Submicroscopic Behavior of Acids
• An acid is a substance that produces
hydronium ions (H3O+) when it dissolves in
water.
• A hydronium ion (H3O+) consists of a
hydrogen ion (H+) attached to a water
molecule (H2O).
Submicroscopic Behavior of Acids (cont.)
• Any hydrogen atom that can be transferred
to water is called an acidic hydrogen.
Properties of Acids and Bases
• Acids taste sour.
• Bases taste bitter and usually have a
slippery feel.
• The reactions of acids and bases are central
to the chemistry of important living,
environmental, and industrial processes.
Properties of Acids and Bases (cont.)
Properties of Acids and Bases (cont.)
• Litmus is a reliable indicator whether a
substance is an acid (red) or a base (blue).
• An acid reacts with metals that are more
active than hydrogen, or with carbonates.
• Bases do not commonly react with metals or
carbonates.
litmus with
base
litmus with
acid
– monoprotic—1 acidic hydrogen
– diprotic—2 acidic hydrogens
– polyprotic—more than 1 acidic hydrogen
Submicroscopic Behavior of Acids (cont.)
• Polyprotic acids lose their acidic hydrogens
one at a time.
Submicroscopic Behavior of Acids (cont.)
• The process of forming ions in solution is
called ionization.
• Because acids ionize to form ions in water,
acidic solutions conduct electricity.
• Acids are electrolytes.
Submicroscopic Behavior of Acids (cont.)
Submicroscopic Behavior of Bases
• A base is a substance that produces
hydroxide ions (OH–) when it dissolves in
water.
• The simplest base is a water-soluble ionic
compound that contains the hydroxide ion as
the negative ion.
Submicroscopic Behavior of Bases (cont.)
• A few bases are covalent compounds that
produce hydroxide ions by an ionization
process when dissolved in water.
• Because a base in water produces ions, it will
conduct electricity.
Submicroscopic Behavior of Bases (cont.)
A base can produce a hydroxide ion (OH-)
by accepting a H+ from water
Acid Rain
• Due to the carbon dioxide in the atmosphere,
rainwater is always slightly acidic but
additional oxides such as sulfur and nitrogen
create acid rain.
– Lime used to treat soil
CaO(s) + H2O(l) → Ca(OH)2(aq)
Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq)
– Soap
Na2O(s) + H2O(l) → 2Na(OH)(aq)
Na(OH)(aq) → Na+(aq) + OH–(aq)
The Macroscopic-Submicroscopic
Acid-Base Connection (cont.)
The pH Scale
• The pH scale was created to make it easier
to work with the large range of
concentrations present in different acids
and bases.
• pH is a mathematical scale in which the
concentration of hydronium ions in a solution
is expressed as a number from 0 to 14.
The pH Scale (cont.)
• In the relationship between hydronium and
hydroxide ions, as the concentration of one
increases, the concentration of other must
decrease.
The pH Scale (cont.)
• Neutral solutions exist at a pH of 7, where
hydronium and hydroxide ion
concentrations are equal.
• Solutions with a pH lower than 7 have a
higher concentration of hydronium ions and
are acidic.
The pH Scale (cont.)
• Solutions with a pH higher than 7 have a
higher concentration of hydroxide ions and
are basic.
The pH Scale (cont.)
Section Assessment
A base is a substance that produces ___
when it dissolves in water.
A. hydronium ions
B. electrolytes
C. hydroxide ions
D. polyprotic ions
Section Assessment
An example of a base that accepts the
transfer of a hydrogen ion when it is
dissolved in water is:
A. ammonia
B. sodium hydroxide
C. calcium hydroxide
D. aluminum hydroxide
Section Assessment
If a litmus strip turns blue, the substance
must be a(n):
A. base
B. acid
Strong Acids and Bases
• Acids and bases are
categorized depending upon
their strength, which is the
degree to which they form
ions.
Strong Acids and Bases (cont.)
• A strong base is a base that completely
dissociates into ions when dissolved in
water.
• A strong acid is an acid that completely
ionizes in water.
Weak Acids and Bases
• A weak acid is an acid that only ionizes
partially in solution.
Weak Acids and Bases (cont.)
• The molecular structure of a weak acid
determines the extent to which the acid
ionizes in water.
Weak Acids and Bases (cont.)
• A weak base ionizes only partially in
solution. Most of the molecules do not
react with water to form ions.
• The combination of strength and
concentration ultimately determines the
behavior of a solution.
• http://www.mhhe.com/physsci/chemistry/e
ssentialchemistry/flash/acid13.swf
• Strong vs. weak acid
What is a convenient way to compare the
acidity and basicity of solutions?
A. pH scale
B. ionization indicator
C. pH table
D. neutrality diagram
If a solution has a pH of 8, it is:
A. basic
B. acidic
C. neutral
If a solution has a pH of 5, it is:
A. basic
B. acidic
C. neutral
Key Concepts
• The concentrations of hydrogen (H+) ions and
hydroxide ions (OH–) determine whether an aqueous
solution is acidic, basic or neutral.
• Acidic anhydrides are nonmetallic oxides that react
with water to form acids. Basic anhydrides are
metallic oxides that react with water to form bases.
Key Concepts
• Most acids and bases are weak. Only a small
percentage of their molecules dissociate to form ions.
• The pH scale is a convenient way to compare the
acidity and basicity of solutions.
• Acidic solutions have a pH less than 7, basic solutions
have a pH greater than 7, and neutral solutions have a
pH of exactly 7.