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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
183
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 18
The equilibrium constant expression for the ionization of formic
acid in water is as follows.
K a ϭ
K a , called the acid ionization constant, is the value of the
equilibrium constant expression for the ionization of a weak acid.
The value of K a indicates the extent of ionization of the acid. The
weakest acids have the smallest K a values. For formic acid,
K a ϭ 1.8 ϫ 10 Ϫ4 at 298 K; this is considered a moderately
weak acid.
In the case of a polyprotic acid, there is a K a value for each ionization, and the K a values decrease for each successive ionization.
For example, the second ionization of phosphoric acid is represented
by this equation.
H 2 PO 4
Ϫ (aq) ϩ H 2 O(l) 3 H 3 O ϩ (aq) ϩ HPO 4
2Ϫ (aq)
The corresponding acid ionization constant expression is as follows.
K a ϭ
Practice Problems
3. Write ionization equations and acid ionization constant
expressions for the following acids.
a. hydrofluoric acid (HF)
b. hypobromous acid (HBrO)
4. Write the ionization equation and the acid ionization constant
expression for the second ionization of sulfurous acid (H 2 SO 3 )
in water.
Strengths of bases Metallic hydroxides, such as potassium
hydroxide, are strong bases because they dissociate entirely into
metal ions and hydroxide ions in aqueous solution.
KOH(s) 0 K ϩ (aq) ϩ OH Ϫ (aq)
A weak base ionizes only partially in dilute aqueous solution to
form an equilibrium mixture. An example is the ionization of the
weak base aniline (C 6 H 5 NH 2 ).
▲
[H 3 O ϩ ][HPO 4
2Ϫ ]
ᎏᎏ
[H 2 PO 4
Ϫ ]
[H 3 O ϩ ][HCOO Ϫ ]
ᎏᎏ
[HCOOH]
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
183
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 18
The equilibrium constant expression for the ionization of formic
acid in water is as follows.
K a ϭ
K a , called the acid ionization constant, is the value of the
equilibrium constant expression for the ionization of a weak acid.
The value of K a indicates the extent of ionization of the acid. The
weakest acids have the smallest K a values. For formic acid,
K a ϭ 1.8 ϫ 10 Ϫ4 at 298 K; this is considered a moderately
weak acid.
In the case of a polyprotic acid, there is a K a value for each ionization, and the K a values decrease for each successive ionization.
For example, the second ionization of phosphoric acid is represented
by this equation.
H 2 PO 4
Ϫ (aq) ϩ H 2 O(l) 3 H 3 O ϩ (aq) ϩ HPO 4
2Ϫ (aq)
The corresponding acid ionization constant expression is as follows.
K a ϭ
Practice Problems
3. Write ionization equations and acid ionization constant
expressions for the following acids.
a. hydrofluoric acid (HF)
b. hypobromous acid (HBrO)
4. Write the ionization equation and the acid ionization constant
expression for the second ionization of sulfurous acid (H 2 SO 3 )
in water.
Strengths of bases Metallic hydroxides, such as potassium
hydroxide, are strong bases because they dissociate entirely into
metal ions and hydroxide ions in aqueous solution.
KOH(s) 0 K ϩ (aq) ϩ OH Ϫ (aq)
A weak base ionizes only partially in dilute aqueous solution to
form an equilibrium mixture. An example is the ionization of the
weak base aniline (C 6 H 5 NH 2 ).
▲
[H 3 O ϩ ][HPO 4
2Ϫ ]
ᎏᎏ
[H 2 PO 4
Ϫ ]
[H 3 O ϩ ][HCOO Ϫ ]
ᎏᎏ
[HCOOH]