Acids and Bases
Special kinds of aqueous solutions
“Ionization”
http://www.unit5.org/chemistry/AcidBase.html
Properties
electrolytes
electrolytes
sour taste
bitter taste
turn litmus red
turn litmus blue
react with metals to
form H2 gas
slippery feel
vinegar, milk, soda,
apples, citrus fruits
ammonia, lye, antacid,
baking soda
ChemASAP
Common Acids
Sulfuric Acid
H2SO4
Battery acid
Nitric Acid
HNO3
Used to make fertilizers
and explosives
Phosphoric Acid
H3PO4
Food flavoring
Hydrochloric Acid
HCl
Stomach acid
Acetic Acid
Carbonic Acid
CH3COOH
H2CO3
Vinegar
Carbonated water
Common Bases
Name
Formula
Common Name
Sodium hydroxide
NaOH
lye or caustic soda
Potassium hydroxide
KOH
caustic potash
Magnesium hydroxide
Mg(OH)2
milk of magnesia
Calcium hydroxide
Ca(OH) 2
slaked lime
Ammonia water
NH
H 2O
NH43.OH
household ammonia
NH41+ + OH1ammonium hydroxide
Definitions
 Arrhenius
- In aqueous solution…
• Acids form hydronium ions (H3O+)
HCl + H2O  H3O+ + Cl–
H
H
Cl
O
H
O
H
H
–
+
Cl
H
acid
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Definitions
 Arrhenius
- In aqueous solution…
• Bases form hydroxide ions (OH-)
NH3 + H2O  NH4 +
+
H
H
H
N
H
O
H
–
+
O
N
H
H
OH
H
H
base
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H
Definitions: Brønsted-Lowry
Acid = any substance that donates a proton.
Base = any substance that accepts a proton.
d+
1-
1+
d-
+
HCl
H2O
H3O+
Cl-
(acid)
(base)
hydronium ion
chloride ion
Definitions: Brønsted-Lowry
d-
1-
1+
d+
+
NH3
H2O
(base)
(acid)
NH4+
ammonium ion
OHhydroxide ion
Conjugate Acid-Base Pairs
conjugates
HCl
+
base
acid
H2O
H3O+
+
acid
Clbase
conjugates
HCl
acid
+
H 2O
H3O+
base
CA
+
ClCB
Conjugate Acid-Base Pairs
conjugates
acid
NH3
+
H2O
base
base
NH41+
+
OH-
acid
conjugates
NH3
base
+
H2O
acid
NH41+
CA
+ OHCB
Acid Strength
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 508
Strength
(measured [H+] and [OH-])
Strong Acids/Bases
-
+
– 100% ionized in water
– strong electrolytes
HCl
HNO3
H2SO4
HBr
HI
HClO3
HClO4
Group 1
Hydroxides
(plus Sr(OH)2,
Ba(OH)2, and
Ca(OH)2)
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Strength
(measured [H+] and [OH-])
Weak Acids/Bases
-
+
• do not ionize completely
• weak electrolytes
Examples:
HF
CH3COOH
H3PO4
H2CO3
HCN
Example:
NH3
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
`
pH scale: measures acid/basic concentration
Soren Sorensen
(1868 - 1939)
ACID
BASE
10x10x
100x 10x
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
NEUTRAL
Each step on pH scale represents a factor of 10.
pH 6 to pH 5
pH 3 to pH 5
pH 8 to pH 13
(10X more acidic)
(100X less acidic)
(100,000X less acidic)
Basic
7
Acid
14
Neutral
pH Scale
Acidic
0
Base
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515
[H+]
pH
10-14
14
10-13
13
10-12
12
10-11
11
10-10
10
10-9
9
10-8
8
10-7
7
10-6
6
10-5
5
10-4
4
10-3
3
10-2
2
10-1
1
100
0
1 M NaOH
Ammonia
(household
cleaner)
Blood
Pure water
Milk
Vinegar
Lemon juice
Stomach acid
1 M HCl
pH of Common Substance
More acidic
More basic
pH
NaOH, 0.1 M
Household bleach
Household ammonia
Lime water
Milk of magnesia
Borax
Baking soda
Egg white, seawater
Human blood, tears
Milk
Saliva
Rain
Black coffee
Banana
Tomatoes
Wine
Cola, vinegar
Lemon juice
Gastric juice
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
[H1+]
[OH1-]
1 x 10-14
1 x 10-13
1 x 10-12
1 x 10-11
1 x 10-10
1 x 10-9
1 x 10-8
1 x 10-7
1 x 10-6
1 x 10-5
1 x 10-4
1 x 10-3
1 x 10-2
1 x 10-1
1 x 100
1 x 10-0
1 x 10-1
1 x 10-2
1 x 10-3
1 x 10-4
1 x 10-5
1 x 10-6
1 x 10-7
1 x 10-8
1 x 10-9
1 x 10-10
1 x 10-11
1 x 10-12
1 x 10-13
1 x 10-14
pOH
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
[H+] [OH-] = 1 x 10-14 M (ionization constant of water (Kw))
pH = - log [H+]
pOH = - log [OH-]
Given: pH = 4.6
pH = - log [H+]
choose proper equation
4.6 = - log [H+]
substitute pH value in equation
- 4.6 =
2nd
log
Determine [H+]
- 4.6 =
log [H+]
log [H+]
[H+] = 2.51x10-5 M
multiply both sides by -1
take antilog of both sides
Recall, [H+] = [H3O+]
10x
antilog
You can check your answer by working backwards.
pH = - log [H+]
pH = - log [2.51x10-5 M]
pH = 4.6
Litmus Paper
Indicators
phenolphthalein
bromthymol blue
universal indicator
colorless
weak acid
yellow
strong acid
pink
strong base
blue
strong base
R O Y G B I V
pH 4
7
12
pH Paper
pH 0
1
2
3
4
5
6
pH 7
8
9
10
11
12
13
Acid-Base Neutralization
1-
1+
+
+
H3O+
OH-
H2O
H2O
Hydronium ion
Hydroxide ion
Water
Water
Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 584
Neutralization
ACID + BASE  SALT + WATER
HCl + NaOH  NaCl + H2O
strong
strong
neutral
HC2H3O2 + NaOH  NaC2H3O2 + H2O
weak
strong
basic
• Salts can be neutral, acidic, or basic.
• Neutralization does not mean pH = 7.
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100% Neutralization
+
O
moles H3 = moles
MVn = MVn
M: Molarity
V: volume
n: # of H+ ions in the acid
or OH- ions in the base
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OH
Titration
 Equivalence
point (endpoint)
• Point at which equal amounts
of H3O+ and OH- are present.
• Determined by…
• indicator color change
• dramatic change in pH
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Titration
 42.5
mL of 1.3M KOH are required to
neutralize 50.0 mL of H2SO4. Find the
molarity of H2SO4.
H3O+
OH-
M=?
M = 1.3M
V = 50.0 mL
n=2
V = 42.5 mL
n=1
MVn = MVn
M(50.0mL)(2)
=(1.3M)(42.5mL)(1)
M = 0.55M H2SO4
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Neutralization of Bug Bites
Wasp - stings with base
Red Ant - bites with acid
(neutralize with lemon juice or vinegar)
(neutralize with baking soda)
Range and Color Changes of Some
Common Acid-Base Indicators
pH Scale
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Indicators
Methyl orange
Methyl red
Bromthymol blue
Neutral red
Phenolphthalein
3.1 – 4.4
red
red
4.4
yellow
yellow
6.2
6.2
red
colorless
6.8
yellow
7.6
8.0
8.0
blue
yellow
10.0
red
Bromthymol blue indicator would be used in titrating a strong acid with a strong base.
Phenolpthalein indicator would be used in titrating a weak acid with a strong base.
Methyl orange indicator would be used in titrating a strong acid with a weak base.
colorless beyond 13.0