PDF GB/T 3050-2000 English (GB/T 3050-1982: Older version)
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Inorganic chemical products for industrial use. General method for determination of chloride content. Potentiometric method
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Inorganic chemical products for industrial use--General method for determination of chloride content--Potentiometric method
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GB/T 3050-2000: PDF in English (GBT 3050-2000) GB/T 3050-2000
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.040.40
G 10
neq ISO 6227:1982
Inorganic chemical products for industrial use -
General method for determination of chloride content
- Potentiometric method
ISSUED ON: JULY 31, 2000
IMPLEMENTED ON: MARCH 01, 2001
Issued by: State Bureau of Quality Technical Supervision
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative reference ... 5
3 Method summary ... 5
4 Reagents and materials ... 6
5 Instruments and equipment... 8
6 Analytical procedures ... 8
7 Expression of analysis results ... 9
Appendix A (Normative) Preparation method of silver-silver sulfide electrode10
Appendix B (Normative) Selection of standard solution and electrode type ... 11
Appendix C (Normative) Example of test record format ... 12
Appendix D (Informative) Interference in the determination ... 13
Appendix E (Informative) Elimination method of ions interfering with
determination ... 14
Inorganic chemical products for industrial use -
General method for determination of chloride content
- Potentiometric method
1 Scope
This standard specifies the general method for the determination of chloride
content in inorganic chemical products - Potentiometric titration.
This standard applies to test solutions, which have a chloride ion content of 1
mg/L ~ 1500 mg/L. The chloride (calculated as Cl) content in the test solution,
which is used 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 shall
be carried out in an ethanol-water solution.
does not interfere with the determination. The ions that form insoluble
precipitates or complexes with Ag+, as well as , etc. interfere with the
determination. For the limit and elimination method, please refer to Appendix D
(informative) and Appendix E (informative).
2 Normative reference
The provisions contained in the following standards constitute the provisions of
this standard through quotation in this standard. When this standard is
published, the versions shown are valid. All standards will be revised. All parties
using this standard shall explore the possibility of using the latest version of the
following standards.
GB/T 603-1988 Chemical reagent - Preparations of reagent solutions for use
in test methods
GB/T 6682-1992 Water for laboratory use - Specifications (neq ISO
3696:1987)
3 Method summary
In acidic water or ethanol-water solution, use silver (silver-silver sulfide)
electrode as the measuring electrode [see Appendix B (normative) for the
selection of electrode types]; use calomel electrode as the reference electrode;
use silver nitrate standard titration solution for titration. The end point of the
reaction is determined by means of a potential jump.
4 Reagents and materials
The reagents and water, which are used in this standard, refer to analytical
reagents and the grade 3 water, which are specified in GB/T 6682, unless
otherwise specified.
The preparations and products, which are used in this standard, shall be
prepared in accordance with the provisions of GB/T 603, unless otherwise
specified.
4.1 95% ethanol.
4.2 Saturated potassium nitrate solution.
4.3 Sodium hydroxide solution: 200 g/L.
4.4 Nitric acid solution 2 + 3.
4.5 Potassium chloride standard solution: c (KCl) = 0.1 mol/L. Accurately weigh
3.728 g of the reference potassium chloride (accurate to 0.001 g), which was
previously baked at 130 °C to a constant weight. Place it in a beaker. After
adding water to dissolve, transfer it into a 500 mL volumetric flask. Use water
to dilute it to the mark. Shake well.
Potassium chloride standard titration solution of 0.01 mol/L, 0.005 mol/L, 0.001
mol/L or other concentration: Accurately dilute the 0.1 mol/L potassium chloride
standard titration solution to the required multiple.
4.6 Silver nitrate standard titration solution: c (AgNO3) = 0.1 mol/L.
Silver nitrate standard titration solution of 0.01 mol/L, 0.005 mol/L, 0.001 mol/L
or other concentrations: Accurately dilute the 0.1 mol/L silver nitrate standard
titration solution to the required multiple.
Calibration:
Use a pipette to take 5 mL or 10 mL of the potassium chloride standard solution
of the selected concentration. Place it in a 50 mL beaker. Add 1 drop of
bromophenol blue indicator solution. Add 1 ~ 2 drops of nitric acid solution, to
make the solution just yellow. Then add 15 mL or 30 mL of ethanol. Put in the
electromagnetic stirrer. Place the beaker on the electromagnetic stirrer. Start
the stirrer. Insert the measuring electrode and the reference electrode into the
Where:
c0 - The concentration of the potassium chloride standard solution taken,
mol/L;
V2 - The volume of the potassium chloride standard solution taken, mL.
4.7 Bromophenol blue indicator solution: 0.1% ethanol solution.
5 Instruments and equipment
5.1 Potentiometer: The accuracy is 2 mV/div. The range is -500 mV ~ +500 mV.
5.2 Reference electrode: Double-liquid junction type saturated calomel
electrode, filled with saturated potassium chloride solution. During titration, the
outer tube is filled with saturated potassium nitrate solution AND is connected
to the calomel electrode.
5.3 Measuring electrode: Silver electrode or 0.5 mm silver wire (with 99.9%
silver content; use shielded wire when connecting with potentiometer)
When the concentration of the silver nitrate standard solution used is lower than
0.005 mol/L, it shall use a silver electrode with a silver sulfide coating. The
preparation method is detailed in Appendix A (normative)
5.4 Micro burette: The graduation value is 0.02 mL or 0.01 mL.
6 Analytical procedures
6.1 Preparation of test solution
Weigh an appropriate amount of the specimen. Treat it with an appropriate
method. OR otherwise pipette an appropriate amount of the test solution after
chemical treatment [to make the interference ion not greater than the specified
limit, see Appendix D (informative)]. Place it in a beaker. Add 1 drop of
Bromophenol blue indicator solution. Use sodium hydroxide solution or nitric
acid solution to adjust the color of the solution just yellow. Transfer it to a
volumetric flask of appropriate size. Add water to the mark. Shake well. This
test solution is solution A. The concentration of chloride ions is 1 mg/L ~ 1.5 x
103 mg/L.
6.2 Titration
Appendix E
(Informative)
Elimination method of ions interfering with determination
This Appendix cannot include the elimination methods of all interfering
substances. It shall check the possible interference frequently. The processing
methods described in E1 to E5 cannot cover all situations.
E1 Iodine and bromine
In addition to fluorine, iodine and bromine will react with silver nitrate, while
titrating chlorine, which will interfere with the determination. The elimination
method is to first use oxidant (such as hydrogen peroxide) to make oxidization,
in a dilute nitric acid medium; then use an appropriate solvent to extract it.
E2 Oxidant
In an acidic solution, and etc., can oxidize Cl- to Cl2, which
interferes with the determination. The elimination method is to control the pH of
the tested solution, to make titration at pH 5 ~ 6.
reacts with chlorine AND interferes with the determination. The
elimination method is to slowly add an appropriate amount of 30%H2O2-1 mol/L
HNO3 mixed solution (1 + 10) in the test solution, to make fade.
The oxidant can oxidize the silver electrode. Use sodium sulfite, ascorbic acid
solution or other reducing agents, that do not affect the measurement, to
destroy the oxidant.
E3 Nitrite
and Ag+ generate AgNO2 precipitation. The elimination method of
interference is to drop 10% sulfamic acid solution into the test solution; then
heat and boil it, after there is no air bubble.
E4 Cyanide, thiocyanate, sulfide, thiosulfate, sulfite, etc.
The anions in these salts form insoluble precipitates with Ag+, which interfere
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; finally boil until it, until there is no small bubble.
E5 Ammonium salt and iron (III) salt
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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