Buffering of a acid : (vinegar) Total number of drops ofVinegar Distilled Water
ID: 1017508 • Letter: B
Question
Buffering of a acid : (vinegar)
Total number of drops ofVinegar
Distilled Water
(pH)
NaHCO3
(pH)
Na2CO3
(pH)
Buffer
(pH)
0 (start)
7.15
8.23
10.94
9.84
2
4.40
8.27
10.87
9.80
4
4.27
8.32
10.86
9.77
6
4.00
8.33
10.85
9.76
8
3.91
8.34
10.82
9.74
10
3.80
8.35
10.81
9.73
12
3.76
8.37
10.77
9.72
Buffering of a base: (Ammonia)
Total number of drops of Ammonia
Distilled Water
(pH)
NaHCO3
(pH)
Na2CO3
(pH)
Buffer
(pH)
0 (Start)
16.60
5.57
11.23
9.79
1
10.68
8.80
11.22
9.85
2
10.65
8.66
11.17
9.85
3
10.71
8.70
11.12
9.86
4
10.89
8.72
11.10
9.86
5
10.90
8.74
11.08
8.87
6
10.99
8.75
11.07
9.88
1- The acid you used was vinegar, and the base you used was ammonia. Which substance caused a greater change in the pH of each system, and why do you think this is so? (Keep in mind that the pH of pure vinegar is about three and pure ammonia is about 12).
2-Write the total ionic equations for a) the addition of the acid to the buffer, and b) the addition of base to the buffer.
3-Write the net ionic equations for a) and b) from the previous questions?
4-Buffers are only useful over a certain pH range. For what pH is this buffer solution useful?
Total number of drops ofVinegar
Distilled Water
(pH)
NaHCO3
(pH)
Na2CO3
(pH)
Buffer
(pH)
0 (start)
7.15
8.23
10.94
9.84
2
4.40
8.27
10.87
9.80
4
4.27
8.32
10.86
9.77
6
4.00
8.33
10.85
9.76
8
3.91
8.34
10.82
9.74
10
3.80
8.35
10.81
9.73
12
3.76
8.37
10.77
9.72
Explanation / Answer
1) the addition of vinegar caused a greater change in the pH of buffer, as we have taken basic buffer and it will react with the base of buffer causing change in pH more than that due to addition of base (ammonia)
2) Total ionic equations will be
(i) addition of acid to the buffer
H+ + NaCO3- --> NaHCO3
(ii) addition of base to the buffer
OH- + NaHCO3 --> H2O + NaCO3-
3)Net ionic equation is
H+ + CO3-2 --> HCO3-
OH- + HCO3- --> H2O + CO3-2
4)The pH range of carbonate buffers= 6- 8
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