Chapter 13
Section 1
Dissociation, Ionization,
Electrolytes &
Net Ionic Equations
SOLUTION VOCABULARY
Solution A homogeneous mixture of two or
more substances in a single phase (solute
dissolved in a solvent)
Dissociation occurs when an ionic compound
dissolves to form its constituent ions.
.
Ionization occurs when ions are formed from the
separation of particles in a molecular
compound
Compounds in Aqueous Solution
Dissociation
• Dissociation is separation of ions that occurs when
an ionic compound dissolves.
H2O
NaCl(s ) 
 Na  (aq ) + Cl– (aq )
1 mol
1 mol
1 mol
H2O
CaCl2 (s ) 
 Ca2 (aq ) + 2Cl– (aq )
1 mol
1 mol
2 mol
Dissociation of NaCl
Dissociation
•Sample Problem A
Write the equation for the dissolution of
aluminum sulfate, Al2(SO4)3 , in water.
How many moles of aluminum ions and
sulfate ions are produced by dissolving 1
mol of aluminum sulfate? What is the total
number of moles of ions produced by
dissolving 1 mol of aluminum sulfate?
Dissociation
Sample Problem A Solution
•Given:
amount of solute = 1 mol Al2(SO4)3
solvent identity = water
•Unknown: a. moles of aluminum and sulfate ions
b. total number of moles of solute ions produced
•Solution
H2O
Al2 (SO4 )3 (s) 
 2Al3 (aq ) + 3SO2–
4 (aq )
a. 1 mol Al2 (SO4 )3  2 mol Al3 + 3 mol SO2–
4
b. 2 mol Al3 + 3 mol SO2–
 5 mol of solute ions
4
Molecules in Aqueous Solution
Ionization
Ions can be formed from solute molecules by the
action of the solvent in a process called ionization.
• When a molecular compound dissolves and ionizes
in a polar solvent, multiple ions are formed where
none existed before the molecule dissolve.
• Hydrogen chloride, HCl, is a molecular compound
that ionizes in aqueous solution.
• HCl contains a highly polar bond.
H2O
HCl 
 H (aq ) + Cl– (aq )
Ionization
The Hydronium Ion
The “Acid” ion
• Some molecular compounds ionize in an aqueous
solution to release H+.
• The H+ ion attracts other molecules or ions so
strongly that it does not normally exist alone.
H2O
HCl 
 H3O (aq ) + Cl– (aq)
• The H3O+ ion is known as the hydronium ion.
Why is the formation of ions important?
Electrolytes:
• Electrolytes are substances that yield ions
and conduct an electric current in solution.
(95% of all chemical reactions occur when the chemicals are in
solution.)
• The strength with which substances conduct
an electric current is related to their ability to
form ions in solution.
• Strong and weak electrolytes differ in the
degree of ionization or dissociation.
Types of solutions
Strong Electrolytes  a compound that
completely or largely dissociates in an
aqueous solution. Solutions with strong
electrolytes conduct electricity very well.
Weak Electrolyte  a compound that
dissociates only to a small extent in
aqueous solution. Solutions of weak
electrolytes do not conduct electricity as
well as solutions with strong
electrolytes.
Strong and Weak Electrolytes
and Nonelectrolytes
Strong and Weak Electrolytes
and Nonelectrolytes
• A strong electrolyte is any compound whose dilute
aqueous solutions conduct electricity well; this is due
to the presence of all or almost all of the dissolved
compound in the form of ions.
• To whatever extent they dissolve in water, they yield
only ions.
• HCl, HBr, HI
• All soluble ionic compounds
Strong and Weak Electrolytes
and Nonelectrolytes
• A weak electrolyte is any compound whose dilute
aqueous solutions conduct electricity poorly; this is
due to the presence of a small amount of the
dissolved compound in the form of ions.
• Some molecular compounds form aqueous solutions
that contain not only dissolved ions but also some
dissolved molecules that are not ionized.

–


HF 
H
O
(
aq
)
+
F
(aq )
 3
[HF] >> [H+] and [F–]
Compounds in Aqueous Solution
• Write equations for the dissolution of soluble
ionic compounds in water.
• Predict whether a precipitate will form when
solutions of soluble ionic compounds are
combined, and write net ionic equations for
precipitation reactions.
• Compare dissociation of ionic compounds
with ionization of molecular compounds.
Dissociation
Net Ionic Equations
• A net ionic equation includes only
those compounds and ions that
undergo a chemical change in a
reaction in an aqueous solution.
• Ions that do not take part in a chemical
reaction and are found in solution both
before and after the reaction are
spectator ions.
Net Ionic Equations
Cd(NO3)2 + (NH4)2S 
Overall ionic equation
Cd2 (aq ) + 2NO3– (aq ) + 2NH4 (aq ) + S2– (aq ) 
CdS(s ) + 2NO3– (aq ) + 2NH4 (aq )
net ionic equation
Cd2 (aq ) + S2– (aq )  CdS(s )
Writing a Net Ionic Equation
Net Ionic Equation
•Sample Problem B
Identify the precipitate that forms when
aqueous solutions of zinc nitrate and
ammonium sulfide are combined. Write the
equation for the possible doubledisplacement reaction. Then write the
formula equation, overall ionic equation,
and net ionic equation for the reaction.
Net Ionic Equation
Sample Problem B Solution
• Given: identity of reactants: zinc nitrate and
ammonium sulfide
• Unknown:
a. equation for the possible
double-displacement reaction
b. identity of the precipitate
c. formula equation
d. overall ionic equation
e. net ionic equation
Net Ionic Equation
• Solution:
Zn(NO3 )2 (aq ) + (NH4 )2 S(aq )  ZnS(? ) + 2NH4NO3 (? )
Table 1 reveals that zinc sulfide is not a soluble
sulfide and is therefore a precipitate.
Ammonium nitrate is soluble according to
the table.
The formula equation
Zn(NO3 )2 (aq ) + (NH4 )2 S(aq )  ZnS(s ) + 2NH4NO3 (aq )
Net Ionic Equation
The overall ionic equation
Zn2 (aq ) + NO3– (aq ) + NH4 (aq ) + S2– (aq )
 ZnS(s ) + NH4 (aq ) + NO3– (aq )
The ammonium and nitrate ions appear on
both sides of the equation as spectator ions.
The net ionic equation
Zn2 (aq ) + S2– (aq )  ZnS(s )