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122 Special Topic I
Copyright © 2017 Pearson Education, Inc.
Problems on pH,
p
K
a
,
and Buffers
1.
Calculate the pH of each of the following solutions:
a.
1
*
10
-
3
M HCl
b.
0.60 M HCl
c.
1.40
*
10
-
2
M HCl
d.
1
*
10
-
3
M KOH
e.
3.70
*
10
-
4
M NaOH
f.
a 1.20 M solution of an acid with a
p
K
a
=
4.23
g.
1.60
*
10
-
2
M sodium acetate
1
p
K
a
of acetic acid
=
4.76
2
2.
Calculate the pH of each of the following buffer solutions:
a.
A buffer prepared by mixing 20 mL of 0.10 M formic acid and 15 mL of 0.50 M sodium formate
1
p
K
a
of formic acid
=
3.75
2
.
b.
A buffer prepared by mixing 10 mL of 0.50 M aniline and 15 mL of 0.10 M HCl
1
p
K
a
of the anilinium ion
=
4.60
2
.
c.
A buffer prepared by mixing 15 mL of 1.00 M acetic acid and 10 mL of 0.50 M NaOH
1
p
K
a
of acetic acid
=
4.76
2
.
3.
What fraction of a carboxylic acid with a
p
K
a
=
5.23
will be ionized at
pH
=
4.98
?
4.
What will be the concentration of formic acid and sodium formate in a 1.00 M buffer solution with a
pH
=
3.12
1
p
K
a
of formic acid
=
3.75
2
?
5.
You have found a bottle labeled 1.00 M RCOOH. You want to identify the carboxylic acid, so you decide to
determine its
p
K
a
value. How can you do this?
6.
a.
How can you prepare 100 mL of a buffer solution that is 0.30 M in acetic acid and 0.20 M in sodium
acetate using a 1.00 M acetic acid solution and a 2.00 M sodium acetate solution?
b.
The
p
K
a
of acetic acid is 4.76. Will the pH of the above solution be greater or less than 4.76?
7.
You have 100 mL of a 1.50 M acetic acid/sodium acetate buffer solution that has a
pH
=
4.90.
How can
you change the pH of the solution to 4.50?
8.
You have 100 mL of a 1.00 M solution of an acid with a
p
K
a
=
5.62
to which you add 10 mL of 1.00 M
sodium hydroxide. What fraction of the acid will be in the acidic form? How much more sodium hydroxide
will you need to add so that 40% of the acid is in its acidic form (that is, with its proton)?