HJ 649-2013Soil. Determination of exchangeable acidity by potassium chloride extraction. Titration method (English PDF)

5.1 Freshly boiled distilled water

The distilled water is boiled and evaporated in a beaker (evaporation amount 10%), sealed and sealed, and sealed for use. It should be used now.

5.2 Hydrochloric acid solution. c (HCl) = 1.0mol/L

83 ml of concentrated hydrochloric acid (rho = 1.19 g/ml) was diluted with water to 1 L.

5.3 Potassium chloride solution. c (KCl) = 1.0mol/L

Weigh 74.55g of potassium chloride, dissolve it in water, transfer it to a 1L volumetric flask, dilute to the mark with water, and mix.

5.4 Potassium hydrogen phthalate standard solution. c (C8H5KO4) = 0.01mol/L

Weigh 0.5106g of potassium hydrogen phthalate, which has been dried by 105°C~110°C, dissolved in appropriate amount of water and transferred to 250ml.

In the volumetric flask, add water (5.1) to the mark and mix.

5.5 Sodium hydroxide standard solution. c (NaOH) = 0.01 mol/L

Weigh 0.4g of sodium hydroxide in an appropriate amount of water, and after the solution is cooled, transfer it to a 1L volumetric flask, dilute to the mark, mix and store.

In polyethylene plastic containers. Calibration was carried out using potassium hydrogen phthalate standard solution (5.4).

Calibration method. Pipette 25.00ml of hydrogen phthalate standard solution (5.4) into a beaker, put a stirrer in the beaker, insert when entering the electrode, titrate with sodium hydroxide solution (5.5). Until the pH reaches 7.80 ± 0.08, it is stable for 30 seconds. At the same time, do a blank test.

The measurement was performed three times in succession, and the average value of the calibration results was taken three times.

The sodium hydroxide standard solution concentration is calculated according to formula (1).

1 VV

Vcc -

Where. c1 - sodium hydroxide standard solution concentration, mol/L;

C2 -- concentration of potassium hydrogen phthalate solution, mol/L;

V0-- blank test consumes the volume of sodium hydroxide solution, ml;

V1-- the volume of the sodium hydroxide solution consumed by the calibration, ml;

V2-- volume of potassium hydrogen phthalate solution, ml.

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

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

Transfer to a 1000ml volumetric flask, dilute to the mark with water, and mix.

5.7 Quartz sand. 30-60 mesh, heated at 300 ° C for 2 h before use.

7.1 Sample collection and preservation

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

7.2 Air drying and preparation of samples

Air dried samples were prepared as required by HJ/T 166. Air dry the sample through a 2 mm pore size sieve, mix well and mix well.

Take two parts of the method, one for the stock and one for the other.

7.3 Preparation of samples

Weigh 5.00g of air-dried soil sample, place it in the funnel with the filter paper, and rinse it with a small amount of potassium chloride solution (5.3).

The addition of the potassium chloride solution must be carried out after the filtrate in the funnel is filtered. The filtrate is taken up in a 250mL volumetric flask.

Potassium chloride solution (5.3) is made up to volume.

7.4 Preparation of blank samples

The quartz sample was used instead of the soil sample, and a blank sample extract was prepared in the same manner as the sample preparation.

7.5 Determination of moisture content

The moisture content was measured in accordance with HJ 613.

8.1 Determination of exchangeable acidity

8.1.1 Determination

Pipette 100ml sample extract into the beaker and boil for 5min to volatilize the carbon dioxide that may be present in the solution and cool to at room temperature, using a pH meter as an indicator, titrate with a sodium hydroxide solution to a pH of 7.80 ± 0.08, record the volume of sodium hydroxide solution consumed.

The number of milliliters of V1.

8.1.2 Blank test

The 100 ml blank sample extract (7.4) was simultaneously titrated by the method of 8.1.1, and the amount of the consumption of the sodium hydroxide solution volume V was recorded.

8.2 Determination of exchangeable hydrogen

8.2.1 Determination

Pipette 100ml sample extract into the beaker, add 2.5ml sodium fluoride solution (5.6), boil for 5min, and drive out carbon dioxide.

Cool to room temperature, use pH as an indicator, titrate with sodium hydroxide solution to pH 7.80 ± 0.08, record consumption of sodium hydroxide solution the number of milliliters of volume V2.

8.2.2 Blank test

The 100 ml blank sample extract (7.4) was simultaneously titrated by the method of 8.2.1, and the number of milliliters of the volume of the spent sodium hydroxide solution V0 was recorded.

9.1 Calculation of results

The exchangeable acidity in the soil sample is calculated according to formula (2).

1001000) ( 1 w

VcVV

NaOH

×××-= empty (2)

Where. EA-dryable soil exchangeable acidity, mmol/kg;

V1 - direct titration of soil sample consumption sodium hydroxide volume, ml;

V empty - blank sample consumed sodium hydroxide volume, ml;

CNaOH-sodium hydroxide solution concentration, mol/L;

V-extraction final volume, ml;

VS-drop timing removed extract volume, ml;

M-air dry soil quality, g;

W-air dry soil moisture content, mass fraction.

Exchangeable hydrogen and exchangeable aluminum in soil samples are calculated according to equations (3) and (4).

1001000) ( 02 w

VcVV

NaOH

-= HAAl EEE (4)

Where. EH - exchangeable acid hydrogen of soil samples, mmol/kg;

EAl--exchangeable aluminum of soil samples, mmol/kg;

V2--the volume of sodium hydroxide consumed by the soil sample after adding sodium fluoride, ml;

V0--the blank sample consumes sodium hydroxide volume after adding sodium fluoride, ml;

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

9.2 Results representation

When the measurement result is less than 1.0 mmol/kg, it is retained to two decimal places; when it is greater than or equal to 1.0 mmol/kg, three places are retained.

effective number.