Acids, Bases, and pH
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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.
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.
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)
When dissolved in water, they ionize.
This means that they split apart into the ions
that make up the acid. H+ is ALWAYS formed.
HCl
H+ + Cl-
One of the ions formed is the Hydrogen or H+ ion
This can attach to the water molecules to form
hydronium ions, H3O+
H20 + H+
H3O+
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.
Which of the following "molecular" pictures
best represents a concentrated solution of
the weak acid HA?
A
B
Nitric Acid
Since there is complete ionization in water,
this is a strong acid
An electrolyte is a liquid which can conduct
electricity
Nitric Acid conducts electricity well, which
means it is a strong electrolyte
Acetic Acid
This is an example of a weak acid
Weak acids do not conduct electricity well
This means that they are weak electrolytes
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!
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.
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
Like acids, when bases dissolve in water, they
ionize.
This means that they split apart into the ions
that make up the base.
NaOH
Na+ + OH-
Note: Not all bases contain OH-. Some will react
with water to form the hydroxide ion
NH3 + H20
NH4+ + OH-
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.
Like acids, bases are corrosive and can
damage living tissues
Wear safety goggles, gloves, and a lab apron!
How do determine if something is an acid or
a base?
How do we measure acid and base
concentration or strength?
Read pages 293-297.
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.
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
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?
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”?
Read pages 297-300