, a very polar
(hydrophilic) solute such as urea is highly soluble
in highly polar water, less soluble in fairly polar
methanol, and practically insoluble in non-polar
solvents such as benzene.
 Pressure:Henry’s
Law states that the
solubility of a gas is directly proportional
to the pressure of that gas, which may be
written as p=kc
where k is a constant
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Gases can dissolve in liquids: Gases may
dissolve in liquids, for example, carbon
dioxide or oxygen in water.
Gas solubility depends on pressure: A soda
bottle can be considered to be saturated
since there is some soda above the liquid
level and some is in the liquid itself.In an
unopened soda bottle there is much higher
partial pressure of CO₂ in the neck of the
bottle, above the liquid than there is in the air
outside the bottle.Due to this difference in the
pressure the CO₂ dissolves in the liquid.
 The
lowest concentration of oxygen that can
support aquatic life is about 1.3x10-4 mol/L.
The partial pressure of oxygen in water at
sea level adequate to maintain aquatic
life?What is the lowest partial pressure of
oxygen that can support life?
 The
enthalpy change of solution is the
enthalpy change when one mole of a
substance is dissolved completely in a large
volume of a solvent (forming a dilute
solution) at constant pressure.
 The formation of a solution involves the
interaction of solute with solvent molecules.
Many different liquids can be used as
solvents for liquid solutions, and water is the
most commonly used solvent. When water is
used as the solvent, the dissolving process is
called hydration.For other solvents it is
called as solvation.
 Enthalpy
of hydration, Hhyd, of an ion is the
amount of energy released when a mole of
the ion dissolves in a large amount of water
forming an infinite dilute solution in the
process, M2+(g) + mH2O  M2+(aq) where
M2+(aq) represents ions surrounded by water
molecules and dispersed in the solution.
 Enthalpies
of solution in dilute solution can
be expressed as the sum of the lattice
enthalpy and the enthalpy of hydration of
the compound.
 Small, highly charged ions have high
enthalpies of hydration.
 Colligative
properties of solutions are
properties that depend upon the
concentration of solute molecules or ions,
but not upon the identity of the solute.
Colligative properties include
 1. freezing point depression: The difference
between the freezing point of a pure solvent
and that of a solution.
 2. boiling point elevation:The difference
between the boiling point of a solution and
that of the pure solvent.
 3.vapor pressure lowering, and osmotic
pressure.
 Mole
fraction concentration:Mole Fraction
concentration is defined as the moles of one
component divided by Total Moles of
Components in solution.
 Mole Fraction of component 1 = X1 = moles of
component 1 / Total Moles of all components
in the solution.
 Molality of a solution is the number of moles
of solute in a solution divided by the mass of
the solvent in kilograms
Determine the mole fraction of KCl in 3000
grams of aqueous solution containing 37.3 grams
of Potassium Chloride KCl.
 Convert grams KCl to moles KCl using the
molecular weight of KCl 37.3 grams KCl X 1 mole
KCl / 74.6 grams KCl =0.5 mole KCl
 Determine the grams of pure solvent water from
the given grams of solution and solute Total
grams = 3000 grams = Mass of solute + Mass of
water
 3000 grams = 37.3 + grams of pure solvent water
 3000 - 37.3 = grams of pure solvent

 Convert
grams of solvent H2O to mols 2962.7
grams water X 1 mol / 18.0 grams = 164.6 mols
H2O
 Apply the definition for mole fraction mole
fraction = moles of KCl / Total mols of KCl and
water = 0.5 / 0.5 + 164.6 = 0.5 / 165.1 = 0.00303
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How many grams of water must be used to dissolve
100 grams of Sucrose C12H22O11 to prepare a .2
mole fraction of Sucrose in the solution?
Determine moles of Sucrose in 100 grams.
100 grams C12H22O11 X 1 mole C12H22O11 / 342 grams =
0.292 moles
Determine mols of solvent water from given mole fraction
and moles of solute mole fraction = 0.2 =
moles of Sucrose / mols Sucrose + mols water
Let x = mols water
0.2 = 0.292 / 0.292 + x
0.2 (0.292 + x) = .0584 + .2x = 0.292
x = (.292 - .0584)/ .2 = 1.168 mols water
Convert mols of water into grams 1.168 mols water X 18.0
grams water / 1 mol water = 21.0 grams water
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Determine the molality of 3000 grams of solution containing 37.3
grams of Potassium Chloride KCl.
Convert grams KCl to moles KCl using the molecular
weight of KCl
37.3 grams KCl X 1 mole KCl / 74.6 grams KCl =0.5 mole
KCl
Determine the grams of pure solvent from the given
grams of solution and solute
Total grams = 3000 grams = Mass of solute + Mass of
solvent
3000 grams = 37.3 + grams of pure solvent
3000 - 37.3 = grams of pure solvent
Convert grams of solvent to kilograms 2962.7 grams
solvent X 1 kg / 1000 grams = 2.9627 kg
Apply the definition for molality
molality = moles of KCl / kilograms of solvent = 0.5 /
2.9627 = 0.169m
 What
is the molality of a Nacl solution
prepared by dissolving 10.5 grams of sodium
chloride in 250g of water?
 What is the molality of a solution of
benzene, C₆H₆ in toluene, CH3C₆H₅ in which the
mole fraction of benzene is 0.150?
 The
pressure brought by the vapor in
equilibrium with its liquid is called the vapor
pressure.
 It increases upon increasing the
temperature. The vapor pressure of a pure
liquid depends on the rate of escape of the
molecules from the surface. If the liquid is
mixed with another substance, its
concentration is decreased and the rate of
escape is lowered.
 Raoult's
law: The vapor pressure of the
solvent in an ideal solution is equal to the
mole fraction of the solvent times the vapor
pressure of the pure solvent.
 Page
559- 561
 12.5,12.6,12.13,12.36,12.38
 When
a solute is added to a solvent, the
vapor pressure of the solvent (above the
resulting solution) is less than the vapor
pressure above the pure solvent. The boiling
point of a solution, then, will be greater than
the boiling point of the pure solvent because
the solution (which has a lower vapor
pressure) will need to be heated to a higher
temperature in order for the vapor pressure
to become equal to the external pressure
Pure water microscopic view.
Normal boiling
point = 100.0oC.
1.0 M NaCl solution microscopic view.
Normal boiling point
= 101.0oC.
The graph shows the normal boiling point
for water (solvent) as a function of molality
in several solutions containing sucrose (a
non-volatile solute).
 Freezing-point
depression describes the
phenomenon that the freezing point of a
liquid,is depressed when another compound
is added, meaning that a solution has a lower
freezing point than a pure solvent. This
happens whenever a solute is added to a
pure solvent, such as water.
 This phenomenon may be observed in sea
water, which due to its salt content remains
liquid at temperatures below 0°C, the
freezing point of pure water.
 The
addition of 0.24 g sulfur to 100g of
carbon tetrachloride lowers the freezing
point of carbon tetrachloride by 0.28⁰C. What
is the molar mass and molecular formula for
sulfur?
 The
flow of solvent through a membrane into
a more concentrated solution is called as
osmosis.The osmotic pressure is proportional
to the molar concentration of the solute.
 Molarity= osmotic pressure/RT
 In
a hypertonic environment, osmotic
pressure causes water to flow out of the cell.
 In a hypotonic environment has a lower
concentration of solute in the environment
than in the inside of the cell, making the net
flow of water into the cell and eventually
causing cell lysis.
 The
osmotic pressure due to 2.20 g of
polyethylene (PE) a molecular compound
dissolved in enough benzene to produce 100
ml of solution was 1.10x 10-2 atm at
25⁰C.Calculate the average molar mass of the
polymer.
 Page
562
 12.51,12.57, 12.67,12.74,