Download Brønsted-Lowry Acids and Bases

CHEMISTRY CHAPTER 14. ACIDS AND
BASES
SECTION 1. PROPERTIES OF ACIDS AND
BASES
Acids – Quick Survey of General Features
1. Aqueous solutions of acids have a
sour taste.
2. Acids change the color of acid-base
indicators.
3. Some acids react with active
metals and release hydrogen
gas, H2.
4. Acids react with bases to
produce salts and water.
5. Acids conduct electric current.
Acid Nomenclature
• A binary acid is an acid that
contains only two different
elements: hydrogen and one of
the more electronegative
elements.
• HF, HCl, HBr, and HI
• The name of a binary acid
begins with the prefix hydro-.
• The root of the name of the
second element follows this
prefix.
• The name then ends with the
suffix -ic.
• An oxyacid is an acid that is a
compound of hydrogen, oxygen,
and a third element, usually a
nonmetal.
• ex: HNO3, H2SO4
Some Common Industrial Acids
• Sulfuric Acid
• Sulfuric acid is the most
commonly produced industrial
chemical in the world.
• Nitric Acid
• Phosphoric Acid
• Hydrochloric Acid
• Concentrated solutions of
hydrochloric acid are commonly
referred to as muriatic acid.
• Acetic Acid
• Pure acetic acid is a clear,
colorless, and pungent-smelling
liquid known as glacial acetic acid.
Bases - General Features
1. Bitter taste.
2. Change the color of acid-base
indicators.
3. Dilute solutions of bases feel
slippery.
4. React with acids to produce salts
and water.
5. Conduct electric current.
CHEMISTRY CHAPTER 14. ACIDS AND
BASES
SECTION 1. PROPERTIES OF ACIDS AND
BASES
Definitions of Acids and Bases
The book discusses three definitions:
• Arrhenius acids and bases
• Brønsted-Lowry acids and bases
• Lewis acids and bases (we will not
discuss)
Arrhenius Acids and Bases
These are the classical definitions that
we used earlier:
1. An Arrhenius acid is a chemical
compound that increases the
concentration of hydrogen ions, H+, in
aqueous solution.
The H+ actually combines with H2O to
form H3O+ (hydronium ion).
In a solution of hydrogen chloride
in water to form hydrochloric
acid the following reaction
occurs:
HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq)
2. An Arrhenius base is a
substance that increases the
concentration of hydroxide ions,
OH−, in aqueous solution.
a.Ionic hydroxides
ex.: KOH → K+ + OHb.Compounds that react with
water to generate OHex.: NH3 + H2O → NH4+ + OH-
Arrhenius Acids and Bases
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Aqueous Solutions of Acids
• Arrhenius acids are molecular compounds with
ionizable hydrogen atoms.
• Their water solutions are known as aqueous
acids.
• All aqueous acids are electrolytes.
Common Aqueous Acids
Strength of Bases
• The strength of a base depends on the extent
to which the base dissociates.
• Strong bases are strong electrolytes
SECTION 2. ACID-BASE THEORIES
Brønsted-Lowry Acids and Bases
• A Brønsted-Lowry acid is a molecule
or ion that is a proton donor.
• Ex.: HCl when it reacts with H2O or NH3:
HCl + H2O → Cl- + H3O+
HCl + NH3 → Cl- + NH4+
Note that HCl is a Brønsted-Lowry acid in
both cases, even though H3O+ is not
formed in the second reaction.
• Water can act as a BrønstedLowry acid:

–


H2O(l ) + NH3 (aq )  NH4 (aq ) + OH (aq )
• A Brønsted-Lowry base is a
molecule or ion that is a proton
acceptor.
• What are the Brønsted-Lowry
bases in the examples above?
Brønsted-Lowry Acids and
Bases
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Svante Arrhenius
wikipedia
Johannes Brnsted
Thomas Martin Lowry
Conjugate Acids and Bases
When a Brønsted-Lowry acid gives up
a proton, the species that remains is
called the conjugate base of the acid,
because it can accept a proton when
the reaction goes in reverse.
Similarly, the species that forms when
a base gains a proton is the
conjugate acid.
Ex.: HF + H2O → F- +
acid base conj.
base
of HF
H3O+
conj.
acid
of H2O
reverse:
F- + H3O+ → HF + H2O
In general, a reversible acid-base
reaction consists of two –pairs of
conjugate acids and bases:
HF + H2O ↔ F- + H3O+
acid1
base2 base1 acid2
Conjugate Acid-Base Pairs
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Neutralization Reactions
• In aqueous solutions,
neutralization is the reaction of
hydronium ions from an acid and
hydroxide ions from a base to
form water molecules.
• The other product is a salt formed
from the cation of the base plus
the anion from the acid.
Ex. 1: HCl + NaOH + H2O →
H3O+ + Cl- + Na+ + OHH3O+ + Cl- + Na+ + OH- → 2H2O + NaCl
net:
HCl + NaOH → H2O + NaCl
Ex. 2: 2HBr + Ba(OH)2 → BaBr2 + 2H2O
Neutralization Reactions