Reactions of Acids & Bases
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Transcript of Reactions of Acids & Bases
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Reactions of Acids & Bases
Reactions of Acids & Bases
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Self-Ionization of WaterSelf-Ionization of Water
H2O + H2O H3O+ + OH-
Kw = [H3O+][OH-] = 1.0 10-14
In pure water at 25ºC, both H3O+ and OH- ions are found at concentrations of 1.0 x 10-7 M.
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In all solutions at 25ºC, the product of the concentrations of H3O+ and OH- ions is equal to 1.0 x 10-14 M.
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if [H3O+] > 1.0 10-7
It’s an acid …
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if [OH-] > 1.0 10-7
It’s a base …
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if [H3O+] = [OH-] = 1.0 10-7
It’s neutral …
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pH = -log[H3O+]
pH ScalepH Scale
0
7INCREASING
ACIDITY NEUTRALINCREASING
BASICITY
14
pouvoir hydrogène (Fr.)“hydrogen power”
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pH ScalepH Scale
pH of Common SubstancespH of Common SubstancespH of Common SubstancespH of Common Substances
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pH ScalepH Scale
The pH scale runs from 0 to 14, but each unit represents a tenfold change in the concentration.The pH scale runs from 0 to 14, but each unit represents a tenfold change in the concentration.
The HThe H33OO++ concentration of 1 x 10 concentration of 1 x 1000 is not 14 times a concentration of 1 x 10 is not 14 times a concentration of 1 x 10-14-14, but it is a factor of 10, but it is a factor of 101414, which is 100 trillion times!, which is 100 trillion times!
The pH scale runs from 0 to 14, but each unit represents a tenfold change in the concentration.The pH scale runs from 0 to 14, but each unit represents a tenfold change in the concentration.
The HThe H33OO++ concentration of 1 x 10 concentration of 1 x 1000 is not 14 times a concentration of 1 x 10 is not 14 times a concentration of 1 x 10-14-14, but it is a factor of 10, but it is a factor of 101414, which is 100 trillion times!, which is 100 trillion times!
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pH ScalepH Scale
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What is the concentration of OH- ions in saturated lime if [H3O+] = 3.98 x 10-13 M? Is lime acidic, basic, or neutral?
BASIC
Practice Problem #1Practice Problem #1
[OH-] > 1.0 10-7
[H3O+][OH-] = 1.0 10-14
[3.98 10-13][OH-] = 1.0 10-14
[OH-] = 2.5 10-2 M or 0.025 M
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Analysis of a sample of maple syrup reveals that the concentration of OH- ions is 5.0 x 10-8 M. What is the pH? Is it acidic, basic, or neutral?
[H3O+][OH-] = 1.0 10-14
Practice Problem #11Practice Problem #11
AcidicpH = -log[H3O+] pH = 6.7
[H3O+][5.0 x 10-8] = 1.0 10-14
[H3O+] = 2.0 10-7 M
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More Sample Problems More Sample Problems
What is the pH of 0.080 M HNO3?What is the [H3O+] and the [OH-]?
pH = -log[H3O+]
pH = -log[0.080]
pH = 1.1Acidic
[H3O+] = 0.080 M[H3O+][OH-] = 1.0 x 10-14
[ OH-] = 1.0 x 10-14
[H3O+]
[ OH-] = 1.3 x 10-13
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More Sample Problems More Sample Problems
What is the pH of 0.0123 M H2SO4?What is the [H3O+] and the [OH-]?
pH = -log[H3O+]
pH = -log[0.0246]
pH = 1.61Acidic
[H3O+] = 2(0.0123) M = 0.0246 M
[H3O+][OH-] = 1.0 x 10-14
[ OH-] = 1.0 x 10-14
[H3O+]
[ OH-] = 4.07 x 10-13
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More Sample Problems More Sample Problems
The pH of a solution is 4.29What is the [H3O+] and the [OH-]?
pH = -log[H3O+]
Acidic
[H3O+][OH-] = 1.0 x 10-14
[ OH-] = 1.0 x 10-14
[H3O+]
[ OH-] = 1.95 x 10-10
10 = [H3O+]
[H3O+] = 5.13 x 10-5
-pH
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BuffersBuffers
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A buffer is a mixture that is able to release or absorb H+ ions, keeping a solution’s pH constant.
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Most common buffers are mixtures of weak acids and their conjugate bases.
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ExampleExample
H3O+ + C2H3O2 -
H2O + HC2H3O2
Acetic acid and acetate ion
When H3O+ ions are added to this solution, they react with the acetate ion.
pH changes only slightly
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ExampleExample
OH- + HC2H3O2
H2O + C2H3O2 -
Acetic acid and acetate ion
When OH- ions are added to this solution, they react with the acetic acid.
pH changes only slightly
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Buffer Capacity is the amount of acid or base that a buffer can neutralize.
All buffers have a limited capacity to neutralize added H3O+ or OH- ions.
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If you add H3O+ or OH- ions beyond the buffer capacity, the ions will remain in solution, and the pH will change.
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The greater the concentration of buffer in the solution, the greater the buffer capacity.
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The human body must maintain the pH of blood between 7.35 and 7.45.
A pH outside this range can cause extreme illness or death.
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Acid-Base TitrationAcid-Base Titration
Section 19-3Section 19-3
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TitrationTitration
• An acid base titration is a carefully controlled neutralization reaction.
• Find concentration of an unknown solution by using a known “standard” solution
standard solution
unknown solution
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Equivalence point Equivalence point • When enough standard
solution is added to neutralize all the acid or base in the unknown solution.• dramatic change in pH
• Determined by the Endpoint• indicator color change
TitrationTitration
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Strong Acid with Strong Strong Acid with Strong BaseBase
Equivalence Point: pH = 7Equivalence Point: pH = 7 phenolphthaleinphenolphthalein
TitrationTitration
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Weak Acid with Strong BaseWeak Acid with Strong Base Equivalence Point: pH > 7Equivalence Point: pH > 7 Phenolphthalein Phenolphthalein
TitrationTitration
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Weak Weak Base with Strong Acid with Strong Acid Equivalence Point: pH < 7Equivalence Point: pH < 7 Methyl redMethyl red
TitrationTitration
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TitrationTitration
moles H3O+ = moles OH-
MV #a = MV #b
M: MolarityV: volume#: # of H+ ions in the acid
or OH- ions in the base
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TitrationTitration
42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H2SO4. Find the molarity of H2SO4.
H3O+
M = ?V = 50.0 mLn = 2
OH-
M = 1.3MV = 42.5 mLn = 1
MV#a= MV#b
M(50.0mL)(2)=(1.3M)(42.5mL)(1)
M = 0.55M H2SO4