Acid and Base Definitions
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Acid and Bases
Acid and Bases
Acid and Bases
Acids
Have a sour taste. Vinegar is a solution of acetic acid. Citrus
fruits contain citric acid.
React with certain metals to produce hydrogen gas.
React with carbonates and bicarbonates to produce carbon
dioxide gas
Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.
Some Properties of Acids
 Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion
attached to a water molecule)
 Taste sour
 Corrode metals
 Electrolytes
 React with bases to form a salt and water
 pH is less than 7
 Turns blue litmus paper to red “Blue to Red A-CID”
Acid Nomenclature Review
Anion
Ending
No Oxygen
Acid Name
-ide
hydro-(stem)-ic acid
-ate
(stem)-ic acid
-ite
(stem)-ous acid
w/Oxygen
An easy way to remember which goes with which…
“In the cafeteria, you ATE something ICky”
Acid Nomenclature
Flowchart
ACIDS
start with 'H'
2 elements
3 elements
hydro- prefix
-ic ending
no hydro- prefix
-ate ending
becomes
-ic ending
-ite ending
becomes
-ous ending
Acid Nomenclature Review
• HBr (aq)
• H2CO3
• H2SO3

hydrobromic acid

carbonic acid

sulfurous acid
Some Properties of Bases
 Produce OH- ions in water
 Taste bitter, chalky
 Are electrolytes
 Feel soapy, slippery
 React with acids to form salts and water
 pH greater than 7
 Turns red litmus paper to blue
“Basic Blue”
Some Common Bases
NaOH
sodium hydroxide
lye
KOH
potassium hydroxide
liquid soap
Ba(OH)2
barium hydroxide
stabilizer for plastics
Mg(OH)2
magnesium hydroxide
“MOM” Milk of magnesia
aluminum hydroxide
Maalox (antacid)
Al(OH)3
Acid/Base definitions
• Definition #1: Arrhenius (traditional)
Acids – produce H+ ions (or hydronium ions H3O+) in water
Bases – produce OH- ions in water
(problem: some bases don’t have hydroxide ions!)
Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water
Acid/Base Definitions
• Definition #2: Brønsted – Lowry
Acids – proton donor
Bases – proton acceptor
A “proton” is really just a hydrogen atom
that has lost it’s electron!
A Brønsted-Lowry acid is a proton donor
A Brønsted-Lowry base is a proton acceptor
base
acid
conjugate
acid
conjugate
base
ACID-BASE THEORIES
The Brønsted definition means
NH3 is a BASE in water — and
water is itself an ACID
NH3
Base
+
H2O
Acid
NH4+ + OHAcid
Base
Amphoteric Substances
• A substance that is amphoteric can act as
either an acid or a base.
• In the previous slide, water acted as an acid.
• In the following example, water acts as a base.
HCl (g) + H2O (l)  H3O+ (aq) + Cl- (aq)
acid
base
conj. acid conj. base
Conjugate Pairs
Acid-Base Behavior
• Consider a compound having the formula HOX.
• If X is highly electronegative, it will have a strong attraction
for the electrons shared with O.
– The O, will in turn, pull strongly on the electrons held shared
with H.
– This H will then be easily lost = acid
• If X has a low electronegativity, the oxygen will pull the
electrons away from X.
– The hydrogen will remain joined to the oxygen.
– Since the O and H can easily remain together, it is likely that OHwill be formed = base
• Nonmetals tend to have high EN = acids
• Metals tend to have low EN = bases
Acids & Base Definitions
Definition #3 – Lewis
Lewis acid - a substance
that accepts an electron
pair
Lewis base - a substance
that donates an electron
pair
Lewis Acids & Bases
Formation of hydronium ion is also an excellent
example.
•• ••
••
O—H
H O—H
+
H
H
H
ACID
BASE
•Electron pair of the new O-H bond
originates on the Lewis base.
Lewis Acid/Base Reaction
Lewis Acid-Base
Interactions in Biology
• The heme group in
hemoglobin can
interact with O2 and
CO.
• The Fe ion in
hemoglobin is a
Lewis acid
• O2 and CO can act
as Lewis bases
Heme group
HOMEWORK
1) Identify the acid, base, conjugate acid, and conjugate base
in the following reactions (using the Bronsted-Lowry
definition):
a)
b)
HNO3 (aq) + NaOH (aq)  H2O (l) + NaNO3 (aq)
NaHCO3 (aq) + HCl (aq)  NaCl (aq) + H2CO3 (aq)
2) What is the conjugate base of each of the following acids?
a)
b)
H2SO3
H2CO3
c) NH3
d) HF
3) Classify each of the following substances as either a Lewis
acid or a Lewis base:
a)
b)
ClCO32-
c) Na+
d) Br-
MORE HOMEWORK
4) Describe the differences in the three acidbase definitions of this PowerPoint.
5) What are conjugate acids and bases?
6) Name the following substances:
a) HCl (aq)
b) H2SO4
c) KOH
7) What kind of element would you expect to
find in position X of the compound HOX if the
compound is determined to be amphoteric?