Chemistry Reference
In-Depth Information
can react with water in two ways, making the calculation more difficult than is
appropriate even for the general chemistry course.
HA
H
2
O E H
3
O
A
2
HA
OH
H
2
O E H
2
A
The hydronium ion produced by this first reaction reacts with the hydroxide ion
produced by the second, further driving each reaction to the right and compli-
cating the calculations even more.
Snapshot Review
❒
Polyprotic acids ionize in steps, each having its own value for the
dissociation constant.
❒
Since the successive constants are lower than the preceding ones, the
second (or third) ionization does not contribute appreciably to the
hydronium ion concentration of the solution of acid in water, but is
the only source of the doubly (or triply) charged ion.
A. Calculate the pH of 1.00 M .
B. Calculate the pH of a solution of 0.100 M
H
3
PO
4
NaH
2
PO
4
and 0.100 M
Na
2
HPO
4
.
Key Terms
Key terms are defined in the Glossary.
acid dissociation constant (19.2)
acid strength (19.1)
amphiprotic (19.1)
autoionization (19.3)
base dissociation constant (19.2)
base strength (19.1)
Brønsted acid (19.1)
Brønsted base (19.1)
Brønsted theory (19.1)
buffer solution (19.4)
conjugate acid (19.1)
conjugate acid-base pair (19.1)
conjugate base (19.1)
dissociation (19.2)
feeble acid (19.1)
feeble base (19.1)
hydronium ion (19.1)
ionization (19.2)
ionization constant (19.2)
pH (19.3)
polyprotic acid (19.5)
proton (19.1)
proton acceptor (19.1)
proton donor (19.1)
water ionization constant (19.3)
Symbols
K
a
(acid dissociation constant) (19.2)
(base dissociation constant) (19.2)
K
i
(ionization constant) (19.2)
(water ionization constant) (19.3)
K
l
(first dissociation constant) 19.5
K
b
K
w
Summary
T
he Brønsted theory of acids and bases extends the
definition of acids and bases, which allows an explana-
tion of why most salts dissolved in water do not form
neutral solutions. Acids are defined as proton donors,
and bases are proton acceptors. An excess of
H
3
O
ions
OH
over
ions makes an aqueous solution acidic, and
