Buffers Worksheet With Answers Page 3
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1
2
3
4Chem 1B
Dr. Abel
3
2−
[HPO
]
4
7.50 = 7.20 + log
[H
PO
]
2
4
2−
2−
[HPO
]
[HPO
]
4
4
= 1.9952 =
[H
PO
]
0.100M
2
4
2−
[HPO
] = 0.19952M
4
141.96gNa
HPO
0.19952mol
2
4
× 0.250L ×
= 7.1g
L
mol
0.100mol
119.98gNaH
PO
2
4
× 0.250L ×
= 3.00g
L
mol
Weigh out 7.1g Na
HPO
and 3.00g NaH
PO
. Add water to get a total volume of
2
4
2
4
250.00mL.
€
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.
[NH
]
3
9.10 = 9.24 + log
+
[NH
]
4
[NH
]
0.500M
3
= 0.72444 =
+
+
[NH
]
[NH
]
4
4
+
[NH
] = 0.69019M
4
NH
: M
V
= M
V
3
1
1
2
2
(1.00M )V = (0.500M )(1.00L)
V = 0.500L
+
NH
:
4
0.69019mol
53.49gNH
Cl
4
= 37g
×1.00L ×
L
mol
Weigh out 37g NH
Cl. Add 0.500L of the 1.00M NH
. Then add water to get a
4
3
total volume of 1.00 L.
€
8. You have at your lab bench the following chemicals: NaH
PO
(s), Na
HPO
(s),
2
4
2
4
Na
PO
(s), 1.00 M NaOH, 1.00 M HCl, and deionized water. You also have standard
3
4
glassware available. Describe how you would make 1 L of buffer with a pH of 7.00
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