Aqueous Solutions
Solution: Homogeneous mixture; solid
liquid, or gas
Soluble: Capable of being dissolved
Solute: Substance that is dissolved,
present in lesser amounts
Solvent: Dissolving medium; present
in greater amounts
Types of Mixtures
Solutions: particles < 1nm; cannot be
seen; no scattering of light (salt water)
Suspensions: particles > 100 nm; settle to
the bottom (sand & water)
Colloids: particles 1-100 nm; suspended
throughout the medium; exhibit Tyndall
effect
Tyndall Effect: Scattering of light so that
the beam of light can be seen like
headlights in fog; seen in colloids
Hydration
Hydrates: ionic compounds with water
molecules in their structure
specific ratios of water to compound
heating can drive off the water and leave the
anhydrous salt
CuSO4 • 5H2O
(copper (II) sulfate pentahydrate
Hydrates
Effloresce: If a hydrate has a vapor pressure
greater than water vapor, than it will lose its
water of hydration
Hygroscopic: Hydrated salts that have a low
vapor pressure remove water from moist air to
form higher hydrates
Used as drying agents or desiccants
Silica gel
Deliquescent: remove sufficient water from the
air to dissolve completely and form solutions
Types of Solutes
Electrolytes: Conduct an electric current when
dissolved
All Ionic Compounds
Polar Molecules when dissolved in water (ionized)
Weak Electrolyte: fraction of the solute exist as ions
Strong Electrolyte: almost all of the solute exist as
separate ions
Nonelectrolytes: Do not conduct an electric
current when dissolved
Covalent compounds
Polar Molecules in a pure state
Dissociation
Sodium Chloride:
NaCl(s)  Na+1(aq) + Cl-1(aq)
Magnesium nitrate:
Mg(NO3)2(s)  Mg+2(aq) + 2NO3-1(aq)
Dissociation is the “breaking apart” of
ions as an ionic compound dissolves in
water.
Factors Affecting Rate of
Dissolution
Surface Area: Greater surface area
(smaller particle size) = faster dissolution
Agitation: stirring = faster dissolution
Heating: generally means faster
dissolution
Like Dissolves Like
The polarity of water molecules plays an
important role in the formation of
solutions of ionic compounds and other
polar compounds in water.
The positive ends of the water molecules
attract negative ions (dipoles) and the
negative ends of water molecules attract
positive ions (dipoles), pulling them from
the surface of the crystal.
Miscible/Immiscible
Nonpolar molecules do not attract ions of
crystalline solids strongly enough to
overcome forces holding them together
and therefore cannot dissolve polar or
ionic compounds.
Miscible : Two liquids mix; soluble in
one another (Ex: Ethanol & Water)
Immiscible: Do not mix; insoluble in one
another (Ex: Oil & Water)
Relative Concentration
Concentration: a measure of the amount of
solute that is dissolved in a given quantity of
solvent
Unsaturated: Less than the theoretical amount
of solute is dissolved; there is room to dissolve
more
Saturated: The maximum amount of solute that
can be dissolved at a certain temperature has
been reached
Supersaturated: More than the theoretical
amount of solute is dissolved in solvent at a
given temperature
Solubility/Recrystallization
Solubility:
A measure of how much solute can dissolve in a given
amount of solvent at a specific temperature
Dilute Solution: The amount of solute dissolved is small in
relation to the amount of solvent present.
Concentrated Solution: The amount of solute dissolved is large
in relation to the amount of solute present.
At the same time substances are breaking apart,
there are also particles attracted to each other and
remaining together – RECRYSTALLIZATION
Solution Equilibrium:
Rate of dissolution = Rate of recrystallization
Saturation Curve
Changing the temperature of a solvent can
have an effect on solubility!!
180
160
140
g / 100 mL
Supersaturated
Saturated
120
100
80
60
40
Unsaturated
20
0
0 10 20 30 40 50 60 70 80 90 100
°C
180
160
140
g / 100 mL
120
100
A
B
80
60
40
20
0
0 10 20 30 40 50 60 70 80 90 100
°C
Which solute has the greatest solubility at
20°C?
Which solute has the greatest solubility at
50°C?
Gas Solubility
Henry’s Law: S1 /P1 = S2 / P2
The solubility of a gas in a liquid is directly
proportional to the partial pressure of that gas
on the surface of the liquid.
Open a can of pop!! Carbon dioxide is
forced into solution of flavored water at
5-10 atm.
Effervescence: The FIZZING that happens
when you open the pop; the release of gas
from a solution
Concentrations of Solutions
Molarity = M = mol solute
L solution
Molality = m = mol solute
kg solvent
Percent by mass [% m/v] = mass solute x 100
mL solution
Percent by volume [% v/v] = vol solute x 100
vol solution
Dilutions
You have the following stock solutions
available: 2.0 M NaCl; 4.0 M KNO3;
0.5M MgSO4
Calculate the stock volumes you must
dilute to make the following solutions
using
M1V1 = M2V2
500 mL of a 0.50 M sodium chloride
solution
2.0 L of a .20 M magnesium sulfate
solution
Examples/Molarity
What is the molarity of a solution that
contains 212.5 g of sodium nitrate
(NaNO3) in 3.0 liters of solution?
What mass of sucrose, C12H22O11 is
needed to make 300 mL of a 0.50 M
solution?
Examples/Molality
Calculate the molality of a solution made
by dissolving 45.0 g of dextrose, C6H12O6
in 500.0 g of water.
What is the mass of water required to
prepare a 1.00 molal solution containing
10.0 g of NaOH?
Calculate the molality of a solution
prepared by dissolving 6.3 moles of KCN
in 633 g of water
Percent Problems
% m/v: Calculate the number of grams of
solute required to make the following
solutions:
2.5 L of saline solution– 90% NaCl
50 mL of 4% magnesium chloride
%v/v: 10 mL acetic acid is diluted with
water to a total solution volume of 200 mL.
What is the % v/v of acetic acid?
25mL of ethanol and 75 mL of water are
mixed. What is the % v/v of the solution?
Colligative Properties
Depend only on the number of particles
dissolved in a given mass of solvent
Vapor Pressure Lowering
Boiling Point Elevation
Freezing Point Depression
Vapor Pressure Lowering
A nonvolatile solute has a lower vapor pressure
than a pure solvent
As solutes are added the equilibrium is
disrupted and solvent particles form shells
around the solute particles. This reduces the
number of free solvent particles able to escape
the liquid. Equilibrium is eventually reestablished at a lower vapor pressure
Decrease in VP is proportional to the number of
particles the solute makes in solution
Solute that disassociate in large #s have a greater
effect of VP
Boiling Point Elevation
The difference in temperature between the
boiling point of a solution & that of a pure
solvent
Boiling points of solutions are higher than that
of pure solvents
The presence of solutes increase BP
Additional KE is required for particles to
overcome the attractive forces that keep them in
liquid
Boiling Point elevation (ΔTb): directly
proportional to the molal concentration
ΔTb α m
ΔTb = Kb x m
Freezing Point Depression
The Difference in temperature between
the freezing point of a solution and that of
the pure solvent
More KE must be withdrawn from a
solution than from a pure solution to
solidify
Freezing Point Depression (Δ Tf): directly
proportional to the molal concentration
Δ Tf = Kf x m