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Preparation of pH buffer solutions
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Analysis Buffers
For EDTA titrations
For Fluoride (TISAB)
For Determination of Fe.
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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
phosphatepotassium dihydrogen orthophosphate
monobasic potassium phosphate
monopotassium phosphate
acid potassium phosphate
potassium biphosphateK2HPO4 potassium hydrogen
phosphatedipotassium hydrogen orthophosphate
dipotassium hydrogen phosphate
dibasic potassium phosphate
dipotassium phosphateK3PO4 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 - 2.2Buffer B :
pH 2.2 - 4.00Buffer C :
pH 4.10 - 5.90Buffer D :
pH 5.8 - 8.00Buffer E :
pH 7.0 - 9.0050 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 - 10.80Buffer H :
pH 9.60 - 11.00Buffer I :
pH 10.90 - 12.00Buffer J :
pH 12.00 - 13.00100 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 0.1M HCl or 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 water3 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
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.
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