Aqueous Reactions
Dr. Ron Rusay
Fall 2007
© Copyright 1995-2007 R.J. Rusay
Aqueous Reactions
1There
are several general types:
1) Precipitation: An insoluble salt forms from
the addition of solutions. (Refer to Solubility Rules)
2) Acid-Base Reactions (Neutralization)
generally produces a salt plus water
3) Oxidation-Reduction (Redox) there is a
change in oxidation numbers between reactants
and products
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Solution Test Apparatus
for Electrolytes
Power Source
0 4_ 43
+ 
+
+



+


+
+
(a)
(b)
(c)
Conductivity
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Electrolytes
1Aqueous




solutions can be categorized into 3
types: non-electrolytes, strong electrolytes or
weak electrolytes based on their ability to conduct
electricity.
A solution must have ions to conduct.
Pure Water does not conduct.
Aqueous solutions can be tested for conductivity
which will determine the degree of ionization of
the solutes.
It is possible to have full or partial ionization.
© Copyright 1995-2007 R.J. Rusay
Electrolytes
 1Almost


all ionic compounds and a few molecular
compounds are strong electrolytes.
Several molecular compounds are weak
conductors, most are non-conductors.
Conductivity is directly related to the amount of
ionization, i.e. ions in solution. Table salt, sodium
chloride, is completely ionized:
NaCl(s) + H2O(l) ---> NaCl(aq) --->
0.10M
Na +(aq) + Cl -(aq)
0.00M
0.10M 0.10M
© Copyright 1995-2007 R.J. Rusay
Electrolytes
�
Concentrations:
� CaCl2 (s) + H2O(l) ---> CaCl2(aq) --->
0.10M
Ca 2+(aq) + 2 Cl -(aq)
0.00M
0.10M 0.20M
© Copyright 1995-2007 R.J. Rusay
Electrolytes
 1Sugars
like sucrose are non-ionic, molecular
compounds that dissolve but produce no ions.
C12H22O11 (S) + H2O(l) ----> C12H22O11 (aq)

Some molecular compounds like acetic acid
ionize partially (dissociate) in water
HC2H3O2 (l) + H2O(l) H3O+(aq)+
0.1000M
C2H3O2 -(aq)
0.9987M
0.0013M
© Copyright 1995-2007 R.J. Rusay
Aqueous Acids
�
Any compound that provides a proton can be
considered an acid. Strong acids are sulfuric acid,
nitric acid, perchloric acid, HI, HBr and HCl.
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Electrolytes
� How
would the conductivity of acetic
acid compare to hydrochloric acid?
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Figure 4.6 HCl
is Completely
Ionized
Figure 4.8
Acetic Acid
(HC2H3O2)
Aqueous Bases
1



Any compound that accepts a proton is a base.
The common bases are group IA & IIA metal
hydroxide compounds. They are strong bases,
dissociating completely in water.
An example of a weak base is ammonia.
NH3 (g) + H2O(l)  NH3 (aq) NH4+(aq)+
OH-(aq)
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Figure 4.7 An
Aqueous Solution
of Sodium
Hydroxide
Figure 4.9 The
Reaction of
NH3 in Water
QUESTION
All of the following are weak acids except:
1) HCNO.
2) HBr.
3) HF.
4) HNO2.
5) HCN.
ANSWER
2)
HBr.
Section 4.2 The Nature of Aqueous Solutions:
Strong and Weak Electrolytes (p. 129)
Knowing the list of strong acids will allow one to
determine which acids are strong and which are
weak.
Aqueous Reactions: Neutralization
© Copyright 1995-2007 R.J. Rusay
Aqueous Reactions: Neutralization
Net Ionic Equations
HCl(aq) + NaOH (aq) ---> NaCl (aq) + H2O(l)
___________________________________________________
HCl(aq) ---> H+(aq) + Cl -(aq)
� NaOH (aq) ---> Na+(aq)+ OH-(aq)
� NaCl (aq) ---> Na+(aq)+ Cl-(aq)
�
________________________________________________
Na+(aq)+ OH-(aq) + H+(aq) + Cl -(aq) --->
Na+(aq)+ Cl-(aq) + H2O(l)
_______________________________________________________
H+(aq) + OH -(aq) ---> H2O(l)
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Aqueous Reactions: Acid-Base
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QUESTION
If an antacid contains Al(OH)3 it will form AlCl3 upon
neutralization of stomach acid. How many moles of Cl– ions are in
100.0 mL of 0.010 M AlCl3?
1.
2.
3.
4.
0.001 0 M
0.010 M
0.003 0 M
0.030 M
ANSWER
Choice 3 accounts for both the stoichiometry of dissociation and the
concentration. After multiplying the volume, in liters, by the
molarity of the solution, the stoichiometry must be considered.
AlCl3 dissociates into 3 moles of Cl–.
Section 4.3: The Composition of Solutions
QUESTION
If an antacid contains Al(OH)3 it will form AlCl3 upon
neutralization of stomach acid. What is the molarity of Cl– ions in
100.0 mL of 0.010 M AlCl3?
1.
2.
3.
4.
0.001 0 M
0.010 M
0.003 0 M
0.030 M
ANSWER
Choice 4 accounts for both the stoichiometry of dissociation and the
concentration. Since the volume remains constant the molarity of
the solution is adjusted only by the stoichiometry: 1 mole of AlCl3
dissociates into 3 moles of Cl–.
Section 4.3: The Composition of Solutions
QUESTION
In the balanced molecular equation for the
neutralization of sodium hydroxide with sulfuric
acid, the products are:
1) NaSO4 + H2O
2) NaSO3 + 2H2O
3) 2NaSO4 + H2O
4) Na2S + 2H2O
5) Na2SO4 + 2H2O
ANSWER
5)
Na2SO4 + 2H2O
Section 4.8 Acid-Base Reactions (p. 149)
The salt is made from the anion of the acid and
the cation of the base.
What type of reaction is it?
Double Displacement
& Precipitation
Write a balanced equation
for the reaction.
Pb(NO3)2 (aq) + 2 NaI (aq) 
2 NaNO3(aq) + PbI 2(s)
How do you know the state
of the products: (s) vs. (aq)?
QUESTION
Given the insoluble compound Al2(CO3)3 predict the ions and
coefficients that would be necessary to complete the following net
ionic equation:
__ _____ + ____ _____  Al2(CO3)3
1.
2.
3.
4.
2 AlCl3 + 3 Na2CO3 also include 6 NaCl on right
3 Al3+ + 2 CO32–
2 Al3+ + 3 CO32–
2 Al3+ 6 Cl – + 3 CO32– + 6 Na+
ANSWER
Choice 3 correctly depicts the completed net ionic equation. Only
those soluble reacting ions that form the compound need to be
shown. The other ions could be considered spectator ions.
Section 4.6: Describing Reactions in Solution
Aqueous Reactions: Precipitation
Net Ionic Equations
150mL

of a 0.1M solution of sodium sulfate is
mixed with 50mL of a 0.2M solution of silver
nitrate. What is the result?
Molecular Equation:
?Na2SO4(aq)+ ?AgNO3(aq) --->
1
2
?Ag2SO4(s) + ?NaNO3(aq)
1
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2
Aqueous Reactions: Precipitation
Net Ionic Equations
1
Na
2SO4(aq)+ 2 AgNO3(aq)-->Ag2SO4(s)+
0.1M
0.2M
2 NaNO3(aq)
Ionic Reaction (Reactants):
Na2SO4(aq)  2 Na+(aq) + SO42-(aq)
2 AgNO3(aq)  2 Ag+(aq) + 2 NO31-(aq)
2 Na+(aq)+ SO42-(aq)+ 2 Ag+(aq)+ 2 NO31-(aq)
0.2M
0.1M
© Copyright 1995-2007 R.J. Rusay
0.2M
0.2M
Aqueous Reactions: Precipitation
Net Ionic Equations
1
Na
2SO4(aq)+ 2 AgNO3(aq)-->Ag2SO4(s)+
0.1M
0.2M
2 NaNO3(aq)
Ionic Reaction (Products):
2 NaNO3(aq)  2 Na+(aq) + 2 NO31-(aq)
Ag2SO4(s)  Does not dissolve (ionize)
2Na+(aq)+ 2NO31-(aq) + Ag2SO4(s)
0.2M
0.2M
© Copyright 1995-2007 R.J. Rusay
solid
Aqueous Reactions: Precipitation
Net Ionic Equations
1
Na
2SO4(aq)+ 2 AgNO3(aq)-->Ag2SO4(s)+
2 NaNO3(aq)
Overall Ionic Reaction:
2Na+(aq)+ SO42-(aq) +2Ag+(aq)+ 2NO31-(aq) 
2Na+(aq) + Ag2SO4(s) + 2NO31-(aq)
Net Ionic Equation: (Subtract Spectator Ions)
2Ag+(aq)+ SO42-(aq) 
Ag2SO4(s)
How many moles?
= MNa2SO4 xVNa2SO4 / 1:1stoichiometry
© Copyright 1995-2007 R.J. Rusay
= 0.10M x 0.050 L/ 1
= 0.0050 mol
QUESTION
The net ionic equation for the reaction of
aluminum sulfate and sodium hydroxide
contains which of the following species?
3+
1) 3Al (aq)
–
2) OH (aq)
–
3) 3OH (aq)
3+
4) 2Al (aq)
5) 2Al(OH)3(s)
ANSWER
3)
–
3OH (aq)
Section 4.6 Describing Reactions in Solution
(p. 145)
The net ionic equation is found by canceling the
spectator ions from the total ionic equation.
Pb(NO3)2 (aq) + 2 NaI (aq) 
2 NaNO3(aq) + PbI 2(s)
Write a balanced Net Ionic
equation for the reaction.
Pb 2+ (aq) + 2 I 1- (aq)  PbI 2(s)
What are the spectator ions
in the reaction?
2 Na 1+ (aq); 2 NO31- (aq)
QUESTION
Which of the following salts is insoluble in
water?
1) Na2S
2) K3PO4
3) Pb(NO3)2
4) CaCl2
5) All of these are soluble in water.
ANSWER
5)
All of these are soluble in water.
Section 4.5 Precipitation Reactions (p. 140)
According to the solubility rules for ionic
compounds, compounds containing Group IA
ions or nitrate ions will always be soluble.
Compounds containing halides are generally
soluble, aside from silver, lead and mercury(I)
halides.
QUESTION
If you began a reaction with the following ions in solution (all
would be written with an aq subscript) how would you represent
the proper final net ionic equation? (Consult a solubility Table.)
6Na+ + 2PO43– + 3Fe2+ + 6NO3– 
1.
2.
3.
4.
3Na+ + PO43– + Fe2+ + 2NO3–  No Reaction
6Na+ + 2PO43– + 3Fe2+ + 6NO3–  Fe3(PO4)2 (s)+ 6NaNO3
3Na+ + PO43– + Fe2+ + 2NO3–  Fe3(PO4)2 (s)+ 6 Na+ + 6 NO3–
2PO43– + 3Fe2+  Fe3(PO4)2 (s)
ANSWER
Choice 4 correctly depicts the reacting ions and the resulting solid
product. Use the chart to determine if an insoluble solid will be
produced by the combination of ions given. If so, write that and
balance the atoms. If soluble ions from strong electrolytes are
present, they may cancel out from the left and right side of the
equation.
Section 4.5: Precipitation Reactions
Aqueous Reactions:
Oxidation - Reduction
�
In the following reaction, identify what is being
oxidized and what is being reduced. What is
the total number of electrons involved in the
process?
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QUESTION
In a redox reaction, oxidation and reduction must both occur.
Which statement provides an accurate premise of redox chemistry?
1. The substance that is oxidized must be the oxidizing agent.
2. The substance that is oxidized must gain electrons.
3. The substance that is oxidized must have a higher oxidation
number afterwards.
4. The substance that is oxidized must combine with oxygen.
ANSWER
Choice 3 displays the proper connection between oxidation and
oxidation number. During oxidation negatively charged electrons
leave the atom thereby increasing the oxidation number charge.
Section 4.9: Oxidation–Reduction Reactions
© Copyright 1995-2007 R.J. Rusay