Calibration of pH meters requires tools and raw materials
Standard buffer solution (a standard buffer solution with a pH value close to the test solution should be selected). Currently, there are 7 standard solutions, and the following 3 solutions are generally used in China: (pH value at 25 ℃)
1. Potassium hydrogen phthalate (KHC8H4O4) pH 4.003; 0.05M
2. Mixed phosphate (Na2HPO4): Potassium dihydrogen phosphate and disodium hydrogen phosphate mixed salt solution with pH 6.864; 0.025M
3. Borax (Na2B4O7 · l0H2O) pH 9.182; 0.01M
The preparation methods for these three standard buffer solutions are as follows:
1. PH 4, potassium hydrogen phthalate standard buffer:
Accurately 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):
Accurately weigh 4.303g of anhydrous disodium hydrogen phosphate and 1.179g of potassium dihydrogen phosphate dried at 115 ± 5 ℃ for 2-3 hours, dissolve with water, and dilute to 1000ml.
Additionally, phosphate standard buffer solution (pH 6.8) was used to accurately weigh 3.533g of anhydrous disodium hydrogen phosphate and 3.387g of potassium dihydrogen phosphate, dried at 115 ± 5 ℃ for 2-3 hours. Water was added 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.
