HG 5-1342-1980 Determination of free phenol content in phenolic resin HG5-1342-1980 Standard download decompression password: www.bzxz.net

Standard of the Ministry of Chemical Industry of the People's Republic of China Determination of free phenol content in phenolic resin 1 Key points of the method
HG5-1342-80
1.1 Free phenol in the resin is easy to volatilize when heated. Taking advantage of this property, the free phenol is distilled out by steam distillation. Before distillation, the resin is dissolved in ethanol, and the separated phenol is determined by the bromine method. 1.2 In an acidic solution, phenol is brominated with an excess of KBr and KBrO3 mixed solution to generate tribromophenol. 5KBr+KBrO,+6HCl-→3Br2+6KCI+3H,OOH
1.3 Excess bromine precipitates an equivalent amount of iodine when potassium iodide is added. OH
KI+HCI-HI+KCI
Br2+2HI-Iz+2HBr
1.4 The precipitated iodine is titrated with sodium thiosulfate standard solution, using starch solution as an indicator. I,+2Na,S,O,→Na2SO.+2Nal
1.5 At the same time, use potassium bromide-potassium bromate solution for a blank test. 2 Required reagents
2.1 Potassium bromide-potassium bromate standard solution: 0.1N, weigh 10 grams of potassium bromide and 28 grams of potassium bromate, dissolve them in a 1000 ml volumetric flask with distilled water, dilute to the scale, and then calibrate. 2.2 Concentrated hydrochloric acid: specific gravity 1.19, chemically pure. 2.3 Potassium iodide: solid, chemically pure.
2.4 Sodium thiosulfate standard solution: 0.1N. 2.5 Starch solution: 1%, weigh 1 gram of soluble starch, mix with a small amount of water, and slowly pour into 100 ml of boiling water while stirring.
3 Required instruments
3.1 Weighing bottle: 25 ml, 1 piece.
3.2 Volumetric flask: 250 ml, 1 piece; 1000 ml, 1 piece. 3.3 Iodine volumetric flask: 50 ml, 1 piece.
3.4 ​​Pipette: 10 ml, 1 piece.
3.5 Graduated cylinder: 50 ml, 1 piece.
3.6 Burette: 50 ml, 2 pieces.
4 Determination method
4.1 Weigh 1-2g of phenolic resin, accurate to 0.0002g, put it into a 250ml round-bottom flask, add 20ml of ethanol, add 100ml of distilled water after shaking to dissolve, and add more than half a bottle of distilled water into the water vapor generating bottle. The determination device is shown in the figure below. The generated steam evaporates phenol, and the distillation rate is suitable to be 1ml per minute. The distillate was collected in a 1000 ml volumetric flask receiver until the distillate did not become turbid when bromine water was added. Dilute to the mark on the flask. Phenol determination device 1—steam generating bottle 2—round bottom flask, 3—condenser, 4—receiver 4.2 Absorb 25 Transfer the distilled solution from 100 ml to a 250 ml ground-mouth conical flask, accurately add 20 ml of 0.1N potassium bromide-potassium bromate standard solution and 5 ml of hydrochloric acid with a specific gravity of 1.19, plug the bottle, shake it and place it in a dark place for 15 minutes, then quickly add 2 grams of potassium iodide, cover the bottle and carefully mix the mixture, place it in a dark place for 10 minutes, calibrate it with 0.1N sodium thiosulfate standard solution, and when the solution turns light yellow, add about 1 ml of starch solution and continue titrating until the blue disappears, which is the end point. Read the volume V2 of the used 0.1N sodium thiosulfate solution. www.bzxz.net
4.3 Accurately measure 20 ml of 0.1N potassium bromide-potassium bromate standard solution at the same time, perform a blank test according to the same method, and read the standard volume V1 of 0.1N sodium thiosulfate solution used for titration. 4.4 Calculate
Free phenol content (%)
Where: Vi-
(V-V2) N
62.72 (V,-V,)N
Volume of standard solution used for blank titration, ml; Volume of standard solution used for sample titration, ml; Equivalent concentration of sodium thiosulfate standard solution: Sample weight, g;
Milligram equivalent of phenol.
Additional remarks:
This standard was proposed and managed by the Chemical Machinery Research Institute of the Ministry of Chemical Industry. This standard was drafted by Shenyang Chemical Machinery Factory. The main drafter of this standard is Zhen Tongxin.
Standard exchange mesh belt m, b
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