GB/T 10666-2019Calcium hypochlorite (English PDF)

5.3 Determination of available chlorine

5.3.1 Principle of the method In an acidic medium, hypochlorite reacts with potassium iodide to precipitate iodine. Use starch as an indicator, titrate by sodium thiosulfate standard titration solution, and the disappearance of blue is the end point. The reaction formula is as follows:

5.3.2 Reagents and solutions Warning - sulfuric acid is highly corrosive.

5.3.2.1 Potassium iodide solution: 100g/L. Take 100g of potassium iodide and dissolve it in 1000mL of water.

5.3.2.2 Sulfuric acid solution: 3+100. Take 30mL of sulfuric acid; slowly pour it into 1000mL of water; cool off; and shake well.

5.3.2.3 Sodium thiosulfate standard titration solution: c(Na2S2O3) = 0.1mol/L.

5.3.2.4 Soluble starch solution: 10g/L. The use period is two weeks.

5.3.3 Apparatus

5.3.3.1 General laboratory equipment.

5.3.3.2 Burette: 50mL, Grade-A, scale value of 0.1mL.

5.3.3.3 One-mark pipette: 25mL, Grade-A. The water and toluene in the sample azeotrope when heated; use the nature that the toluene and water are immiscible to separate the water.

5.4.1.2 Reagents Toluene. Dehydrate before use.

5.4.1.3 Apparatus 5.4.1.3.1 General laboratory equipment. 5.4.1.3.2 Moisture measuring device: moisture measuring device and glycerin bath or adjustable temperature electric heating jacket (accuracy of ± 1°C, see Figure 1). 5.4.1.3.3 Moisture measuring device: 500mL round bottom flask and measuring tube. Among them, the volume of the measuring tube is 10mL (the scale value of 0mL~0.3mL is 0.03mL).

5.4.1.4 Test procedures Take about 100g of the sample (accurate to 0.01g); place it in a dry 500mL flask (b in Figure 1); and add 200mL of toluene (limited to the submerged sample). Install the instrument according to Figure 1; the system is airtight; and turn on the cooling water of the condenser (d in Figure 1). Slowly heat in a glycerin bath or adjustable temperature electric heating jacket (a in Figure 1); keep the temperature at 135°C ~140°C; perform reflux; and control the reflux speed to 2 drops/s~4 drops/s. When the water layer of the solution in the metering tube (c in Figure 1) no longer increases, stop heating and cooling. After the interface between toluene and water in the measuring tube (c in Figure 1) is clear, record the volume of water V2. Refer to Appendix A for the density of water at different temperatures. more than 0.2%. Take the arithmetic mean of the parallel determination results as the measurement result.

5.4.2 Drying method

5.4.2.1 Principle of the method Lay the quantitative sample in a weighing bottle for the specified size and heat it at the specified temperature. Then weigh it.

5.4.2.2 Apparatus 5.4.2.2.1 General laboratory equipment. 5.4.2.2.2 Infrared quick dryer or electric heating blast drying oven, may be controlled at 105°C ~115°C. 5.4.2.2.3 Weighing bottle: phi60mm×30mm.

5.4.2.3 Test procedures Use a weighing bottle to weigh about 5g of sample (accurate to 0.01g); place it in the middle of the infrared lamp of the rapid dryer or in a drying oven; and dry it at 105°C ~115°C for 30min. Cool to room temperature and weigh it.

5.4.2.4 Test data processing The moisture is expressed by the mass fraction, w3, of water (H2O), and calculated according to Formula (3): Where: m3 - the value of mass of the sample, in g; m4 - the value of the mass of the dried sample, in g.

5.4.2.5 Tolerance The absolute value of the difference between the parallel determination results is no more than 0.2%. Take the arithmetic mean of the parallel determination results as the measurement result.

5.5 Stability inspection - determination of the available chlorine loss

5.5.1 Principle of the method Type inspection shall also be carried out in one of the following situations:

--- The key production process has changed;

--- The main raw materials have changed;

--- Resume production after stopping production;

--- After major production equipment are adjusted significantly.

6.2.1 Judgment rules

6.2.1.1 Product quality indicators shall be judged according to the "Round-off Comparison Method " specified in GB/T 8170.

6.2.1.2 The product shall be inspected by the quality inspection department of the manufacturer in accordance with the provisions of this Standard; and the quality of the product shall be judged based on the inspection results and standard requirements; and a quality certificate shall be provided.

6.2.1.3 When the product leaves the factory, each batch of products shall be accompanied by a quality certificate, which includes: the name of the company, product name, model, batch number or production date, batch size, product quality certification that conforms to this Standard, the implementation standard number, and the company's quality control seal.

6.2.2 Reinspection rules If an indicator of the inspection result does not meet the requirements of this Standard, double sampling units from the same batch of products shall be taken for reinspection. Even if there is an indicator that does not meet the requirements of this standard in the reinspection results, this batch of products is judged to be unqualified.