Transcript Acids, Bases, and pH

Chapter 9
Section 1

D12 - Explain the chemical composition of
acids and bases, and explain the change of
pH in neutralization reactions.
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What do you know about acids?
Can you name some acids?
Have you ever had lemonade? The juice of a
lemon is an acid. So, this means that not all
acids are alike, since you can safely drink
lemonade, but not some other acids.
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Acids are compounds, which means that they
are made of more than one type of element.
One of the elements is always HYDROGEN.
Properties:
◦ They taste sour
◦ They will turn blue litmus paper red
◦ They will conduct electric current
◦ They are corrosive
◦ They react with metal to form Hydrogen gas
◦ They can sting in an open cut (weaker acids),
or can damage your skin (stronger acids)
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When dissolved in water, they ionize.
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This means that they split apart into the ions
that make up the acid. H+ is ALWAYS formed.
HCl
H+ + Cl-
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One of the ions formed is the Hydrogen or H+ ion
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This can attach to the water molecules to form
hydronium ions, H3O+
H20 + H+
H3O+
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Strong acids ionize completely
Each molecule splits into its ions
This makes a high concentration of hydrogen
and hydronium ions in the liquid.
Weak acids do not ionize completely.
This makes a lower concentration of
hydronium ions in the liquid.
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Which of the following "molecular" pictures
best represents a concentrated solution of
the weak acid HA?
A
B
Nitric Acid
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Since there is complete ionization in water,
this is a strong acid
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An electrolyte is a liquid which can conduct
electricity
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Nitric Acid conducts electricity well, which
means it is a strong electrolyte
Acetic Acid
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This is an example of a weak acid
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Weak acids do not conduct electricity well
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This means that they are weak electrolytes
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Acids are corrosive
They can damage living tissues
Acidic vapors can be harmful to eyes, mouth
and lungs
Wear safety goggles, gloves, lab apron
Overall, be careful!
Bases!
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What do you know about bases?
Can you name some bases?
Do you use soaps or detergents? These are
bases. Like acids, not all bases are alike.
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A base is a compound that increases the
number of hydroxide ions (OH-) when
mixed with water.
Properties:
A basic solution tastes bitter.
A basic solution feels slippery.
A base can conduct electricity when
dissolved in water
They will turn red litmus paper blue.
Strong bases can also damage the skin.
Strong bases can react with glass
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Like acids, when bases dissolve in water, they
ionize.
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This means that they split apart into the ions
that make up the base.
NaOH
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Na+ + OH-
Note: Not all bases contain OH-. Some will react
with water to form the hydroxide ion
NH3 + H20
NH4+ + OH-
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These work in a way that is similar to acids.
Strong bases cause a high concentration of
OH- ions in the solution.
Weak bases cause a low concentration of OHions in the solution.
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Like acids, bases are corrosive and can
damage living tissues
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Wear safety goggles, gloves, and a lab apron!
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How do determine if something is an acid or
a base?
How do we measure acid and base
concentration or strength?
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Read pages 293-297.
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You can determine if a substance is an acid
or base by using an indicator.
INDICATOR - A substance that changes
color in the presence of an acid or a base.
Indicators measure the level of hydronium
ions. This level determines if a substance is
acidic or basic.
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Cabbage juice can be used as an indicator.
Litmus paper is a common indicator.
Litmus strips are small pieces of paper that
are treated with a substance that changes
color when exposed to acids and bases
 An
acid turns blue litmus paper red
 A base turns red litmus paper blue
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Litmus papers only function to let you know if
a substance is acidic or basic.
They do not indicate strength or weakness of
the solution.
To determine how acidic or basic a solution
is, we use pH values.
pH is the measure of the concentration of
hydronium ions in a solution.
N
E
U
T
R
A
L
ACIDIC
0
1
2
3
4
5
6
7
BASIC
8
9
10
11
The pH Scale
12
13
14
N
E
U
T
R
A
L
ACID
0
1
2
3
4
5
6
7
BASE
8
9
10
11
The pH Scale
12
13
14
[H+]
Stronger
Weaker
0
Acids
1
2 3 4
Base – substance
that produces OHions in aqueous
solution
[OH-]
Weaker
5 6
pH Scale
7 8
9
Ion Concentration
Neutral Pure H2O
Ion Concentration
Acid – substance
that produces H+
ions in aqueous
solution
Stronger
10 11 12 13 14
Bases
 Lemon
juice has a pH
of 2.2. Is it an acid or
a base?
 Which
does it contain,
hydronium ions or
hydroxide ions?
 Detergents
such as
Tide have a pH of
about 10. Is Tide an
acid or a base?
 Which
does it
contain, hydronium
ions or hydroxide
ions?
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Seawater has a
pH of 8.2. Is
seawater an
acid or a base?
Which does it
contain,
hydronium
ions or
hydroxide
ions?
 The
inside of
your mouth
has a pH of
7. Is it an
acid or a
base?
 How
do you
think we
came up
with the
term “acid
rain”?
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Read pages 297-300