Acids and Bases
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Transcript Acids and Bases
Acids and Bases
Definitions of Acids
Arrhenius Acid-any substance that
produces hydrogen ions (H+) when
dissolved in water.
Bronsted Lowry acid-any substance
that donates protons to form
hydronium ions (H3O+)
Examples of acids: HCl, HNO3, H2SO4,
HC2H3O2
Electrolytes
Solutions that conduct an electric
current efficiently contain strong
electrolytes.
Strong electrolytes are substances
that completely ionize in water.
Acids that ionize completely and are
classified as strong electrolytes are
also classified as strong acids.
Strong acids
The following are classified as strong
acids:
HCl, HBr, HI, H2SO4, HNO3,HClO3, HClO4
All other acids are classified as weak
acids (they do not ionize completely
in water).
Note: a classification of strong vs weak acid is
independent of the concentration-for example,
a strong acid can be very dilute and a weak
acid can be very concentrated.
Properties of Acids
Taste sour
React with metals
Conduct electricity (to some degree
based on strength)
pH<7
Turn litmus red
Turn phenolphthalein colorless
Definitions of Bases
Arrhenius Base-any substance that
produces hydroxide ions (OH-) when
dissolved in water.
Bronsted Lowry Base- any substance
that accepts protons.
Examples of bases: NaOH, Ca(OH)2,
Mg(OH)2, NH3
Bases as electrolytes
Bases are also classified as strong vs
weak, based on the degree of
ionization.
The strong bases (strong electrolytes)
are: (group 1A hydroxides, Sr(OH)2 and
Ba(OH)2 )
All other bases are classified as weak
bases.
Properties of Bases
Taste bitter
Feel slippery
Conduct electricity
pH>7
Turn litmus blue
Turn phenolphthalein pink
Naming Acids
Binary acids- consist of hydrogen and
one other element.
Use the prefix –hydro and change the
ending of the element to –ic.
Example: HCl hydrochloric acid
HBr hydrobromic acid
H2S hydrosulfuric acid
Naming acids
Oxyacids-consist of hydrogen, oxygen, and
one additional element.
If the polyatomic ion ends in –ate, change
the ending to –ic.
If the polyatomic ion ends in –ite, change
the ending to –ous.
Example: H2SO4 sulfuric acid (diprotic)
H2SO3
sulfurous acid (diprotic)
HNO3
nitric acid (monoprotic)
HNO2 nitrous acid (monoprotic)
H3PO4
phosphoric acid (triprotic)
Naming bases
All bases consist of the hydroxide ion
and one additional element.
Name the element followed by
hydroxide.
Example: NaOH sodium hydroxide
Ca(OH)2 calcium hydroxide
Al(OH)3 aluminum hydroxide
NaOH is an example of a(n)
1. Acid
2. Base
3. Neither
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A substance that is a proton
acceptor is a(n)
1. Acid
2. Base
3. neither
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HCl is an example of a(n)
1. Acid
2. Base
3. Neither
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Lemon juice is an example of a(n)
1. Acid
2. Base
3. Neither
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A substance that is a proton donor
is an example of a(n)
1. Acid
2. Base
3. Neither
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Drain cleaner is an example of a(n)
1. Acid
2. Base
3. Neither
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Vinegar is an example of a(n)
1. Acid
2. Base
3. Neither
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Water is an example of a(n)
1. Acid
2. Base
3. Neither
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A substance that turns litmus red is
a(n)
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Acid
Base
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A substance that conducts
electricity is a(n)
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Acid
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Which of the following is the
correct name of HBr?
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2.
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Hydrobromic acid
Bromic acid
Bromous acid
Bromine hydroxide
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Which of the following is the
correct name of H2CO3?
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2.
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Hydrocarbonic acid
Carbonic acid
Carbonous acid
Hydrogen coarbon oxide
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Which of the following is the
correct name of Ba(OH)2?
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Hydrobaric acid
Baric acid
Barous acid
Barium hydroxide
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Autoionization of Water
Because water is amphoteric, water
can transfer a proton from one water
molecule to another to produce a
hydronium ion and a hydroxide ion.
2 H2O (l) <---> H3O+ (aq) + OH- (aq)
Experiments show that at 25oC,
[H3O+] = [OH-] = 1x10-7 M
Autoionization of Water
In any aqueous solution at 25oC, no
matter what it contains, the product of
[H3O+] and [OH-] must always equal
1x10-14. There are three possible
situations:
1. A neutral solution, where [H3O+] = [OH-]
2. An acidic solution, where [H3O+] > [OH-]
3. A basic solution, where [H3O+] < [OH-]
Sample Problems
Calculate the [H3O+] and [OH-] for
each of the following and state
whether the solution is acidic, basic,
or neutral.
a) 1.0 x 10-5 M OHb) 1.0 x 10-7 M OHc) 10.0 M H30+
The pH Scale
Because [H3O+] is typically very
small, the pH scale provides a
convenient way to represent
solution acidity.
The pH scale is a logarithmic scale
used to quantitatively represent
the strength (concentration) of an
acid.
Calculating pH
pH = -log[H3O+]
The greater the concentration of the
hydrogen ion (H+), the stronger the acid
and the lower the pH.
For a solution where [H3O+] =
1.0 x 10-7 M, pH = 7.00
Sample Problems
What is the pH of a solution in which
[H+] = 1 x 10-2?
pH = 2
What is the pH of a solution in which
[H+] = 1 x 10-6?
pH = 6
Which is more concentrated?
pH=2
Similar log Scales
Similar log scales are used for
representing other quantities:
The pOH scale is a logarithmic scale
used to quantitatively represent the
strength (concentration) of a base.
pOH = -log[OH-]
The greater the concentration of the
hydroxide ion (OH-), the stronger the
base and the lower the pOH.
**** pH + pOH = 14.00
Practice Problems
Calculate the pH and pOH of solutions
with the following concentrations and
classify as acidic, basic, or neutral.
a. [OH-] = 1 x 10-9
b. [H+] = 1 x 10-7
c. [H+] = 1 x 10-4
d. [OH-] = 1 x 10-2
pH Scale
Indicators and pH
Indicators are substances that change
color depending on the concentration
of hydrogen ions (H+) in a solution.
Litmus and phenolphthalein are
examples of indicators.
Indicators can be used to determine
the pH of a solution.
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A solution with a pH of 3 is
10
1. Acidic
2. Basic
3. Neutral
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Which of the following is an expected
pH for a sample of lemon juice?
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A substance with a pH of 12.7 is
a(n)
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Acid
Base
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A solution with a [H+] =1x 10-5
has a pH of
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A solution with a pH of 8 has a
pOH of
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A solution with a [OH-]=1x10-3
has a [H+] =
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1 x 1011
1 x 10-11
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Neutralization Reactions
Neutralization reactions occur when acids react
with bases and produce a salt and water.
A salt is an ionic compound consisting of the
positive ion of the base and the negative ion of
the acid.
Example: HCl + NaOH NaCl + H2O
acid
base
salt
water
If the [H+] = [OH-], the resulting solution will
be neutral (pH=7).
Neutralization reactions are a specific type of
double displacement reaction.
What salt is formed?
HCl + KOH
H3PO4 + NaOH
Ca(OH)2 + H2SO4
Mg(OH)2 + HF
HNO3 + NaOH
Titration
A titration is a method for
determining the concentration of a
solution by reacting a known volume
of that solution with a solution of
known concentration.
The reaction that takes place is a
neutralization reaction.
Procedure for carrying out
titrations.
A measured volume of
an acid or base is added
to a beaker or flask.
A buret is filled with a
solution of known
concentration (titrant).
The solution of known
concentration is added
until the solution in the
beaker has been
completely neutralized.
This point is called the
equivalence point.
Titrations Continued
You will recognize the
equivalence point
because the indicator will
change colors at this
point.
This is also referred to as
the end point of the
titration.
The volume that is added
to reach this point is
used to calculate the
unknown molarity.
Example
25.0 mL of HCl is titrated to the
endpoint with 50.0 mL of 2.0 M
NaOH. What is the molarity of the
HCl?
MxV=MxV
X (25.0) = 2.0 (50.0)
X= 4.0 M
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Pre-lab: Which is the most
effective antacid?
What makes an antacid effective?
How does the antacid affect the acid?
How will you determine which antacid
is most effective at neutralizing the
stomach acid?