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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.

FormulaName of saltOther names
KH2PO4potassium dihydrogen
phosphate
potassium dihydrogen orthophosphate
monobasic potassium phosphate
monopotassium phosphate
acid potassium phosphate
potassium biphosphate
K2HPO4potassium hydrogen
phosphate
dipotassium hydrogen orthophosphate
dipotassium hydrogen phosphate
dibasic potassium phosphate
dipotassium phosphate
K3PO4potassium phosphatetribasic 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 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


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).


Phosphate buffer solutions ph 7 - 11


Make up the following solutions
(1) 0.1M disodium hydrogen phosphate (14.2g / l)
(2) 0.1M HCl
(3) 0.1M NaOH
Mix in the following proportions to get the required ph

phvol. of phosphatevol. of 0.1M HClvol. of 0.1M NaOH
7756.0 mls244 mls 
8955.1 mls44.9 mls 
9955.0 mls45.0 mls 
10966.4 mls 33.6
11965.3 mls 34.7


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, then made up to 1 liter to give the relevant buffer solution 4.

pHSalt mixture
Dilute each mixture to 1 liter solution with distilled water
310.21g potassium hydrogen phthalate and 223ml of 0.01M HCl
410.21g potassium hydrogen phthalate and 1ml of 0.01M HCl
510.21g potassium hydrogen phthalate and 226ml of 0.01M NaOH
66.81g potassium dihydrogen phOsphate and 56ml of 0.01M NaOH
76.81g potassium dihydrogen phosphate and 291ml of 0.01M NaOH
86.81g potassium dihydrogen phosphate and 467ml of 0.01M NaOH
94.77g sodium tetraborate and 46ml of 0.01M HCl
104.77g sodium tetraborate and 183ml of 0.01M NaOH
112.10g sodium bicarbonate 227ml of 0.01M NaOH


منبع:http://delloyd.50megs.com/moreinfo/buffers2.html

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.

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.
pHmls of 0.2M HCl addedpHmls of 0.1M HCl addedpHmls of 0.1M NaOH addedpHmls of 0.1M NaOH addedpHmls of 0.1 M HCl added
1.00134.02.2099.04.102.65.807.27.0093.2
1.10105.62.3091.64.206.05.909.27.1091.4
1.2085.02.4084.44.309.46.0011.27.2089.4
1.3067.22.5077.64.4013.26.1013.67.3086.8
1.4053.22.6070.84.5017.46.2016.27.4084.0
1.5041.42.7064.24.6022.26.3019.47.5080.6
1.6032.42.8057.84.7027.26.4023.27.6077.0
1.7026.02.9051.44.8033.06.5027.87.7073.2
1.8020.43.0044.64.9038.86.6032.87.8069.0
1.9016.23.1037.65.0045.26.7038.67.9064.0
2.0013.03.2031.45.1051.06.8044.88.0058.4
2.1010.23.3025.85.2057.66.9051.88.l052.4
2.207.83.4020.85.3063.27.0058.28.2045.8
3.5016.45.4068.27.1064.28.3039.8
3.6012.65.5073.27.2069.48.4034.4
3.709.05.6077.67.3074.08.5029.4
3.805.85.7081.27.4078.28.6024.4
3.902.85.8084.67.5082.28.7020.6
4.000.25.9087.47.6085.68.8017.0
7.7088.48.9014.0
7.8090.69.0011.4
7.9092.2
8.0093.4



Buffer F: pH 8.0 - 9.10Buffer 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.
pHmls of 0.1M HCl addedpHmls of 0.1M NaOH addedpHmls of 0.1M NaOH addedpHmls of 0.1M NaOH addedpHmls of 0.2M NaOH added
8.0041.09.201.89.6010.010.906.612.0012.0
8.1039.49.307.29.7012.411.008.212.1016.0
8.2037.69.4012.49.8015.211.1010.212.2020.4
8.3035.49.5017.69.9018.211.2012.612.3025.6
8.4033.29.6022.210.0021.411.3015.212.4032.4
8.5030.49.7026.210.1024.411.4018.212.5040.8
8.6027.09.8030.010.2027.611.5022.212.6051.2
8.7023.29.9033.410.3030.411.6027.012.7064.4
8.8019.210.0036.610.4033.011.7032.412.8082.4
8.9014.210.1039.010.5035.611.8038.812.90106.0
9.009.210.2041.010.6038.211.9046.013.00132.0
9.104.010.3042.610.7040.412.0053.8
10.4044.210.8042.4
10.5045.410.9044.0
10.6046.611.0045.4
10.7047.6
10.8048.5