19.1 acids, base and salts By Hamdy Karim

Acids, Bases and Salts
By Hamdy Karim
H. K.
1

Chapter 19
Acids, Bases, and Salts
19.1 Acid-Base Theories
19.2 Hydrogen Ions and Acidity
19.3 Strengths of Acids and Bases
19.4 Neutralization Reactions
19.5 Salts in Solution
2
H. K.19.1 Acids – Bases Theories ˃ Arrhenius Acid- BaseAcid- Base

•Nitrogen compounds
in bat urine can
decompose and release
ammonia into the air.
Why are high levels of ammonia harmful
to you?
3

•Arrhenius Acids and Bases
How did Arrhenius define an acid and
a base?
4

Acids and bases have distinct properties.
• Acids give foods a tart or sour taste.
• Aqueous solutions of acids are strong or
weak electrolytes.
• Acids cause certain dyes, called indicators,
to change color.
• Many metals, such as zinc and magnesium,
react with aqueous solutions of acids to
produce hydrogen gas.
5

Acids and bases have distinct properties.
• Soap is a familiar material that has the
properties of a base.
– The bitter taste is a general property of bases.
– The slippery feel of soap is another property of
bases.
• Bases will cause an indicator to change color.
• Bases also form aqueous solutions that are
strong or weak electrolytes.
6

In 1887, the Swedish chemist Svante
Arrhenius proposed a new way of defining
and thinking about acids and bases.
According to Arrhenius, acids are hydrogen-
containing compounds that ionize to yield
hydrogen ions (H+
) in solution. Bases are
compounds that ionize to yield hydroxide
ions (OH–
) in aqueous solution.
7

Arrhenius Acids
Some Common Acids
Name Formula
Hydrochloric acid HCl
Nitric acid HNO3
Sulfuric acid H2SO4
Phosphoric acid H3PO4
Ethanoic acid CH3COOH
Carbonic acid H2CO3
Acids vary in the number of hydrogens they contain that can form hydrogen
ions.
8

A hydrogen atom that can form a hydrogen
ion is described as ionizable.
• Nitric acid (HNO3) has one ionizable hydrogen.
Nitric acid is classified as a monoprotic acid.
– The prefix mono- means “one,” and the stem protic
reflects the fact that a hydrogen ion is a proton.
Arrhenius Acids
9

A hydrogen atom that can form a hydrogen
ion is described as ionizable.
• Nitric acid (HNO3) has one ionizable hydrogen.
Nitric acid is classified as a monoprotic acid.
• Acids that contain two ionizable hydrogens,
such as sulfuric acid (H2SO4), are called
diprotic acids.
• Acids that contain three ionizable hydrogens,
such as phosphoric acid (H3PO4), are called
triprotic acids.
Arrhenius Acids
10

Not all compounds that contain hydrogen are
acids.
• Only a hydrogen that is bonded to a very
electronegative element can be released as
an ion. Such bonds are highly polar.
• When a compound that contains such bonds
dissolves in water, it releases hydrogen ions.
Arrhenius Acids
11

In an aqueous solution, hydrogen ions are
not present. Instead, the hydrogen ions are
joined to water molecules as hydronium
ions.
• A hydronium ion (H3O+
) is the ion that forms
when a water molecule gains a hydrogen ion.
Arrhenius Acids
12

Methane (CH4) is an example of a
hydrogen-containing compound that is not
an acid.
• The four hydrogen atoms in methane are
attached to the central carbon atom by
weakly polar C—H bonds.
• Methane has no ionizable hydrogens and is
not an acid.
Arrhenius Acids
13

Ethanoic acid (CH3COOH), which is
commonly called acetic acid, is an example
of a molecule that contains both hydrogens
that do not ionize and a hydrogen that does
ionize.
• Although its molecules contain four hydrogens,
ethanoic acid is a monoprotic acid.
Arrhenius Acids
14

Arrhenius Acids
• The three hydrogens attached to a carbon atom
are in weakly polar bonds.
– They do not ionize.
• Only the hydrogen bonded to the highly
electronegative oxygen can be ionized.
15

H. K.19.1 Acids – Bases Theories ˃
Arrhenius Bases
Some Common Bases
Name Formula Solubility in Water
Sodium hydroxide NaOH High
Potassium hydroxide KOH High
Calcium hydroxide Ca(OH)2 Very low
Magnesium hydroxide Mg(OH)2 Very low
The table below lists four common bases.
Arrhenius Acid- BaseAcid- Base
16

H. K.19.1 Arrhenius Acid- BaseAcid- BaseAcids – Bases Theories ˃
The base sodium hydroxide
(NaOH) is known as lye.
• Sodium hydroxide is an ionic solid.
• It dissociates into sodium ions in aqueous
solution.
Arrhenius Bases

The base sodium hydroxide
(NaOH) is known as lye.
Arrhenius Bases
• Sodium hydroxide is extremely
caustic.
– A caustic substance can burn or eat away materials
with which it comes in contact.
– This property is the reason that sodium hydroxide is a
major component of products that are used to clean
clogged drains.

Potassium hydroxide (KOH) is another
ionic solid.
• It dissociates to produce potassium ions and
hydroxide ions in aqueous solution.
Arrhenius Bases

Sodium and potassium are Group 1A
elements. Elements in Group 1A, the alkali
metals, react violently with water.
• The products of these reactions are aqueous
solutions of a hydroxide and a hydrogen gas.
Arrhenius Bases

Sodium hydroxide and potassium
hydroxide are very soluble in water.
• The solutions would typically have the bitter
taste and slippery feel of a base, but you
would not want to test these properties.
• The solutions are extremely caustic to the
skin. They can cause deep, painful, slow-
healing wounds if not immediately washed
off.
Arrhenius Bases

Visitors to Bracken Cave wear
protective gear to keep ammonia gas
out of their eyes and respiratory tracts.
Think about the properties of bases.
Why are high levels of ammonia
harmful?

Visitors to Bracken Cave wear
protective gear to keep ammonia gas
out of their eyes and respiratory tracts.
Think about the properties of bases.
Why are high levels of ammonia
harmful?Ammonia is a base, and
bases are caustic in high
concentrations.

Calcium hydroxide, Ca(OH)2, and
magnesium hydroxide, Mg(OH)2, are
compounds of Group 2A metals.
• These compounds are not very
soluble in water. Their solutions
are always very dilute, even when saturated.
– The low solubility of magnesium
hydroxide makes the suspension safe
to consume.
– Some people use this suspension as an antacid.
Arrhenius Bases

Can every hydrogen from every
molecule form hydrogen ions,
therefore acting as an Arrhenius
acid?

No. Only hydrogens that are bonded to a
very electronegative element can be
released as ions. That means that only
molecules containing hydrogens bonded to
very electronegative elements are
Arrhenius acids.
Can every hydrogen from every
molecule form hydrogen ions,
therefore acting as an Arrhenius
acid?

•Brønsted-Lowry Acids and Bases
What distinguishes an acid from a
base in the Brønsted-Lowry theory?

Sodium carbonate (Na2CO3) and ammonia
(NH3) act as bases when they form
aqueous solutions.
• Neither of these compounds is a hydroxide-
containing compound, so neither would be
classified as a base by the Arrhenius
definition.

In 1923, the Danish chemist Johannes
Brønsted and the English chemist Thomas
Lowry were working independently.
• Each chemist proposed the same definition
of acids and bases.

According to the Brønsted-Lowry
theory, an acid is a hydrogen-ion
donor and a base is a hydrogen-ion
acceptor.
• This theory includes all the acids and
bases that Arrhenius defined.
• It also includes some compounds that
Arrhenius did not classify as bases.

You can use the Brønsted-Lowry theory to
understand why ammonia is a base.
• When ammonia dissolves in water, hydrogen
ions are transferred from water to ammonia
to form ammonium ions and hydroxide ions.

You can use the Brønsted-Lowry theory to
understand why ammonia is a base.
• When ammonia dissolves in water, hydrogen
ions are transferred from water to ammonia
to form ammonium ions and hydroxide ions.
– Ammonia is a Brønsted-Lowry base because it
accepts hydrogen ions.
– Water is a Brønsted-Lowry acid because it
donates hydrogen ions.

When the temperature of an aqueous
solution of ammonia is increased, ammonia
gas is released.
• HNH4
+
reacts with OH–
to form more NH3 and H2O.
• In the reverse reaction, ammonium ions donate hydrogen ions to
hydroxide ions.
• NH4
+
(the donor) acts as a Brønsted-Lowry acid, and
OH−
(the acceptor) acts as a Brønsted-Lowry base.
Conjugate Acids and Bases

34
H. K.Arrhenius Acid- BaseAcid- BaseAcids – Bases Theories ˃19.1
In essence, the reversible reaction of
ammonia and water has two acids and two
bases.

35
A conjugate acid is the ion or molecule
formed when a base gains a hydrogen ion.
• NH4
+
is the conjugate acid of the base NH3.

36
A conjugate base is the ion or molecule
that remains after an acid loses a hydrogen
ion.
• OH–
is the conjugate base of the acid H2O.

37
H. K.Acids – Bases Theories ˃19.1 Brønsted-Lowry Acids and BasesBrønsted-Lowry Acids and Bases
In this reaction, hydrogen chloride is the hydrogen-
ion donor and is by definition a Brønsted-Lowry
acid. Water is the hydrogen-ion acceptor and a
Brønsted-Lowry base.
• The chloride ion is the conjugate base of the acid HCl.
• The hydronium ion is the conjugate acid of the water
base.

38
The figure below shows the reaction that takes
place when sulfuric acid dissolves in water.
• The products are hydronium ions and hydrogen
sulfate ions.
• Use the figure to identify the two conjugate acid-
base pairs.

39
Interpret DataInterpret Data
Some Conjugate
Acid-Base Pairs
Acid Base
HCl Cl–
H2SO4 HSO4
–
H3O+
H2O
HSO4
–
SO4
2–
CH3COOH CH3COO–
H2CO3 HCO3
−
HCO3
–
CO3
2–
NH4
+
NH3
H2O OH–
Acids – Bases Theories ˃19.1

40
Amphoteric Substances Some Conjugate
Acid-Base Pairs
Acid Base
HCl Cl–
H2SO4 HSO4
–
H3O+
H2O
HSO4
–
SO4
2–
CH3COOH CH3COO–
H2CO3 HCO3
−
HCO3
–
CO3
2–
NH4
+
NH3
H2O OH–
Note that water appears
in both the list of acids
and the list of bases.
• Sometimes water
accepts a hydrogen ion.
• At other times, it
donates a hydrogen ion.
• How water behaves
depends on the other
reactant.

41
A substance that can act as either an acid
or a base is said to be amphoteric.
• Water is amphoteric.
– In the reaction with hydrochloric acid,
water accepts a proton and is therefore a
base.
– In the reaction with ammonia, water
donates a proton and is therefore an acid.
Amphoteric Substances

42
H. K.Acids – Bases Theories ˃19.1
How can one substance, such as
water, be both an acid and a base,
according to the Brønsted-Lowry
definition?

43
How can one substance, such as
water, be both an acid and a base,
according to the Brønsted-Lowry
definition?
Because water can act as both a
hydrogen-ion donator and a hydrogen-ion
acceptor, it can act as both an acid and a
base according to the Brønsted-Lowry
definition.

44
•Lewis Acids and Bases
How did Lewis define an acid and a
base?
Lewis Acids and Bases

45
According to Gilbert Lewis, an acid
accepts a pair of electrons and a base
donates a pair of electrons during a
reaction.
• This definition is more general than
those offered by Arrhenius or by
Brønsted and Lowry.
Lewis Acids and Bases

46
H. K.Acids – Bases Theories ˃19.1 Lewis Acids and Bases
• A Lewis acid is a substance that can
accept a pair of electrons to form a
covalent bond.
• A Lewis base is a substance that can
donate a pair of electrons to form a
covalent bond.
– The Lewis definitions include all the
Brønsted-Lowry acids and bases.

47
Consider the reaction of H+
and OH–
.
• The hydrogen ion donates itself to the
hydroxide ion.
– H+
is a Brønsted-Lowry acid, and OH−
is a
Brønsted-Lowry base.

48
Consider the reaction of H+
and OH–
.
• The hydroxide ion can bond to the hydrogen ion
because it has an unshared pair of electrons.
– OH−
is also a Lewis base, and H+
, which
accepts the pair of electrons, is a Lewis
acid.

49
A second example of a reaction between a
Lewis acid and a Lewis base is what
happens when ammonia dissolves in water.
• Hydrogen ions from the dissociation of water
are the electron-pair acceptor and the Lewis
acid.
• Ammonia is the electron-pair donor and the
Lewis base.

50
• The Lewis definition is the broadest.
• It extends to compounds that the Brønsted-Lowry
theory does not classify as acids and bases.
Acid-Base Definitions
Type Acid Base
Arrhenius H+
producer OH–
producer
Brønsted-Lowry H+
donor H+
acceptor
Lewis electron-pair acceptor electron-pair donor
This table compares the definitions of acids
and bases.
Interpret DataInterpret DataAcids – Bases Theories ˃19.1

51
Acids – Bases Theories ˃19.1 Sample Problem 19.1Sample Problem 19.1
Identifying Lewis Acids and Bases
Identify the Lewis acid and
the Lewis base in this reaction
between ammonia and boron
trifluoride.
NH3 + BF3 → NH3BF3

52
When a Lewis acid reacts with a
Lewis base, the base donates a pair
of electrons and the acid accepts the
donated pair.
Analyze Identify the relevant concepts.1
Sample Problem 19.1Sample Problem 19.1

53
Solve Apply concepts to this problem.2
Identify the reactant with the unshared
pair of electrons and the reactant that
can accept the pair of electrons.
• Ammonia has an unshared pair of
electrons to donate.
• The boron atom can accept the donated
electrons.
Draw electron dot
structures to identify which
reactant has an unshared
pair of electrons.

54
Solve Apply concepts to this problem.2
Classify the reactants based on their
behavior.
• Lewis bases donate a pair of electrons, so
ammonia is the Lewis base.
• Lewis acids accept a pair of electrons, so
boron trifluoride is the Lewis acid.

55
Are hydrogen-ion donors also
electron-pair acceptors?

56
Are hydrogen-ion donors also
electron-pair acceptors?
Yes. All substances defined as acids by
the Brønsted-Lowry definition (an acid is a
hydrogen-ion donor) are also defined as
acids by the Lewis definition (an acid is an
electron-pair acceptor). That means that
these substances are both hydrogen-ion
donors and electron-pair acceptors.

57
Acids – Bases Theories ˃19.1 Key ConceptsKey Concepts
According to Arrhenius, acids are hydrogen-
containing compounds that ionize to yield
hydrogen ions in aqueous solution. Bases are
compounds that ionize to yield hydroxide ions in
aqueous solution.
According to Brønsted-Lowry theory, an acid is a
hydrogen-ion donor and a base is a hydrogen-ion
acceptor.
According to Lewis, an acid accepts a pair of
electrons and a base donates a pair of electrons.

58
• hydronium ion (H3O+
): the positive ion formed
when a water molecule gains a hydrogen ion
• conjugate acid: the particle formed when a base
gains a hydrogen ion; NH4
+
is the conjugate acid of
the base NH3
• conjugate base: the particle that remains when an
acid has donated a hydrogen ion; OH–
is the
conjugate base of the acid water
Glossary TermsGlossary Terms

59
• conjugate acid-base pair: two substances that are
related by the loss or gain of a single hydrogen
ion; ammonia (NH3) and the ammonium ion (NH4
+
)
are a conjugate acid-base pair
• amphoteric: a substance that can act as both an
acid and a base
• Lewis acid: any substance that can accept a pair of
electrons to form a covalent bond
• Lewis base: any substance that can donate a pair
of electrons to form a covalent bond
Glossary Terms

60
• Chemists define acids and bases
according to the ions they yield in
aqueous solution.
• Chemists also define acids and bases
based on whether they accept or
donate hydrogen ions, and whether
they are electron-pair donors or
acceptors.
BIG IDEABIG IDEA
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