Aqueous Reactions
Dr. Ron 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
Solution Test Apparatus
for Electrolytes
Conductivity
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.
Molarity (M) = Moles solute / Liter solution
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)
0.10M
0.00M
NaCl(aq)
Na +(aq) + Cl -(aq)
0.10M 0.10M
Molarity (M) = Moles solute / Liter solution
Electrolytes
Concentrations:
 CaCl2 (s) + H2O(l)
CaCl2(aq)
0.10M
Ca 2+(aq) + 2 Cl -(aq) 0.00M
0.10M 0.20M

Molarity (M) = Moles solute / Liter solution
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)
0.1000M
0.9987M
H3O+(aq)+
C2H3O2 -(aq)
0.0013M
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.
Electrolytes
 How
would the conductivity of acetic
acid compare to hydrochloric acid?
HCl
Completely
Ionized
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)
Consider that aqueous ammonia is in equilibrium with
ammonium hydroxide. The names have often been used
interchangeably.
An Aqueous Solution of
Sodium Hydroxide
NH3 in Water
QUESTION
ANSWER
Aqueous Reactions: Neutralization
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)
QUESTION
An aqueous solution of H2SO4 is added to aqueous Ba(OH)2. The
reaction is monitored using a conductivity tester.
Predict the correct statement(s).
I) Both H2SO4 and Ba(OH)2 are strong electrolytes.
II) This is a neutralization reaction.
III) This is a precipitation reaction.
IV) The light bulb will glow at the neutralization point.
A) II
B) I and II
C) I, II and III
D) I, II, III and IV
ANSWER
An aqueous solution of H2SO4 is added to aqueous Ba(OH)2. The
reaction is monitored using a conductivity tester.
Predict the correct statement(s).
I) Both H2SO4 and Ba(OH)2 are strong electrolytes.
II) This is a neutralization reaction.
III) This is a precipitation reaction.
IV) The light bulb will glow at the neutralization point.
A) II
B) I and II
C) I, II and III
D) I, II, III and IV
Aqueous Reactions: Acid-Base
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?
A.0.0010 M
B.0.010 M
C.0.0030 M
D.0.030 M
Molarity (M) = Moles solute / Liter solution
ANSWER
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?
A.0.0010 M
B.0.010 M
C.0.0030 M
D.0.030 M
AlCl3 dissociates into 3 moles of Cl–.
Molarity (M) = Moles solute / Liter solution
QUESTION
ANSWER
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
A.2 AlCl3 + 3 Na2CO3 also include 6 NaCl on right
B.3 Al3+ + 2 CO32–
C.2 Al3+ + 3 CO32–
D.2 Al3+ 6 Cl – + 3 CO32– + 6 Na+
ANSWER
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
A.2 AlCl3 + 3 Na2CO3 also include 6 NaCl on right
B.3 Al3+ + 2 CO32–
C.2 Al3+ + 3 CO32–
D.2 Al3+ 6 Cl – + 3 CO32– + 6 Na+
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
2
Aqueous Reactions: Precipitation
Net Ionic Equations
1 SO
Na
2
4(aq)+ 2 AgNO3(aq) Ag2SO4(s)+ 2 NaNO3(aq)
0.1M
0.2M
Ionic Reaction (Reactants):
Na2SO4(aq)
2 AgNO3(aq)
2 Na+(aq) + SO42-(aq)
2 Ag+(aq) + 2 NO31-(aq)
2 Na+(aq)+ SO42-(aq)+ 2 Ag+(aq)+ 2 NO31-(aq)
0.2M
0.1M
0.2M
0.2M
Aqueous Reactions: Precipitation
Net Ionic Equations
1 SO
Na
2
4(aq)+ 2 AgNO3(aq) Ag2SO4(s)+ 2 NaNO3(aq)
0.1M
0.2M
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
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)
M x Vsolution= mol
Ag2SO4(s)
How many moles?
= MNa2SO4 xVNa2SO4 / 1:1stoichiometry
= 0.10M x 0.050 L/ 1
= 0.0050 mol
QUESTION
ANSWER
–
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
ANSWER
E) All of these are soluble in water.
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– 
A.
B.
C.
D.
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
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– 
A.
B.
C.
D.
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)
Oxidation-Reduction
 Oxidation
is the loss of electrons.
 Reduction is the gain of electrons.
 The reactions occur together. One does
not occur without the other.
 The terms are used relative to the
change in the oxidation state or
oxidation number of the reactant(s).
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?
Oxidation Reduction Reactions
QUESTION
In a redox reaction, oxidation and reduction must both occur.
Which statement provides an accurate premise of redox chemistry?
A.The substance that is oxidized must be the oxidizing agent.
B.The substance that is oxidized must gain electrons.
C.The substance that is oxidized must have a higher oxidation
number afterwards.
D.The substance that is oxidized must combine with oxygen.
ANSWER
In a redox reaction, oxidation and reduction must both occur.
Which statement provides an accurate premise of redox chemistry?
A.The substance that is oxidized must be the oxidizing agent.
B.The substance that is oxidized must gain electrons.
C.The substance that is oxidized must have a higher oxidation
number afterwards.
D.The substance that is oxidized must combine with oxygen.
QUESTION
ANSWER
B) NO2
Oxygen almost always has an oxidation state of
–2 when part of a compound. The exception is
when it is part of a peroxide. For example,
hydrogen peroxide H2O2. Then it has an
oxidation state of –1.