HJ 631-2011Soil. Determination of exchangeable acidity by barium chloride extraction-titration method (English PDF)

5.1 Carbon dioxide free water

The distilled water was boiled and evaporated in a beaker (evaporation amount of about 10%), and after cooling, it was used, and the electrical conductivity was <=0.20 mS/m (25 ° C).

Available when used.

5.2 Hydrochloric acid solution (HCl). 15.

5.3 Barium chloride solution. c (BaCl2 · 2H2O) = 0.10 mol/L

Weigh 24.43g of barium chloride (BaCl2·2H2O) dissolved in 1000 ml of water, mix and transfer to a polyethylene bottle for storage.

5.4 Sodium hydroxide standard solution. c (NaOH) = 0.1 mol/L

Weigh 110g of sodium hydroxide in 100ml of water, shake it, pour it into a polyethylene container, and seal it to the solution.

bright. 5.4 ml of the supernatant was placed in a 1000 ml volumetric flask, diluted with water to the mark, shaken, and transferred to a polyethylene bottle.

save.

Calibration. Weigh the standard reagent potassium hydrogen phthalate dried to constant weight in a constant temperature drying oven at 105 ° C ~ 110 ° C 0.75g (accurate to 0.0001g), add 50ml of water to dissolve it, add 2 drops of phenolphthalein indicator (5.7), to be calibrated the sodium hydroxide standard solution was titrated to pink and kept for 30 s without fading. At the same time, use water as a blank test. Sodium hydroxide standard the concentration of the quasi-solution (mol/L) is calculated according to formula (1).

22.204) (

1000) NaOH (

Mc (1)

In the formula.

c(NaOH)-- concentration of sodium hydroxide standard solution, mol/L;

M-- the mass of potassium hydrogen phthalate, g;

V1-- The volume of sodium hydroxide standard solution consumed when calibrating the potassium hydrogen phthalate standard solution, ml;

V2-- The volume of the sodium hydroxide standard solution consumed when the blank solution is calibrated, ml;

204.22-- molar mass of potassium hydrogen phthalate, g/mol.

Note. The sodium hydroxide standard solution should be calibrated before each batch of samples.

5.5 Sodium hydroxide standard solution. c (NaOH) = 0.0020 mol/L

Accurately measure 10.00 ml of sodium hydroxide standard solution (5.4) into a 500 ml volumetric flask and dilute to the mark with water. Storage Store in a polyethylene bottle.

5.6 Sodium fluoride solution. c (NaF) = 1.0 mol/L

Weigh 42.0 g of sodium fluoride dissolved in water, dilute to about 900 ml, and adjust the pH to 7.0 with hydrochloric acid solution (5.2).

Make up to 1000ml with water.

5.7 Phenolphthalein indicator

Weigh 1 g of phenolphthalein in a small amount of ethanol (95%) and dilute to 100 ml with ethanol (95%).

7.1 Sample collection and preservation

Soil samples were collected and stored in accordance with the relevant regulations of HJ/T 166.

7.2 Preparation of samples

Air dried samples were prepared in accordance with the relevant regulations of HJ/T 166. Air dry the sample through a 2 mm pore size sieve and stir well Mix well, take two parts by quadruple method, one spare, and another one to stock the stock.

7.3 Determination of moisture

Accurately weigh the appropriate amount of air-dried sample and determine its moisture content according to the provisions of HJ 613.

8.1 Preparation of samples

Add 2.50 g sample (7.2) and 30.00 ml cesium chloride solution (5.3) to a 50 ml polyethylene centrifuge tube and place the shaker was shaken for 1 h, then centrifuged at 3000 r/min for 10 min on a centrifuge, and the tube was removed. Supernatant Move into a 100ml volumetric flask. The extraction was repeated twice more, and all the supernatants were combined into the above 100 ml volumetric flask, most Afterwards, the volume was adjusted to 100 ml with a cesium chloride solution (5.3), to be tested.

Note. When there are a small amount of animal and plant residues in the sample, it can be filtered and measured.

8.2 Preparation of Blank Samples

Without adding a sample, a blank sample was prepared in accordance with the same procedure as in 8.1.

8.3 Determination of exchangeable acidity

Measure 50.00 ml of the sample (8.1) in a 100 ml beaker, add a magnetic stirrer, place on a magnetic stirrer, insert Enter the pH meter electrode and titrate directly to pH=7.8 with sodium hydroxide standard solution (5.5); or use phenolphthalein as indicator.

Titrate until the color turns pink and ends at 30s without discoloration. Record the consumption of sodium hydroxide standard solution Dosage (ml). At the same time, take 50.00ml blank sample (8.2) instead of the sample to do the blank test, record the consumption of hydrogen and oxygen the amount of sodium standard solution (ml).

Empty V

8.4 Determination of exchangeable hydrogen

Measure 50.00 ml of the sample (8.1) in a 100 ml beaker, add a magnetic stirrer, place on a magnetic stirrer, insert Put into the pH meter electrode, add 2.5ml sodium fluoride solution (5.6), titrate with sodium hydroxide standard solution (5.5) to pH = 7.8;

Or use phenolphthalein as an indicator, titrate until the color just turns pink, and the end point is maintained for 30s without discoloration. Record elimination the amount of sodium hydroxide standard solution used (ml). At the same time, take 50.00ml blank sample (8.2) instead of the sample to short in the white test, the amount (ml) of the sodium hydroxide standard solution was recorded.

9.1 Calculation of results

The exchangeable acidity (mmol/kg) of the soil sample was calculated according to formula (2).

1001000) ( 1 w

VcVV

NaOH

×××-= empty (2)

In the formula.

AE - exchangeable acidity of soil samples, mmol/kg;

1V -- the volume of the sodium hydroxide standard solution consumed by the direct titration sample, ml;

Empty V -- directly titration blank sample consumption volume of sodium hydroxide standard solution, ml;

NaOHc - concentration of sodium hydroxide standard solution, mol/L;

V -- the volumetric volume of the extract, ml;

sV -- direct titration to measure the volume of the sample, ml;

M-- sample size, g;

W-- Moisture content of the sample, %.

The exchangeable hydrogen (mmol/kg) of the soil sample was calculated according to formula (3).

1001000) ( 02 w

VcVVE

NaOH

In the formula.

HE -- exchangeable hydrogen in soil samples, mmol/kg;

2V -- volume of sodium hydroxide standard solution consumed when titrating the sample after adding sodium fluoride, ml;

0V -- The volume of the sodium hydroxide standard solution consumed by titration of the blank sample after adding sodium fluoride, ml.

The meaning of other parameters is shown in equation (2).

9.2 Results representation

The valid number of the measurement result is up to 3 digits, and the maximum number of digits after the decimal point is 2 digits.