Chapter #7
Reactions in Aqueous Media
Aqueous Ionic Compounds
Most ionic compounds dissolve in water to produce
solutions that conduct electricity. The degree to which
a solution will conduct electricity is used to determine
if a solute is a strong or weak electrolyte. Solutions
that do not conduct electricity are called
nonelectrolytes. Molecular compounds that dissolve in
water to that conduct electricity, are acids. Strong
acids are referred to as strong electrolytes since there
ae solutions are good conductors of electricity. Weak
acid solutions do not conduct electricity well and are
called weak electrolytes
Aqueous Ionic Compounds
Most ionic compounds dissolve in water to produce
solutions that conduct electricity. The degree to which
a solution will conduct electricity is used to determine
if a solute is a strong or weak electrolyte. Solutions
that do not conduct electricity are called
nonelectrolytes. Molecular compounds that dissolve in
water to that conduct electricity, are acids. Strong
acids are referred to as strong electrolytes since there
are solutions are good conductors of electricity. Weak
acid solutions do not conduct electricity well and are
called weak electrolytes.
How do we tell if a solution conducts electricity?
Solution Conductivity
Strong electrolyte
Weak electrolyte
Nonelectrolyte
The Solution Process
Earlier in the quarter we defined a solution as a
homogeneous mixture; a random combination of two or
more things. The part of the solution we have the most
of is the solvent and the minor components of a solution
are referred to as the solutes. Water is the most
common solvent and a good one for ionic solutes. Half
of a water molecule is slightly positive and the other half
is slightly negative and because of this is called polar.
When forming a solution between an ionic compound
and water, the positive region of the water attracts to an
anion in the solute crystal while the negative region of
another water molecule attracts to the cation in the
crystal lattice
Types of Aqueous Solutions
Solutions are homogeneous mixtures of a solute
and a solvent.
• The solute is the solution component in the smallest
amount while the solvent is the larger component of a
solution.
• Solutes whose solutions conduct electricity are called
electrolytes
• Solutes whose solutions do not conduct electricity are
called nonelectrolytes
• Electrolytes are solutes that form ions when they
dissolve. Ionic solutes or acids usually form solutions
that conduct electricity.
Solution Formation
Water is one of the best solvents known. It is able
to dissolve ionic solutes, such as sodium chloride,
to produce solutions that conduct electricity.
Molecules, containing a positive and negative
regions, are called polar. Water is an example of a
polar molecule and can dissolve ionic solutes by
the positive region of water attracting to the
negative ion of an ionic solute thus separating the
crystal lattice in to a solution of solvated ions.
Sodium Chloride Crystal Lattice
The Solvation Process
If the attractive force between the surface ion and the
solvent is greater than the forces between the ion and
the solid then the ion will enter the solution phase.
-
+
+
-
H2O The ion that has left the solid
and becomes completed
surrounded by water
molecules. It has become
solvated or hydrated.
-
+
+
K+
+
+
-
+
+
Solvated Ions
The process continues as new water molecules approach the crystal
until the crystal has been fully dissolved.
-
+
-
+
+
-
+
+
Note the different
orientation of water
molecules around the
oppositely charged
ions.
+
Reaction Driving Forces
Five Driving Forces Favor Chemical Change
1.
2.
3.
4.
5.
Formation of a solid
Formation of water
Transfer of electrons
Formation of a gas
Formation of a weak electrolyte
Precipitation
Precipitation is the formation of a solid when
two solutions are combined.
Solubility Rules
How do we determine if an ionic solute will
dissolve in water?
Solubility Rules
How do we determine if an ionic solute will
dissolve in water? Use the solubility rules
Writing Ionic Equations
Ionic compounds that are water soluble are indicated with
and (aq) after the symbol, and if insoluble then (s) goes
after the symbol.
Consider the following equation.
AgNO3 (aq) + NaCl (aq)
What are the products?
Writing Ionic Equations
Ionic compounds that are water soluble are indicated with
and (aq) after the symbol, and if insoluble then (s) goes
after the symbol.
Consider the following equation.
AgNO3 (aq) + NaCl (aq)
NaNO3 (aq) + AgCl (s)
Called a formula equation
Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq)
Na+(aq) + NO3-(aq) + AgCl (s)
Called an ionic equation
Writing Ionic Equations
Ionic compounds that are water soluble are indicated with
and (aq) after the symbol, and if insoluble then (s) goes
after the symbol.
Consider the following equation.
AgNO3 (aq) + NaCl (aq)
NaNO3 (aq) + AgCl (s)
Called a formula equation
Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq)
Na+(aq) + NO3-(aq) + AgCl (s)
Called an ionic equation
Spectator Ions
Writing Ionic Equations
Ionic compounds that are water soluble are indicated with
and (aq) after the symbol, and if insoluble then (s) goes
after the symbol.
Consider the following equation.
AgNO3 (aq) + NaCl (aq)
NaNO3 (aq) + AgCl (s)
Called a formula equation
Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq)
Na+(aq) + NO3-(aq) + AgCl (s)
Called an ionic equation
Spectator Ions
Ag+ (aq) + Cl-(aq)
AgCl (s)
Called the net ionic equation
Writing Ionic Equations
Ionic compounds that are water soluble are indicated with
and (aq) after the symbol, and if insoluble then (s) goes
after the symbol.
Consider the following equation.
AgNO3 (aq) + NaCl (aq)
NaNO3 (aq) + AgCl (s)
Called a formula equation
Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq)
Na+(aq) + NO3-(aq) + AgCl (s)
Called an ionic equation
Spectator Ions
Ag+ (aq) + Cl-(aq)
AgCl (s)
Called the net ionic equation
This reaction goes to completion because the solid silver chloride is
formed. It is called a precipitate.
Ionic Equations
It is possible for all of the reactants and products
to be water soluble and thus produce all
spectator ions. If this is the case then all of the
ions cancel out and there is no net ionic
equation. When this occurs we say that there is
No Reaction, and give the label NR. This
makes sense, since in order for reactions to go
to completion a solid, water, gas, or electron
transfer must occur in order for a reaction to go
to completion.
Reaction Driving Forces
Five Driving Forces Favor Chemical Change
1.
2.
3.
4.
5.
Formation of a solid
Formation of water
Transfer of electrons
Formation of a gas
Formation of a weak electrolyte
Water Formation
Formation of water is a normal product between
acids and bases. Since acids and bases dissolve
in water to make solutions that are electrolytes,
then we conclude that acids and bases have
some ionic character. Since water does not
ionize, then when water is formed, we will also
have a net ionic equation and then a chemical
reaction.
Acids as Electrolytes
Strong acids and bases ionize 100%!
Memorized Strong acids and bases:
Acids
HCl (aq)
HI (aq)
HBr (aq)
HNO3
H2SO4
HClO4
Bases
Hydroxides of
group I and II
metals, except Be
and Mg
Acid-Base Reactions
Acids undergo characteristic double replacement
reactions with oxides, hydroxides, carbonates and
bicarbonates.
2HCl (aq) + CuO (s)  CuCl2 (aq) + H2O (l)
2HCl (aq) + Ca(OH)2 (aq)  CaCl2 (aq) + 2H2O (l)
2HCl (aq) + CaCO3 (aq)  CaCl2 (aq) + H2O (l) + CO2 (g)
2HC l (aq) + Sr(HCO3)2 (aq)  SrCl2 (aq) + 2H2O (l) + 2CO2 (g)
Acid-Base Reactions
Acids undergo characteristic double replacement
reactions with oxides, hydroxides, carbonates and
bicarbonates.
2HCl (aq) + CuO (s)  CuCl2 (aq) + H2O (l)
2HCl (aq) + Ca(OH)2 (aq)  CaCl2 (aq) + 2H2O (l)
2HCl (aq) + CaCO3 (aq)  CaCl2 (aq) + H2O (l) + CO2 (g)
2HC l (aq) + Sr(HCO3)2 (aq)  SrCl2 (aq) + 2H2O (l) + 2CO2 (g)
Acid-Base Reactions
Bases undergo a double replacement reaction with
acids called neutralization:
NaOH (aq) + HCl (aq)  H2O (l) + NaC l (aq)
In words this well known reaction is often described as:
“acid plus base = salt plus water”
We previously discussed this reaction when describing
types of reactions.
Acid-Base Reactions
We have discussed the double replacement reactions
and ionic equations before. Since the acids and
bases undergo double replacement reactions called
neutralization reactions, then they can have ionic
equations too.
Formula equation:
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
Total ionic equation:
H+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq)  Na+ (aq) + Cl- (aq) + H2O (l)
Net ionic equation:
H+ (aq) + OH- (aq)  H2O (l)
Acid-Base Reactions
Another property of acids is their reaction with certain metals to produce
hydrogen gas, H2 (g).
Zn (s) + 2HC l (aq)  H2 (g) + ZnCl2 (aq)
This is an example of a single replacement reaction and is a redox reaction.
Total ionic equation:
Zn (s) + 2H+ (aq) + 2Cl- (aq)  H2 (g) + Zn2+ (aq) + 2Cl- (aq)
Net ionic equation:
Zn (s) + 2H+ (aq)  H2 (g) + Zn2+ (aq)
Reaction Driving Forces
Five Driving Forces Favor Chemical Change
1.
2.
3.
4.
5.
Formation of a solid
Formation of water
Transfer of electrons
Formation of a gas
Formation of a weak electrolyte
Electron Transfer
Electron transfer reactions (REDOX) were discussed in
the previous chapter Power Point Presentation about
types of chemical reactions. All types of reactions,
combination, decomposition, single replacement and
combustion were discussed and were noted as electron
transfer reactions thus giving chemical change. Double
replacement reactions are not electron transfer
reactions, and typically do not produce products unless
solids, water, or weak electrolytes are formed.
The End