Chemical Reactions
9.3: Reactions in Aqueous
Solutions
Objectives
Describe aqueous solutions.
 Write complete ionic and net ionic
equations for chemical reactions in
aqueous solutions.
 Predict whether reactions in aqueous
solutions will produce a precipitate, water,
or a gas.

Review
A solution is a
homogeneous mixture.
Solutes are the
substances that are
dissolved. The
solvent is the
substance that does
the dissolving.
Water is the solvent in
an aqueous solution.
Aqueous Solutions

There can be many possible solutes in an
aqueous solution:
Ionic Compounds
Dissolves
Does not
dissolve
Molecular Compounds
Review
When an ionic compound dissolves in
water, the ions in the compound will
dissociate or separate from one another.
(See previous slide).
 When the solute is a molecular compound,
the molecules will not come apart; they
will simply exist as separate molecules in
solution. (See previous slide)
 Recall that ionic compounds that produce
hydrogen ions when in solution are called
acids.

Aqueous Solutions
When two aqueous solutions of ionic
compounds combine (both solutions then
contain ions as solutes), the ions MAY
react with one another. The solvent
(water) molecules do not react.
 Recall that these reactions are double
replacement reactions.

3
types of products can form - a precipitate,
water, or a gas.
Precipitate Reactions
2KI + Pb(NO3)2
2KNO3 + PbI2
The reaction in detail:
K+
NO3K+
II-
NO3Pb+2
KI and Pb(NO3)2
exist as IONS!
NO3K+
K+
NO3-
PbI2 (the precipitate)
Precipitate Reactions

A chemical equation does not show what is
really going on - we need to write an ionic
equation to do that.
A
complete ionic equation shows all the particles
in a solution as they really exist.
2K+ + 2I- + Pb+2 + 2NO3-
PbI2 (s) + 2K+ +
2NO3-
Practice Problem
The reaction above produces a solid copper
compound. Write a balanced chemical equation
and then a complete ionic equation.
Practice Problem
The reaction above produces a solid copper
compound. Write a balanced chemical equation
and then a complete ionic equation.
1. Na2CO3 + CuCl2
CuCO3 (s) + 2NaCl
2. 2Na+ + CO3-2 + Cu+2 + 2ClCuCO3 (s) + 2Na+ + 2Cl-
Practice Problem
A solution of silver nitrate and sodium
chloride are mixed and a compound
containing silver precipitates out. Write a
balanced chemical equation and a
complete ionic equation for this reaction .
Practice Problem
A solution of silver nitrate and sodium
chloride are mixed and a compound
containing silver precipitates out. Write a
balanced chemical equation and a
complete ionic equation for this reaction.
1. AgNO3 + NaCl
AgCl (s) + NaNO3
2. Ag+ + NO3- + Na+ + ClAgCl (s) + Na+ + NO3-
Spectator ions
Notice that on both sides of this reaction
there are ions that do NOT participate in the
reaction. These ions are called spectator
ions.
Net Ionic Equations

To write a net ionic equation, cross out
all of the spectator ions.
 Ag+

+ Cl-
AgCl (s)
Practice:
2K+ + 2I- + Pb+2 + 2NO32Na+ + CO3-2 + Cu+2 + 2Cl-
PbI2 + 2K+ +
2NO3
CuCO3 (s) + 2Na+ + 2Cl-
More Practice!

Write the chemical, complete ionic, and
net ionic equations for the precipitate
reactions below.
 Solutions
of barium nitrate and sodium
carbonate are mixed, forming the precipitate
barium carbonate.
 Solutions of aluminum chloride and sodium
hydroxide are mixed, forming the precipitate
aluminum hydroxide.
Reactions that form Water
Another type of double-replacement
reaction that occurs in an aqueous
solution produces water molecules.
 Since water is colorless and odorless,
there is no observable evidence that a
reaction occurred.

 HBr
+ NaOH
NaBr + H2O
 H+ + Br- + Na+ + OHNa+ + Br-+ H2O
 H+ + OHH2O
Practice Problems

Write the chemical, complete ionic, and
net ionic equations for the reactions
below, which all produce water.
 sulfuric
acid and potassium hydroxide
 phosphoric acid and magnesium hydroxide
 nitric acid and ammonium hydroxide
Reactions that form Gases
A 3rd type of double-replacement reaction
that occurs in aqueous solutions results in
the formation of a gas.
 Common gases produced are:

 Carbon
dioxide (CO2)
 Hydrogen cyanide (HCN)
 Hydrogen sulfide (H2S)
Practice Problems

Write the chemical, complete ionic, and
net ionic equations for the reactions
below, which all produce a gas.
 Sulfuric
acid reacts with sodium cyanide
 Hydrochloric acid reacts with sodium sulfide
 Hydroiodic acid reacts with lithium sulfide
CO2 Production

When you combine any acidic solution and
a carbonate (such as sodium hydrogen
carbonate - aka sodium bicarbonate or
baking soda), 2 reactions occur almost
simultaneously.
 HCl
+ NaHCO3
H2CO3 + NaCl
double replacement
 H2CO3
H2O (l) + CO2 (g)
decomposition
CO2 Production
By adding these 2 reactions, one chemical
equation can be written.
HCl + NaHCO3
H2CO3 + NaCl
H2CO3
H2O (l) + CO2 (g)
HCl + NaHCO3
NaCl + H2O (l) + CO2 (g)

CO2 Production

Now take the overall equation and write a
complete ionic equation and a net ionic
equation.
 HCl
+ NaHCO3
NaCl + H2O (l) + CO2 (g)
CO2 Production

Now take the overall equation and write a
complete ionic equation and a net ionic
equation.
 HCl
+ NaHCO3
NaCl + H2O (l) + CO2 (g)
 H+ + Cl- + Na+ + HCO3Na+ + Cl- + H2O (l) + CO2 (g)
 H+ + HCO3H2O (l) + CO2 (g)
Practice Problems

Write the chemical, complete ionic, and
net ionic equations for the reactions
below.
 Perchloric
acid (HClO4) reacts with potassium
carbonate
 Hydrobromic acid reacts with ammonium
carbonate