How to prepare pH buffer solutions:
The reagent required for buffer solution preparation are;
- Potassium dihydrogen phosphate
- Potassium biphthalate
- Potassium tetraoxalate
- Sodium tetraborate
- Potassium hydrogen tartrate
- Potassium dihydrogen phosphate (0.0087M) & Disodium hydrogen phosphate (0.0303M)
- Anhydrous disodium hydrogen phosphate
- Calcium hydroxide
- Potassium dihydrogen citrate
- Sodium carbonate 0.025M & Sodium bicarbonate 0.025M
- Water ( Co2 free)
Preparation of Reagents:
Potassium Tetraborate 0.05M (pH 1.68 at 25°C): Dissolve 3.1525 g of potassium tetraborate (KH3 (C2O4)2. 2H2O) in water to make 250ml.
Potassium Biphthalate 0.05M (pH 4.01 at 25°C): Dissolve 2.53 g of potassium biphthalate (KHC8H4O4) previously dried at 110°C for 1 hour, in water to make 250ml.
Equimolal Phosphate 0.05M (pH 6.86 at 25°C): Dissolve 0.8825 g of anhydrous disodium hydrogen phosphate (Na2HPO4) and .8475 g of potassium dihydrogen phosphate (KH2Po4) each previously dried at 120°C for 2 hours, in water to make 250ml.
Sodium Tetraborate 0.01M (pH 9.18 at 25°C): Dissolve 0.95 g of sodium tetraborate (Na2B4O7.10H2O) in water to make 250ml, protect from absorption of carbon dioxide.
Calcium Hydroxide saturated (pH 12.45 at 25°C): Shake the excess of calcium hydroxide with water and decant at 25°C before use. Protect from absorption of carbon dioxide.
Potassium Hydrogen Tartrate, saturated at 25°C: Add potassium hydrogen tartrate (C4H5KO6) to water until saturation is exceeded at 25°C. Then filter or decant.
Potassium dihydrogen citrate 0.05M: Dissolve 11.41g potassium dihydrogen citrate (C6H7KO4) and dilute with water to make 1000ml.
Potassium dihydrogen phosphate (0.0087M) & Disodium hydrogen phosphate (0.0303M): Dissolve 1.18g of KH2Po4 and 4.3 g Na2HPO4, each dried at 120°C for 2 hours, in 1000ml and dilute with water.
Sodium carbonate 0.025M & Sodium bicarbonate 0.025M: Dissolve 2.64 g of Na2Co3 and 2.09g NaHCO3 and dilute with water to make 1000ml.
Preparation of pH buffer solutions:
Buffer solutions for standardization are to be prepared as per above mentioned table.
Buffer solutions should be stored in appropriate containers that ensure the stability pH through out the expiry date.
For buffer solutions greater than 11, the storage should be in containers that are resistant to or reduce Co2 intrusion which would lower of the buffer. For buffer solutions lower than 11, they should typically be prepared in interval not to exceed 3 months. For buffer solution greater than 11, they should typically be prepared and used fresh unless carbon dioxide ingress is restricted.
In mentioned table pH of buffer solution changes according to temperature change.
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