GB/T 8834-1988 Determination of relevant physical and mechanical properties of ropes
Some standard content:
National Standard of the People's Republic of China
Method for determination of soil organic matter
Method for determination of soil organic matter1 Subject content and scope of application
This standard specifies the principle, steps and calculation method of the soil organic matter determination method. This standard is applicable to the determination of soils with a soil organic matter content of less than 15%. 2 Determination principle
UDC 631.423
GB 9834—88
Use a quantitative potassium dichromate-sulfuric acid solution to oxidize the organic carbon in the soil under the condition of electric sand bath heating. The remaining potassium dichromate is titrated with ferrous sulfate standard solution, and silicon dioxide is used as an additive for reagent blank calibration. The amount of organic carbon is calculated based on the difference in the mass of the oxidant before and after oxidation, and then multiplied by the coefficient 1.724 to obtain the soil organic matter content. 3. Apparatus and equipment
3.1 Analytical balance: sensitivity 0.0001g
3.2 Electric sand bath,
3.3 Ground-mouth triangle flask: 150mL,
Ground-mouth simple air condenser: diameter 0.9cm, length 19cm,3.4
3.5 Timer;
Automatic zeroing burette: 10.00, 25.00mL3.7
Small daylight titration table,
Thermometer: 200～300℃,
Copper wire sieve: aperture 0.25mm
Porcelain mortar.
4 Reagents
Unless otherwise specified, all reagents used were analytical grade. 4.1 Potassium dichromate (GB642-77);
4.2 Sulfuric acid (GB 625-77),
4.3 Ferrous sulfate (GB664-77);
4.4 Silver sulfate (HG3--945-76): grind into powder; 4.5 Silicon dioxide (Q/HG22-562-76): powder, 4.6 O-phenanthroline indicator: weigh 1.490g of o-phenanthroline and dissolve it in 100mL of aqueous solution containing 0.700g of ferrous sulfate (4.3). This indicator is easy to deteriorate and should be stored in a sealed brown bottle for future use. 4.70.4mol/L potassium dichromate-sulfuric acid solution: Weigh 39.23g potassium dichromate (4.1), dissolve it in 600~800mL distilled water, dilute it to 1L with water after it is completely dissolved, transfer the solution to a 3L beaker, take another 1L of concentrated sulfuric acid (4.2) with a specific gravity of 1.84, slowly pour it into the potassium dichromate aqueous solution, stirring continuously. To avoid a rapid temperature rise of the solution, pause for a while after adding about 100mL of sulfuric acid, and place the beaker in a basin of cold water to cool it down. When the temperature of the solution drops to a level that is not hot to the touch, add another portion of sulfuric acid until all the solution has been added. 4.8 Potassium dichromate standard solution: Weigh 9.807g of high-grade pure potassium dichromate (4.1) that has been dried at 130℃ for 1.5h, dissolve it in a small amount of water, then transfer it to a 1L volumetric flask and add water to make up the volume. The concentration of this solution is c (1/6K, Cr, O) = 0.2000mol/L. 4.9 Ferrous sulfate standard solution: Weigh 56g of ferrous sulfate (4.3), dissolve it in 600-800mL of water, add 20mL of concentrated sulfuric acid (4.2), stir evenly, add water to make up to 1L (filter if necessary), and store it in a brown bottle. This solution is easily oxidized by air, and the accurate concentration must be calibrated every day when used.
The calibration method of ferrous sulfate standard solution is as follows: take 20mL of potassium dichromate standard solution (4.8), put it into a 150mL conical flask, add 3mL of concentrated sulfuric acid (4.2) and 3-5 drops of o-phenanthroline indicator (4.6), titrate with ferrous sulfate solution, and calculate the concentration of ferrous sulfate standard solution according to the consumption of ferrous sulfate solution.
Wu Zhong: C2--
-Concentration of ferrous sulfate standard solution, mol/L, -Concentration of potassium dichromate standard solution, mol/L, V-Volume of potassium dichromate standard solution taken, mL, V2-Volume of ferrous sulfate solution consumed during titration, mL. 5 Sample selection and preparation
: (1)
5.1 Select a representative soil sample, remove organic residues such as plant roots and leaves with tweezers, and then use a wooden stick to press the soil block to make it pass through a 1mm sieve. After thorough mixing, take out 10-20g of the sample, grind it, and let it pass through a 0.25mm sieve, and put it into a ground-mouth bottle for later use. 5.2 For newly collected paddy soil or soil that has been in waterlogging conditions for a long time, the soil must be dried and crushed, spread into a thin layer, turned over once a day, and exposed to the air for about a week before grinding the sample. 6 Determination steps
6.1 According to the provisions of the organic matter content in Table 1, weigh 0.05-0.5g of the prepared air sample, accurate to 0.0001g. Place it in a 150mL conical flask, add 0.1g of powdered silver sulfate (4.4), and then use an automatic zeroing burette (3.6) to accurately add 10mL of 0.4mol/L potassium dichromate-sulfuric acid solution (4.7) and shake well.
Table 1 Sample weight of different soil organic matter contents Organic matter content, %
2 Below
7～10
10 ~ 15
Sample mass, g
6.2 Place a simple air condenser (3.4) in the conical bottle containing the sample and move it to the electric sand bath (3.2) preheated to 200～230℃ for heating (see Figure 1). When the first drop of condensate falls from the lower end of the simple air condenser, start timing and boil for 5±0.5min. 2G0
Yunzhu Chuanshe
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GB 9834-88
Figure 1 Digestion device
1—Simple air condenser: 2 Erlenmeyer flask; 3 Electric sand bath 6.3 After digestion, remove the flask from the electric sand bath, cool the plate, rinse the inner wall of the condenser and the outer wall of the bottom end with water, and let the washing liquid flow into the original flask. The total volume of the solution in the flask should be controlled at 60-80mL. Add 3-5 drops of o-phenanthroline indicator (4.6) and titrate the remaining potassium dichromate with ferrous sulfate standard solution (4.9). The color change process of the solution is from orange-yellow to blue-green, and then to brown-red, that is, the end point is reached. If the milliliters of ferrous sulfate standard solution used for sample titration are less than 1/3 of the milliliters of ferrous sulfate standard solution consumed for blank calibration, the soil sample should be reduced and re-measured. 6.4 Each batch of sample determination must be simultaneously subjected to 2 to 3 blank calibrations. Take 0.500 g of powdered silicon dioxide (4.5) instead of the sample. The other steps are the same as the sample determination, and the average value is taken. 7 Result calculation
7.1 Soil organic matter content X (calculated by drying + soil), calculated by formula (2): X = (Vo-V) c2 × 0. 003 × 1.724 × 100 (2)
Formula: XWww.bzxZ.net
Soil organic matter content, %,
The volume of ferrous sulfate standard solution consumed during blank titration, mL, the volume of ferrous sulfate standard solution consumed during sample determination, mLC2—Concentration of ferrous sulfate standard solution, mol/L; Molar mass of 1/4 carbon source, g/mol
Coefficient for converting organic carbon to organic matter; Mass of 1 dried sample, g.
The results of the determination are expressed as the arithmetic mean, retaining three significant figures. 7.2 Allowable difference: When the soil organic matter content is less than 1%, the difference between parallel determination results shall not exceed 0.05%; when the content is 1%-4%, it shall not exceed 0.10%; when the content is 4%-7%, it shall not exceed 0.30%; when the content is above 10%, it shall not exceed 0.50%. 261
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Additional notes:
GB9834-88
This standard is under the jurisdiction of the National Technical Committee for Agricultural Analysis and Standardization. This standard was drafted by the Loess Plateau Agricultural Testing Center of Shaanxi Academy of Clothing Sciences. The main drafters of this standard are Li Hongen, Cheng Yan, Liu Huirong and Li Guo. 262
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