GB/T 3050-2000 General method for determination of chloride content in inorganic chemical products - Potentiometric titration
Some standard content:
GB/T3050-2000
This standard adopts ISO6227:1982 "General method for determination of chloride content in chemical products - potentiometric titration" in a non-equivalent manner, and is a revision of GB/T3050-1982 "General method for determination of chloride content in inorganic chemical products - potentiometric titration". The main differences between this standard and ISO6227:1982 are as follows: The chloride ion content in the solution taken for titration is 0.01mg~~75mg, while ISO6227:1982 is 0.05mg~75mg. This is because this standard reduces the titration volume and thus expands the measurement range; - ethanol is used instead of acetone, which is less toxic, economical and easy to obtain, and has equivalent effects; the indicator electrode uses Ag-Ag2S electrode, and the appendix of the corresponding preparation method is added; - 0.001mol/L silver nitrate standard titration solution and the corresponding potassium fluoride calibration solution are added; - the method for eliminating interfering substances is added.
The main differences between this standard and the original national standard are as follows: the expression of the scope of application has been modified;
The exclusion and treatment of interfering substances in ISO6227:1982 have been added. Appendix A, Appendix B and Appendix C of this standard are standard appendices; Appendix D and Appendix E are prompt appendices. This standard replaces GB/T3050-1982 from the date of implementation. This standard was proposed by the former Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of the Inorganic Chemical Branch of the National Technical Committee for Chemical Standardization. The drafting units of this standard are Qingdao Entry-Exit Inspection and Quarantine Bureau and Tianjin Chemical Research and Design Institute. The main drafters of this standard are Fan Guoqiang, Zhang Ping, Mao Xubin, Liu Liang and Cui He. This standard was first issued in April 1982.
This standard is entrusted to the Inorganic Chemical Branch of the National Technical Committee for Chemical Standardization for interpretation. 17
1 Scope
National Standard of the People's Republic of China
General method for determination of chloride content in inorganic chemical products-Potentiometric method
Inorganic chemical products for industrial useGeneral method for determination of chloride content-Potentiometric methodGB/T 3050-2000
neq Iso 6227:1982
Replaces GB/T3050-1982
This standard specifies the general method for determination of chloride content in inorganic chemical products-potentiometric titration. This standard is applicable to test solutions with chloride ion content of 1 mg/L to 1 500 mg/L. The chloride content (as Cl) in the test solution taken for titration is 0.01 mg~~75 mg. When the concentration of the silver nitrate standard solution used is less than 0.02 mol/L, the titration should be carried out in ethanol-water solution.
K+, Na+, Ca2+, Mg2+, Mn2+, Pb2+, Cu2+, Ba2+, NO:, SOr-, BO-, CO-, PO- do not interfere with the determination. Ions that form insoluble precipitates or complexes with Ag+ and MnO, etc., interfere with the determination. For their limits and exclusion methods, please refer to Appendix D (suggestive Appendix) and Appendix E (suggestive Appendix).
2 Cited Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard was published, the versions shown were valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T603-1988 Preparation of preparations and products used in test methods for chemical reagents GB/T6682-1992 Specifications and test methods for water used in analytical laboratories (neqISO3696:1987) 3 Method summary
In acidic water or ethanol-water solution, use a silver (silver-silver sulfide) electrode as the measuring electrode [see Appendix B (Standard Appendix) for the selection of electrode types], a calomel electrode as the reference electrode, and titrate with a silver nitrate standard titration solution. Determine the reaction endpoint by means of a potential gradient. 4 Reagents and materials
The reagents and water used in this standard, unless otherwise specified, refer to analytically pure reagents and grade 3 water specified in GB/T6682. The preparations and products used in this standard, unless otherwise specified, are prepared in accordance with the provisions of GB/T603. 4.1 95% ethanol.
4.2 Saturated potassium nitrate solution.
4.3 Sodium hydroxide solution: 200g/L.
4.4 Nitric acid solution: 2+3.
4.5 Potassium chloride standard solution: c(KCl)=0.1mol/L. Accurately weigh 3.728g of standard potassium chloride (weighed to 0.001g) that has been pre-dried at 130℃ to constant weight, place it in a beaker, add water to dissolve it, transfer it to a 500mL volumetric flask, dilute it to the scale with water, and shake it well. 0.01mol/L, 0.005mol/L, 0.001mol/L or other concentrations of potassium chloride standard titration solution: accurately dilute 0.1mol/L potassium chloride State Administration of Quality and Technical Supervision approved on July 31, 2000 18
2001~03-01 implementation
standard titration solution to the required multiple. GB/T3050—2000
4.6 Silver nitrate standard titration solution: c(AgNO) 0.1mol/L. 0.01mol/L, 0.005mol/L, 0.001mol/L or other concentrations of silver nitrate standard titration solution: dilute 0.1mol/L silver nitrate standard titration solution accurately to the required multiple. Calibration: bzxZ.net
Use a pipette to take 5mL or 10mL of the selected concentration of potassium fluoride standard solution and place it in a 50mL beaker. Add 1 drop of bromophenol blue indicator solution, 1 to 2 drops of nitric acid solution, so that the solution is just yellow, then add 15mL or 30mL of ethanol and put in an electromagnetic stirrer. Place the beaker on an electromagnetic stirrer, start the stirrer, insert the measuring electrode and the reference electrode into the solution, connect the potentiometer wiring, adjust the potentiometer zero point, and record the starting potential value.
Use the silver nitrate standard titration solution corresponding to the concentration of the potassium chloride standard solution for titration. First add 4mL or 9mL, and then add a certain volume of silver nitrate standard titration solution with a concentration of 0.01mol/L, 0.005mol/L, and 0.001mol/L successively. The amount added each time is 0.05mL, 0.1mL and 0.2mL respectively (it can be increased appropriately if necessary). Record the total volume and the corresponding potential value E after adding the silver nitrate standard titration solution each time, and calculate the continuously increasing potential value △E, and the difference △E2 between AE1. The maximum value of △E, is the endpoint of the titration. After the endpoint, continue to record a potential value E. The recording format is detailed in Appendix C (Standard Appendix). When calibrating the 0.1mol/L silver nitrate standard titration solution, take 25mL of potassium chloride standard solution (0.1mol/L) and add 2ml of nitric acid solution. It is carried out in aqueous solution, and the other operations are the same as the above steps. The volume of silver nitrate standard titration solution consumed to the end point (V) is calculated according to formula (1): V = V. + Vi X b/B
Wherein: V. ——The volume of silver nitrate standard titration solution added before the potential increment △E reaches the maximum value, mL, V,——The volume of silver nitrate standard titration solution added for the last time before the potential increment △E reaches the maximum value, mL; b——The last positive value of △E2:
B---The sum of the absolute values of the last positive value and the first negative value of △E2 [see Appendix C (Standard Appendix)], V The volume of silver nitrate standard titration solution consumed during titration, mL. The concentration of silver nitrate standard titration solution (c) is calculated according to formula (2): CoV2
Wherein: co---The concentration of potassium chloride standard solution taken, mol/LV---The volume of potassium chloride standard solution taken, mL. 4.7 Bromophenol blue indicator solution: 0.1% ethanol solution. 5 Instruments and equipment
5.1 Potentiometer: accuracy is 2mV/grid, range is -500mV～+500mV. ..( 1)
（2）
5.2 Reference electrode: double liquid junction saturated calomel electrode, filled with saturated potassium fluoride solution, when titrating, the outer sleeve is filled with saturated potassium nitrate solution and connected to the calomel electrode.
5.3 Measuring electrode: silver electrode or 0.5mm silver wire (containing 99.9% silver, shielded wire should be used when connected to the potentiometer). When the concentration of the silver nitrate standard solution used is lower than 0.005mol/L, a silver electrode with silver sulfide coating should be used. For the preparation method, please refer to Appendix A (Standard Appendix).
5.4 Microburette: the graduation value is 0.02mL or 0.01mL. 6 Analysis steps
6.1 Preparation of test solution
Weigh an appropriate amount of sample and treat it with an appropriate method, or transfer an appropriate amount of test solution after chemical treatment [so that the interfering ions are not greater than the specified limit, see Appendix D (Suggested Appendix), place it in a beaker, add 1 drop of bromophenol blue indicator solution, adjust the color of the solution to yellow with sodium hydroxide solution or nitric acid solution, transfer it to a volumetric flask of appropriate size, add water to the scale, and shake well. This test solution is solution A, and the concentration of chloride ions is 1 mg/L~1.5×103mg/L.
6.2 Titration
Accurately transfer a certain amount of solution A to make the chlorine content 0.01mg~75mg, place it in a 50mL beaker, add ethanol, and make the volume ratio of ethanol to the solution A taken to 3:1, and the total volume is not more than 40mL. When the concentration of the silver nitrate standard titration solution used is greater than 0.02 mol/L, ethanol may not be added. The following operations shall be carried out according to the provisions after adding ethanol in 4.6, but 4 mL (or 9 mL) of silver nitrate standard titration solution shall not be added again.
When the chloride ion concentration in the test solution is too low and the volume of the silver nitrate standard titration solution consumed by the titration is less than 1 mL, the standard addition method may be used for determination. When calculating the result, the volume of the silver nitrate standard titration solution consumed by the chlorine in the added potassium chloride standard solution shall be deducted. Perform a blank test at the same time.
7 Expression of analysis results
The chloride content (in terms of Cl) expressed as mass percentage is calculated according to formula (3): x(%) =,=V)c× 0. 035 45 × 100m
c(V. - Vi) X 3. 545
Wherein: c
concentration of standard silver nitrate titration solution, mol/L; volume of standard silver nitrate titration solution consumed in titration, mL; V3-
V.—volume of standard silver nitrate titration solution consumed in blank titration, mL; m—mass of titrated sample, g
mass of chloride (in terms of Cl) equivalent to 1.00 mL standard silver nitrate titration solution [c(AgNO3)=1.000 mol/L], expressed in grams.
GB/T30502000
Appendix A
(Appendix of the standard)
Preparation method of silver-silver sulfide electrode
Use metallographic sandpaper (M14) to polish a silver wire with a length of 15cm to 20cm and a diameter of 0.5mm, then clean it with absorbent cotton soaked in ethanol, dry it, immerse it in an appropriate amount of equal volume mixed solution of 0.2mol/L sodium chloride and 0.2mol/L sodium sulfide (temperature is about 25℃), the immersion depth is 3cm to 5cm, the immersion time is 30min, take it out, rinse it with tap water for about 10min, and then wash it with distilled water for use.
When the prepared electrode is calibrated with 0.005mol/L silver nitrate standard titration solution against 0.005mol/L potassium chloride standard solution, the endpoint potential jump value should be greater than 60mV.
Appendix B
(Standard Appendix)
Selection of standard solution and electrode type
This appendix provides the expected chloride content (measured in CI) in the test solution and the recommended standard solution concentration and measuring electrode type, see Table B1.
Content of CI in the test solution, mg / L
10~100
100~250
250~1500
Volume of standard silver nitrate titration solution
Concentration of selected standard solution (AgNO: and KCl), mol/L0.001
Appendix C
(Appendix of standard)
Example of test record format
Potential value E
V=4.90+0.10×37/(37+49)=4.94Type of measuring electrode selected
Ag-Ag2S
Ag-AgzS
Note: The first and second columns record the total volume of the added silver nitrate standard solution and the corresponding potential value E respectively. The third column records the continuously increasing potential values △E, and the fourth column records the difference △E2 between the increasing potential values △E. This difference can be positive or negative. 21
GB/T 3050-- 2000
Appendix D
(Suggestive Appendix)
Interference in Determination
This appendix provides the ions that do not interfere with the determination and the ions that interfere with the determination and the reasons for the specified limits, see Table D1 and Table D2. Table D1 Ions that do not interfere with the determination
Ion concentration +/L
Ion name
[Fe(CN), J*-
[Fe(CN), 3-
Cations
Mg*+、Pb2+
Ca2+、Cu*+、Zn*+
Na*、Mn2+
Anions
BOi-、H,PO
NO:、SO2-、CIO:、F-、HPO}~、PO3-C O, HCO:, Cr2O Table D2 Ions interfering with determination
Limit of no interference
1×103
2×102
Reasons for setting limit
Forming AgBr precipitate
Forming AgI precipitate
Oxidation by CI-
Forming AgNO, precipitating
Forming Ag2S precipitate
Forming AgzSO: precipitate
Forming AgzS20, precipitating
Forming AgCNS precipitate
Forming a complex with Ag+
Reducing the jump of endpoint potential
Reducing the jump of endpoint potential
Forming Ag[Fe(CN), precipitating
Forming Ag:[Fe(CN). ]Precipitation
Appendix E
(Suggestive Appendix)
Methods for eliminating interfering ions
Applicable elimination methods
See Appendix E E1
See Appendix E E2
See Appendix E E3
See Appendix E E4
See Appendix E E5
See Appendix E E6
This Appendix cannot include all the elimination methods for interfering substances. Possible interferences should be checked frequently, and the treatment methods described in E1 to E5 cannot cover all situations. 22
E1 Iodine and bromine
GB/T 3050--2000
Except fluorine, iodine and bromine will react with silver nitrate during the titration of chlorine and interfere with the determination. The elimination method is to oxidize with an oxidant (such as hydrogen peroxide) in a dilute nitric acid medium, and then extract with an appropriate solvent. E2 Oxidants
In acidic solutions, Cr2O- and CIO: can oxidize CI- to C12, interfering with the determination. The elimination method is to control the pH of the solution to be measured at 5~~6 for titration.
MnO: reacts with chlorine and interferes with the determination. The elimination method is to slowly drop an appropriate amount of 30% H2O2-1mol/LHNO, and the mixed solution (1+10) is added to the test solution to make MnO fade.
Oxidants can oxidize silver electrodes, and the oxidants can be destroyed by treating with sodium sulfite, ascorbic acid solution or other reducing agents that do not affect the determination.
E3 Nitrite
NOz reacts with Ag+ to form AgNO. precipitation. The elimination method for interference with the determination is to drop 10% aminosulfonic acid solution into the test solution, and heat to boil after no bubbles are generated.
E4 Anions in salts such as cyanide, thiocyanate, sulfide, sulfate, and sulfite generate insoluble precipitates with Ag*, interfering with the determination. The elimination method is to slowly add an appropriate amount of 30% hydrogen peroxide solution in an alkaline medium, slowly heat it, and finally boil it until no small bubbles are generated. E5 Ammonium salts and iron (II) salts
interfere with the determination when they exist in large quantities. Ammonium salts are evaporated to dryness in a water bath by adding an appropriate amount of 5% sodium carbonate solution to drive away NHs. Iron (II) salts are added with excess sodium hydroxide solution, boiled, and filtered to remove the generated iron (II) hydroxide precipitate. A small amount of iron (II) can also be removed by complexation (such as EDTA).
E6 Ferrocyanide and ferrocyanide
Add 2 to 3 times the amount of zinc nitrate as the sample in the test solution, heat to boiling, and cool. Transfer all of it into a volumetric flask, add water to the mark, spread evenly, place it in layers, dry filter it with slow filter paper, discard the initial filtrate, and use the remaining filtrate for determination.Precipitation, interference with determination. The elimination method is to add 10% aminosulfonic acid solution to the test solution, heat and boil until no bubbles are generated.
E4 Anions in salts such as cyanide, thiocyanate, sulfide, sulfate, and sulfite react with Ag* to form insoluble precipitates, which interfere with determination. The elimination method is to slowly add an appropriate amount of 30% hydrogen peroxide solution in an alkaline medium, slowly heat, and finally boil until no small bubbles are generated. E5 Ammonium salts and iron (II) salts
When present in large quantities, they interfere with determination. Ammonium salts are added with an appropriate amount of 5% sodium carbonate solution and evaporated on a water bath to drive away NHs. Iron (II) salts are added with excess sodium hydroxide solution, boiled, and filtered to remove the generated iron (II) hydroxide precipitate. A small amount of iron (II) can also be removed by complexation (such as EDTA).
E6 Ferrocyanide and ferrocyanide
Add 2 to 3 times the amount of zinc nitrate as the sample to the test solution, heat to boiling, and cool. Transfer all to a volumetric flask, add water to the scale, spread evenly, let it stand for stratification, dry filter with slow filter paper, discard the initial filtrate, and use the remaining filtrate for determination. 23
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