Ions in Aqueous Solutions and Colligative Properties
Chapter 13
Modern Chemistry
Sections 1 & 2
Compounds in Aqueous Solutions
Colligative Properties of a Solution
1
Section 13.1
Compounds in Aqueous Solutions
Chapter 13 Section 1 Comp. in
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2
VOCABULARY
Dissociation Equation
Precipitate
Net Ionic Equation
Spectator Ion
Ionization
Hydronium Ion
Strong Electrolyte
Weak Electrolyte
Chapter 13 Section 1 Comp. in
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3
Concept Map 13.1
DISSOCIATION
EQUATION
PRECIPITATE
REACTIONS
SPECTATOR
IONS
NET IONIC EQUATIONS
DISSOCIATION
IONIZATION
HYDRONIUM ION
STRONG ELECTROLYTE
WEAK ELECTROLYTE
Chapter 13 Section 1 Comp. in
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4
Dissociation Equations
• Dissociation is the separation of ions that
occurs when an ionic compound dissolves
• Dissociation equations show how an ionic solid
breaks into ions when it dissociates.
NaCl (s)  Na1+(aq) + Cl1-(aq)
CaCl2 (s)  Ca2+(aq) + 2Cl1-(aq)
• Don’t forget to balance the equation or add
state of matter symbols.
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5
Dissociation Equations
CaCl2
(s)
 Ca2+(aq) + 2Cl1-(aq)
• CaCl2 gives three ions per formula unit – one
calcium and two chlorine.
• When one mole of CaCl2 dissociates…
• One mole of calcium ions are produced
• Two moles of chloride ions are produced
• Three moles of ions – total- are produced
Chapter 13 Section 1 Comp. in
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6
Dissociation Sample Problem
1. 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?
Al2(SO4)3 (s)  2Al3+
(aq)
+ 3SO4
2−
(aq)
2 mol aluminum ions, 3 mol sulfate ions
p. 436
5 ions total
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7
Dissociation Practice Problems
p. 436
1. Write the equation for the dissolution of each
of the following in water, and then determine
the number of moles of each ion produced as
well as the total number of moles of ions
produced.
a. 1 mol ammonium chloride
b. 1 mol sodium sulfide
c. 0.5 mol barium nitrate
Chapter 13 Section 1 Comp. in
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8
Dissociation Practice Problems
a. NH4Cl (s)  NH4 1+
(aq)
+ Cl
1−
(aq)
1 mol ammonium ions; 1 mol chloride ions; 2
mol total ions
b. Na2S (s)  2Na1+ (aq) + S 2−(aq)
2 mol sodium ions; 1 mol sulfide ions; 3 mol
total ions
c. Ba(NO3)2 (s)  Ba2+
(aq)
+ 2NO3
1−
(aq)
p. 436
1 mol barium ions; 2 mol nitrate ions; 3 mol
total ions
Chapter 13 Section 1 Comp. in
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9
Solubility of Ionic Compounds
p. 437
Chapter 13 Section 1 Comp. in
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10
General Solubility Guidelines
p. 437
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11
General Solubility Guidelines
Chapter 13 Section 1 Comp. in
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12
General Solubility Guidelines
Chapter 13 Section 1 Comp. in
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13
(NH4)2S + Cd(NO3)2
p. 438
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14
NET IONIC EQUATION
• Write the balanced equation for the reaction
between ammonium sulfide and cadmium II
nitrate. Be sure to include states of matter
• What type of reaction is it? What are the
products?
(NH4)2S
(aq)
+ Cd(NO3)2 (aq) 
2 NH4NO3
Chapter 13 Section 1 Comp. in
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(aq)
+ CdS (s)
15
NET IONIC EQUATION
(NH4)2S
(aq)
+ Cd(NO3)2 (aq)  2 NH4NO3
(aq)
+ CdS (s)
Each (aq) is dissociated.
The (s) is not dissociated; it is the precipitate.
Write the dissociation equation for each (aq).
(NH4)2S (s)  2 (NH4)1+ (aq) + S2-(aq)
Cd(NO3)2 (s)  Cd2+(aq) + 2 NO31- (aq)
2 NH4NO3 (aq)  2 NH41+ (aq) + 2 NO31- (aq)
Chapter 13 Section 1 Comp. in
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16
NET IONIC EQUATION
(NH4)2S
2
+ Cd
Cd(NO
(NO3) 2 (aq)  2 NH44NO3
(aq)
(aq)
+ CdS (s)
1+
2-
2+
1-
1+
1-
(aq)
(aq)
(aq)
(aq)
(aq)
(aq)
+
+
+2
2
+2
+
(s)
Break all (aq) into ions; not the (s)
Balance and add states
Chapter 13 Section 1 Comp. in
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17
NET IONIC EQUATION
(NH4)2S
(aq)
+ Cd(NO3)2 (aq)  2 NH4NO3
(aq)
+ CdS (s)
1+
2-
2+
1-
1+
1-
(aq)
(aq)
(aq)
(aq)
(aq)
(aq)
2 (NH4) + S + Cd + 2 (NO3)  2 NH4 + 2 NO3 + CdS
+

Identify spectator ions and remove
Write what’s left.
Chapter 13 Section 1 Comp. in
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18
(s)
NET IONIC EQUATION
(NH4)2S
(aq)
1+
2 (NH4) +
+ Cd(NO3)2 (aq)  2 NH4NO3
+ CdS (s)
1-
1+
1-
(aq)
(aq)
(aq)
+ 2 (NO3)  2 NH4 + 2 NO3 +
+
(aq)
Cd
(aq)
2+
(aq)
+
S
2(aq)

CdS
(s)
This is the net ionic equation.
Chapter 13 Section 1 Comp. in
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19
Ag(NO3) + NaCl
Chapter 13 Section 1 Comp. in
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20
NET IONIC EQUATION
• Write the balanced equation for the reaction
between sodium chloride and silver nitrate. Be
sure to include states of matter
• What type of reaction is it? What are the
products?
NaCl
(aq)+
Ag(NO3) (aq)  NaNO3
Chapter 13 Section 1 Comp. in
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(aq)+
AgCl (s)
21
NET IONIC EQUATION
NaCl
(aq)
+ AgNO3 (aq)  NaNO3
(aq)
+ AgCl (s)
Each (aq) is dissociated.
The (s) is not dissociated; it is the precipitate.
Write the dissociation equation for each (aq).
NaCl (s)  Na1+ (aq) + Cl1-(aq)
Ag(NO3) (s)  Ag1+(aq) + NO31- (aq)
NaNO3 (aq)  Na1+ (aq) + NO31- (aq)
Chapter 13 Section 1 Comp. in
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22
NET IONIC EQUATION
NO3 (aq)  NaNO
NaNO33
NaCl (aq) + Ag
AgNO
1+
1+
1-
+
(aq)
+
(aq)
1-

+
(aq)
(aq)
(aq)
1+
+
(aq)
+ AgCl (s)
1-
+
(s)
(aq)
Break all (aq) into ions; not the (s)
Balance and add states
Chapter 13 Section 1 Comp. in
Aq. Soln p. 434-445
23
NET IONIC EQUATION
NaCl
(aq)
+ AgNO3 (aq)  NaNO3
1+
1-
(aq)
(aq)
1+
(aq)
+ AgCl (s)
1-
1+
1-
(aq)
(aq)
(aq)
Na + Cl + Ag + NO3  Na + NO3 + AgCl
(aq)
+
(s)

Identify spectator ions and remove
Write what’s left.
Chapter 13 Section 1 Comp. in
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NET IONIC EQUATION
NaCl
(aq)
1+
Na +
+ AgNO3 (aq)  NaNO3
(aq)
Ag
(aq)
+ AgCl (s)
1-
1+
1-
(aq)
(aq)
(aq)
+ NO3  Na + NO3 +
+
1+
(aq)
+
1-
Cl

(aq)
AgCl
(s)
This is the net ionic equation.
Chapter 13 Section 1 Comp. in
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25
NET IONIC EQUATION
(NH4)2S
(aq)
1+
2 (NH4) +
+ Cd(NO3)2 (aq)  2 NH4NO3
+
(aq)
2+
Cd
(aq)
(aq)
+ CdS (s)
1-
1+
1-
(aq)
(aq)
(aq)
+ 2 (NO3)  2 NH4 + 2 NO3 +
+
2-
S
(aq)

CdS
(s)
This is the net ionic equation.
Chapter 13 Section 1 Comp. in
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26
Sample Problem p. 440
Identify the precipitate that forms when aqueous
solutions of zinc nitrate and ammonium
sulfide are combined. Write the equation for
the possible double-displacement reaction.
Then write the formula equation, overall ionic
equation, and net ionic equation for the
reaction.
p. 440
Zn 2+ (aq) + S 2 (aq)  ZnS (s)
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Practice Problems p. 440
1. Will a precipitate form if solutions of
potassium sulfate and barium nitrate are
combined? If so, write the net ionic equation
for the reaction.
1. Yes; Ba 2+ (aq) + SO4 2 (aq) BaSO4 (s)
2. Will a precipitate form if solutions of
potassium nitrate and magnesium sulfate are
combined? If so, write the net ionic equation
for the reaction.
p. 440
2. No
Chapter 13 Section 1 Comp. in
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Practice Problems p. 440
3. Will a precipitate form if solutions of barium
chloride and sodium sulfate are combined? If
so, identify the spectator ions and write the
net ionic equation.
3. Yes; Na+ and Cl;
Ba 2+ (aq) + SO4 2 (aq)  BaSO4 (s)
4. Write the net ionic equation for the
precipitation of nickel(II) sulfide.
p. 440
4. Ni 2+ (aq) + S 2 (aq)  NiS (s)
Chapter 13 Section 1 Comp. in
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29
Ionization vs. Dissociation
• Covalent compounds
• Ions are formed from
solute molecules
when they dissolve.
• Ionic compounds
• Ions are already
present – the ions
are separated by
the water
molecules.
Chapter 13 Section 1 Comp. in
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30
Dissociation & Ionization
Chapter 13 Section 1 Comp. in
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Ionization
• Usually occurs with polar molecules
• If the strength of a bond within the solute
molecule is weaker than
the attractive forces of the solvent molecules,
then the covalent bond of the solute breaks
and the molecule is separated into ions.
HCl
(g)

H1+(aq) + Cl1-(aq)
• The ions are hydrated – just like ions from
dissociation.
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32
Hydronium ion, H3
+
O
• H+ ion does not exist by itself.
• H+ ion bonds to a water molecule to form
H3O+, a hydronium ion.
H2O
(l) + HCl
(g)
 H3O+(aq) + Cl-(aq)
• Better described as a reaction.
Chapter 13 Section 1 Comp. in
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Strong Electrolytes
• A solution which contains all (or most) of the
solute in the form of ions.
• The solute is completely dissociated.
CaCl2
1 mole
(s)
 Ca2+(aq) + 2Cl1-(aq)
1 mole
+2
Chapter 13 Section 1 Comp. in
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2 moles
-1
-1
34
Weak Electrolytes
• A solution which contains some of the solute in
the form of ions, but most of the molecules
stay intact.
• The solute is slightly ionized.
HF
(aq)
1 mole
+ H2O
(l)
 H3O+(aq) + F1-(aq)
0.05 mol
Chapter 13 Section 1 Comp. in
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0.05mol
35
Electrolytes
p. 442*
Chapter 13 Section 1 Comp. in
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