GB/T 11213.5-2006Sodium hydroxide for chemical fiber use -- Determination of sulphate content (English PDF)

3.1 Principle

In acidic medium (hydrochloric acid), barium ions react with sulfate ions to form insoluble barium sulfate.

When the sulfate ion content is very small, the barium sulfate will be suspended within a certain period of time, making the solution turbid; and the sulfate content can be determined by visual turbidimetry.

3.2 Reagents and materials

The reagents and water used in this method, unless otherwise specified, refer to analytical reagents and third-grade water (free of carbon dioxide) specified in GB/T 6682. The standard solutions, preparations and products required in the test, unless otherwise specified, shall be prepared according to the provisions of GB/T 603.

3.2.1 Hydrochloric acid.

3.2.2 Hydrochloric acid solution: The mass fraction is 20%.

3.2.3 Potassium sulfate ethanol solution: 0.2 g/L. Weigh 0.02g of potassium sulfate and dissolve

it in a solution of 30 mL of ethanol and 70 mL of water.

3.2.4 Barium chloride (BaCl2 - 2H2O) solution: 250 g/L. Weigh 25g of barium chloride

dihydrate, dissolve in water, and dilute to 100mL.

WARNING -- Barium chloride is toxic, irritant and harmful if inhaled or ingested. After contact with skin, rinse immediately with plenty of water.

3.2.5 Sulfate standard solution: 0.1 mg/mL. Weigh 0.100g of anhydrous sodium sulfate that has

been dried at (105~110) °C in advance and has a constant mass; dissolve it in water; transfer it all into a 1000 mL volumetric flask; dilute with water to the mark; and shake well.

3.2.6 Sulfate standard solution: 0.01 mg/mL. Dilute the sulfate standard solution (3.2.5) to 10

times with water; and prepare this solution before use.

3.2.7 Phenolphthalein indicator solution: 10 g/L.

3.3 Apparatus

General laboratory instruments and the following instruments.

3.3.1 25 mL colorimetric tube.

3.3.2 Spectrophotometer.

3.4 Preparation of specimen solution

3.4.1 Solution I: Weigh 50 g of laboratory samples, accurate to 0.01 g; dissolve in 200 mL of water; and then dilute to 250 mL.

3.4.2 Solution II: Take 50 mL of solution I by a pipette; use phenolphthalein (3.2.7) as the indicator solution; neutralize it with hydrochloric acid solution (3.2.1); and dilute to 100 mL with water after cooling.

3.5.6 Use visual turbidimetry to compare the turbidity of the specimen with the turbidity

presented by the specified standard comparison solution.

If the turbidity of the specimen is close to the turbidity of the standard comparison solution and cannot be judged accurately by visual inspection; a spectrophotometer can be used to select a suitable cuvette for comparison at a wavelength of 450 nm.

4.1 Principle

After the sodium hydroxide product is dissolved in water, filter out the insoluble matter; add barium chloride solution; barium ions react with sulfate ions to form insoluble barium sulfate;

and the sulfate content in the product can be calculated by weighing the quality of barium sulfate.

4.2 Reagents and materials

The reagents and water used in this method, unless otherwise is specified, refer to analytical reagents and Grade-3 water (free of carbon dioxide) specified in GB/T 6682. The standard solutions, preparations and products required in the test, unless otherwise is specified, shall be prepared according to the provisions of GB/T 603.

4.2.1 Hydrochloric acid.

4.2.2 Nitric acid.

4.2.3 Barium chloride (BaCl2 - 2H2O) solution: 250 g/L. Weigh 25g of barium chloride

dihydrate; dissolve in water, and dilute to 100mL.

4.2.4 Silver nitrate solution: 5g/100mL. Weigh 5g of silver nitrate; dissolve it in a small amount of water; add 5 mL of nitric acid (4.2.2); and dilute with water to 100mL.

4.2.5 Methyl orange indicator solution: 1g/L.

4.3 Instruments and equipment

General laboratory instruments and the following equipment.

4.3.1 Porcelain crucible: 30mm×30mm.

4.3.2 Oven.

4.3.3 High temperature furnace.

4.4 Analytical procedures