Buffers Worksheet With Answers
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2
3
4Chem 1B
Dr. Abel
1
Worksheet 8 - Buffers KEY
1. What is the pH of a buffer containing 0.25 M NH
and 0.45 M NH
Cl?
3
4
0.25
pH = 9.24 + log
= 8.98
0.45
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?
€
+
+
H
O
NH
NH
+ H
O
+
→
3
3
4
2
0.050mol
0.25 mol
0.45 mol
-0.050 mol
- 0.050 mol
+ 0.050 mol
0 mol
0.20 mol
0.50 mol
0.20mol
[NH
] =
= 0.20M
3
1.00L
0.50mol
+
[NH
] =
= 0.50M
4
1.00L
0.20M
pH = 9.24 + log
0.50M
pH = 8.84
ΔpH = 8.84 − 8.98 = −0.14
The pH decreases by 0.14 pH units
3, What is the pH of a buffer that is prepared by mixing 35.0mL of 0.250 M acetic acid and
25.0 mL of 0.180 M NaOH?
€
-
-
HC
H
O
(aq)
+
OH
(aq)
C
H
O
(aq) + H
O(l)
→
2
3
2
2
3
2
2
Start:
0.00875
0.00450
0
React
-0.00450
-0.00450
+0.00450
End:
0.00425
0
0.00450
0.00450 /0.00600
pH = 4.74 + log
= 4.76
0.00425 /0.00600
4. How many grams of sodium formate 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?
(look up formula for formic acid
a
and/or formate: Sodium formate – NaCOOH)
€
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