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Table 1 Technical indicators
5 Test method
5.
Some test procedures specified in the test method may lead to dangerous situations, and the operator should take appropriate safety and protective measures
5.
The reagents and water used in this standard refer to analytical reagents and the tertiary water specified in GB/T6682 unless other requirements are indicated
5.
In the colorimetric tube, add laboratory samples, visually inspect under the mouth light or mouth light
5.
5.
Using phenolphthalein as indicator, titrate with sodium hydroxide standard titration solution
5.
5.
5.
5.
Weigh (0.
5.
The mass fraction w 1 of formic acid , the value is expressed in %, calculated according to formula (1):
Where:
V—The value of the volume of the standard titration solution (5.
4.
2.
1) of sodium hydroxide consumed by the sample, in milliliters (mL);
c— The exact value of the concentration of sodium hydroxide standard titration solution.
The unit is moles per liter (mol/L):
M— The value of the molar mass of formic acid , in grams per mole (g/mol) (M=46.
03);
m—The value of the mass of the sample, in grams (g)
.
Take the arithmetic average of the two parallel determination results as the report result, and the absolute difference between the two parallel determination results shall not exceed 0.
2%
.
5.
5 Determination of chromaticity
According to the provisions of GB/T3143
.
5.
6 Dilution test
5.
6.
1 Method summary
The laboratory sample is turbidity with water or sulfur standard bath after being diluted with water
.
5.
6.
2 Reagents
5.
6.
2.
1 Formic acid: the mass fraction is above 88% (mixed with water in any proportion to be slightly turbid, then it can be used)
.
5.
6.
2.
2 Sulfur (S) standard solution: Weigh (0.
01±0.
001)g sulfur, add about 900mL formic acid in a 1000mL Erlenmeyer flask, heat to dissolve, cool to room temperature, transfer to a 1000mL volumetric flask, add formic acid to the mark, Shake well and set aside
.
5.
6.
3 Analysis steps
5.
6.
3.
1 Preparation of standard turbidity solution
Measure (7.
0±0.
05) mL of sulfur (S) standard solution in a 50 mL colorimetric tube, add water to 40 mL, shake well, and place for 1 hour (operate simultaneously with laboratory samples)
.
5.
6.
3.
2 Determination
Measure (10.
0±0.
05) mL of laboratory sample, place it in a 50mL colorimetric tube, add 30mL of water, shake it, and place it for 1h.
It will be turbidity with the same volume of water
.
If it appears turbid, it will be axially turbid compared to the standard turbidity solution
.
5.
6.
4 Presentation of results
If the sample is not turbid compared with water, it means that it is not turbid, and the turbidity of the sample is not greater than the turbidity of the standard turbidity solution to pass the test
.
Related links: Formic acid for industrial use (1)