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1.2 Application This method is applicable to the determination of various soil pH values.
1.3 The main equipment 1 acidity meter;
2pH glass electrode;
3 saturated calomel electrode;
4 mixer.
1.4 Reagents 11molL 1 potassium chloride solution: Weigh 74.6 potassium chloride (chemically pure) was dissolved in 800ml of water, dilute potassium hydroxide and dilute hydrochloric acid to adjust the solution batch pH of 5.5 ~ 6.0, diluted to 1L;
2pH4.01 (25 °C) standard buffer solution: Weighed by 110 ~ 120 °C drying 2 ~ 3h of potassium dibenzoate potassium dihydrogen phosphate 10.21 dissolved in water, into a 1L volumetric flask, water volume, stored in polyethylene bottles;
3pH6.87 (25°C) Standard Buffer Solution: Weigh 3.533g of disodium hydrogenphosphate and 2.388g of potassium dihydrogenphosphate, dried at 110-130°C for 2-3 hours, and dissolve in water. Transfer to a 1L volumetric flask and dilute to volume with water. Store in polyethylene bottles;
4pH9.18 (25 °C) standard buffer solution: Weigh the balance of borax (Na2B4O7 · 10H2O) 3.800g dissolved in CO2-free water, transferred to 1L volumetric flask, water volume, stored in polyethylene bottles;
Balanced treatment of borax: The borax was equilibrated for two days and nights in a desiccator containing saturated aqueous solution of sucrose and salt;
5 Remove CO2 distilled water.
1.1 Method summary Potentiometric method for the determination of soil pH is the insertion of a pH glass electrode and a calomel electrode into a soil suspension or leachate to determine the electromotive force value and convert it to a pH value. The pH meter can be directly read after the standard solution is determined. The proportion of soil and water has a great influence on the pH value, especially for the effect of the dilution effect of calcareous soil, so it is appropriate to adopt a small ratio of water to soil. This law stipulates that the soil pH is 1:1. At the same time, in addition to determining the pH value of the soaked soil in acid soils, the salt soaking pH should also be measured, ie, after leaching the soil H+ with 1 mol Lˉ1 potassium chloride solution, it was measured by potentiometric method.