Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
190 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 18
[CH 3 COOH] ϭ 0.200M Ϫ 1.9 ϫ 10 Ϫ3 M ϭ 0.198M
Substitute the known values into the equation for K a and solve.
K a ϭ
ϭ 1.8 ϫ 10 Ϫ5
This K a value indicates that CH 3 COOH is a moderately weak acid.
Practice Problems
10. Calculate K a for the following acids using the information
provided.
a. 0.100M solution of sulfurous acid (H 2 SO 3 ), pH ϭ 1.48
b. 0.200M solution of benzoic acid (C 6 H 5 COOH), pH ϭ 2.45
18.4 Neutralization
The reaction of an acid and a base in aqueous solution is called a
neutralization reaction. The products of a neutralization reaction
are a salt and water. A salt is an ionic compound composed of a positive ion from a base and a negative ion from an acid. An example of
an acid-base neutralization is the reaction of nitric acid and calcium
hydroxide to form calcium nitrate and water.
2HNO 3 (aq) ϩ Ca(OH) 2 (aq) 0 Ca(NO 3 ) 2 (aq) ϩ 2H 2 O(l)
Acid-base neutralizations are used in the procedure called titration,
which is a method for determining the concentration of a solution by
reacting it with another solution of known concentration. For example, to find the concentration of an acid solution, you would slowly
add a basic solution of known concentration. The neutralization
reaction would proceed until it reaches the equivalence point,
where the moles of H ϩ ion from the acid equal the moles of OH Ϫ
ion from the base. At the equivalence point, a large change in pH
occurs that can be detected by a pH meter or an acid-base
indicator, which is a chemical dye whose color is affected by pH
changes. The pH at the equivalence point depends upon the relative
strengths of the acid and base used in the titration. For the reaction
of a strong acid with a strong base, the pH at the equivalence point
is 7. However, the pH at the equivalence point may be greater than 7
for a weak acid-strong base titration, or less than 7 for a strong acid(1.9 ϫ 10 Ϫ3) (1.9 ϫ 10 Ϫ3 )
ᎏᎏᎏ
0.198
190 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 18
[CH 3 COOH] ϭ 0.200M Ϫ 1.9 ϫ 10 Ϫ3 M ϭ 0.198M
Substitute the known values into the equation for K a and solve.
K a ϭ
ϭ 1.8 ϫ 10 Ϫ5
This K a value indicates that CH 3 COOH is a moderately weak acid.
Practice Problems
10. Calculate K a for the following acids using the information
provided.
a. 0.100M solution of sulfurous acid (H 2 SO 3 ), pH ϭ 1.48
b. 0.200M solution of benzoic acid (C 6 H 5 COOH), pH ϭ 2.45
18.4 Neutralization
The reaction of an acid and a base in aqueous solution is called a
neutralization reaction. The products of a neutralization reaction
are a salt and water. A salt is an ionic compound composed of a positive ion from a base and a negative ion from an acid. An example of
an acid-base neutralization is the reaction of nitric acid and calcium
hydroxide to form calcium nitrate and water.
2HNO 3 (aq) ϩ Ca(OH) 2 (aq) 0 Ca(NO 3 ) 2 (aq) ϩ 2H 2 O(l)
Acid-base neutralizations are used in the procedure called titration,
which is a method for determining the concentration of a solution by
reacting it with another solution of known concentration. For example, to find the concentration of an acid solution, you would slowly
add a basic solution of known concentration. The neutralization
reaction would proceed until it reaches the equivalence point,
where the moles of H ϩ ion from the acid equal the moles of OH Ϫ
ion from the base. At the equivalence point, a large change in pH
occurs that can be detected by a pH meter or an acid-base
indicator, which is a chemical dye whose color is affected by pH
changes. The pH at the equivalence point depends upon the relative
strengths of the acid and base used in the titration. For the reaction
of a strong acid with a strong base, the pH at the equivalence point
is 7. However, the pH at the equivalence point may be greater than 7
for a weak acid-strong base titration, or less than 7 for a strong acid(1.9 ϫ 10 Ϫ3) (1.9 ϫ 10 Ϫ3 )
ᎏᎏᎏ
0.198