Phosphate and Acetate buffers
The different names for phosphate salts. Standardization buffers pH 4 and pH 7. Ph range of some buffer systems. Making up buffer solutions by adding an adjuster solution (acid or base) to a known volume and concentration of a primary salt solution.
Potassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, potassium hydrogen phthalate, sodium acetate,sodium tetraborate, tris aminomethane.
Phosphates
Phosphate salts are known by several names and the correct phosphate must be used to prepare buffer solutions.
One phosphate cannot be substituted for another phosphate. Check formula of salt to be certain.
| Formula | Name of salt | Other names |
|---|
| KH2PO4 | potassium dihydrogen
phosphate
| potassium dihydrogen orthophosphate
monobasic potassium phosphate
monopotassium phosphate
acid potassium phosphate
potassium biphosphate |
| K2HPO4 | potassium hydrogen
phosphate
| dipotassium hydrogen orthophosphate
dipotassium hydrogen phosphate
dibasic potassium phosphate
dipotassium phosphate |
| K3PO4 | potassium phosphate | tribasic potassium phosphate
tripotassium phosphate |
Standardization buffers
For pH=7.00 :
Add 29.1 ml of 0.1 molar NaOH to 50 ml 0.1 molar potassium dihydrogen phosphate.
Alternatively :
Dissolve 1.20g of sodium dihydrogen phosphate and 0.885g of disidium hydrogen phosphate in 1 liter volume distilled water.
For pH= 4.00 :
Add 0.1 ml of 0.1 molar NaOH to 50 ml of 0.1 molar potassium hydrogen phthalate .
Alternatively :
Dissolve 8.954g of disodium hydrogen phosphste.12 H2O and 3.4023g of potassium dihydrogen phosphate in 1 liter volume distilled water.
|
Range of common buffer systems ¹
Buffering system
|
Useful buffering pH range @ 25°C
|
|---|
| Hydrochloric acid/ Potassium chloride | 1.0 - 2.2
|
| Glycine/ Hydrochloric acid | 2.2 - 3.6 |
| Potassium hydrogen phthalate/ Hydrochloric acid | 2.2 -
4.0 |
| Citric acid/ Sodium citrate | 3.0 - 6.2 |
| Sodium acetate/ Acetic acid | 3.7 - 5.6 |
| Potassium hydrogen phtaalate/ Sodium hydroxide | 4.1 -
5.9 |
| Disodium hydrogen phthalate / Sodium dihydrogen orthophospate
| 5.8 - 8.0 |
| Dipotassium hydrogen phthalate / Potassium dihydrogen
orthophospate | 5.8 - 8.0 |
| Potassium dihydrogen orthophosphate / sodium hydroxide
| 5.8 - 8.00 |
| Barbitone sodium / Hydrochloric acid | 6.8 - 9.6
|
| Tris (hydroxylmethyl) aminomethane / Hydrochloric acid
| 7.0 - 9.00 |
| Sodium tetraborate/ Hydrochloric acid | 8.1 - 9.2
|
| Glycine/ Sodium hydroxide | 8.6 - 10.6 |
| Sodium carbonate/ Sodium hydrogen carbonate | 9.2 - 10.8
|
| Sodium tetraborate/ Sodium hydroxide | 9.3 - 10.7
|
| Sodium bicarbonate / Sodium hydroxide | 9.60 - 11.0
|
| Sodium hydrogen orthophosphate / Sodium hydroxide | 11.0
- 11.9 |
| Potassium chloride/ Sodium hydroxide | 12.0 - 13.0
|
Preparing a Buffer Solution ²
This page gives tabulated info on the preparation of buffers by mixing adjusters with a known volume of the primary salt solution, and made up to 200ml with distilled water.
BUFFERS 1.00 - 9.00
Buffer A :
pH 1.0 -
2.2 |
Buffer B :
pH 2.2 - 4.00 |
Buffer C :
pH 4.10 - 5.90 |
Buffer D :
pH 5.8 - 8.00 |
Buffer E :
pH 7.0 - 9.00 |
|
50 ml 0.2 M KCl + mls of 0.2 M HCl
|
100 ml 0.1 M potassium hydrogen phthalate + mls of 0.1 M
HCl.
|
100 ml 0.1 M potassium hydrogen phthalate + mls of 0.1 M
NaOH |
. 100 ml 0.1 M KH2PO4 + mls of 0.1 M NaOH. |
100 ml 0.1 M tris (hydroxymethyl) aminomethane + mls of
0.1 M HCl. |
| pH |
mls of 0.2M HCl added |
pH |
mls of 0.1M HCl
added |
pH |
mls of 0.1M NaOH
added |
pH |
mls of 0.1M NaOH
added |
pH |
mls of 0.1 M HCl
added |
| 1.00 |
134.0 |
2.20 |
99.0 |
4.10 |
2.6 |
5.80 |
7.2 |
7.00 |
93.2 |
| 1.10 |
105.6 |
2.30 |
91.6 |
4.20 |
6.0 |
5.90 |
9.2 |
7.10 |
91.4 |
| 1.20 |
85.0 |
2.40 |
84.4 |
4.30 |
9.4 |
6.00 |
11.2 |
7.20 |
89.4 |
| 1.30 |
67.2 |
2.50 |
77.6 |
4.40 |
13.2 |
6.10 |
13.6 |
7.30 |
86.8 |
| 1.40 |
53.2 |
2.60 |
70.8 |
4.50 |
17.4 |
6.20 |
16.2 |
7.40 |
84.0 |
| 1.50 |
41.4 |
2.70 |
64.2 |
4.60 |
22.2 |
6.30 |
19.4 |
7.50 |
80.6 |
| 1.60 |
32.4 |
2.80 |
57.8 |
4.70 |
27.2 |
6.40 |
23.2 |
7.60 |
77.0 |
| 1.70 |
26.0 |
2.90 |
51.4 |
4.80 |
33.0 |
6.50 |
27.8 |
7.70 |
73.2 |
| 1.80 |
20.4 |
3.00 |
44.6 |
4.90 |
38.8 |
6.60 |
32.8 |
7.80 |
69.0 |
| 1.90 |
16.2 |
3.10 |
37.6 |
5.00 |
45.2 |
6.70 |
38.6 |
7.90 |
64.0 |
| 2.00 |
13.0 |
3.20 |
31.4 |
5.10 |
51.0 |
6.80 |
44.8 |
8.00 |
58.4 |
| 2.10 |
10.2 |
3.30 |
25.8 |
5.20 |
57.6 |
6.90 |
51.8 |
8.l0 |
52.4 |
| 2.20 |
7.8 |
3.40 |
20.8 |
5.30 |
63.2 |
7.00 |
58.2 |
8.20 |
45.8 |
|
|
3.50 |
16.4 |
5.40 |
68.2 |
7.10 |
64.2 |
8.30 |
39.8 |
|
|
3.60 |
12.6 |
5.50 |
73.2 |
7.20 |
69.4 |
8.40 |
34.4 |
|
|
3.70 |
9.0 |
5.60 |
77.6 |
7.30 |
74.0 |
8.50 |
29.4 |
|
|
3.80 |
5.8 |
5.70 |
81.2 |
7.40 |
78.2 |
8.60 |
24.4 |
|
|
3.90 |
2.8 |
5.80 |
84.6 |
7.50 |
82.2 |
8.70 |
20.6 |
|
|
4.00 |
0.2 |
5.90 |
87.4 |
7.60 |
85.6 |
8.80 |
17.0 |
|
|
|
|
|
|
7.70 |
88.4 |
8.90 |
14.0 |
|
|
|
|
|
|
7.80 |
90.6 |
9.00 |
11.4 |
|
|
|
|
|
|
7.90 |
92.2 |
|
|
|
|
|
|
|
|
8.00 |
93.4 |
|
|
BUFFERS 08 - 13
| Buffer F: pH 8.0 - 9.10 |
Buffer G :
pH 9.2 - 10.80 |
Buffer H :
pH 9.60 - 11.00 |
Buffer I :
pH 10.90 - 12.00 |
Buffer J :
pH 12.00 - 13.00 |
|
100 mL 0.025 M Na2B4O7.10H2O (borax) + mls of 0.1 M HCl.
|
100 mL 0.025 M Na2B4O7.10H2O (borax) + mls of 0.1 M
NaOH.
|
100 mL 0.05 M NaHCO3 + mls of 0.1 M NaOH. |
100 mL 0.05 M Na2HPO4 + mls of 0.1 M NaOH.
|
50 mL 0.2 M KCl + volume indicated (in mL) 0.2 M NaOH.
|
| pH |
mls of 0.1M HCl
added |
pH |
mls of 0.1M NaOH
added |
pH |
mls of 0.1M NaOH
added |
pH |
mls of 0.1M NaOH
added |
pH |
mls of 0.2M NaOH
added |
| 8.00 |
41.0 |
9.20 |
1.8 |
9.60 |
10.0 |
10.90 |
6.6 |
12.00 |
12.0 |
| 8.10 |
39.4 |
9.30 |
7.2 |
9.70 |
12.4 |
11.00 |
8.2 |
12.10 |
16.0 |
| 8.20 |
37.6 |
9.40 |
12.4 |
9.80 |
15.2 |
11.10 |
10.2 |
12.20 |
20.4 |
| 8.30 |
35.4 |
9.50 |
17.6 |
9.90 |
18.2 |
11.20 |
12.6 |
12.30 |
25.6 |
| 8.40 |
33.2 |
9.60 |
22.2 |
10.00 |
21.4 |
11.30 |
15.2 |
12.40 |
32.4 |
| 8.50 |
30.4 |
9.70 |
26.2 |
10.10 |
24.4 |
11.40 |
18.2 |
12.50 |
40.8 |
| 8.60 |
27.0 |
9.80 |
30.0 |
10.20 |
27.6 |
11.50 |
22.2 |
12.60 |
51.2 |
| 8.70 |
23.2 |
9.90 |
33.4 |
10.30 |
30.4 |
11.60 |
27.0 |
12.70 |
64.4 |
| 8.80 |
19.2 |
10.00 |
36.6 |
10.40 |
33.0 |
11.70 |
32.4 |
12.80 |
82.4 |
| 8.90 |
14.2 |
10.10 |
39.0 |
10.50 |
35.6 |
11.80 |
38.8 |
12.90 |
106.0 |
| 9.00 |
9.2 |
10.20 |
41.0 |
10.60 |
38.2 |
11.90 |
46.0 |
13.00 |
132.0 |
| 9.10 |
4.0 |
10.30 |
42.6 |
10.70 |
40.4 |
12.00 |
53.8 |
|
|
|
|
10.40 |
44.2 |
10.80 |
42.4 |
|
|
|
|
|
|
10.50 |
45.4 |
10.90 |
44.0 |
|
|
|
|
|
|
10.60 |
46.6 |
11.00 |
45.4 |
|
|
|
|
|
|
10.70 |
47.6 |
|
|
|
|
|
|
|
|
10.80 |
48.5 |
|
|
|
|
|
|
Acetate buffer solutions pH 3 - 6 ³
Make up the following solutions
(1) 0.1M acetic acid
(2) 0.1M sodium acetate (tri-hydrate) (13.6g / l)
Mix in the following proportions to get the required ph
| ph |
Vol. of 0.1M acetic acid |
Vol. of 0.1M sodium acetate |
| 3 |
982.3 mls |
17.7 mls |
|
| 4 |
847.0 mls |
153.0 mls |
| 5 |
357.0 mls |
643.0 mls |
| 6 |
52.2 mls |
947.8 mls |
Acetate buffer solutions pH 3.6 - 5.6
Make up the following solutions
(1) 0.1M acetic acid
(2) 0.1M sodium acetate (tri-hydrate) (13.6g / l)
Mix in the following proportions to get the required ph [Pearse 1980]
| ph |
Vol. of 0.1M acetic acid |
Vol. of 0.1M sodium acetate |
| 3.6 |
185 mls |
15 mls |
|
| 3.8 |
176 mls |
24 mls |
| 4.0 |
164 mls |
36 mls |
| 4.2 |
147 mls |
53 mls |
| 4.4 |
126 mls |
74 mls |
| 4.6 |
102 mls |
98 mls |
| 4.8 |
80 mls |
120 mls |
| 5.0 |
59 mls |
141 mls |
| 5.2 |
42 mls |
158 mls |
| 5.4 |
29 mls |
171 mls |
| 5.6 |
19 mls |
181 mls |
Phosphate buffer solutions ph 5.8 - 8.0
Make up the following solutions 5
(1) 0.2M KH2PO4 (g/ l)
(2) 0.2M NaOH
Add the vol. of 0.2M NaOH in table to 50 mls of 0.2M KH2PO4 and dilute to 200 mls.
| ph |
Vol. of Naoh |
ph |
Vol. of NaOH |
| 5.8 |
3.72 mls |
7.0 |
29.63 mls |
| 6.0 |
5.70 mls |
7.2 |
35.00 mls |
| 6.2 |
8.60 mls |
7.4 |
39.50 mls |
| 6.4 |
12.60 mls |
7.6 |
42.80 mls |
| 6.6 |
17.80 mls |
7.8 |
45.20 mls |
| 6.8 |
23.65 mls |
8.0 |
46.80 mls |
Addition of acid or base to a salt pH 3 - 11
Here, the primary salt is a solid and is weighed out in grams. A measured amount of 0.10M HCl or 0.10M NaOH is added and made up to 1 liter to give the required ph. 4
| pH | Salt mixture
Dilute each mixture to 1 liter solution with distilled water |
|---|
| 3 | 10.21g potassium hydrogen phthalate and 223ml of 0.10M HCl |
| 4 | 10.21g potassium hydrogen phthalate and 1ml of 0.10M HCl |
| 5 | 10.21g potassium hydrogen phthalate and 226ml of 0.10M NaOH |
| 6 | 6.81g potassium dihydrogen phosphate and 56ml of 0.10M NaOH |
| 7 | 6.81g potassium dihydrogen phosphate and 291ml of 0.10M NaOH |
| 8 | 6.81g potassium dihydrogen phosphate and 467ml of 0.10M NaOH |
| 9 | 4.77g sodium tetraborate and 46ml of 0.10M HCl |
| 10 | 4.77g sodium tetraborate and 183ml of 0.10M NaOH |
| 11 | 2.10g sodium bicarbonate and 227ml of 0.10M NaOH |
1. The Physical and Theoretical Laboratory, Oxford
University.
2. "Electrolyte solutions" Robinson, R. A., and Stokes, R. H.,
2nd ed., rev. London,
Butterworths, 1968.
3. "Practical chemistry" J. Lambert and T.A. Muir, 3rd. Ed. Heineman, London.
4. pdf file, www.bc.ca/bcsc/resources/ (Canadian Teachers Federation).
5. "Determination of hydrogen Ions" Clark and Lubs, Williams and Wilkins, Baltimore, 1928.
|
