HG/T 2221-1991 Determination of free acid content in triple superphosphate Volumetric method HG/T2221-1991 Standard download decompression password: www.bzxz.net

Chemical Industry Standard of the People's Republic of China
HG 2221—91
Determination of free acid content in superphosphate by volumetric method
Published on November 15, 1991bzxZ.net
Ministry of Chemical Industry of the People's Republic of China
Implementation on July 1, 1992
W Chemical Industry Standard of the People's Republic of China
Determination of free acid content in superphosphate by volumetric method
1 Subject content and scope of application
This standard specifies the determination of free acid content in superphosphate by volumetric method. This standard is applicable to the determination of free acid content (measured in P205) in superphosphate. 2 Reference standards
GB601 Preparation of standard solutions for chemical reagent titration analysis (volume analysis) GB603 Preparation of preparations and products used in chemical reagent test methods 3 Principle
HG2221-91
The free acid in the superphosphate extract is titrated with sodium hydroxide solution. According to the titration end point indicated by the change of the electrode potential of the acidometer with the pH value of the solution, the free acid content is obtained from the amount of sodium hydroxide consumed. 4 Reagents and solutions
In the analysis, unless otherwise specified, only analytical reagents, distilled water or water of equivalent purity are used. 4.1 Sodium hydroxide (GB629) standard titration solution: c(NaOH)=0.1mol/L, prepared and calibrated according to GB601; 4.2 Distilled water without carbon dioxide: prepared according to GB603. 5 Instruments
Usually used laboratory instruments and
5.1 Oscillator: about 35~40r/min;
5.2 Microburette: 5 or 10mL;
5.3 Acidometer: equipped with electromagnetic stirrer, calomel electrode and glass electrode. 6 Operation steps
Weigh about 5g of sample (accurate to 0.001g), transfer to a 500mL volumetric flask, add about 200mL of carbon dioxide-free distilled water (4.2), cover the bottle stopper, oscillate on an oscillator for 15min, dilute to scale with carbon dioxide-free distilled water, mix, filter with dry filter paper and funnel, and discard the initial part of the filtrate. Pipette 50.0mL of the filtrate into a 250mL beaker and dilute to 150mL with carbon dioxide-free distilled water. Place the beaker on an electromagnetic stirrer, immerse the calomel electrode and glass electrode in the solution, add a stirrer, and titrate with sodium hydroxide standard titration solution (4.1) under stirring until the pH meter reading is 4.5.
7 Expression of results
7.1 The free acid content (in terms of P2Os) expressed as a mass percentage, X, is calculated according to the following formula: Approved by the Ministry of Chemical Industry of the People's Republic of China on November 15, 1991 and implemented on July 1, 1992
WHG2221-91
_c·VX0.071,
c·VX71
Wherein: c—concentration of standard sodium hydroxide titration solution, mol/L; V——volume of standard sodium hydroxide titration solution used for titration, mL; mo——mass of the sample, g
0.071——mass of phosphorus pentoxide in grams equivalent to 1.00mL standard sodium hydroxide titration solution [c(Na0H)=1.000mol/L].
The result should be expressed to two decimal places.
7.2 Allowable difference
7.2.1 The arithmetic mean of the parallel determination results shall be taken as the determination result. 7.2.2 The absolute difference of the parallel determination results shall not exceed 0.15%. 7.2.3 The absolute difference of the determination results of different laboratories shall not exceed 0.30%. Additional remarks:
This standard is proposed by the Science and Technology Department of the Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of the Shanghai Research Institute of Chemical Industry of the Ministry of Chemical Industry. This standard was drafted by the Shanghai Research Institute of Chemical Industry of the Ministry of Chemical Industry and Yunnan Phosphate Fertilizer Plant. The main drafters of this standard are Yin Yongkang, Chen Xuezhi, Xie Ruiming and Hua Xiaoxian. 2
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