Brass, a solid solution of Zn and Cu, is used to make
musical instruments and many other objects.
14.1 General Properties of Solutions
14.2 Solubility
14.3 Rate of Dissolving Solids
14.4 Concentration of Solutions
14.5 Colligative Properties of Solutions
14.6 Osmosis and Osmotic Pressure
General Properties of Solutions
Solution: a homogeneous mixture of one or more
solutes and a solvent.
Solute: substance being dissolved.
Solvent: dissolving agent that is usually the
most abundant substance in the mixture.
Note: a solution does not always just refer to liquids.
Example: Air is a solution composed
of N2, O2, Ar and CO2
N2 is the solvent as it composes 78% of air.
Soda is a mixture of sugar in water.
Which substance is the solute?
a. sugar
b. water
c. soda
A solution is prepared by adding 25 mL of ethyl alcohol
to 75 mL of water. Which substance is the solvent?
a. ethyl alcohol
b. water
Common Types of Solutions
Properties of a True Solution
1. A homogeneous mixture of two or more components
whose ratio can be varied.
2. The dissolved solute is molecule or ionic in size
(< 1 nm).
3. Can be colored or colorless, though solutions are usually transparent.
4. The solute remains dissolved and does not settle
(precipitate) out of solution over time.
5. The solute can be separated from solvent by physical means (usually
evaporation).
Solubility
Solubility: the amount of a substance that will dissolve
in a specific amount of solvent at a given temperature.
Example
27 g KBr/100g H2O at 23 ºC
Miscible: when two liquids dissolve in each other.
Immiscible: when two liquids do not dissolve
one another.
A mixture of oil and water
is immiscible.
Solubility Rules
Soluble
Insoluble
Na+, K+, NH4+
Nitrates (NO3-)
Acetates, (C2H3O2-)
Cl-, Br-, I-
Except
Ag+, Hg22+, Pb2+
Sulfates (SO42-),
Ag+, Ca2+ (slightly)
Except
Ba2+, Sr2+, Pb2+
Except
Carbonates (CO32-)
Phosphates (PO43-)
OH-, Sulfides (S2-)
NH4+, Group I
Predict the solubility of barium sulfate.
a. soluble
b. insoluble
Most sulfates are soluble, except Ba2+.
Predict the solubility of NaCl.
a. soluble
b. insoluble
All Na+ salts are soluble.
Solutions Practice
Predict the solubility of silver nitrate.
a. soluble
All NO3- salts are soluble.
b. insoluble
Predict the solubility of silver hydroxide.
a. soluble
b. insoluble
Most hydroxides are insoluble.
Predict the solubility of ammonium carbonate.
a. soluble
b. insoluble
All NH4+ salts are soluble.
Factors Affecting Solubility
“Like Dissolves Like”
Polar compounds dissolve in polar solvents.
Ethanol (CH3OH) dissolves in water (HOH).
Nonpolar compounds dissolve in nonpolar solvents.
Carbon tetrachloride (CCl4) dissolves in
hexanes (CH3(CH2)4CH3).
Factors Affecting Solubility
Ionic Compound Solubility in Polar Solvents
Several ionic compounds dissolve in water,
due to strong ion-dipole forces.
The individual cations and anions are surrounded
by H2O molecules (i.e., hydrated).
The cation is attracted to the
partially negative O atom.
The anion is attracted to the
partially positive H atoms.
Temperature and Solubility
Solubility increases with
temperature for most
solids (red lines)
Solubility decreases with
temperature for all gases
(blue lines).
As a gas increases in temperature, the kinetic energy increases,
which means it interacts less with the liquid, making it less easy to
solvate.
Pressure and Solubility
Pressure does not affect solubility of liquids or solids.
Gas solubility in a liquid is proportional to
the gas pressure over the liquid.
Example: A bottle of root beer is under high pressure.
As the bottle opens, the pressure decreases,
and the bubbles formed indicate gas loss
from the liquid.
Saturated and Unsaturated Solutions
There are limits to the solubility of a compound
at a given temperature.
Saturated solutions: contain the maximum amount of dissolved
solute in a solvent.
Saturated solutions are still dynamic; dissolved solute
is in equilibrium with undissolved solute.
undissolved solute
dissolved solute
Unsaturated solutions: contain less than the maximum amount of
possible dissolved solute in a solvent.
Supersaturated Solutions
Supersaturated solutions: contain more solute than
needed to saturate a solution at a given temperature.
How is this possible?
Heating a solution can allow more to dissolve.
Upon cooling to ambient temperature,
the solution is supersaturated.
These solutions are unstable -- disturbing the solutions
can cause precipitation of solute.
Some hotpacks release heat by crystallization
of a supersaturated solution of sodium acetate.
Solubility Practice
Will a solution prepared by adding 9.0 g of KCl to
20.0 g of H2O be saturated or unsaturated at 20 ºC?
Using Table 14.3, 34.0 g of KCl will dissolve
in 100.0 g of H2O at 20 ºC.
6.8 g of KCl will then dissolve in
20.0 g of water at that temperature.
The KCl solution should be saturated.
Rate of Dissolving Solids
Effect of Particle Size:
A solid can only dissolve at a surface that
is in contact with the solvent.
Since smaller crystals have a higher surface to volume
area, smaller crystals dissolve faster than larger ones.
Rate of Dissolving Solids
Effect of Temperature
Increasing the temperature normally increases the rate
of dissolution of most compounds.
Solvent molecules strike the solid surface more often,
causing the solid to dissolve more rapidly.
The solute molecules are more easily separate from the
solid due to a higher kinetic energy.
Rate of Dissolving Solids
Effect of Solute Concentration
Rate is highest at higher concentration and
decreases at lower concentration.
As the solution approaches the saturation point,
the rate of solute dissolving decreases.
Rate of Dissolving Solids
Effect of Agitation/Stirring
Stirring a solution briskly breaks up a solid
into smaller pieces, increasing surface area,
thereby increasing the rate of dissolution.
Surface Area of Two Crystals
Surface area = 6(side)2 = 6(1cm)2 = 6 cm2
1000 cubes have a total surface area of
1000 x 0.06 cm2 = 60 cm2
Solutions: A Reaction Medium
The purpose of dissolving reactants in a solution is
often to allow them to come in close contact to react.
Example:
Solid-solid reactions are generally very slow
at ambient temperature
KCl (s) + AgNO3 (s)
No Reaction
By dissolving both compounds in water,
the ions can collide with one another and react
to form an insoluble compound.
KCl (aq) + AgNO3 (aq)
K+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)
AgCl (s) + KNO3 (aq)
AgCl(s) + K+(aq) + NO3-(aq)
Concentration of Solutions
Qualitative Expressions of Concentrations
Dilute: a solution that contains a relatively small
amount of dissolved solute.
Example: A 0.1 M HCl solution is dilute acid.
Concentrated: a solution that contains a relatively large
amount of dissolved solute.
Example: A 12 M HCl solution is concentrated acid.
Concentration of Solutions
Quantitative Expressions of Concentrations:
Units
Symbol
Mass percent
% m/m
Part per million
ppm
Mass/Volume percent
% m/v
Volume percent
% v/v
Molarity
M
Molality
m
Definition
mass solute
x 100
mass solution
mass solute
mass solution x 1,000,000
mass solute
x 100
mL solution
mL solute
x 100
mL solution
mol solute
L solution
mol solute
kg solvent
Mass Percent Practice
Calculate the mass % of NaCl in a solution prepared
by dissolving 50.0 g of NaCl in 150.0 g of H2O.
Knowns 50.0 g NaCl (solute mass)
150.0 g H2O (solvent mass)
200.0 g solution (solute + solvent mass)
Formula
mass % =
mass solute x 100
mass solution
Calculate
mass % =
50 g NaCl
200 g soln
x 100 = 25% NaCl
What is the mass of Na2CO3 needed to make
350.0 g of a 12.3% aqueous solution?
Knowns 12.3% solution (mass %)
350.0 g solution (solute + solvent mass)
Formula
mass % =
mass solute
x 100
mass solution
Calculate
mass solute =
Solve for mass
of solute
(Na2CO3)
mass solute = (mass %) x (mass soln)
100
12.3 x 350.0 g
100
= 43.1 g Na2CO3
What volume of a 3.0% H2O2 solution
will contain 10.0 g of H2O2?
a. 33.0 mL soln
b. 330. mL soln
c. 3.00 L soln
d. 165 mL soln
Knowns
10.0 g H2O2 (desired solute mass)
3.0 m/v%
Solve for volume of solution
Formula
g solute
m/v % =
mL solution
Calculate
mass solute =
x 100
mL solution =
10.0 g
3.0
x 100
g solute
m/v %
= 330. mL sln
x 100
What volume of soda that is 6.0 % by volume alcohol
contains 200.0 mL of ethanol (CH3CH2OH)?
A solution is prepared by mixing 20.0 mL of propanol
with enough water to produce 400.0 mL of solution.
What is the volume percent of propanol?
a. 20.0 %
b. 2.00 %
c. 5.00 %
d. 10.0 %
Molarity
molarity =
A common unit for solution concentration
due to convenience.
mol solute
L solution
Example:
To prepare a 1.0 M KCl
solution, 1.0 mol of KCl is
dissolved in enough water to
make 1.0 L of solution.
Calculate the molarity of a solution prepared by
dissolving 9.35 g of KCl in enough water to
prepare a 250.0 mL solution.
Molarity Practice
How many grams of KOH are required to prepare
600.0 mL of a 0.450 M KOH solution?
a. 0.270 g KOH
b. 4.81 g KOH
c. 1.52 x 104 g KOH
d. 15.1 g KOH
Solution Stoichiometry
Similar to previous stoichiometry problems, but we can
now use molarity as an additional conversion factor.
How many mL of 0.175 M Hg(NO3)2 are needed
to precipitate 2.50 g of KI?
Hg(NO3)2 (aq) + 2 KI (aq)
Plan
g KI
mol KI
2 KNO3 (aq) + HgI2 (s)
mol Hg(NO3)2
mL soln
Calculate
2.50 g KI
1 mol KI
×
166.00 g KI
×
1 mol Hg(NO3)2
2 mol KI
1000 mL soln
×
0.175 mol Hg(NO3)2
= 43.0 mL Hg(NO3)2
How many grams of AgCl will form by adding enough
AgNO3 to react fully with 1500. mL of
0.400 M BaCl2 solution?
2 AgNO3 (aq) + BaCl2(aq)
a. 172 g AgCl
b. 86.0 g AgCl
c. 8.37 x 10-3 g AgCl
d. 36.0 g AgCl
2 AgCl (s) + Ba(NO3)2 (aq)
Dilution
Dilution: Adding a solvent to a concentrated solution to
make the solution less concentrated (i.e. dilute).
When a solution is diluted, only the volume changes.
The number of moles of solute remains constant.
moles before dilution = moles after dilution
Molarity1 x Volume1 = Molarity2 x Volume2
M1 × V1 = M2 × V2
What volume of 12 M HCl is needed to make
500.0 mL of a 0.10 M HCl?
Dilution Practice
Calculate the molarity of a NaOH solution prepared by
mixing 100. mL of 0.20 M NaOH with 150 mL of H2O.
a. 2.0 M NaOH
b. 0.050 M NaOH
c. 0.080 M NaOH
d. 12.5 M NaOH