SOLUTIONS
Properties of Solutions (electrolytes) Chapter 9.1
Concentration (Section 9.5, 13.3)
·
·
·
·
·
molarity
mass %
mole fraction
ppm
molality
M
%
Xi
m
Solution process (energy changes)
Solubility
•  Saturation
•  supersaturation
Factors that Affect Solubility
•  temperature
•  intermolecular interactions
•  pressure
Mary J. Bojan
Chem 110
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SOLUTIONS: start with definitions
Homogeneous mixture: is uniformly mixed on a
molecular level.
Solute: the component of a mixture that is present
in smaller quantity.
Solvent: the component of a mixture that is present
in greatest quantity.
Aqueous solutions: water is the solvent
Mary J. Bojan
Chem 110
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What is an electrolyte?
DEMO to see which solutions can conduct electricity
·  For bulb to light, some minimum amount of current is needed.
·  amount of current is related to the CONDUCTIVITY of the solution.
CONDUCTIVITY: ability to conduct electricity
Which Bulbs
Light Up?
Bulb Wattage
7.5
25
40
Distilled H2O
Tap H2O
NaCl(aq)
0.1M HCl(aq)
0.1M CH3COOH
sugar(aq)
CH3OH
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Chem 110
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Why do electrolytes conduct electricity?
·  Strong electrolytes – Good conductors
NaCl(s) + H2O ! Na+(aq) + Cl!(aq) + H2O
HCl(aq) + H2O ! H3O +(aq) + Cl!(aq)
·  Weak electrolytes – Poor conductors
NH3(aq) + H2O ! NH4+(aq) + OH!(aq)
CH3COOH(aq)+H2O ! CH3COO!(aq)+H3O+(aq)
·  Nonelectrolytes – Non-conductors (do not conduct electricity)
(glucose)
C6H12O6(s)+H2O ! C6H12O6(aq)+ H2O
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Chem 110
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Electrolytes are an acid, a base or salt.
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Chem 110
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Electrolytes are an acid, a base or salt.
A.  Is the compound ionic or molecular?
Ionic:
Note:
Molecular ???
B.  If it is molecular, is it an acid or a base?
Yes:
No:
Examples of electrolytes (strong or weak)
Acids
donate H+(aq)
Bases
accept H+(aq)
Salts
formed by replacing one or more
H+ of an acid with another cation
Examples of non-electrolytes:
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Alcohols
Carbohydrates (sugar)
Aldehydes, ketones
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FYI: Ionic vs. Molecular
Ionic compounds: compound that
consist of + and ! ions
Eg.
Metal + nonmetal (usually)
NaCl
K2SO4
Mg(NO3)2
NH4Cl
Ionic compounds have high melting
points and are brittle.
Molecular compounds: compounds
consisting of individual molecules
All nonmetals or nonmetals and
metalloids.
Eg.
HCl
H 2O
CH3COOH
NH3
Molecular compounds usually have low
melting points
Mary J. Bojan
Chem 110
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How do you identify strong and weak
electrolytes?
•  Assume all salts are strong electrolytes.
•  Memorize strong acids (Table 9.1) and bases
•  If a compound is an acid or a base, but NOT one of the strong
acids or bases, then it MUST be a weak electrolyte.
Common misconception:
Only ionic compounds are electrolytes: this is NOT CORRECT!!!
The TRUTH:
·  Strong electrolytes are ionic or molecular compounds that
ionize completely in solution.
·  Weak electrolytes are molecular compounds that are partially
ionized in solution.
•  Nonelectrolytes are molecular compounds that do not ionize
in solution
Mary J. Bojan
Chem 110
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Expressing Concentration
mass fraction
= mass of component
total mass
weight %
= mass fraction "100%
mole fraction
= Xi = moles of component
total moles
parts per million (ppm) = Xi " 106
= mass fraction "106
parts per billion (ppb) = Xi " 109
parts per trillion (ppt) = Xi " 1012
molarity M
=
moles of solute
liters of solution
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molality m =
moles of solute
mass (kg) of solvent
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When a solution is diluted, the number of moles
remains constant.
DILUTION
Making a weaker solution by adding solvent.
M = concentration (molarity) of solution
& moles of solute #
M = molarity = $$
!!
% vol.of solution (L) "
V = volume of solution (L)
Number of moles of solute remains the same or:
Moles of solute = M V
SO#
Moles of solute (initial) = moles of solute (final = dilute)
Minit Vinit = Mfinal Vfinal
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Chem 110
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Solution process means solute molecules or ions separate
and are surrounded by solvent
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Chem 110
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Focus on the energy associated with the
solution process
1.  break solute-solute
interactions
2.  break solventsolvent
interactions
!  COSTS ENERGY
3. Form solute-solvent
interactions
!  ENERGY IS
RELEASED
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Chem 110
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The enthalpy change of the overall process depends on !H
for each of these steps.
Demonstrate the energy
changes in solution
CuSO4(s)
NH4NO3(s)
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Chem 110
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Why Do Endothermic
Processes Occur?
NH4NO3(s)
Things do not tend to occur
spontaneously unless"
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Chem 110
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Enthalpy is only part of the picture
Processes occur spontaneously when:
CCl4
energy is released (exothermic)
C6H14
disorder increases (increase in entropy)
CCl4
+
C6H14
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Chem 110
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Solution process involves dissolution and
crystallization of solute by the solvent.
When rates are equal
DYNAMIC EQUILIBRIUM
Saturated solution:
Supersaturated solution:
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Chem 110
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SOLUBILITY:
FACTORS THAT AFFECT SOLUBILITY
Temperature
–  Effect of Temperature on solubility of ionic solids
–  Effect of temperature on solubility of gases
Type of intermolecular interactions and their
strengths
(LIKE DISSOLVES LIKE)
Pressure
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Chem 110
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How does solubility of ionic solids change with
temperature?
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Chem 110
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How does solubility of gases change with
temperature?
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Chem 110
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How do intermolecular forces affect solubility?
In general: like dissolves like
–  polar solvents dissolve polar (and ionic solutes)
–  nonpolar solvents dissolve non-polar solutes
If intermolecular forces broken and formed are ~ the
same, dissolution is probable.
Which one of the following will be most soluble in benzene
(C6H6(! ))?
1.
2.
3.
4.
5.
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H2O(!)
CH3OH(!)
HCl(!)
CH3CH2OH(!)
heptane
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Like dissolves like
As length of hydrocarbon chain increases, solubility
of alcohol in water decreases.
Alcohol
solubility in water
at 25°C (g/100g of H2O)
CH3OH
total
CH3CH2OH
total
CH3CH2CH2OH
total
CH3CH2CH2CH2OH
8.06
CH3CH2CH2CH2CH2OH
2.82
CH3CH2CH2CH2CH2CH2OH
0.62
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Chem 110
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Put these in order of increasing solubility in water.
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Chem 110
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Demonstration: Like dissolves like
I2(s)
purple
CuSO4(s)
blue
H2O(!)
heptane(!)
Which solid is likely to dissolve in
H2O(!)
heptane(!)
Is water soluble in heptane? (like dissolves like?)
Mary J. Bojan
Chem 110
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Chem 110
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Which vitamin is soluble in fat?
Which vitamin is water soluble?
Fat soluble vitamins
can be stored in the
body
Water soluble vitamins
are not stored in
appreciable amounts
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How does solubility of gases change with pressure?
Increase Psolute(gas); increase solubility
Decrease Psolute(gas); decrease solubility
HENRY S Law
C g = k Pg
solubility
partial pressure
Cg
Pg
amount of gas dissolved (Cg) is
proportional to the partial pressure of
that gas (Pg) above the solution.
k = Henry s Law constant
Mary J. Bojan
Chem 110
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Deep Sea Diving
Solubility increases with
increasing P
# amount of N2 in blood
increases as depth
increases.
As divers rise, N2 bubbles out
of blood causing painful
bends .
Solution: use He/O2 mixture when diving deep.
He is not as soluble in blood.
!
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Chem 110
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Ammonia Fountain
H2O + phenolphthalein
(pink in base)
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Chem 110
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Test yourself
To increase the solubility of N2 in water
1.
2.
3.
4.
increase T
decrease T
increase P
decrease P
How will the solubility of KClO3 be effected by an
increase in pressure?
1. increase solubility
2. decrease solubility
3. no effect on solubility
Mary J. Bojan
Chem 110
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