Chapter Menu
Chapter Menu
Section 18.1
Section 18.3
Section 18.4
Introduction to Acids and
Bases
Hydrogen Ions and pH
Neutralization
Section 18.1 Intro to Acids and Bases
Objectives:
• Compare the Arrhenius, Brønsted-Lowry,
and Lewis models of acids and bases.
• Identify the physical and chemical properties
of acids and bases.
• Predict and explain the final results of an
acid-base reaction.
Different models help describe the
behavior of acids and bases.
Properties of Acids and Bases
Properties of an Acid
• Acids have a sour taste.
• Acids react with active metals to produce
hydrogen gas. (Activity series)
• Acids change blue litmus paper to red.
• Acids corrode metals.
• Acids react with bases to produce a salt & water
in a neutralization reaction.
Properties of Acids and Bases
Properties of a Base
• Bases have a bitter taste.
• Bases are slippery.
• Bases are poisonous and corrosive.
(never taste or touch to identify them)
• Bases change red litmus paper to blue.
• Bases react with acids to produce a salt & water
in a neutralization reaction.
Section 18.1 A Definition of Acids and Bases
Arrhenius Acids
• Any compound that contains hydrogen and
ionizes in aqueous solution to form hydrogen
ions (H+ ion)
HCl(g) + H2O ------> H2O H + Cl(H3O+)
• Hydrogens are found in front of acid formula.
• More than one can be ionized.
• H3O+ is called a hydronium ion.
Section 18.1 Acids and Bases Definition (cont.)
Arrhenius Base
• Any compound that contains OH- ions and
dissociates to produce OH- ions (hydroxide ions)
in an aqueous solution.
NaOH(s) ----->
Na+(aq) + OH-(aq)
• OH ions are found in the second position of a
base’s formula.
Section 18.1 A Definition of Acids and Bases
Categorize the following substances as Acids or
Bases using the Arrhenius Definitions of Acid
and Base.
HCl
KOH
Ca(OH)2
NH4OH
H2SO4
Mg(OH)2
____
____
____
____
____
____
H3BO3
NaOH
HNO3
CH3COOH
HClO3
H3PO4
____
____
____
____
____
____
Section 18.1 The Brønsted-Lowry Model
• The Brønsted-Lowry Model of acids and
bases states that an acid is a hydrogen
ion donor, and a base is a hydrogen ion
acceptor.
• The Brønsted-Lowry Model is a more
inclusive model of acids and bases.
Section 18.1 The Brønsted-Lowry Model
(cont.)
• A conjugate acid is the species produced
when a base accepts a hydrogen ion.
• A conjugate base is the species produced
when an acid donates a hydrogen ion.
• A conjugate acid-base pair consists of two
substances related to each other by donating
and accepting a single hydrogen ion.
Section 18.1 The Brønsted-Lowry Model
(cont.)
• Hydrogen fluoride—a Brønsted-Lowry acid
– HF(aq) + H2O(l)
H3O+(aq) + F–(aq)
– HF = acid, H2O = base, H3O+ = conjugate acid,
F– = conjugate base
Section 18.1 The Brønsted-Lowry Model
(cont.)
• Ammonia— Brønsted-Lowry base
– NH3(aq) + H2O(l)
NH4+(aq) + OH–(aq)
– NH3 = base, H2O(l) = acid, NH4+ = conjugate
acid, OH– = conjugate base
• Water and other substances that can act as
acids or bases are called amphoteric.
Section 18.1 Monoprotic and Polyprotic Acids
• An acid that can donate only one hydrogen
ion is a monoprotic acid.
• Only ionizable hydrogen atoms can be donated.
Section 18.1 Monoprotic and Polyprotic Acids
(cont.)
• Acids that can donate more than one
hydrogen ion are polyprotic acids.
Section 18.1 Types of Acid-Base Reactions
• A neutralization reaction is a reaction of an acid
with a base in aqueous solution to produce water
and a salt.
acid + base
salt + water
• The hydronium ion (H+) and the hydroxide (OH-)
ions combine chemically to form water.
• The anion from the acid and the cation from the
base then forms a salt.
Section 18.1 Types of Acid-Base Reactions (cont.)
What to the following produce?
HCl(aq) +
NaOH(aq) ------>
H2SO4(aq) + Mg(OH)2(aq) ----->
Section 18.1 Types of Acid-Base Reactions
(cont.)
• Salt is a general term used in chemistry to
describe the ionic compound formed from the
negative part of the acid and the positive part
of the base.
Properties of a Salt
• Some taste salty, some taste bitter.
• Many dissolve well in water, others slightly, a
few not at all.
• Salts usually form crystals
• Most salts are white in color.
• Salts are a neutral substance. (7 pH)
• Salts have high melting points
• Salts are solids at room temperature
• Salts are ionic compounds.
• Salts are good conductors of electricity when
molten or dissolved in water.
Section 18.3 Hydrogen Ions and pH
Objectives:
• Calculate pH, given the hydronium ion
concentration.
• Classify solutions as acidic, basic, or neutral.
pH and pOH are logarithmic scales that express
the concentrations of hydrogen ions and
hydroxide ions in aqueous solutions.
Section 18.3 pH and Acids and Bases
• All water solutions contain hydrogen ions
(H+) and hydroxide ions (OH–).
• An acidic solution contains more hydrogen
ions than hydroxide ions.
• A basic solution contains more hydroxide
ions than hydrogen ions.
Section 18.3 pH and Acids and Bases (cont.)
• The usual solvent for acids and bases is
water—water produces equal numbers of
hydrogen and hydroxide ions in a process
called self-ionization.
H2O(l) + H2O(l)
H3O+(aq) + OH–(aq)
• The hydronium ion is H3O+.
Section 15.2 pH
• Concentrations of H+ ions are often
small numbers expressed in
exponential notation.
• pH is the negative logarithm of the
hydrogen ion concentration of a
solution.
pH = –log [H+]
• pH is the measure of the hydronium
ion concentration. It indicates how
acidic a solution is.
Section 15.2 pH (cont.)
• pH means the “Power of Hydrogen”
• The pH scale is 0 to 14
• 0-6 represents acidic solutions (many H+)
• 7 represents neutral solutions (H+ = OH-)
• 8-14 represents basic solutions (little H+)
• The stronger the acid or base, the more extreme
the pH number.
• Litmus paper and a pH meter with electrodes
can determine the pH of a solution.
Section 15.2 pH problems
Sample Problem #1: Calculating the pH of a solution
What is the pH of a 0.001 M solution of HCl, a strong
acid?
Section 15.2 pH problems (cont.)
Sample Problem #2
What is the pH of a solution if [H3O+] = 3.4 x 10-5 M?