Grade 12 Chemistry
Advanced
Academic Year 2020/2021 – Term 1
1
Chapter-3
Acids and Bases
Lesson no. 1
Lesson name: Introduction to Acids
and Bases
Date: 11th to 15th October
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• Identify the physical and chemical
properties of acids and bases.
Learning
objectives
• Classify solutions as acidic, basic or
neutral.
• Compare the Arrhenius, Brønsted-Lowry,
and Lewis models of acids and bases
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Keywords
•
•
•
•
•
•
•
•
Acidic solution.
Basic solution.
Arrhenius model.
Brønsted-Lowry model.
Conjugate acid.
Conjugate base.
Conjugate acid-base pair.
Amphoteric.
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Starter Activity
• Share your thoughts about acids and bases on this link.
• https://padlet.com/bushrakhalifeh/40s7jxel4qtvbfju
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Introduction to Acids and Bases
Different models help describe the behavior of acids and bases.
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General properties of Acids and Bases
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Properties of Acids and Bases
complete the following Table using the Properties mentioned below
as physical or chemical properties.
Reactions with metals
and
metal carbonates.
Taste
Physical Properties
Texture
Electrical conductivity
Reaction with litmus paper.
Chemical Properties
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Properties of Acids and Bases
• Physical Properties
Acids
Bases
Taste sour
Taste bitter and feel slippery
Aqueous solutions of acids conduct
electricity.
Aqueous solutions of bases conduct
electricity.
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Properties of Acids and Bases
• Chemical Properties
A. Reactions with litmus
(one of the dyes commonly used
to distinguish solutions of acids
and bases).
B. Acids reactions with metal
and metals carbonates.
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• Chemical Properties
Acids
Bases
• Reactions with
litmus
Turn blue litmus paper to red
• Reactions with
metals and
metal carbonates
Magnesium (Mg) and zinc (Zn) react •
with aqueous solutions of acids to
produce hydrogen gas
•
Turn red litmus paper to blue
Metal carbonates and hydrogen carbonates also react
with aqueous solutions of acids to produce carbon
dioxide (CO2) gas.
When vinegar is added to baking soda, a foaming
reaction occurs between acetic acid (HC2H3O2)
dissolved in the vinegar, and sodium hydrogen
carbonate (NaHCO3). The production of CO2 gas
accounts for the bubbling.
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Reaction of Vinegar (Acetic Acid) with Baking Soda
(Sodium Hydrogen Carbonate)
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Solutions
Acidic solution
Neutral solution
Basic solution
Contains more
hydrogen ions (H+)
than hydroxide ions
(OH-).
Contains equal
concentrations of
hydrogen ions (H+)
and hydroxide ions
(OH-).
Contains more
hydroxide ions (OH-)
than hydrogen ions
(H+).
[H+] < [OH-]
[H+] = [OH-]
*Recall: [x] means the concentration of x in mol/L
[OH-] < [H+]
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Hydronium and hydroxide ions
Note how [H+] and [OH]
change simultaneously.
As [H+] decreases to
the right, [OH-] increases
to the right.
Identify the point in the diagram at which the two ion concentrations are equal.
It will be the neutral line, [H+] = [OH]
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Hydronium and hydroxide ion
• 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
(H3O+) and a hydroxide ion (OH-).
• The hydronium ion is a hydrogen ion which has a water molecule attached to
it by a covalent bond.
• The symbols H+ and H3O+ can be used interchangeably, as this simplified selfionization equation shows.
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Period 2
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Starter
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Models of Acids and Bases
1. The Arrhenius Model.
3. Lewis Model.
2.We
The focused
Brønsted-Lowry
on theModel.
H+
Mine is about electron-pairs.
and proposed that
A Lewis acid an electron-pair
I proposed that
+
an acid is H donor and
acceptor.
acids produce H+
+ acceptor A Lewis base is
a
base
is
H
while bases produce
an electron-pair donor.
-
OH
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1. The Arrhenius Model
• Arrhenius Acid
A substance that contains hydrogen and ionizes
to produce hydrogen ions (H+) in aqueous
solution.
• Example
HCl molecules ionize to form H+ ions,
which make the solution acidic
H+
Cl-
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1. The Arrhenius Model
• Arrhenius Base
A substance that contains a hydroxide group and
dissociates to produce a hydroxide ion in aqueous
solution.
• Example
Sodium hydroxide (NaOH) dissolves in water,
it dissociates to produce OH- ions, which
make the solution basic.
Na+
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1. The Arrhenius Model (summary)
Arrhenius Acid
Arrhenius Base
Definition
A substance that contains hydrogen and
ionizes to produce hydrogen ions in
aqueous solution.
A substance that contains a hydroxide
group and dissociates to produce a
hydroxide ion in aqueous solution.
Example
HCl molecules ionize to form H+ ions,
Sodium hydroxide (NaOH) dissolves
which make the solution acidic
in water, it dissociates to produce OHions, which make the solution basic.
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1. The Arrhenius Model
Shortcomings of Arrhenius model
• Some substances do not contain a hydroxide group (OH-), yet these
substances produce hydroxide ions in solution and are well-known bases.
• For example, ammonia (NH3) and sodium carbonate (Na2CO3).
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2. The Brønsted-Lowry Model
• Brønsted-Lowry Acid:
• Hydrogen ion (H+) donor
• Conjugate base
• The species produced when an acid donates
a hydrogen ion
Hydrogen fluoride (a Bronsted-Lowry Acid)
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Activity: What does conjugate means?
Conjugate acid-base pair
Conjugate acid-base pair
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2. The Brønsted-Lowry Model
EXAMPLE 1
Hydrogen fluoride (a Bronsted-Lowry Acid)
 In this EXAMPLE, Hydrogen fluoride HF, the acid in the forward reaction(
),
produces its conjugate base F-, the base in the reverse reaction(
).
 Water, the base in the forward reaction, produces its conjugate acid H3O+ , the acid in
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the reverse reaction.
2. The Brønsted-Lowry Model
EXAMPLE 1
Hydrogen fluoride (a Bronsted-Lowry Acid)
Hydrogen fluoride is used to
manufacture a variety of
fluorine-containing
compounds, such as the
nonstick coating on the
kitchenware.
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2. The Brønsted-Lowry Model
• Brønsted-Lowry Base:
• Hydrogen ion (H+) acceptor
• Conjugate acid
The species produced when a base accepts
a hydrogen ion (H+)
- Ammonia (NH3)(a Bronsted-Lowry Base)
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2. The Brønsted-Lowry Model
EXAMPLE 2
Ammonia (a Brønsted-Lowry Base)
 In this EXAMPLE, When ammonia (NH3) dissolves in water, water is a Brønsted-Lowry acid
in the forward reaction. Because the NH3 molecule accepts a H+ ion to form the
ammonium ion (NH4 +), ammonia is a Brønsted-Lowry base in the forward reaction.
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2. The Brønsted-Lowry Model
EXAMPLE 2
Ammonia (a Bronsted-Lowry Base)
• In the reverse reaction, the ammonium ion (NH4 +) gives up a H+ ion to form the molecule
ammonia and thus acts as a Brønsted-Lowry acid. The ammonium ion is the conjugate
acid of the base ammonia.
• The hydroxide ion accepts a H+ ion to form a water molecule and is thus a Brønsted-Lowry
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base. The hydroxide ion is the conjugate base of the acid water.
2. The Brønsted-Lowry Model
Acids
Definition
Hydrogen ion
(H+) donor
Bases
Conjugate
acid
Hydrogen ion (H+) The species produced
acceptor
when a base accepts
a hydrogen ion
Conjugate
base
Conjugate
acid-base
pair
The species
produced when an
acid donates a
hydrogen ion
Consists of two
substances related
to each other by
the donating and
accepting of a
single hydrogen ion
EXAMPLE1
Note*
The symbol X
represents
nonmetallic
elements or
negative
polyatomic
ions.
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2. The Brønsted-Lowry Model
EXAMPLE 2
Water (a Bronsted-Lowry Acid and Base)
• Recall that when HF dissolves in water, water acts a base; when NH3 dissolves in water,
water acts as an acid. Depending on what other substances are in the solution, water
can act as either an acid or a base.
• Water and other substances that can act as both acids and bases are said to be
amphoteric.
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PRACTICE Problems
Identify the conjugate acid-base pairs in each equation
a. NH4+(aq) + OH-(aq) ⇌ NH3(aq)+ H2O(l)
b. HBr(aq) + H2O(l) ⇌ H3O+ (aq) + Br-(aq)
c. CO32- (aq) + H2O(l) ⇌ HCO3- (aq) + OH-(aq)
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PRACTICE Problems
Answers
Acid
NH4+
HBr
H2O
Conjugate
base
NH3
BrOH-
Base
OHH2O
CO32-
Conjugate
acid
H2O
H3O+
HCO3-
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SUMMARY
 The concentrations of hydrogen ions and hydroxide ions determine
whether an aqueous solution is acidic, basic, or neutral.
 An Arrhenius acid must contain an ionizable hydrogen atom. An
Arrhennius base must contain an ionizable hydroxide group.
 A Brønsted-Lowry acid is a hydrogen ion donor. A Brønsted-Lowry
base is a hydrogen ion acceptor.
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Period 3
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Starter Activity
[www.menti.com]
Answer the following question using the code 16 39 82 0
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Ionizable hydrogen atoms
Figure .9 Whether a hydrogen is ionizable
depends on the polarity of its bond. In
acetic acid, oxygen is more electronegative
than hydrogen. The bond between oxygen
and hydrogen is polar, so the hydrogen
atom can ionize in solution. In hydrogen
fluoride, fluorine is highly electronegative,
so HF is an acid in solution. In benzene,
there is little electronegativity difference
between the carbon and hydrogen atoms,
so benzene is not an acid.
• 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.
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Ionizable hydrogen atoms
Figure .9 Whether a hydrogen is ionizable
depends on the polarity of its bond. In
acetic
acid,
oxygen
is
more
electronegative than hydrogen. The bond
between oxygen and hydrogen is polar, so
the hydrogen atom can ionize in solution.
In hydrogen fluoride, fluorine is highly
electronegative, so HF is an acid in
solution. In benzene, there is little
electronegativity difference between the
carbon and hydrogen atoms, so benzene
is not an acid.
• The hydrogen atom in hydrogen fluorine is bonded to the highly
electronegative fluorine atom, so the hydrogen-fluorine bond is polar, and
the fluorine atom is ionizable to a certain extent.
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Ionizable hydrogen atoms
Figure .9 Whether a hydrogen is ionizable
depends on the polarity of its bond. In
acetic
acid,
oxygen
is
more
electronegative than hydrogen. The bond
between oxygen and hydrogen is polar, so
the hydrogen atom can ionize in solution.
In hydrogen fluoride, fluorine is highly
electronegative, so HF is an acid in
solution. In benzene, there is little
electronegativity difference between the
carbon and hydrogen atoms, so benzene
is not an acid.
• However, the hydrogen atoms in benzene are each bonded to a carbon
atom.
• Carbon atoms have about the same electronegativity as hydrogen.
• These bonds are non-polar, so benzene is not an acid.
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Monoprotic and Polyprotic Acids
Monoprotic Acids
Diprotic Acids
Triprotic Acids
Definition
An acid that can donate
only one hydrogen ion (H+)
Acids with three
hydrogen ions
(3H+)to donate
Examples
HCl (Hydrochloric Acid)
HF (Hydrogen Fluoride)
HClO4 (Perchloric Acid)
HNO3 (Nitric Acid)
CH3COOH = (HC2H3O2)
Acids that contain
two ionizable
hydrogen atoms (H+)
per molecule
H2SO4
(Sulfuric Acid)
H2CO3
(Carbonic Acid)
H3PO4
(Phosphoric Acid)
H3BO3
(Boric Acid)
Acetic Acid
 The term polyprotic acid can be used for any acid that has more than one ionizable hydrogen atom. 40
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Ionizable hydrogen atoms
• All polyprotic acids ionize in steps.
• The three ionizations of phosphoric acid are described by the following
equations.
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Models of Acids and Bases
1. The Arrhenius Model.
2. The Brønsted-Lowry Model.
3. Lewis Model.
electron-pairs.
A Lewis acid an electronpair acceptor.
A Lewis base is
an electron-pair donor.
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3. The Lewis Model
Definition
Lewis Acid
Lewis Base
An electron-pair acceptor
An electron-pair donor
An acid is an ion or molecule with a
vacant atomic orbital that can accept
(share) an electron pair
A base is an ion or molecule with a
lone electron pair that it can donate
(share)
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3. The Lewis Model
EXAMPLE 1
• In this reaction, the H+ ion is the Lewis acid. Its vacant 1s orbital accepts an electron pair
from the F- ion. The fluoride ion is the Lewis base.
• It donates a lone electron pair to form the hydrogen-fluorine bond in HF.
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3. The Lewis Model
Note that this reaction also conforms to the Brønsted-Lowry
model of acids and bases because H+ can be considered a hydrogenion donor and F- a hydrogen-ion acceptor.
Note that the Lewis model includes all the substances classified as
Brønsted-Lowry acids and bases and many more.
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3. The Lewis Model
EXAMPLE 2
 Recall from Chapter 8 that the boron atom (B) in BF3 (a Lewis acid) has
six valence electrons, so a vacant orbital can accept an electron pair from
a Lewis base (NH3).
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3. The Lewis Model
EXAMPLE 3
 Another Lewis acid-base reaction occurs when gaseous sulfur trioxide
(SO3) is brought into contact with solid magnesium oxide (MgO).
 The acid-base part of the reaction involves sulfur trioxide (SO3) and the
oxide ion (O2-) of magnesium oxide. The product is the sulfate ion (SO42-).
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3. The Lewis Model
 The reaction of SO3 and MgO is important because it produces magnesium sulfate, a salt
that forms the heptahydrate known as Epsom salt(MgSO4·7H2O).
Epsom salt uses
1. Health: Soothing sore muscles.
2. Agriculture: Plant nutrient.
3. Environmental Application: next slide
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3. The Lewis Model
Environmental applications
When MgO is injected into the
flue gases of coal-fired power
plants, it reacts with and
removes SO3.
Activity: what are
the effects of acid
rain on earth?
If SO3 is allowed to enter
the atmosphere, it can
combine with water in
the air to form sulfuric
acid, which falls to Earth
as acid precipitation.
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Three Models for Acids and Bases
Table 2
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Three Models for Acids and Bases
Arrhenius
Acid: H+ producer
Base: OH- producer
Brønsted-Lowry Model
Acid: H+ donor
Base: H+ acceptor
Lewis Model
A: Acid
B: Base
H+: Hydrogen ion
OH-: Hydroxide ion
Acid: electron-pair acceptor
Base: electron-pair donor
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SECTION 1 REVIEW
1. Compare the physical and chemical properties of acids and bases.
2. Identify the conjugate acid-base pairs in the following equation.
3. Write the Lewis structure for phosphorus trichloride (PCl3). Is
PCl3 Lewis acid, a Lewis base, or neither?
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SECTION 1 REVIEW
ANSWERS
1. Slide 7- 12.
2. HNO3 (acid) and NO2- (conjugate base), H2O (base) and H3O+
(conjugate acid).
3. Phosphorous in PCl3 has three electrons, which it shares with
three chlorines (3Cl) and an unshared pair of electrons. The
unshared pair of electrons can act as a Lewis base.
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SECTION SUMMARY
• The concentrations of hydrogen ions and hydroxide ions determine whether
an aqueous solution is acidic, basic, or neutral.
•
An Arrhenius acid must contain an ionizable hydrogen atom.
An Arrhennius base must contain an ionizable hydroxide group.
• A Brønsted-Lowry acid is a hydrogen ion donor.
A Brønsted-Lowry base is a hydrogen ion acceptor.
• A Lewis acid accepts an electron pair. A Lewis base donates an electron pair.
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