UNIVERSIDAD AUTÓNOMA DE NUEVO LEON
STAGE III: ACIDS AND BASES,
OPPOSITES THAT NEUTRALIZE
Formative Objective: The student solves
theoretical and experimental problems
related to acidic and basic solutions in daily
life. Thinks about the negative effects of acid
rain in the surroundings and propose
possible solutions to this environmental
•In aqueous solution, conduct electricity
•React with bases to form salt and water
•React with metals to form hydrogen gas
•React with carbonates to form carbon
dioxide, water and a salt
•Contain hydrogen ions (H+)
•Have a pH lower than 7
•Turn blue litmus paper to a red colour
•Feel slippery or soapy
•In aqueous solution, conduct
•React with acids to form salts and
•Contain hydroxyl ions (OH-)
•Have a pH higher than 7
•Turn red litmus paper to a blue colour
Magnesium and zinc react with aqueous
solutions of acids to produce hydrogen gas.
Metal carbonates and hydrogen carbonates
also react with aqueous solutions of acids to
produce carbon dioxide (CO2) gas.
All water solutions contain hydrogen ions (H+)
and hydroxide ions (OH-).
An acidic solution contains more hydrogen ions than
A basic solution contains more hydroxide ions than
A neutral solution contains equal concentrations of
hydrogen ions and hydroxide ions
Pure water produces equal numbers of H +
ions and OH- ions in a process called self-ionization,
in which water molecules react to
form a hydronium ion and a hydroxide ion.
ions in water
ions in water
States that an acid is a substance
that contains hydrogen and ionizes to produce
hydrogen ions in aqueous solution.
A base is a substance that contains a hydroxide
group and dissociates to produce a hydroxide ion in
BUT, Ammonia (NH3) and sodium carbonate (Na2CO3)
do not contain a hydroxide group, yet both
substances produce hydroxide ions in solution and
are well-known bases.
Base is a proton
hydrogen ion, H+
Acid is a proton
donor; it donates
a hydrogen ion,
When a molecule of acid HX dissolves in
water, it donates a H + ion to a water
molecule. The water molecule acts as a base
and accepts the H + ion.
◦ The hydronium ion is an acid because it has an
extra H + ion that it can donate.
◦ X - is a base because it has a negative charge and
can readily accept a positive hydrogen ion.
Conjugate acid: is produced when a base
accepts a hydrogen ion.
Conjugate base: is produced when an acid
donates a hydrogen ion.
Conjugate acid-base pair consists of two
substances related to each other by the donating
and accepting of a single hydrogen ion.
Hydrogen fluoride: A Brønsted-Lowry acid
Ammonia: A Brønsted-Lowry base
Water: a Brønsted-Lowry acid and base; water
is AMPHOTERIC because can act as both acid
To write the conjugate base of an acid:
◦ A H+ is lost
◦ The compound becomes more negative.
ACIDS CONJUGATE BASES
To write the conjugate acid of a base:
◦ A H+ is added
◦ The compound becomes more positive.
BASES CONJUGATE ACIDS
• Can donate only one hydrogen ion
(proton) per formula unit.
• Ex: HCl, HNO3, HC2H3O2
• Contain two ionizable hydrogen atoms per
• Ex: H2SO4
• Contain three hydrogen ions to donate
Triprotic acids • Ex: H3PO4
• Any acid that has more than one ionizable
hydrogen atomPolyprotic acids .
The difference between acetic acid’s ionizable
hydrogen atom and the other three hydrogen
atoms is that the ionizable atom is bonded to
the element oxygen, which is more
electronegative than hydrogen. The
difference in electronegativity makes the
bond between oxygen and hydrogen polar
Observe the following reaction:
H2O + CH3NH2 → OH- + CH3NH3
Is an acid-base reaction according to
Arrhenius model? If so, identify the acid and
Is an acid-base reaction according to
Bronsted-Lowry model? If so, identify the acid
and the base.
Electrolyte: an ionic compound whose
aqueous solution conducts an electric
Strong acids: Acids that ionize completely.
Because strong acids produce the maximum
number of ions, they are good conductors of
Weak acids: An acid that ionizes only partially
in dilute aqueous solution; produce fewer
ions and thus cannot conduct electricity as
well as strong acids.
“The conjugate base of a strong acid is very
“The conjugate base of a weak acid is strong”
Strong bases: A base that dissociates entirely
into metal ions and hydroxide ions.
Weak bases: ionize only partially in dilute
Pure water contains equal concentrations of H+ and OH- ions
produced by self-ionization.
The ion product constant for water is the value of the equilibrium
constant expression for the self-ionization of water.
In pure water at 25º C:
[H3O+] = 1.0 x 10-7 M
[OH-] = 1.0 x 10-7 M
In pure water, the concentration of
hydronium ions equals the concentration of
hydroxide ions. This product is called the ion
product constant of water Kw
Acidic solutions • The [H+] is greater than 1.0 x 10-7 M
Basic solutions • The [H+] is lower than 1.0 x 10-7 M
• The [H+] is equal to 1.0 x 10-7 M
Substances that change color depending on
the concentration of hydrogen ions in a
The reaction of an acid with a base in
aqueous solution to produce a salt and water.
The salt is an ionic compound made up of a
cation from a base and an anion from an acid.
Buffers are solutions that resist changes in pH
when limited amounts of acid or base are
Is a mixture of a weak acid and its conjugate
base or a weak base and its conjugate acid.
The mixture of ions and molecules in a buffer
solution resists changes in pH by reacting
with any hydrogen ions or hydroxide ions
added to the buffered solution.
A buffer solution’s capacity to resist pH
change can be exceeded by the addition of
too much acid or base. The amount of acid or
base a buffer solution can absorb without a
significant change in pH is called the buffer
capacity of the solution.
The greater the concentrations of the
buffering molecules and ions in the solution,
the greater the solution’s buffer capacity.