Acids & Bases
Properties of Acids & Bases

Acids
 Aqueous solutions of
acids have a sour taste
 Turn blue litmus paper to
red
 React with metals to
produce hydrogen gas
(single replacement by
more active metals)
 React with bases to
produce salt and water
 Many acids are
electrolytes

A binary acid is an acid that contains only
two different elements: hydrogen and one
of the more electronegative elements

An oxyacid is an acid that is a compound of
hydrogen, oxygen, and a third element,
usually a nonmetal
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Bases
 Aqueous solutions
taste bitter
 Turn red litmus paper
blue
 Dilute solutions feel
slippery
 Bases react with acids
to produce a salt and
water
 Bases are electrolytes
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An Arrhenius acid is a chemical
compound that increases the
concentration of hydrogen ions (H+) in
aqueous solution
An Arrhenius base is a substance that
increases the concentration of hydroxide
ions (OH-) in aqueous solution

A strong acid is one that ionizes
completely in aqueous solution

Increasingly strong with increasing
polarity and decreasing bond energy

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Acids that are weak electrolytes are also
weak acids
Molecules with multiple hydrogens are not
necessarily strong acids, their equilibrium
may not favor the products
Organic acids contain carboxylic acid
functional group (-COOH)

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Organic acids are generally weak
acids
Many common bases contain metal
cations and hydroxide ions (these
are polar)
When a base completely dissociates
in water to yield hydroxide ions, the
solution is referred to as alkaline
Ammonia is a base because it
produces hydroxide ions when it
reacts with water
NH3 + H2O ---> NH4+ + OH-

The strength of a base depends on
the extent to which the base
dissociates

The alkalinity depends on the
concentration of hydroxide ions in
solution
Acid-Base Theories
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The Arrhenius definition of acids and bases
was limited (had to be aqueous)
Bronsted and Lowry independently expanded
the definition
They defined acids as proton donors and
bases as proton acceptors

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An acid that can donate only one
proton per molecule is known as a
monoprotic acid
A polyprotic acid is an acid that can
donate more than one proton per
molecule



Sulfuric acid is know as diprotic
Phosphoric acid is know as triprotic
These are not necessarily stronger acids,
depends on the degree of dissociation

A Lewis acid is an atom, ion, or molecule
that accepts an electron pair to form a
covalent bond – A Lewis base donates an
electron pair

This is the broadest definition
Acid Base Reactions

The species that remains after a
Bronsted-Lowry acid has given up a
proton is the conjugate base of that
acid (The base also produces a
conjugate acid)

Typically equilibrium systems with a forward
and reverse reaction
NH3  H 2O

44

NH
NH OH
OH

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The stronger an acid, the weaker its
conjugate base; the stronger a base, the
weaker its conjugate acid
Proton-transfer reactions favor the
production of the weaker acid and the
weaker base

Any species that can react as either an
acid or a base is described as amphoteric

-OH groups can be amphoteric or acidic
 The more polar the –OH group, the more
acidic the compound
 The more electronegative atoms of
nonmetals form acids with hydroxyl (OH) groups
 Electronegative oxygens will draw the
electron density away from the hydroxyl
group, making it more polar
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In aqueous solutions, neutralization
is the reaction of hydronium ions
and hydroxide ions to form water
molecules
A salt is also produced (an ionic
compound composed of the cation
from a base and the anion from an
acid)