Transcript Chapter 4 - AP Chemistry with dr hart

Chemistry, The Central Science, 11th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chapter 4
Aqueous Reactions and
Solution Stoichiometry
John D. Bookstaver
St. Charles Community College
Cottleville, MO
Aqueous
Reactions
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Solutions
• Solutions are defined as
homogeneous mixtures
of two or more pure
substances.
• The solvent is present in
greatest abundance.
• All other substances are
solutes.
Aqueous
Reactions
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Dissociation
• When an ionic
substance dissolves
in water, the solvent
pulls the individual
ions from the crystal
and solvates them.
• This process is called
dissociation.
Aqueous
Reactions
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Dissociation
• An electrolyte is a
substances that
dissociates into ions
when dissolved in
water.
Aqueous
Reactions
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Electrolytes
• An electrolyte is a
substances that
dissociates into ions
when dissolved in
water.
• A nonelectrolyte may
dissolve in water, but
it does not dissociate
into ions when it does
Aqueous
so.
Reactions
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Electrolytes and
Nonelectrolytes
Soluble ionic
compounds tend
to be electrolytes.
Aqueous
Reactions
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Electrolytes and
Nonelectrolytes
Molecular
compounds tend to
be nonelectrolytes,
except for acids and
bases.
Aqueous
Reactions
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Electrolytes
• A strong electrolyte
dissociates completely
when dissolved in
water.
• A weak electrolyte
only dissociates
partially when
dissolved in water.
Aqueous
Reactions
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Strong Electrolytes Are…
• Strong acids
• Strong bases
Aqueous
Reactions
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Strong Electrolytes Are…
• Strong acids
• Strong bases
• Soluble ionic salts
Aqueous
Reactions
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Sample Exercise 4.1 (p. 127)
The diagram below represents an
aqueous solution of one of the following
compounds: MgCl2, KCl, or K2SO4.
Which solution does it best represent?
Aqueous
Reactions
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Practice Exercise 1 (4.1)
If you have an aqueous solution that contains
1.5 moles of HCl, how many moles of ions are
in the solution?
a) 1.0
b) 1.5
c) 2.0
d) 2.5
e) 3.0
Aqueous
Reactions
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Practice Exercise 1 (4.1)
If you have an aqueous solution that contains
1.5 moles of HCl, how many moles of ions are
in the solution?
a) 1.0
b) 1.5
c) 2.0
d) 2.5
e) 3.0
Aqueous
Reactions
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Practice Exercise 2 (4.1)
If you were to draw diagrams (such as that
shown on the left of p. 128) representing
aqueous solutions of each of the following
ionic compounds, how many anions would
you show if the diagram contained six
cations?
a)NiSO4
b)Ca(NO3)2
c) Na3PO4
d)Al2(SO4)3
Aqueous
Reactions
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Precipitation Reactions
When one mixes ions
that form compounds
that are insoluble (as
could be predicted by
the solubility
guidelines), a
precipitate is formed.
Aqueous
Reactions
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Aqueous
Reactions
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Sample Exercise 4.2 (p. 130)
Classify the following ionic compounds
as soluble or insoluble in water:
a) sodium carbonate (Na2CO3)
b) lead sulfate (PbSO4)
Aqueous
Reactions
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Practice Exercise 1 (4.2)
Which of the following compounds is insoluble
in water?
a) (NH4)2S
b) CaCO3
c) NaOH
d) Ag2SO4
e) Pb(CH3COO)2
Aqueous
Reactions
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Practice Exercise 1 (4.2)
Which of the following compounds is insoluble
in water?
a) (NH4)2S
b) CaCO3
c) NaOH
d) Ag2SO4
e) Pb(CH3COO)2
Aqueous
Reactions
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Practice Exercise 2 (4.2)
Classify the following compounds as soluble
or insoluble in water:
a) cobalt (II) hydroxide
b) barium nitrate
c) ammonium phosphate
Aqueous
Reactions
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Metathesis (Exchange) Reactions
• Metathesis comes from a Greek word that
means “to transpose.”
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Aqueous
Reactions
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Metathesis (Exchange) Reactions
• Metathesis comes from a Greek word that
means “to transpose.”
• It appears the ions in the reactant
compounds exchange, or transpose, ions.
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Aqueous
Reactions
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Sample Exercise 4.3 (p. 131)
a) Predict the identity of the precipitate
that forms when solutions of BaCl2
and K2SO4 are mixed.
b) Write the balanced chemical equation
for the reaction.
Aqueous
Reactions
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Practice Exercise 1 (4.3)
Yes or No: Will a precipitate form when
solutions of Ba(NO3)2 and KOH are mixed?
Aqueous
Reactions
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Practice Exercise 1 (4.3)
Yes or No: Will a precipitate form when
solutions of Ba(NO3)2 and KOH are mixed?
Aqueous
Reactions
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Practice Exercise 2 (4.3)
a) What compound precipitates when solutions
of Fe2(SO4)3 and LiOH are mixed?
b) Write a balanced equation for the reaction.
c) Will a precipitate form when solutions of
Ba(NO3)2 and KOH are mixed?
Aqueous
Reactions
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Solution Chemistry
• It is helpful to pay attention to exactly
what species are present in a reaction
mixture (i.e., solid, liquid, gas, aqueous
solution).
• If we are to understand reactivity, we
must be aware of just what is changing
during the course of a reaction.
Aqueous
Reactions
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Molecular Equation
The molecular equation lists the reactants
and products in their molecular form.
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Aqueous
Reactions
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Ionic Equation
• In the ionic equation all strong electrolytes (strong
acids, strong bases, and soluble ionic salts) are
dissociated into their ions.
• This more accurately reflects the species that are
found in the reaction mixture.
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) 
AgCl (s) + K+ (aq) + NO3- (aq)
Aqueous
Reactions
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Net Ionic Equation
• To form the net ionic equation, cross out anything
that does not change from the left side of the
equation to the right.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
Aqueous
Reactions
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Net Ionic Equation
• To form the net ionic equation, cross out anything
that does not change from the left side of the
equation to the right.
• The only things left in the equation are those things
that change (i.e., react) during the course of the
reaction.
Ag+(aq) + Cl-(aq)  AgCl (s)
Aqueous
Reactions
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Net Ionic Equation
• To form the net ionic equation, cross out anything
that does not change from the left side of the
equation to the right.
• The only things left in the equation are those things
that change (i.e., react) during the course of the
reaction.
• Those things that didn’t change (and were deleted
from the net ionic equation) are called spectator ions.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
Aqueous
Reactions
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Writing Net Ionic Equations
1. Write a balanced molecular equation.
2. Dissociate all strong electrolytes.
3. Cross out anything that remains
unchanged from the left side to the
right side of the equation.
4. Write the net ionic equation with the
species that remain.
Aqueous
Reactions
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Sample Exercise 4.4 (p. 132)
Write the
a) molecular equation
b) total ionic equation and the
c) net ionic equation
for the precipitation reaction that occurs
when solutions of calcium chloride and
sodium carbonate are mixed.
Aqueous
Reactions
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Practice Exercise 1 (4.4)
What happens when you mix an aqueous
solution of sodium nitrate with an aqueous
solution of barium chloride?
a) There is no reaction; all possible products
are soluble.
b) Only barium nitrate precipitates.
c) Only sodium chloride precipitates.
d) Both barium nitrate and sodium chloride
precipitate.
e) Nothing; barium chloride is not soluble and itAqueous
Reactions
stays as a precipitate.
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Practice Exercise 1 (4.4)
What happens when you mix an aqueous
solution of sodium nitrate with an aqueous
solution of barium chloride?
a) There is no reaction; all possible products
are soluble.
b) Only barium nitrate precipitates.
c) Only sodium chloride precipitates.
d) Both barium nitrate and sodium chloride
precipitate.
e) Nothing; barium chloride is not soluble and itAqueous
Reactions
stays as a precipitate.
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Practice Exercise 2 (4.4)
Write the net ionic equation for the
precipitation reaction that occurs when
aqueous solutions of silver nitrate and
potassium phosphate are mixed.
Aqueous
Reactions
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Acids
• Arrhenius defined acids
as substances that
increase the
concentration of H+
when dissolved in water.
• Brønsted and Lowry
defined them as proton
donors.
Aqueous
Reactions
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Acids
There are only seven
strong acids:
•
•
•
•
•
•
•
Hydrochloric (HCl)
Hydrobromic (HBr)
Hydroiodic (HI)
Nitric (HNO3)
Sulfuric (H2SO4)
Chloric (HClO3)
Perchloric (HClO4)
Aqueous
Reactions
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Bases
• Arrhenius defined bases
as substances that
increase the
concentration of OH−
when dissolved in water.
• Brønsted and Lowry
defined them as proton
acceptors.
Aqueous
Reactions
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Bases
The strong bases
are the soluble
metal salts of
hydroxide ion:
•
•
•
•
Alkali metals
Calcium
Strontium
Barium
Aqueous
Reactions
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Acid-Base Reactions
In an acid-base
reaction, the acid
donates a proton
(H+) to the base.
Aqueous
Reactions
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Sample Exercise 4.5 (p. 134)
The diagrams below represent aqueous
solutions of three acids (HX, HY, and HZ)
with water molecules omitted for clarity. Rank
them from strongest to weakest.
Aqueous
Reactions
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Practice Exercise 1 (4.5)
A set of aqueous solutions are prepared
containing different acids at the same
concentration: acetic acid, chloric acid and
hydrobromic acid. Which solution(s) are the
most electrically conductive?
a) chloric acid
b) hydrobromic acid
c) acetic acid
d) both chloric acid and hydrobromic acid
e) all three solutions have the same electrical
conductivity
Aqueous
Reactions
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Practice Exercise 1 (4.5)
A set of aqueous solutions are prepared
containing different acids at the same
concentration: acetic acid, chloric acid and
hydrobromic acid. Which solution(s) are the
most electrically conductive?
a) chloric acid
b) hydrobromic acid
c) acetic acid
d) both chloric acid and hydrobromic acid
e) all three solutions have the same electrical
conductivity
Aqueous
Reactions
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Practice Exercise 2 (4.5)
Imagine a diagram showing 10 Na+ ions
and 10 OH- ions. If this solution were
mixed with the one pictured above for
HY, what would the diagram look like
that represents the solution after any
possible reaction?
Aqueous
Reactions
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Sample Exercise 4.6 (p. 135)
Classify each of the following dissolved
substances as a strong electrolyte, weak
electrolyte, or nonelectrolyte:
CaCl2
HNO3
C2H5OH (ethanol)
HCHO2 (formic acid)
KOH
Aqueous
Reactions
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Practice Exercise 1 (4.6)
Which of these substances, when dissolved in
water, is a strong electrolyte?
a) ammonia
b) hydrofluoric acid
c) folic acid
d) sodium nitrate
e) sucrose
Aqueous
Reactions
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Practice Exercise 1 (4.6)
Which of these substances, when dissolved in
water, is a strong electrolyte?
a) ammonia
b) hydrofluoric acid
c) folic acid
d) sodium nitrate
e) sucrose
Aqueous
Reactions
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Practice Exercise 2 (4.6)
Consider solutions in which 0.1 mol of each
of the following compounds is dissolved in 1 L
of water: Ca(NO3)2 (calcium nitrate), C6H12O6
(glucose), NaC2H3O2 (sodium acetate), and
HC2H3O2 (acetic acid).
Rank the solutions in order of increasing
electrical conductivity, based on the fact
that the greater the number of ions in
solution, the greater the conductivity.
Aqueous
Reactions
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Neutralization Reactions
Generally, when solutions of an acid and a base are
combined, the products are a salt and water.
CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l)
Aqueous
Reactions
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Neutralization Reactions
When a strong acid reacts with a strong base, the net
ionic equation is…
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
Aqueous
Reactions
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Neutralization Reactions
When a strong acid reacts with a strong base, the net
ionic equation is…
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) 
Na+ (aq) + Cl- (aq) + H2O (l)
Aqueous
Reactions
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Neutralization Reactions
When a strong acid reacts with a strong base, the net
ionic equation is…
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) 
Na+ (aq) + Cl- (aq) + H2O (l)
H+ (aq) + OH- (aq)  H2O (l)
Aqueous
Reactions
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Sample Exercise 4.7 (p. 136)
a) Write a balanced complete chemical
equation for the reaction between
aqueous solutions of acetic acid
(CH3COOH) and barium hydroxide
(Ba(OH)2).
b) Write the net ionic equation for this
reaction.
Aqueous
Reactions
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Practice Exercise 1 (4.7)
Which is the correct net ionic equation for the
reaction of aqueous ammonia with nitric acid?
a) NH4+(aq) + H+(aq)  NH52+(aq)
b) NH3(aq) + NO3-(aq)  NH2-(aq) + HNO3(aq)
c) NH2-(aq) + H+(aq)  NH3(aq)
d) NH3(aq) + H+(aq)  NH4+(aq)
e) NH4+(aq) + NO3-(aq)  NH4NO3(aq)
Aqueous
Reactions
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Practice Exercise 1 (4.7)
Which is the correct net ionic equation for the
reaction of aqueous ammonia with nitric acid?
a) NH4+(aq) + H+(aq)  NH52+(aq)
b) NH3(aq) + NO3-(aq)  NH2-(aq) + HNO3(aq)
c) NH2-(aq) + H+(aq)  NH3(aq)
d) NH3(aq) + H+(aq)  NH4+(aq)
e) NH4+(aq) + NO3-(aq)  NH4NO3(aq)
Aqueous
Reactions
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Practice Exercise 2 (4.7)
For the reaction of phosphorous acid
(H3PO4) and potassium hydroxide (KOH),
write
a) the balanced molecular equation
b) the net ionic equation
Aqueous
Reactions
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Gas-Forming Reactions
• Some metathesis reactions do not give the
product expected.
• In this reaction, the expected product (H2CO3)
decomposes to give a gaseous product
(CO2).
CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)
Aqueous
Reactions
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Gas-Forming Reactions
When a carbonate or bicarbonate reacts with
an acid, the products are a salt, carbon
dioxide, and water.
CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)
NaHCO3 (aq) + HBr (aq) NaBr (aq) + CO2 (g) + H2O (l)
Aqueous
Reactions
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Gas-Forming Reactions
Similarly, when a sulfite reacts with an acid,
the products are a salt, sulfur dioxide, and
water.
SrSO3 (s) + 2 HI (aq) SrI2 (aq) + SO2 (g) + H2O (l)
Aqueous
Reactions
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Gas-Forming Reactions
• This reaction gives the predicted product, but
you had better carry it out in the hood, or you
will be very unpopular!
• But just as in the previous examples, a gas is
formed as a product of this reaction.
Na2S (aq) + H2SO4 (aq)  Na2SO4 (aq) + H2S (g)
Aqueous
Reactions
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Oxidation-Reduction Reactions
• An oxidation occurs
when an atom or ion
loses electrons.
• A reduction occurs
when an atom or ion
gains electrons.
• One cannot occur
without the other.
Aqueous
Reactions
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Oxidation Numbers
To determine if an oxidation-reduction
reaction has occurred, we assign an
oxidation number to each element in a
neutral compound or charged entity.
Aqueous
Reactions
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Oxidation Numbers
• Elements in their elemental form have
an oxidation number of 0.
• The oxidation number of a monatomic
ion is the same as its charge.
Aqueous
Reactions
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Oxidation Numbers
• Nonmetals tend to have negative
oxidation numbers, although some are
positive in certain compounds or ions.
Oxygen has an oxidation number of −2,
except in the peroxide ion in which it has
an oxidation number of −1.
Hydrogen is −1 when bonded to a metal,
+1 when bonded to a nonmetal.
Aqueous
Reactions
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Oxidation Numbers
• Nonmetals tend to have negative
oxidation numbers, although some are
positive in certain compounds or ions.
Fluorine always has an oxidation number
of −1.
The other halogens have an oxidation
number of −1 when they are negative; they
can have positive oxidation numbers,
Aqueous
however, most notably in oxyanions.
Reactions
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Oxidation Numbers
• The sum of the oxidation numbers in a
neutral compound is 0.
• The sum of the oxidation numbers in a
polyatomic ion is the charge on the ion.
Aqueous
Reactions
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Examples of Oxidation-Reduction
Reactions
Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g)
0
2 x+1 2x-1
+2 2x-1
0
Note: The transfer of electrons during
oxidation-reduction reactions often produce
energy (when spontaneous), which can be in
the form of electricity.
And electrical energy can be used to make
nonspontaneous chemical reactions occur.
Aqueous
Reactions
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Examples of Redox Reactions
1.Combustion: “rapid oxidation reaction
in which a large amount of heat and
usually light are released”
C + O2  CO2, CO
S + O2  SO2
What was oxidized?
What was reduced?
Aqueous
Reactions
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Examples of Redox Reactions
2. Metal + acid (SR)
Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g)
Total ionic equation:
What was oxidized?
What was reduced?
What was not changed?
Net Ionic equation:
Aqueous
Reactions
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Examples of Redox Reactions
3.
Metal + salt (SR)
Mg(s) + CoSO4(aq)  MgSO4(aq) + Co(s)
Total ionic equation:
What was oxidized?
What was reduced?
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.8 (p. 141)
Determine the oxidation state of sulfur
in each of the following:
a) H2S
b) S8
c) SCl2
d) Na2SO3
e) SO42Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.8)
In which compound is the oxidation state
of oxygen -1?
a) O2
b) H2O
c) H2SO4
d) H2O2
e) KCH3COO
Aqueous
Reactions
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Practice Exercise 1 (4.8)
In which compound is the oxidation state
of oxygen -1?
a) O2
b) H2O
c) H2SO4
d) H2O2
e) KCH3COO
Aqueous
Reactions
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Practice Exercise 2 (4.8)
What is the oxidation state of the
boldfaced element in each of the
following:
a) P2O5
b) NaH
c) Cr2O72d) SnBr4
e) BaO2
Aqueous
Reactions
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Displacement Reactions
• In displacement reactions,
ions oxidize an element.
• The ions, then, are
reduced.
Aqueous
Reactions
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Displacement Reactions
In this reaction,
silver ions oxidize
copper metal.
Cu (s) + 2 Ag+ (aq)  Cu2+ (aq) + 2 Ag (s)
Aqueous
Reactions
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Displacement Reactions
The reverse reaction,
however, does not
occur.
x Cu (s) + 2 Ag+ (aq)
Cu2+ (aq) + 2 Ag (s) 
Aqueous
Reactions
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• Metals often produce H2(g) when they
react with acids.
e.g. Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
• The metal is oxidized and the H+ is
reduced.
Aqueous
Reactions
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• Metals may be oxidized in the presence
of a salt:
e.g.
Fe(s)+ Ni(NO3)2(aq) Fe(NO3)2(aq)+ Ni(s)
Net ionic equation:
Fe(s) + Ni2+(aq)  Fe2+(aq) + Ni(s)
Fe has been oxidized to Fe2+ while Ni2+
has been reduced to Ni.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.9 (p. 143)
Write the balanced molecular and net
ionic equations and half-reactions for
the reaction of aluminum with
hydrobromic acid.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.9)
Which of the following statements is true about
the reaction between zinc and copper(II)
sulfate?
a) Zinc is oxidized, and copper ion is reduced.
b) Zinc is reduced, and copper ion is oxidized.
c) All reactants and products are soluble strong
electrolytes.
d) The oxidation state of copper in copper(II)
sulfate is 0.
e) More than one of the previous choices is
Aqueous
Reactions
true.
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Practice Exercise 1 (4.9)
Which of the following statements is true about
the reaction between zinc and copper(II)
sulfate?
a) Zinc is oxidized, and copper ion is reduced.
b) Zinc is reduced, and copper ion is oxidized.
c) All reactants and products are soluble strong
electrolytes.
d) The oxidation state of copper in copper(II)
sulfate is 0.
e) More than one of the previous choices is
Aqueous
Reactions
true.
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Practice Exercise 2 (4.9)
a) Write the balanced molecular and net
ionic equations for the reaction
between magnesium and cobalt (II)
sulfate.
b) What is oxidized and what is reduced
in the reaction?
c) Write the half-reactions.
Aqueous
Reactions
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Activity Series
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.10 (p. 145)
Will an aqueous solution of iron (II)
chloride oxidize magnesium metal?
If so, write the balanced molecular and
net ionic equations for the reaction.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.10)
Which of these metals is the easiest to
oxidize?
a) gold
b) lithium
c) iron
d) sodium
e) aluminum
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.10)
Which of these metals is the easiest to
oxidize?
a) gold
b) lithium
c) iron
d) sodium
e) aluminum
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.10)
Which of the following metals will be
oxidized by Pb(NO3)2: Zn, Cu, Fe?
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Molarity
• Two solutions can contain the same
compounds but be quite different because the
proportions of those compounds are different.
• Molarity is one way to measure the
concentration of a solution.
Molarity (M) =
moles of solute
L solution
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.11 (p. 146)
Calculate the molarity of a solution made
by dissolving 23.4 g of sodium sulfate
(Na2SO4) in enough water to form 125 mL
of solution.
(1.32 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.11)
What is the molarity of a solution that is made
by dissolving 3.68 g of sucrose (C12H22O11) in
sufficient water to form 275.0 mL of solution?
a) 13.4 M
b) 7.43 x 10-2 M
c) 3.91 x 10-2 M
d) 7.43 x 10-5 M
e) 3.91 x 10-5 M
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.11)
What is the molarity of a solution that is made
by dissolving 3.68 g of sucrose (C12H22O11) in
sufficient water to form 275.0 mL of solution?
a) 13.4 M
b) 7.43 x 10-2 M
c) 3.91 x 10-2 M
d) 7.43 x 10-5 M
e) 3.91 x 10-5 M
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Mixing a Solution
• To create a solution of a
known molarity, one
weighs out a known mass
(and, therefore, number of
moles) of the solute.
• The solute is added to a
volumetric flask, and
solvent is added to the line
on the neck of the flask.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Expressing the Concentration
of an Electrolyte
When an ionic compound dissolves, the
relative concentrations of the ions in the
solution depend on the chemical formula of
the compound.
e.g.: 1.0 M solution of NaCl: 1.0 M in Na+
ions and 1.0 M in Cl– ions.
e.g.: 1.0 M solution of Na2SO4: 2.0 M in Na+
ions and 1.0 M in SO42– ions.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.11)
Calculate the molarity of a solution made
by dissolving 5.00 g of glucose (C6H12O6)
in sufficient water to form exactly 100.0
mL of solution.
(0.278 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.12 (p. 148)
What is the molar concentration of each
ion present in a 0.025 M aqueous solution
of calcium nitrate?
(0.025 M Ca2+)
0.050 M NO3-)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.12)
What is the ratio of the concentration of
potassium ions to the concentration of
carbonate ions in a 0.015 M soluton of
potassium carbonate?
a) 1:0.015
b) 0.015:1
c) 1:1
d) 1:2
e) 2:1
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.12)
What is the ratio of the concentration of
potassium ions to the concentration of
carbonate ions in a 0.015 M soluton of
potassium carbonate?
a) 1:0.015
b) 0.015:1
c) 1:1
d) 1:2
e) 2:1
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.12)
What is the molar concentration of K+ ions
in a 0.015 M solution of potassium
carbonate?
(0.030 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Interconverting Molarity,
Moles, and Volume
• The definition of molarity contains three
quantities: molarity, moles of solute, and
liters of solution.
• If we know any two of these, we can
calculate the third.
• Use dimensional analysis to help you.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.13 (p. 146)
How many grams of Na2SO4 are
required to make 0.350 L of 0.500 M
Na2SO4?
(24.9 g)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.13)
What is the concentration of ammonia in a
solution made by dissolving 3.75 g of ammonia
in 120.0 L of water?
a) 1.83 x 10-3 M
b) 3.78 x 10-2 M
c) 0.0313 M
d) 1.83 M
e) 7.05 M
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.13)
What is the concentration of ammonia in a
solution made by dissolving 3.75 g of ammonia
in 120.0 L of water?
a) 1.83 x 10-3 M
b) 3.78 x 10-2 M
c) 0.0313 M
d) 1.83 M
e) 7.05 M
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.13)
a) How many grams of Na2SO4 are there
in 15 mL of 0.50 M Na2SO4?
(1.1 g)
b) How many milliliters of 0.50 M Na2SO4
solution are needed to provide 0.038
mol of this salt?
(76 mL)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Dilution
• One can also dilute a more concentrated
solution by
– Using a pipet to deliver a volume of the stock
solution to a new volumetric flask, and
– Adding solvent to the line on the neck of the new
flask.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Dilution
The molarity of the new solution can be determined
from the equation
Mc  Vc = Md  Vd,
where Mc and Md are the molarity of the concentrated and dilute
solutions, respectively, and Vc and Vd are the volumes of the
two solutions.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Remember: Moles are central!
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Example - Dilution
How do you prepare 1.0 L of 2.0 M CuSO4
from a stock solution of 8.0 M CuSO4?
First, figure out how much of the
concentrated acid you need:
Vconc = MdilVdil = (2.0 M)(1.0 L) = 0.25 L of 8.0 M CuSO4
Mconc
(8.0 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Example - Dilution
How do you prepare 1.0 L of 2.0 M CuSO4
from a stock solution of 8.0 M CuSO4?
• Measure 250 mL of the concentrated (8.0 M)
CuSO4, using either a graduated cylinder or a
250 mL volumetric flask. Pour into 1 L
volumetric flask.
• Add distilled water until total volume is 1000 mL
or 1.0 L.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.14 (p. 150)
How many milliliters of 3.0 M H2SO4 are
needed to make 450 mL of 0.010 M
H2SO4?
(1.5 mL)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.14)
What volume of a 1.00 M stock solution of
glucose must be used to make 500.0 mL of a
1.75 x 10-2 M glucose solution in water?
a) 1.75 mL
b) 8.75 mL
c) 48.6 mL
d) 57.1 mL
e) 28,570 mL
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.14)
What volume of a 1.00 M stock solution of
glucose must be used to make 500.0 mL of a
1.75 x 10-2 M glucose solution in water?
a) 1.75 mL
b) 8.75 mL
c) 48.6 mL
d) 57.1 mL
e) 28,570 mL
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.14)
a)
What volume of 2.50 M lead nitrate solution
contains 0.0500 mol of Pb2+?
(20.0 mL)
b)
How many milliliters of 5.0 M K2Cr2O7 solution must
be diluted to prepare 250 mL of 0.10 M solution?
(5.0 mL)
c)
If 10.0 mL of a 10.0 M stock solution of NaOH is
diluted to 250 mL, what is the concentration of the
resulting solution?
(0.40 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Connections
Where we have been:
stoichiometry
metathesis (precipitation and acid-base)
reactions
redox reactions
molarity
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Connections
Now we are going to combine all these together:
• apply stoichiometry to problems that
contain molar concentrations
• context = metathesis (precipitation and acid-base)
reactions and redox reactions
• practical application  titrations
• Reminder: MOLES ARE CENTRAL!
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Using Molarities in
Stoichiometric Calculations
Recognize that there are two different types
of units:
Laboratory units (the macroscopic units that
we measure in lab) and
Chemical units (the microscopic units that
relate to moles).
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Using Molarities in
Stoichiometric Calculations
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Stoichiometry Reminder
1.
2.
3.
4.
Write the equation
Get to moles (of known) ASAP
Switch to unknown via mole ratio
Put answer in required unit
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.15 (p. 152)
+ more
How many grams of calcium hydroxide
are needed to neutralize 25.0 mL of
0.100 M HNO3?
1. Write the equation:
2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2 H2O(l)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.15 (p. 152)
+ more
2.
Get to moles (of known) ASAP
(i.e. M  mol, in this example)
3.
Switch to moles of unknown, using mole ratio.
25.0 mL ( 1 L ) (0.100 mol HNO3)(1 mol Ca(OH)2)
103 mL
1L
2 mol HNO3
= 1.25 x 10-3 mol Ca(OH)2
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.15 (p. 152)
+ more
4. a) How many grams of calcium hydroxide
are needed to neutralize 25.0 mL of 0.100
M HNO3?
(the original question)
1.25 x 10-3 mol Ca(OH)2 (74.10 g Ca(OH)2)
1 mol Ca(OH)2
= 9.26 x 10-2 g Ca(OH)2
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.15 (p. 152)
+ more
4. b) How many mL of 0.50 M Ca(OH)2
are needed to completely neutralize
25.0 mL of 0.100 M HNO3?
1.25 x 10-3 mol Ca(OH)2( 1 L
)(103 mL)
0.50 mol Ca(OH)2 1 L
= 2.5 mL
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.15 (p. 152)
+ more
4. c) 15.0 mL of a Ca(OH)2 solution are
needed to neutralize 25.0 mL of 0.100 M
HNO3. What is the molarity of the solution?
1.25 x 10-3 mol Ca(OH)2 (103 mL)
15.0 mL
1L
= 0.0833 M Ca(OH)2
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.15 (p. 152)
(see front board)
How many grams of calcium hydroxide
are needed to neutralize 25.0 mL of
0.100 M HNO3?
(0.0926 g)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.15)
How many milligrams of sodium sulfide are
needed to completely react with 25.00 mL of a
0.0100 M aqueous solution of cadmium nitrate,
to form a precipitate of CdS(s)?
a) 13.8 mg
b) 19.5 mg
c) 23.5 mg
d) 32.1 mg
e) 39.0 mg
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.15)
a) How many grams of NaOH are needed to
neutralize 20.0 mL of 0.150 M H2SO4
solution?
(0.240 g)
b) How many liters of 0.500 M HCl(aq) are
needed to react completely with 0.100 mol
of Pb(NO3)2(aq), forming a precipitate of
PbCl2(s)?
(0.400 L)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration
Titration is an
analytical
technique in
which one can
calculate the
concentration
of a solute in
a solution.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration
= A method of volumetric analysis in
which a volume of one reagent is added
to a known volume of another reagent
slowly from a buret until an end point is
reached. If one of the solutions has a
known concentration, the concentration
of the other can be calculated, via
stoichiometry.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration
Standard solution = reagent solution of known
concentration
Titrant = reagent solution of unknown concentration
Equivalence point = the point at which
stoichiometrically equivalent quantities are brought
together
End point = color change (v. close to equivalence
point)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Change in appearance of a solution containing
phenolphthalein as base indicator
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Example Titration
• Predict the number of mL of ~0.10 M
NaOH needed to neutralize 10.0 mL of
0.25 M HCl.
• We want to know the exact molarity of
the NaOH solution.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration Practice Problems
Remember: Moles are central!
1. In the titration of 35 mL of liquid drain
cleaner containing NaOH, 50. mL of
0.40 M HCl must be added to reach
the equivalence point. What is the
molarity of the base in the cleaner?
(0.57 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration Practice Problems
Remember: Moles are central!
2. A 20.0 mL sample of an HCl solution is
titrated with 27.4 mL of a standard
solution of Ba(OH)2.
The concentration of the standard is
0.0154 M. What is the molarity of the
HCl?
(0.0422 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration Practice Problems
Remember: Moles are central!
3. How many mL of 0.25 M Ca(OH)2
must be added to titrate 46 mL of
0.40 M HClO4?
(37 mL)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Titration Practice Problems
Remember: Moles are central!
4. What is the molar hydrogen ion
concentration in a 3.00 L solution of
HNO3 in which 1.90 g of HNO3 is
present? Assume the acid is a strong
acid. What is its pH?
(0.010 M, 2)
molarity problem, not truly titration
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.16 (p. 153)
One commercial method used to peel potatoes is to
soak them in a solution of NaOH for a short time,
remove them from the NaOH, and spry off the peel.
The concentration of NaOH is normally in the range
of 3 to 6 M. The NaOH is analyzed periodically. In
one such analysis, 45.7 mL of 0.500 M H2SO4 is
required to neutralize a 20.0 mL sample of NaOH
solution. What is the concentration of the NaOH
solution?
(2.28 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.16)
What is the molarity of an HCl solution if 27.3
mL of it neutralizes 134.5 mL of 0.0165 M
Ba(OH)2?
a) 0.0444 M
b) 0.0813 M
c) 0.163 M
d) 0.325 M
e) 3.35 M
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.16)
What is the molarity of an HCl solution if 27.3
mL of it neutralizes 134.5 mL of 0.0165 M
Ba(OH)2?
a) 0.0444 M
b) 0.0813 M
c) 0.163 M
d) 0.325 M
e) 3.35 M
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.16)
What is the molarity of an NaOH
solution if 48.0 mL is needed to
neutralize 35.0 mL of 0.144 M H2SO4?
(0.210 M)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Exercise 4.17 (p. 154)
The quantity of Cl- in a water supply is determined by
titrating the sample with Ag+:
Ag+(aq) + Cl-(aq)  AgCl(s)
a) How many grams of chloride ion are in a sample of
the water if 20.2 mL of 0.100 M Ag+ is needed to
react with all the chloride in the sample?
(7.17 x 10-2 g Cl-)
b) If the sample has a mass of 10.0 g, what percent Cldoes it contain?
(0.717% Cl-)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.17)
A mysterious white powder is found at a crime scene. A
simple chemical analysis concludes that the powder is a
mixture of sugar and morphine (C17H19NO3), a weak
base similar to ammonia. The crime lab takes 10.00 mg
of the mysterious white powder, dissolves it in 100.00
mL water, and titrates it to the equivalence point with
2.84 mL of a standard 0.0100 M HCl solution. What is
the percentage of morphine in the white powder?
a) 8.10%
b) 17.3%
c) 32.6%
d) 49.7%
Aqueous
Reactions
e) 81.0%
© 2009, Prentice-Hall, Inc.
Practice Exercise 1 (4.17)
A mysterious white powder is found at a crime scene. A
simple chemical analysis concludes that the powder is a
mixture of sugar and morphine (C17H19NO3), a weak
base similar to ammonia. The crime lab takes 10.00 mg
of the mysterious white powder, dissolves it in 100.00
mL water, and titrates it to the equivalence point with
2.84 mL of a standard 0.0100 M HCl solution. What is
the percentage of morphine in the white powder?
a) 8.10%
b) 17.3%
c) 32.6%
d) 49.7%
Aqueous
Reactions
e) 81.0%
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.17)
A sample of an iron ore is dissolved in acid,
and the iron is converted to Fe2+. The sample
is then titrated with 47.20 mL of 0.02240 M
MnO4-. The oxidation-reduction reaction that
occurs during titration is as follows:
MnO4-(aq) + 5 Fe2+(aq) + 8 H+(aq) 
Mn2+(aq) + 5 Fe3+(aq) + 4 H2O(l)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.17)
a) How many moles of MnO4- were added
to the solution?
(1.057 x 10-3 mol MnO4-)
b) How many moles of Fe2+ were in the
sample?
(5.286 x 10-3 mol Fe2+)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Practice Exercise 2 (4.17)
c) How many grams of iron were in the
sample?
(0.2952 g)
d) If the sample had a mass of 0.8890 g,
what is the percentage of iron in the
sample?
(33.21%)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Integrative Exercise 4
(p. 155)
A sample of 70.5 mg potassium
phosphate is added to 15.0 mL of
0.050 M silver nitrate, resulting in the
formation of a precipitate.
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.
Sample Integrative Exercise 4
(p. 155)
a) Write the molecular equation for the
reaction.
b) What is the limiting reactant in the reaction?
c) Calculate the theoretical yield, in grams, of
the precipitate that forms.
(0.10 g Ag3PO4)
Aqueous
Reactions
© 2009, Prentice-Hall, Inc.