Chemistry 101
Prof. Hammon
CHAPTER 15 –ACIDS & BASES
Arrhenius defined Acid as – a substance that produces H+
(hydrogen ion) in water.
H atom has ___ proton and ___ electron
loose an eH atom
H+ proton
+1
H+ combines with H2O:
H+ +
H2O
H3O+
hydronium ion
Example:
HCl(g)
+
H2O(l)
H3O+(aq)
+ Cl-(aq)
Hydrogen chloride (g) in water is hydrochloric acid.
Hydrochloric acid is the gastric fluid in your stomach (5%).
Chemistry 101
Prof. Hammon
Base: A substance that produces OH- (hydroxide ion) in water.
Examples:
NaOH (s)
H O
2
Na+(aq) +
OH-(aq)
Ca(OH)2 (s)
H O
Ca2+(aq) +
2OH-(aq)
2
Strengths of Acid and Bases
Strong acids almost completely react forming H3O+ ions in
water (use up reactants forming lots of ions (product)).
(strong acids: HClO4, H2SO4, HI, HBr, HCl, HNO3)
Example:
HCl
H3O+
+ H2O
+
Cl-
More than 99% ions
Weak acids form a few H3O+ ions in water (reacts a little bit
with water).
CH3COOH + H2O
(acetic acid)
CH3COOH + H3O+ (aq) + CH3OO-(aq)
99%
1% ions
Chemistry 101
Prof. Hammon
Strong Bases disassociate in water forming OH- ions.
(strong bases: LiOH, KOH, NaOH, Ba(OH)2, Ca(OH)2 Sr(OH)2)
Example:
NaOH
H O
2
Na+
OH-
+
100% ions
Weak Bases slightly react with water forming a few OH- ions.
NH3
+ H2O
NH3
99%
+
NH4+
+
OH-
less than 1%
Chemistry 101
Prof. Hammon
Bronsted-Lowry Acids and Bases
Acid – a proton donor (gives up a H+)
Base – a proton acceptor (accepts a H+)
Example:
HCl
+
acid
H2O
H3O+
+
Cl-
base
(proton donor)
(proton acceptor)
Example:
H2O
+ NH3
acid
base
(proton donor)
NH4+
+
OH-
(proton acceptor)
Amphoteric – a substance that acts as an acid or base
Chemistry 101
Prof. Hammon
Conjugate Acids and Bases
Conjugate Base: what the acid becomes after it loses its proton
(H+)
Example:
HCl
+
H3O+
H2O
acid
+
Cl-
base
(proton donor)
(proton acceptor)
HCl
acid
-H+
Clconjugate base
Conjugate Acid: what the base becomes after it gains a proton.
H2O
Base
+
+H
H3O+
conjugate acid
Chemistry 101
Prof. Hammon
What are the conjugate bases for the following acids:
Acid
HBr
HSO4NH4+
Conjugate Base
-H+
What are the conjugate acids for the following bases:
Base
Conjugate Acid
H2O
NH3
Cl-
+H+
A person suffering from heartburn may take Alka-Seltzer
(contains NaHCO3) to neutralize the stomach acidity. What are
the conjugate acid and bases for the following reaction?
H3O+
acid
+
HCO3base
Monoprotic – acids that give up one proton
(i.e. HCl, HNO3, HBr)
Diprotic – acids that give up 2 protons
(i.e. H2SO4, H2CO3)
Triprotic – acids that give up 3 protons
(i.e. H3PO4)
Chemistry 101
Prof. Hammon
Self Ionization of Water
Water can act as an acid & a base. Water reacts with itself
producing very few ions.
H2O
acid
+
H2O
base
H3O+
Ion Product of Water (Kw):
Kw = [H3O+] [OH-]
At 25oC, Kw = 1.0 x 10-14
So concentrations of H3O+ and OH- are:
1.0 x 10-14 = [H3O+] [OH-]
1.0 x 10-14 = [x][x]
x = ___________
At 25oC, a neutral solution has
[H3O+] = 1.0 x 10-7 moles/liter
[OH-] = 1.0 x 10-7moles/liter
+
OH-
Chemistry 101
Prof. Hammon
Example:
If the [H3O+] = 1.0 x 10-3M, what is the [OH-]?
Kw = [H3O+] [OH-]
Example:
If the [OH-] = 1.0 x 10-2M, what is the [H3O+]?
Solutions with a [H3O+] higher than1.0 x 10-7M are acidic
(if [H3O+] >[OH-], then we have an acid).
Solutions with a [OH-] higher than1.0 x 10-7M are basic
(if [OH-] > [H3O+], then we have a base).
If [OH-] = [H3O+], then we have a neutral solution.
Chemistry 101
Prof. Hammon
pH
power of hydrogen ion (hydronium ion)
A mathmatical way to express the [H3O+]
pH = -log[H3O+]
if [H3O+] = 1.0 x 10-3M, then
pH = ____ (pH is just the exponent without the neg. sign)
or plug into calculator
 if pH < 7.0, solution is acidic
 if pH > 7.0, solution is basic
 if pH = 7.0, solution is neutral
Examples
1.The [H3O+] of tomato juice is 1.0 x 10-4M, what is the pH?
pH =
2.The [OH-] of liquid soap is 1.0 x 10-5M, what is the pH?
Kw = [H3O+] [OH-]
Chemistry 101
Prof. Hammon
If [H3O+] not expressed in this form: 1.0 x 10-9M, then must
use calculator to find pH.
Examples
1. What is the pH of a solution whose [H3O+] is 6.0 x 10-9M? Is
the solution acidic or basic?
pH = -log[H3O+]
2. The [H3O+] of blood is 4.0 x 10-8 M, what is the pH?
pOH:
pOH = -log[OH-]
Examples
1. What is the pOH of a solution whose [OH-] is 1.0 x 10-4M?
pOH =
2. What is the pOH of a solution whose [H3O+] is 5.0 x 10-4M?