Chapter 16: Acids and Bases

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Chapter 16 Acids and Bases

• Understand the Arrhenius and Bronsted-Lowry
  models for acids and bases.
• Understand acid strength
• Understand the relationship between acid strength
  and strength of the conjugate base
• Learn about the ionization of water
• Understand and uses the terms pH and pOH
• Learn methods for measuring the pH of a solution
• Learn to calculate the pH of solutions of strong
  acids.
• Learn about acid-base titration.
• Understand the general characteristics of
  buffered solutions.

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Chapter 16.1 Acids and Bases

• Objective To learn about 2 models of acids
• and bases and the relationship of conjugate
  acid-base pairs.

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Chapter 16 Acids and Bases

• Why do we study them?
• Lemons (citric acid)
• Digest food (HCl)
• Sulfuric acid is the chemical produced in the
  greatest amount in the U.S.
• 80 billion pounds of acids are used each year
• To make fertilizers, detergents, plastics,
  pharmaceuticals, storage batteries and metals.

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16-1 Properties of Acids and Bases

• Were first recognized as substances that taste
  sour.
• Vinegar (acetic acid)
• Lemon (citric acid)
• Bases alkalis
• Bitter taste, slippery feel
• Most hand soaps and commercial preparations for
  unclogging drains are highly basic.

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16-1 Arrhenius Model

• Arrhenius postulated that acids produce H ions
  in aqueous solution
• HCl H Cl-
• strong acids
• Bases produce OH- ions
• NaOH Na OH-

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16-1 Bronsted-Lowry Model

• Acid is a proton donor
• Base is a proton acceptor
• HA(aq) H2O(l) H3O(aq) A-(aq)
• Acid Base conj. Conj.
• acid base
• Conjugate acid-base pair consists of 2 substances
  related to each other by the donating and
  accepting of a single proton.

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16-1 Writing Conjugate Bases

• HClO4
• H3PO4
• CH3NH3

H ClO4-
Acid
conjugate base
H H2PO4-
Acid
conjugate base
H CH3NH2
Acid
conjugate base
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16.2 Acid Strength

• Objectives To understand what acid strength
  means.
• To understand the relationship between acid
  strength and that strength of the conjugate base.

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16.2 Acid Strength

• Strong acid completely ionized or completely
  dissociated.
• HA(aq) H2O H3O(aq) A-(aq)
• Weak acidHA(aq) H2O H3O(aq)
  A-(aq)

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Figure 16.1 Representation of the behavior of
acids of different strengths in aqueous solution.
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Figure 16.2 Relationship of acid strength and
conjugate base strength for the dissociation
reaction.
Strong acids are sulfuric acid,
hydrochloric acid, nitric acid, perchloric acid,
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Strong Acids/weak acids

• Oxyacids acidic hydrogen is attached to
• An oxygen atom.
• Phosphoric acid, acetic acid, hypochlorous,
• Nitrous acid.
• Organic acids those with a carbon-atom
• Backbone, commonly contain the carboxyl group.
  
• CO
• OH

Weak acids
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16.3 Water as an Acid and a Base

• Objective To learn about the ionization of
  water.
• Amphoteric behave as either an acid or
• as a base.
• Ionization of water
• H2O(l) H2O(l) H3O(aq) OH-(aq)

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16.3 Water as an Acid and a Base

• H3O OH- 1.0x10-7 M
• At 25o C, the product of the ions is constant.
• Kw H3O OH-1.0 x 10-14M
• Kw is called the ion-product constant for water.

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16.3 Water as an Acid and a Base

• H3O OH- 1.0x10-7 M
• A neutral solution, where H OH-
• An acidic solution, where H gt OH-
• A basic solution, where OH-gt H
• Kw H3O OH-1.0 x 10-14M

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16.3 Water as an Acid and a Base

• Calculate H or OH- as required for each of
  the following solutions at 25oC.
• 1x10-4M H
• 1x10-8M H
• 1x10-9M OH-
• 1x10-3M OH-

1x10-10 M OH-
1x10-6M OH-
1x10-5M H
1x10-11M H
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16.4 The pH scale

• Objective To understand pH and pOH
• To learn to find pOH and pH for various
  solutions.
• To learn to use a calculator in these
  calculations.

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16.4 The pH scale

• Logarithm scale that helps to represent
• exponents.
• LOGS ARE EXPONENTS!! Using log10 ("log to the
  base 10") log10100 2 is equivalent to 102
  100
• where 10 is the base, 2 is the logarithm (i.e.,
  the exponent or power) and 100 is the number
• 10 to the x power 1000

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The pH scale provides a convenient way to
represent solution acidity.
pH -log H
H1x10-3M OH-1x10-5M
pOH -logOH-
pOH pH 14.00
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16.5 Measuring pH

• Objective To learn methods for measuring the pH
  of a solution.
• INDICATORS substances that exhibit different
  colors in acidic and basic solutions.

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Figure 16.4 Useful pH ranges for several common
indicators.
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16.5 Measuring pH

• Indicator paper (litmus paper) paper coated with
  a combination of indicators. Indicator paper
  turns a specific color for each pH value.
• Electronically, pH meter contains a probe that is
  sensitive to the H. H produces a voltage
  that appears as a reading on the pH meter.

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16.7 Acid-Base Titrations

• Neutralization reaction equal amounts of H and
  OH-. Result solution with pH7.
• Titration test that chemists perform to analyze
  the acid/base content of a solution.
• Deliver a measured volume of a solution (w/ known
  concentration) the titrant into the solution
  being analyzed analyte.

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16.7 Acid-Base Titrations

• Titration
• Titrant standard solution (solution w/known
  concentration).
• Titrant is loaded into a buret.

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Figure 16.8 Microscopic picture of the
solutions in the titration of 0.200 M HNO3 with
0.100 M NaOH.
Buret
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Figure 16.9 The pH curve for the titration of
50.0 mL of 0.200 M HNO3 with 0.100 M NaOH.
Titration curve (pH Curve)
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16.8 Buffered Solutions

• Objectives To understand the general
  characteristics of buffered solutions.
• Buffered solution is one that resists a change in
  its pH even when a strong acid or base is added
  to it.

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16.8 Buffered solutions

• Why are they important?
• Many organisms can only exist in a narrow range
  of conditions.
• Blood (pH 7.35-7.45)

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16.8 Buffered solutions

• Characteristics of a Buffer
• Solution contains a weak acid HA and its
  conjugate base A-
• The buffer resists changes in pH by reacting with
  any added H or OH- so that these ions dont
  accumulate
• Any added H reacts with the base A-.
• Any added OH- reacts with the weak acid HA.

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16.8 Buffered solutions

• Examples
• HC2H3O2, NaC2H3O2
• In solution.
• HCl H Cl-
• H(aq) C2H3O2- HC2H3O2
• NaOH
• OH- HC2H3O2 H2O HC2H3O2