Buffers Worksheet With Answers
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1
2Chem 1B
Dr. White
Worksheet 8: Buffers (answers at end)
1. What is the pH of a buffer containing 0.25 M NH
and 0.45 M NH
Cl?
3
4
2. By how much will the pH change if 0.050 mol HCl is added to 1.00 L of the buffer in
the previous problem?
3. What is the pH of a buffer that is prepared by mixing 35.0 mL of 0.250 M acetic acid
and 25.0 mL of 0.180 M NaOH?
4. How many grams of sodium formate (NaCOOH) would have to be dissolved in 1.0 L of
0.12 M formic acid (pK
3.74) to make the solution have a pH of 3.80?
a
5. Select a good buffer system for a buffer with a pH of 6.8 (look at a K
table in your text)
a
6. Calculate the pH of a buffer that is made by dissolving 2.85 g of benzoic acid (Benzoic
-5
C
H
O
K
= 6.4x10
acid - H
) with 3.78 g of sodium benzoate in water to a final
7
5
2
a
volume of 500 mL. How would this pH differ if the final volume was 250 mL.
7. You have at your lab bench the following chemicals: NaH
PO
(s), Na
HPO
(s),
2
4
2
4
Na
PO
(s), NH
Cl(s), NaCH
COO(s), CH
COOH(l), 1.00 M NH
, and deionized water.
3
4
4
3
3
3
You also have standard glassware available.
Acid
pKa
H
PO
2.15
3
4
-
H
PO
7.20
2
4
-2
HPO
12.3
4
NH
+
9.24
4
CH
COOH
4.75
3
a. Describe how you would make 250.00 mL of buffer with a pH of 7.50 using
only the materials listed above and deionized water so that the
concentration of the acid in the buffer is 0.100 M. Give the amounts of the
pure materials in grams if they are solid or mL if they are liquid.
b. Describe how you would make 1.00 L of a buffer with a pH of 9.10 using
only the materials listed above and deionized water so that the
concentration of the base in the buffer is 0.500 M. Give the amounts of the
pure materials in grams if they are solid or mL if they are liquid.
8. You have at your lab bench the following chemicals: NaH
PO
(s), Na
HPO
(s), Na
PO
(s),
2
4
2
4
3
4
1.00 M NaOH, 1.00 M HCl, and deionized water. You also have standard glassware
available. Describe how you would make 1 L of buffer with a pH of 7.00 using one of the
solid materials and one of the 1.00 M solutions (HCl or NaOH) so that the concentration of
the acid in the conjugate acid-base pair is 0.100 M. Give the mass in grams and the volume
of solution in mL.
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