Chapter 16 acids and bases
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Petrucci • Harwood • Herring • Madura. GENERAL. Ninth Edition. CHEMISTRY. Principles and Modern Applications. Chapter 16: Acids and Bases. Juana Mendenhall, Ph.D. Assistant Professor Morehouse College. Objectives.

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Chapter 16: Acids and Bases

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Chapter 16 acids and bases

Petrucci • Harwood • Herring • Madura

GENERAL

Ninth

Edition

CHEMISTRY

Principles and Modern Applications

Chapter 16: Acids and Bases

Juana Mendenhall, Ph.D.

Assistant Professor

Morehouse College

General Chemistry: Chapter 16


Objectives

Objectives

Calculate values of Ka for cations and Kb for anions from ionization constants of their conjugates and Kw of water, and calculate the pH values of salt solutions in which hydrolysis occurs

Use the relative strengths of Brønsted-Lowry acids and bases to predict the direction of acid-base reactions.

Predict whether certain oxides and hydroxo compounds are acidic, basic, or neutral.

Define what an oxoacid is and predict the relative strengths of oxoacids from their molecular structures.

General Chemistry: Chapter 16


16 7 ions as acids and bases

[NH3] [H+]

Ka=

[NH4+]

1.010-14

KW

[NH3][H+] [OH-]

Ka=

= 5.610-10

=

=

1.810-5

Kb

[NH4+] [OH-]

16-7 Ions as Acids and Bases

NH4+(aq)NH3(aq)+ H+(aq)

base

acid

NH3(aq)+ H2O(l)NH4+(aq) + OH-(aq)

[NH4+][OH-]

Kb

=

base

acid

[NH3]

H+(aq) + OH-(aq)

H2O(l)

[NH4+][OH-]

KaxKb =

[NH3][H+]

Kw

[OH-][H+]

x

=

=

[NH4+]

[NH3]

KaKb = Kw

pKa + pKb = pKw = 14.00

General Chemistry: Chapter 16


Examples

Calculate the a) base-dissociation constant, Kb, for the fluoride ion, F-

Examples

Ka = 6.8 x 10-4

b) Calculate the acid-dissociation constant, Ka, for the ammonium ion,

NH4+ (Kb = 1.8 x 10-5)

General Chemistry: Chapter 16


Hydrolysis

Hydrolysis

  • is the reaction of ions with water to generate H+ or -OH.

  • Water (hydro) causing cleavage (lysis) of a bond.

Na+ + H2O → Na+ + H2O

No reaction

No reaction

Cl- + H2O → Cl- + H2O

Hydrolysis

NH4+ + H2O → NH3 + H3O+

General Chemistry: Chapter 16


16 8 molecular structure and acid base behavior

16-8 Molecular Structure and Acid-Base Behavior

  • Why is HCl a strong acid, but HF is a weak one?

  • Why is CH3CO2H a stronger acid than CH3CH2OH?

  • There is a relationship between molecular structure and acid strength.

  • Bond dissociation energies are measured in the gas phase and not in solution.

  • Strength depends on properties of the solvent and temperature.

General Chemistry: Chapter 16


Strengths of binary acids

Strengths of Binary Acids

HIHBrHClHF

Bond length

160.9>141.4>127.4>91.7 pm

Bond energy

297<368<431<569 kJ/mol

Acid strength

109>108>1.3106 >> 6.610-4

HF + H2O → [F-·····H3O+] F- + H3O+

ion pair

H-bonding

free ions

General Chemistry: Chapter 16


16 9 lewis acids and bases

16-9 Lewis Acids and Bases

  • Lewis Acid

    • A species (atom, ion or molecule) that is an electron pair acceptor.

  • Lewis Base

    • A species that is an electron pair donor.

acid

base

adduct

Since BF3 accepts electrons from NH3 it is a lewis acid

General Chemistry: Chapter 16


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