CHAPTER 14
AP CHEMISTRY
NATURE OF ACIDS AND BASES
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Acids - sour
Bases (alkali) - bitter and slippery
Brønsted-Lowry
Acid is a proton [H+] donor, base is a proton acceptor
H+ never found in water, will always form the hydronium ion
HA(aq) + H2O(l) --> H3O+(aq) + A-(aq)
Acid
Base
Conj. Acid Conj. Base
ka = [H+][A-]
[HA]
Diprotic acid - forms two protons
Page 627 table 14.1
Continue
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Carboxyl group
Page 628 table 14.2
Arrange the following species to strength as a base H2O,
F-, CN-, Cl-, NO2-
WATER AS AN ACID OR BASE
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Amphoteric - can be either an acid or base
OH- — H2O — H3O+
NH2- — NH3 — NH4+
Any aqueous solution that contains H3O+ ions
and OH- ions will eventually reach equilibrium
2 H2O <==> H3O+(aq) + OH-(aq)
Continue
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Any pure solids or liquids do not have concentrations, therefore
they are not placed in the equation
kw = [ H3O+][OH-] = 1.0 X 10-14 at 25 °C
When [ H3O+] = [OH-] = 1.0 X 10-7 a reaction will be neutral
[ H3O+] < [OH-] the solution is basic
[ H3O+] > [OH-] the solution is acidic
Calculate the [H3O+] or [OH-] opposite of what you have and
state if the solution is neutral, acidic, or basic
2.0 X 10-5 M H3O+
3.0 X 10-9 M OH1.0 X 10-7 M OHOrange juice demo
pH SCALE
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pH = -log [H+]
Significant figures of the concentration is equal to the
number of places after the decimal point.
1.0 X 10-9 two sig. figs. so the pH will have two
decimal places pH = 9.00
pOH = -log[OH-]
pk = -log k
[H+] = 10-pH
pH = 7 neutral, pH < 7 acidic, pH > 7 basic
STRONG ACIDS
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HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3
Look for the major components found in the solution
HCl(aq) has H+, Cl-, and H2O
Look at what can give H+
H2O <=> H+ + OHHCl ---> H+ + ClWater gives such a small amount of hydrogen ions we
can ignore it
WEAK ACID
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HF(aq) species are H+, F-, H2O. Look at those
which can give H+
HF(aq) <=> H+ (aq) + F-(aq) ka = 7.2 X 10-4
H2O(aq) <=> H+(aq) + OH-(aq) ka = 1 X 1014
HF is a weak acid but it is stronger than water so
it is the dominant source of H+
HX(aq) + H2O(l) <=> H3O+(aq) + X-(aq)
Continue
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Go over example page 639
% dissociation = amount dissociated X 100
Initial concentration
Page 641 example
STRONG BASES - group 1 metals, calcium,
barium, and strontium
AMINE GROUPS
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B(aq) + H2O(l) <=> BH+(aq) + OH-(aq)
kb= [BH+][OH-]
[B]
Page 647 table 14.3
Page 647-650 example
ka X kb = kw
POLYPROPTIC ACID
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Can furnish more than one proton
H3PO4 <=> H+ + H2PO4- ka = 7.5 X 10-3
H2PO4- <=>H+ + HPO42- ka = 6.2 X 10-8
HPO42- <=> H+ + PO43- ka = 4.8 X 10-13
With each proton lost the ka becomes smaller
Page 651 table 14.4
Page 651 example
metallic oxides are strong bases
O2- + H2O <=> 2OH-
ACID-BASE PROPERTIES OF
SALT SOLUTIONS
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Cations
Spectators - derived from a strong base
Li+, Na+, K+, Ca2+, Sr2+, Ba2+
Acidic - all other cations (transition metals included)
Anions
Spectators - derived from a strong acid
Cl-, Br-, I-, NO3-, ClO4-, SO42Basic - derived from a weak acid
F-, NO2-, CO32If the cation is acidic and anion basic, you look at their ka and
kb
ACID-BASE CHARACTERS
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Any molecule with a H-X bond can be an acid
IF TWO rules are followed
In general metal hydrides are basic or have no
acid-base properties
Nonmetal hydrides are acidic or have no acidbase properties
Pages 659-661 examples and tables 14.5, 14.6,
14.7
Read 662-669