GOST 20996.2-82

• gost-209962-82.pdf (225.69 KiB)
  ГОСТ 20996.2-82

GOST 20996.2−82 Selenium technical. Methods for the determination of sulphur (Change No. 1)

GOST 20996.2−82*

Group B59

INTERSTATE STANDARD

SELENIUM TECHNICAL

Methods of determining sulphur

Selenium. Methods of sulphur determination

AXTU 1709

Date of introduction 1983−07−01

Resolution of the USSR State Committee on standards of 22 June 1982, N 2481 date of introduction is established 01.07.83

Limitation of actions taken by Protocol No. 7−95 Interstate Council for standardization, Metrology and certification (ICS 11−95)

REPLACE GOST 20996.2−75

* PUBLISHING (may 2000) with amendment No. 1, approved in December 1987 (IUS 3−88)


This standard specifies photojournalistically and titrimetric methods for the determination of sulfur (with sulfur mass fraction of 0,002−0,6%).

(Changed edition, Rev. N 1).

1. GENERAL REQUIREMENTS

1.1. General requirements for methods of analysis GOST 20996.0−82.

2. PHOTOJOURNALISTICALLY METHOD FOR THE DETERMINATION OF SULFUR

2.1. The essence of the method

The method is based on the formation of a suspension of barium sulfate in the interaction of barium ions with sulfate ions and measuring the intensity of the turbidity of the solution. As a stabilizer of the slurry using glycerol.

2.2. Apparatus, reagents and solutions

Photoelectrocolorimeter.

Barium chloride according to GOST 4108−72, a solution of 100 g/DM.

Glycerin according to GOST 6259−75, a solution of 100 g/DM.

Potassium sulfate according to GOST 4145−74, recrystallized.

Standard solutions of potassium sulfate.

Solution a: a sample of salt mass 0,0544 g dissolved in 50−60 cmof water, transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof solution A contains 0.1 mg of sulfur.

Solution B: aliquot part 10 cmof the solution And transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof a solution contains 0.01 mg of sulfur. The solution is stable for 2 days.

Nitric acid GOST 4461−77.

Hydrochloric acid by the GOST 3118−77 and diluted 1:1.

Sodium carbonate according to GOST 83−79, a solution of 100 g/DM.

(Changed edition, Rev. N

1).

2.3. Analysis

2.3.1. A portion of selenium with a mass of 0.5−4 grams (depending on the mass fraction of sulfur) was placed in a beaker with a capacity of 100−200 cm, pour 1 cmof sodium carbonate solution and 20−25 cmof nitric acid. Beaker cover watch glass (glass plate) and allowed to stand without heating until the cessation of the violent reaction for 40−50 min. Then boil to remove oxides of nitrogen, remove glass (plate) is washed over the glass and the solution cautiously evaporated to dryness.

To the dry residue add 1−2 cmof hydrochloric acid of 10−15 cmof water and heat the solution to boiling. The resulting solution is kept for 1 h.

The solution is placed in a volumetric flask with a capacity of 50 cm, is diluted to the mark with water and mix. If there is precipitate, the solution was filtered through a filter medium density, the cone which is enclosed a little filtrowanie mass.

Aliquot part of the solution is 2−10 cm(or the entire amount depending on the mass fraction of sulfur. In this case, the solution is evaporated to a volume of 10−15 cmand after cooling is placed in a volumetric flask with a capacity of 25 cm) is placed in a volumetric flask with a capacity of 25 cm, add 0.5−1.0 cmof hydrochloric acid (1:1), 10 cmof a solution of glycerine and mix. Then pour 3−3. 5 cmof barium chloride, made up to the mark with water and mix again. After 40 min the solution is mixed again and measured the optical density of the solution on a photoelectrocolorimeter, using a filter with maximum transmittance at a wavelength of 326 nm and cuvette thickness of the absorbing layer is 50 mm.

As a solution comparison, use water.

The mass of sulphur in the sample solution found by calibration g

Rafik.

2.3.2. Construction of calibration curve

Eight volumetric flasks with a capacity of 25 cmis placed 0; 0,5; 1,0; 2,0; 3,0; 4,0; 5,0; 6,0 cmstandard solution B, which corresponds to 0; 0,005; 0,01; 0,02; 0,03; 0,04; 0,05; 0,06 mg of sulfur. Add to each flask in 0.5−1 cmof hydrochloric acid (1:1), water up to 10 cm, 10 cmsolution of glycerin and mix. Then pour 3−3. 5 cmof barium chloride and further analysis is carried out as specified in clause 2.3.1.

2.3.1, 2.3.2. (Changed edition, Rev. N 1).

2.4. Processing of the results

2.4.1. Mass fraction of sulfur in percent is calculated by the formula

,

where is the mass of sulfur in the solution of the sample, was found in the calibration graphics mg;

 — the mass of sulfur in solution in the reference experiment, was found in the calibration graphics mg;

 — volume of test solution in a volumetric flask, cm;

 — the weight of the portion of selenium, g;

 — volume aliquote part of the solution, cm

.

2.4.2. Discrepancies in the results of two parallel measurements and the two tests should not exceed the values given in the table.

2.4.1, 2.4.2. (Changed edition, Rev. N 1).

3. TITRIMETRIC METHOD FOR THE DETERMINATION OF SULFUR

3.1.The essence of the method

The method is based on deposition of sulphur in the form of sulfate ions with a solution of barium chloride, dissolving the resulting precipitate in ammonia solution of Trilon B and titration of the excess magnesium chloride in the presence eriochrome black T as indicator.

3.2. Reagents and solutions

Nitric acid GOST 4461−77.

Hydrochloric acid by the GOST 3118−77.

Barium chloride according to GOST 4108−72, a solution of 100 g/DM.

Salt is the disodium Ethylenediamine-N, N, N', N'-tetraoxane acid, 2-water (Trilon B) according to GOST 10652−73; 0.025 M solution: 9,305 g of salt dissolved in 500−600 cmof hot water. It is then filtered through a loose filter, cooled and transferred into a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix.

The installation of the titer of the solution Trilon B: a sample of zinc metal with a mass of 0.04 g was placed in a conical flask with a capacity of 250−300 cm, add 5−6 cmof hydrochloric acid, evaporated to wet, pour 100−120 cmof water and heated until boiling of the solution.

Cool, add 15−20 cmbuffer solution on the tip of the spatula eriochrome black T and titrate with a solution of Trilon B to switch the color of the solution in the purple-red color.

The titer is calculated by the formula

,

where is the mass of zinc g;

 — volume of solution Trilon B, spent on titration, sm.

Zinc GOST 3640−94.

Ammonia water according to GOST 3760−79.

Ammonium chloride according to GOST 3773−72.

Buffer solution with a pH of 9−9,5: a suspension of ammonium chloride with a mass of 54 g was dissolved in 100−150 cmof water, poured 350 cmof ammonia, add water to 1000 cmand mixed.

Magnesium chloride 6-water according to GOST 4209−77, 0.025 M solution.

Sodium chloride according to GOST 4233−77.

Eriochrome black T indicator: mix with sodium chloride in a ratio of 1:100.

Methyl red, solution 1 g/lin alcohol.

The technical rectified ethyl alcohol GOST 18300−87.

(Changed edition, Rev. N 1).

3.3. Analysis

3.3.1. Selena weighed weighing 1−3 g (depending on the mass fraction of sulfur) was placed in a beaker with a capacity of 250−300 cm, 10−20 cm pour thenitric acid, cover with watch glass (glass plate) and allowed to stand without heating until the cessation of the violent reaction of allocation of oxides of nitrogen. Then boil to remove oxides of nitrogen, remove glass (plate) is washed over the glass and the resulting solution was evaporated to dryness.

To the dry residue add 3−5 cmof nitric acid, 80−100 cmof water and heated to boiling. Add 15−20 cmof a solution of barium chloride, boil for 8−10 min and left for coagulation of sludge from 1 to 6 hours (depending on the mass fraction of sulfur).

The precipitate is filtered through a dense filter and washed 5−6 times with water. Then wash off the residue in the flask, which led the deposition, the flow of 80−100 cmof water, add 10−25 cm(depending on the amount of sulfur in the sample solution) of the solution Trilon B and 5−7 cmof ammonia. Heated to dissolve the precipitate. After cooling, add 20−25 cmbuffer solution on the tip of the spatula eriochrome black T and mix. Added dropwise methyl red until the color of the solution from blue to green. Then titrated magnesium chloride to change the color of the solution violet-red

th.

3.4. Processing of the results

3.4.1. Mass fraction of sulfur in percent is calculated by the formula

,

where is the added volume of solution Trilon B, cm;

 — the volume of magnesium chloride solution, used for titration of excess Trilon B, cm;

the ratio of molar solutions of Trilon B and magnesium chloride: take 10−25 cmof the solution Trilon B and placed in a conical flask with a capacity of 250−300 cm, dilute with water to 100 cm, add 20−25 cmbuffer solution on the tip of a spatula eriochrome black T. Then the solution was added dropwise methyl red until the color of the solution from blue to green and magnesium chloride titrated until the color changes to purple-red.

The ratio is calculated by the formula

,

the titer of the solution Trilon B sulphur, g/cm;

 — weight of selenium,

3.4.2. Allowable absolute differences of the extreme results of the analysis shall not exceed the values given in the table.