19.1
Acid-Base Theories
Bracken Cave, near San
Antonio, Texas, is home to
twenty to forty million bats.
Visitors to the cave must
protect themselves from the
dangerous levels of ammonia
in the cave. Ammonia is a
byproduct of the bats’ urine.
You will learn why ammonia is
considered a base.
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19.1
Acid-Base Theories
> Properties of Acids and Bases
Properties of Acids and Bases
What are the properties of acids and
bases?
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19.1
Acid-Base Theories
> Properties of Acids and Bases
Acids
Acids taste sour, will change the color
of an acid-base indicator, and can be
strong or weak electrolytes in
aqueous solution.
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19.1
Acid-Base Theories
> Properties of Acids and Bases
Citrus fruits contain citric acid. Tea contains
tannic acid.
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19.1
Acid-Base Theories
> Properties of Acids and Bases
Bases
Bases taste bitter, feel slippery, will
change the color of an acid-base
indicator, and can be strong or weak
electrolytes in aqueous solution.
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19.1
Acid-Base Theories
> Properties of Acids and Bases
Antacids use bases to neutralize excess
stomach acid. The base calcium hydroxide is a
component of mortar.
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19.1
Acid-Base Theories
> Arrhenius Acids and Bases
Arrhenius Acids and Bases
How did Arrhenius define an acid and
a base?
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19.1
Acid-Base Theories
> Arrhenius Acids and Bases
Arrhenius said that acids are hydrogencontaining compounds that ionize to
yield hydrogen ions (H+) in aqueous
solution. He also said that bases are
compounds that ionize to yield
hydroxide ions (OH–) in aqueous
solution.
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19.1
Acid-Base Theories
> Arrhenius Acids and Bases
Hydrochloric Acid
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19.1
Acid-Base Theories
> Arrhenius Acids and Bases
Arrhenius Acids
• Acids that contain one ionizable hydrogen,
such as nitric acid (HNO3), are called
monoprotic acids.
• Acids that contain two ionizable hydrogens,
such as sulfuric acid (H2SO4), are called
diprotic acids.
• Acids that contain three ionizable hydrogens,
such as phosphoric acid (H3PO4) are called
triprotic acids.
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19.1
Acid-Base Theories
> Arrhenius Acids and Bases
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19.1
Acid-Base Theories
> Arrhenius Acids and Bases
Arrhenius Bases
Hydroxide ions are one of the products of the
dissolution of an alkali metal in water.
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19.1
Acid-Base Theories
> Arrhenius Acids and Bases
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19.1
Acid-Base Theories
> Brønsted-Lowry Acids and Bases
Brønsted-Lowry Acids and Bases
What distinguishes an acid from a base
in the Brønsted-Lowry theory?
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19.1
Acid-Base Theories
> Brønsted-Lowry Acids and Bases
The Brønsted-Lowry theory defines an
acid as a hydrogen-ion donor, and a
base as a hydrogen-ion acceptor.
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19.1
Acid-Base Theories
> Brønsted-Lowry Acids and Bases
Why Ammonia is a Base
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19.1
Acid-Base Theories
> Brønsted-Lowry Acids and Bases
Conjugate Acids and Bases
• A conjugate acid is the particle formed when
a base gains a hydrogen ion.
• A conjugate base is the particle that remains
when an acid has donated a hydrogen ion.
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19.1
Acid-Base Theories
> Brønsted-Lowry Acids and Bases
• A conjugate acid-base pair consists of two
substances related by the loss or gain of a
single hydrogen ion.
• A substance that can act as both an acid and
a base is said to be amphoteric.
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19.1
Acid-Base Theories
> Brønsted-Lowry Acids and Bases
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19.1
Acid-Base Theories
> Brønsted-Lowry Acids and Bases
A water molecule that gains a hydrogen ion
becomes a positively charged hydronium ion
(H3O+).
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19.1
Acid-Base Theories
> Lewis Acids and Bases
Lewis Acids and Bases
How did Lewis define an acid and a
base?
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19.1
Acid-Base Theories
> Lewis Acids and Bases
Lewis proposed that an acid accepts a
pair of electrons during a reaction, while
a base donates a pair of electrons.
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19.1
Acid-Base Theories
> Lewis Acids and Bases
• A Lewis acid is a substance that can accept
a pair of electrons to form a covalent bond.
• A Lewis base is a substance that can donate
a pair of electrons to form a covalent bond.
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Acid-Base Theories
> Lewis Acids and Bases
Animation 25
Compare the three important definitions of
acids and bases.
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19.1
Acid-Base Theories
> Lewis Acids and Bases
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Acid-Base Theories
>
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Acid-Base Theories
>
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Acid-Base Theories
>
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Practice Problems for Conceptual Problem 19.1
Problem Solving 19.1
Solve Problem 1 with the help of an
interactive guided tutorial.
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19.1 Section Quiz.
1. Which of the following is NOT a characteristic
of acids?
a. taste sour
b. are electrolytes
c. feel slippery
d. affect the color of indicators
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19.1 Section Quiz.
2. Which compound is most likely to act as an
Arrhenius acid?
a. H2O
b. NH3.
c. NaOH.
d. H2SO4.
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19.1 Section Quiz.
3. A Lewis acid is any substance that can accept
a. a hydronium ion.
b. a proton.
c. hydrogen.
d. a pair of electrons.
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19.2
Hydrogen Ions and Acidity
To test a diagnosis of
diabetic coma, a doctor
orders several tests,
including the acidity of
the patient’s blood.
Results from this test
will be expressed in
units of pH. You will
learn how the pH scale
is used to indicate the
acidity of a solution and
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19.2
Hydrogen
Ions from Water
Hydrogen Ions from Water
a. The reaction in which water molecules
produce ions is called the self-ionization
of water.
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19.2
Hydrogen
Ions from Water
a. In the self-ionization of water, a proton
(hydrogen ion) transfers from one water
molecule to another water molecule.
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19.2
Ion Product
Constant for Water
Ion Product Constant for Water
How are [H+] and [OH-] related in an aqueous
solution?
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19.2
Ion Product
Constant for Water
For aqueous solutions, the product of
the hydrogen-ion concentration
and the hydroxide-ion
concentration equals 1.0  10-14.
Any aqueous solution in which [H+] and
[OH-] are equal is described as a
neutral solution.
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19.2
Ion Product
Constant for Water
a. The product of the concentrations of the
hydrogen ions and hydroxide ions in water
is called the ion-product constant for
water (Kw).
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19.2
Ion Product
Constant for Water
a. An acidic solution is one in which [H+] is
greater than [OH-].
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19.2
Ion Product
Constant for Water
a. Unrefined hydrochloric acid, commonly
called muriatic acid, is used to clean stone
buildings and swimming pools.
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19.2
Ion Product
Constant for Water
a. A basic solution is one in which [H+] is
less than [OH]. Basic solutions are also
known as alkaline solutions.
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19.2
Ion Product
Constant for Water
a. Sodium hydroxide, or lye, is commonly
used as a drain cleaner.
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19.1
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19.1
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19.1
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19.1
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for Sample Problem 19.1
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The 19.2
pH Concept
The pH Concept
How is the hydrogen-ion concentration used to
classify a solution as neutral, acidic, or basic?
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The 19.2
pH Concept
a. The pH of a solution is the negative
logarithm of the hydrogen-ion
concentration.
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The 19.2
pH Concept
Calculating pH
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The 19.2
pH Concept
a. A solution in which [H+] is greater than 1 
10–7 M has a pH less than 7.0 and is
acidic. The pH of pure water or a neutral
aqueous solution is 7.0. A solution with a
pH greater than 7 is basic and has a [H+] of
less than 1  10–7 M.
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The 19.2
pH Concept
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The 19.2
pH Concept
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The 19.2
pH Concept
Calculating pOH
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The 19.2
pH Concept
pH and Significant Figures
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19.2
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19.2
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19.2
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19.2
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for Sample Problem 19.2
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19.3
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19.3
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19.3
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19.3
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for Sample Problem 19.3
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19.2
Measuring
pH
Measuring pH
What is the most important characteristic of an
acid-base indicator?
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19.2
Measuring
pH
An indicator is a valuable tool for measuring pH
because its acid form and base form have
different colors in solution.
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19.2
Measurin
g pH
a. Phenolphthalein changes from colorless to
pink at pH 7–9.
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19.4
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19.4
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19.4
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19.4
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for Sample Problem 19.4
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19.2
Measuring
pH
Acid-Base Indicators
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19.2
Measuring
pH
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19.2
Measuring
pH
a. Universal Indicators
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19.2 Section Quiz.
1. If the [OH-] in a solution is 7.65  10-3M, what
is the [H+] of this solution?
a. 7.65  10-17M
b. 1.31  10-12M
c. 2.12M
d. 11.88M
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19.2 Section Quiz.
2. The [OH-] for four solutions is given below.
Which one of the solution is basic?
a. 1.0 x 10-6M
b. 1.0 x 10-8M
c. 1.0 x 10-7M
d. 1.0 x 10-14M
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19.2 Section Quiz.
3. What is the pH of a solution with a hydrogenion concentration of 8.5 x 10-2M?
a. 12.93
b. 8.50
c. 5.50
d. 1.07
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19.3
Strengths of Acids and Bases
Lemons and grapefruits
have a sour taste
because they contain
citric acid. Sulfuric acid
is a widely used
industrial chemical that
can quickly cause
severe burns if it comes
into contact with skin.
You will learn why some
acids are weak and
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19.3
Strong and Weak
Acids and Bases
Strong and Weak Acids and Bases
How does the value of an acid dissociation
constant relate to the strength of an acid?
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19.3
Strong
and Weak Acids and Bases
a. An acid dissociation constant (Ka) is the
ratio of the concentration of the dissociated
(or ionized) form of an acid to the
concentration of the undissociated
(nonionized) form.
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19.3
Strong
and Weak Acids and Bases
Weak acids have small Ka values. The stronger
an acid is, the larger is its Ka value.
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19.3
Strong
and Weak Acids and Bases
a. Strong acids are completely ionized in
aqueous solution.
a. Weak acids ionize only slightly in aqueous
solution.
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19.3
Strong
and Weak Acids and Bases
a. In general, the base dissociation
constant (Kb) is the ratio of the
concentration of the conjugate acid times
the concentration of the hydroxide ion to
the concentration of the base.
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19.3
Strong
and Weak Acids and Bases
a. Strong bases dissociate completely into
metal ions and hydroxide ions in aqueous
solution.
b. Weak bases react with water to form the
hydroxide ion and the conjugate acid of the
base.
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19.3
Strong
and Weak Acids and Bases
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19.3
Calculating
Dissociation Constants
Calculating Dissociation Constants
How can you calculate an acid dissociation
constant (Ka) of a weak acid?
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19.3
Calculating
Dissociation
Constants
To find the Ka of a weak acid or the Kb of a weak
base, substitute the measured concentrations
of all the substances present at equilibrium
into the expression for Ka or Kb.
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Calculating
Dissociation
Constants
19.3
Acid Dissociation Constant
a. The dissociation constant, Ka, of ethanoic
acid is calculated from the equilibrium
concentrations of all of the molecules and
ions in the solution.
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19.3
Calculating
Dissociation
Constants
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19.3
Calculating
Dissociation
Constants
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Calculating
Dissociation
Constants
19.3
Base Dissociation Constant
a. The dissociation constant, Kb, of ammonia
is calculated from the equilibrium
concentrations of all of the molecules and
ions in the solution.
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Calculating
Dissociation
Constants
19.3
Concentration and Strength
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19.5
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19.5
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19.5
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19.5
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for Sample Problem 19.5
Problem Solving 19.23
Solve Problem 23 with the help
of an interactive guided
tutorial.
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19.3 Section Quiz.
1. H2S is considered to be a weak acid because it
a. is insoluble in water.
b. ionizes only slightly.
c. is completely ionized.
d. is dilute.
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19.3 Section Quiz.
2. Calcium hydroxide, Ca(OH)2, is a strong base
because it
a. has a large Kb.
b. has a small Kb.
c. forms concentrated solutions.
d. is highly soluble in water.
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19.3 Section Quiz.
3. If the [H+] of a 0.205M solution of phenol
(C6H5OH) at 25ºC is 2.340  10-6, what is the
Ka for phenol? Phenol is monoprotic.
a. Ka = 2.67 x 10-11
b. Ka = 1.14 x 10-5
c.
Ka = 5.48 x 10-12
d. Ka = 1.53 x 10-3
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19.3 Section Quiz.
4. The Ka of three acids is given below.
(1) 5.1  10–3
(2) 4.8  10–11
(3) 6.3  10–5
Put the acids in order from the strongest acid to the
weakest acid.
a. 1, 3, 2
b. 2, 3, 1
c. 3, 1, 2
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d. 2, 1, 3
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19.3 Section Quiz.
5. The Kb of four bases is given below.
(1) 7.41 x 10-5
(2) 1.78 x 10-5
(3) 4.27 x 10-4
(4) 4.79 x 10-4
Put the bases in order from the strongest base to the weakest base.
a.
2, 3, 4, 1
b.
2, 1, 3, 4
c.
4, 3, 1, 2
d.
1, 4, 3, 2
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19.4
Neutralization Reactions
Excess hydrochloric acid in the stomach can
cause heartburn and a feeling of nausea.
Antacids neutralize the stomach acid and
relieve the pain of acid indigestion. You will
learn what a neutralization reaction is.
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19.4
Acid-Base
Reactions
Acid-Base Reactions
What are the products of the reaction of an acid
with a base?
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19.4
Acid-Base
Reactions
a. In general, the reaction of an acid with a
base produces water and one of a class of
compounds called salts.
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19.4
Acid-Base
Reactions
a. Reactions in which an acid and a base
react in an aqueous solution to produce a
salt and water are generally called
neutralization reactions.
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19.4
Acid-Base
Reactions
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19.4
Titration
Titration
What is the endpoint of a titration?
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19.4
Titration
a. The process of adding a known amount of
solution of known concentration to
determine the concentration of another
solution is called titration.
The point of neutralization is the end point
of the titration.
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19.4
Titration
a. When an acid and base are mixed, the
equivalence point is when the number of
moles of hydrogen ions equals the number
of moles of hydroxide ions.
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19.6
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19.6
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19.6
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19.6
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for Sample Problem 19.6
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19.4
Titration
a. The solution of known concentration is
called the standard solution.
Indicators are often used to determine
when enough of the standard solution
has been added to neutralize the acid or
base.
The point at which the indicator changes
color is the end point of the titration.
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19.4
Titration
Acid solution
with indicator
Added base is
measured with a
buret.
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Color change
shows
neutralization.
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Titration
Simulation 26
Simulate the titration of several acids and bases
and observe patterns in the pH at
equivalence.
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19.4
Titration
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19.7
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19.7
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19.7
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19.7
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for Sample Problem 19.7
Problem Solving 19.33
Solve Problem 33 with the help of
an interactive guided tutorial.
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19.4 Section Quiz
1. When a neutralization takes place, one of the
products is always
a. carbon dioxide.
b. a salt.
c. sodium chloride.
d. a precipitate.
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19.4 Section Quiz
2. In a titration, 45.0 mL of KOH is neutralized by
75.0 mL of 0.30M HBr. What is the
concentration of the KOH solution?
a. 0.18M
b. 0.60M
c. 0.25M
d. 0.50M
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19.4 Section Quiz
3. How many moles of HCl are required to
neutralize an aqueous solution of 2.0 mol
Ca(OH)2?
a. 0.5 mol
b. 1.0 mol
c. 2.0 mol
d. 4.0 mol
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19.4 Section Quiz
4. In which of the following neutralization
titrations of 1-molar solutions of H2SO4 and
NaOH will the equivalence point be reached
at the very end of the additions?
H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) +
2H2O(aq)
a. 200 mL of H2SO4 is slowly added to 100
mL of NaOH
b. 200 mL of H2SO4 is slowly added to 200
mL of NaOH
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19.5
Salts in Solution
The chemical processes inside a living cell are
very sensitive to pH. Human blood is
normally maintained at a pH very close to
7.4. You will learn about chemical processes
that ensure that the pH of blood is kept near
7.4.
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19.5
Salt Hydrolysis
Salt Hydrolysis
When is the solution of a salt acidic or basic?
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19.5
Salt Hydrolysis
In general, salts that produce acidic solutions
contain positive ions that release protons to
water. Salts that produce basic solutions
contain negative ions that attract protons from
water.
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19.5
Salt Hydrolysis
a. In salt hydrolysis, the cations or anions of
a dissociated salt remove hydrogen ions
from or donate hydrogen ions to water.
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19.5
Salt Hydrolysis
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19.5
Salt Hydrolysis
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19.5
Salt Hydrolysis
a. To determine whether a salt solution is
acidic or basic, remember the following
rules:
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19.5
Salt Hydrolysis
a. Vapors of the strong acid HCl(aq) and the
weak base NH3(aq) combine to form the
acidic white salt ammonium chloride
(NH4Cl).
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19.5
Salt Hydrolysis
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19.5
Salt Hydrolysis
a. Universal indicator solution has been
added to each of these 0.10M aqueous
salt solutions.
NH4Cl
pH 5.3
NaCl
pH 7
CH3COONa
pH 5.3
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19.5
Buffers
Buffers
What are the components of a buffer?
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19.5
Buffers
a. A buffer is a solution of a weak acid and
one of its salts, or a solution of a weak
base and one of its salts.
a. The pH of a buffer remains
relatively constant when small
amounts of acid or base are added.
b. The buffer capacity is the amount
of acid or base that can be added to
a buffer solution before a significant
change in pH occurs.
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19.5
Buffers
a. Buffer of Ethanoic Acid and Sodium
Ethanoate
Adding H+ produces additional ethanoic acid.
Adding OH- produces additional ethanoate
ions.
The pH changes very little.
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19.5
Buffers
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Buffers
Animation 26
Discover the chemistry behind buffer action.
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19.5
Buffers
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Conceptual Problem 19.2
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for Conceptual Problem 19.2
Problem Solving 19.39
Solve Problem 39 with the help of
an interactive guided tutorial.
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19.5 Section Quiz.
1. Which of the following reactions would most
likely yield a basic salt solution?
a. strong acid + weak base
b. weak acid + weak base
c. strong acid + strong base
d. weak acid + strong base
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19.5 Section Quiz.
2. Choose the correct words for the spaces. A
buffer can be a solution of a _________ and
its _________.
a. weak acid, salt
b. strong acid, salt
c. weak acid, conjugate base
d. weak base, conjugate acid
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