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6 Test method
Unless otherwise specified, only reagents confirmed to be analytically pure and tertiary water conforming to the provisions of GB/T6682-2008 are used in the analysis.
6.
6.
Acid-base titration
6.
6.
6.
6.
Weigh 1g sample, accurate to 0.
6.
The mass fraction w 1 of oxalic acid ( calculated as H 2 C 2 O 4 ·2H 2 O) , the value is expressed in %, calculated according to formula (1):
Where:
V 1 —The value of the volume of the standard titration solution (6.
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 mass of the sample, in grams (g);
M— The value of the molar mass of oxalic acid (1/2H 2 C 2 O 4 ·2H 2 O), in grams per mole (g/mol) [M=63.
Take the arithmetic mean of the two parallel determination results as the determination result
6.
6.
Sodium carbonate is added to the sample to make the sulfate in oxalic acid produce sulfate , heating decomposes oxalic acid and oxalate to dissolve the residue, and barium chloride solution is added to produce barium sulfate, which is compared with the standard turbidity solution of sulfate
.
6.
2.
2 Reagents
6.
2.
2.
1 Hydrogen peroxide ;
6.
2.
2.
2 Anhydrous sodium sulfate ;
6.
2.
2.
3 Hydrochloric acid solution: 1+1;
6.
2.
2.
4 Sodium carbonate solution; 50g/L;
6.
2.
2.
5 Sulfate standard solution: 0.
1mg/mL;
6.
2.
2.
6 Barium chloride ethanol glycerol solution: Take 10 parts of 100g/L barium chloride solution and 1 part (1+2) ethanol glycerol solution, mix and shake well
.
6.
2.
3 Apparatus
6.
2.
3.
1 Electric furnace: adjustable temperature;
6.
2.
3.
2 High temperature furnace
.
6.
2.
4 Analysis steps
6.
2.
4.
1 Preparation of sample solution
Weigh 1g sample, accurate to 0.
01g, place it in a 50mL volumetric flask, add a small amount of water to dissolve, dilute to the mark with water, and shake well
.
Take 5.
0 mL of this solution in a porcelain crucible (or evaporating dish), add 0.
5 mL of sodium carbonate solution, evaporate to dryness on a water bath, then heat on an electric furnace to decompose oxalic acid, and then burn in a high-temperature furnace at 850°C for 5 min.
After cooling Add 10 mL of water and 2 mL of hydrogen peroxide to the residue , boil for a short time, add 1 mL of hydrochloric acid solution, and then evaporate to dryness on a water bath
.
Add a small amount of water and 0.
5 mL of hydrochloric acid solution to dissolve the residue
.
Wash with water into a 50mL colorimetric tube, add water to 25mL (if the solution is turbid, filter), as the sample solution
.
6.
2.
4.
2 Preparation of standard turbidity solution of sulfate radical
Add (0, 0.
5, 0.
7, 1.
0, 1.
5, 2.
0, 3.
0, 4.
0,.
.
.
) mL sulfate standard solution to each evaporating dish, then add 0.
5 mL sodium carbonate solution, 10 mL water, 2 mL hydrogen peroxide and 1mL of hydrochloric acid solution, evaporate to dryness on a water bath, add a small amount of water and 0.
5mL of hydrochloric acid solution to each residue, dissolve the residue, wash with appropriate amount of water into a 50mL colorimetric tube, add water to 25mL, as a standard turbidity solution of sulfate radical
.
6.
2.
4.
3 Determination
Add 10 mL of barium chloride ethanol glycerol solution to the sample solution and the sulfate standard turbidity solution, shake well, and place for 30 minutes.
Under natural light or fluorescent light, carry out the sample solution and the sulfate standard turbidity solution axially Comparison
.
Take the turbidity closest to the standard turbidity solution of sulfate as the test result
.
If the turbidity of the sample solution is between two standard turbidity sulfate solutions, take the turbidity of the standard turbidity sulfate solution with high turbidity as the test result
.
6.
2.
5 Result calculation
The mass fraction of sulfate ( calculated as SO 4 ) w 2 : the value is expressed in %, calculated according to formula (2):
Where:
V2—The value of the volume of the sulfate standard solution in the standard turbidity solution of sulfuric acid, in milliliters (mL);
m—The value of the mass of the sample, in grams (g):
c—The value of the concentration of the sulfate standard solution, in milligrams per milliliter (mg/mL) [c=0.
1]
.
Take the arithmetic mean of the two parallel determination results as the determination result
.
The absolute difference between the two parallel determination results is not more than 0.
005%
.