Tools and raw materials used for calibrating pH meters
Standard buffer solution (the standard buffer solution close to the pH value of the test solution should be selected). At present, there are 7 kinds of Standard solution, and the following 3 kinds of solutions are generally used in China: (when the pH value is 25 ℃)
1. Potassium hydrogen phthalate (KHC8H4O4) pH 4.003; 0.05M
2. Mixed phosphate (Na2HPO4): Monopotassium phosphate and disodium hydrogen phosphate mixed salt solution pH6.864; 0.025M
3. Borax (Na2B4O7 · l0H2O) pH 9.182; 0.01M
The preparation methods for these three standard buffer solutions are as follows:
1. PH4, Potassium hydrogen phthalate standard buffer solution:
Precisely weigh 10.12g of Potassium hydrogen phthalate [KHC8H4O4] dried at 115 ± 5 ℃ for 2-3 hours, add water to dissolve and dilute to 1000ml.
2. PH 7, phosphate standard buffer (pH 7.4):
Precisely weigh 4.303g of anhydrous disodium hydrogen phosphate and 1.179g of Monopotassium phosphate dried at 115 ± 5 ℃ for 2-3 hours, add water to dissolve and dilute to 1000ml.
In addition: phosphate standard buffer solution (pH6.8) is used to precisely weigh 3.533g of anhydrous disodium hydrogen phosphate and 3.387g of Monopotassium phosphate dried at 115 ± 5 ℃ for 2-3 hours, add water to dissolve and dilute to 1000ml.
3. PH 9, borax standard buffer:
Accurately weigh 3.80g of borax [Na2B4O7 · 10H2O] (note: avoid weathering), add water to dissolve and dilute to 1000ml, place in a polyethylene plastic bottle, close the bottle, and avoid contact with carbon dioxide in the air.
