GB/T 223.11: Evolution and historical versions
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Iron, steel and alloy - Determination of chromium content - Titrimetric method and spectrophotometric method
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GB/T 223.11-2025
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| GB/T 223.11-2008 | English | 85 |
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Iron, steel and alloy -- Determination of chromium content -- Visual titration or potentiometric titration method
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GB/T 223.11-2008
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| GB/T 223.11-1991 | English | 279 |
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Methods for chemical analysis of iron, steel and alloy--The ammonium persulfate oxidation volumetric method for the determination of chromium content
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GB/T 223.11-1991
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Basic data | Standard ID | GB/T 223.11-2025 (GB/T223.11-2025) | | Description (Translated English) | Iron, steel and alloy - Determination of chromium content - Titrimetric method and spectrophotometric method | | Sector / Industry | National Standard (Recommended) | | Date of Implementation | 2026-03-01 | | Older Standard (superseded by this standard) | GB/T 223.11-2008, GB/T 223.12-1991 | GB/T 223.11-2008: Iron, steel and alloy -- Determination of chromium content -- Visual titration or potentiometric titration method
---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Iron, steel and alloy. Determination of chromium content. Visual titration or potentiometric titration method
ICS 77.080.01
H11
National Standards of People's Republic of China
Replacing GB/T 223.11-1991
Steel and alloy - Determination of chromium content
Visual titration or potentiometric titration
(ISO 4937. 1986, MOD)
Posted.2008-09-11
2009-05-01 implementation
General Administration of Quality Supervision, Inspection and Quarantine of People's Republic of China
China National Standardization Administration released
Foreword
GB/T 223 of this Part Replaced GB/T 223.11-1991 "Methods for chemical analysis of iron, steel and alloy ammonium persulfate oxidation capacity
Determination of chromium. "
This part of the revision, the name changed to "Determination of chromium content of steel and alloy visual titration or potentiometric titration", including two analysis
Methods. Method A Visual titration and method Two potentiometric titration.
This part of a method with GB/T 223.11-1991 compared to the main changes made the following.
--- Modify the determination of content range;
--- Increase the theoretical calculation method to correct vanadium interference content;
--- Increasing the analysis of reagents and water instructions and modify the concentration of the solution;
--- Modify the sample size and its representation;
--- Modify the calculation results in the amount of expression and increase the theoretical calculation of vanadium interference correction formula;
--- Reorganize the precision test.
Method 2 of this section is modified using ISO 4937. 1986 "Determination of chromium content of steel or visual titration titration method" and ISO 4937.
1986 compared to the main changes made to the following.
--- Only one of the potentiometric titration method, its technical content consistent with it;
--- In the "instrument" and the "titration of vanadium-containing samples" each add a note.
This part of Appendix A, Appendix B, Appendix C are informative appendix.
This part is proposed by China Iron and Steel Association.
This part of the National Standardization Technical Committee Steel centralized.
This section is responsible for drafting unit. Iron and Steel Research Institute, Taiyuan Iron and Steel Company.
The main drafters of this section. Wang Kejuan, Chang Xiaojun, Luo Qianhua, Dai Xueqian.
This part of the standard replaces the previous editions are.
--- GB/T 223-1963, GB/T 223.11-1982, GB/T 223.11-1991.
Steel and alloy - Determination of chromium content
Visual titration or potentiometric titration
Warning. personnel using this section GB/T 223 should have the formal laboratory work experience. This section does not indicate all that can be
Can safety problem. It is the user's responsibility to take appropriate safety and health measures and to ensure compliance with the requirements of the relevant state laws and regulations.
1 Scope
This section GB/T 223 specifies the use of visual or potentiometric titration chromium content.
This method is suitable for a portion of pig iron, carbon steel, alloy steel, high temperature alloys and precision alloys in the mass fraction of 0.10% to 35.00%
Determination of chromium content; the second method is suitable for the determination of chromium content of 0.25% ~ 35.00% in steel.
2 Normative references
The following documents contain provisions which, through reference in this Part of GB/T 223, become the provisions of this section. Any reference to the date of the citation
All subsequent amendments (not including errata content) or revisions do not apply to this section, however, encouraged to be reached under this section
The parties to the agreement study whether the latest versions of these documents are available. For undated references, the latest version applies to this book
section.
Methods for chemical analysis of iron, steel and alloy - The ferrous ammonium sulfate titrimetric method for the determination of vanadium content
GB/T 223.14 Methods for chemical analysis of iron, steel and alloy - The tantalum reagent extraction photometric method for the determination of vanadium content
GB/T 223.76 Methods for chemical analysis of iron, steel and alloy - The flame atomic absorption spectrometric method for the determination of vanadium content
GB/T 6379.1 Accuracy (accuracy and precision) of measurement methods and results - Part 1. General and definitions
(GB/T 6379.1-2004, ISO 5725-1..1994, IDT)
GB/T 6379.2 Accuracy (accuracy and precision) of measurement methods and results Part 2. Determination of standard measurement method Repeat
Sex and reproducibility of the basic method (GB/T 6379.2-2004, ISO 5725-2..1994, IDT)
GB 12805 Laboratory glassware burette
GB 12806 laboratory glassware single standard line capacity bottle
GB 12808 laboratory glassware single standard pipette
GB/T 20066 Sampling and sample preparation methods for the determination of chemical compositions of steel and iron (GB/T 20066-2006, ISO 14284.
1996, IDT)
GB/T 20125 Determination of multi-element content of low-alloy steel Inductively coupled plasma atomic emission spectrometry
3 methods a visual titration
3.1 principle
After the sample is dissolved in acid, chromium is oxidized to chromium (VI) by ammonium persulfate in sulfuric acid and phosphoric acid medium using silver nitrate as catalyst,
Ferrous ammonium standard solution titration.
Vanadium-containing samples to ferrous phenanthroline solution as an indicator, add an excess of ammonium ferrous sulfate standard titration solution to potassium permanganate solution back
Drop; Or use the appropriate national standard vanadium determination, the theoretical calculation method to correct the interference of vanadium.
The presence of 2mg or less in the test solution does not interfere with the determination of cerium.
3.2 Reagents
Unless otherwise specified, only reagents identified as analytically pure and distilled or deionized water or rather pure water are used in the analysis.
3.2.1 anhydrous sodium acetate.
3.2.2 Hydrochloric acid, p about 1.19 g/mL.
3.2.3 hydrochloric acid, ρ about 1.19g/mL, diluted to 1 +3.
3.2.4 nitric acid, ρ about 1.42g/mL.
3.2.5 Phosphoric acid, p about 1.69 g/mL.
3.2.6 sulfuric acid, ρ about 1.84g/mL, diluted to 1 +1.
3.2.7 sulfuric acid, ρ about 1.84g/mL, diluted to 5 +95.
3.2.8 Hydrofluoric acid, p about 1.15 g/mL.
3.2.9 sulfuric acid - phosphoric acid mixed acid. add 320mL sulfuric acid (3.2.6) and 80mL phosphoric acid (3.2.5) in 600mL water and mix.
3.2.10 silver nitrate solution, 10g/L. Weigh 1.0g silver nitrate dissolved in 100mL water, a few drops of nitric acid (3.2.4), stored in brown
Bottle
3.2.11 ammonium persulfate solution, 300g/L, formulated before use.
3.2.12 sodium chloride solution, 50g/L.
3.2.13 manganese sulfate solution, 40g/L.
3.2.14 Benzene-anthranilic acid solution, 2g/L. Weigh 0.2g reagent placed 300mL beaker, add 0.2g of anhydrous sodium carbonate,
Add 20mL water heating to dissolve, diluted with water to 100mL, mix.
3.2.15 Ferrous - o-phenanthroline solution. Weigh 1.49g o-phenanthroline, 0.98g ferrous ammonium sulfate placed 300mL beaker, add 50mL
Water, heated to dissolve, cooled, diluted with water to 100mL, mix.
3.2.16 chromium standard solution
3.2.16.1 Chromium stock solution, 2.000g/L.
Weigh 5.6578g pre-150 ℃ baked 1h, placed in a desiccator cooled to room temperature potassium dichromate (reference), placed in a beaker,
Dissolved in water, into 1000mL volumetric flask, diluted with water to the mark, mix well.
This solution 1 mL contains 2.000 mg chromium.
3.2.16.2 chromium standard solution A, 1.000g/L.
Pipette 50.00mL chromium stock solution (3.2.16.1) placed in 100mL volumetric flask, diluted with water to the mark, and mix.
1 mL of this solution contains 1.000 mg chromium.
3.2.16.3 chromium standard solution B, 0.500g/L.
Pipette 25.00mL chromium stock solution (3.2.16.1) placed in 100mL volumetric flask, diluted with water to the mark, mix.
This solution 1 mL contains 0.500 mg chromium.
3.2.17 Ferrous ammonium sulfate standard titration solution
3.2.17.1 Preparation
Weigh 6g, 12g, 24g ammonium ferrous sulfate [(NH4) 2Fe (SO4) 2 · 6H2O], were dissolved in sulfuric acid (3.2.7), and sulfuric acid
(3.2.7) diluted to 1000mL mix. The ferrous ammonium sulfates with concentrations of 0.015 mol/L, 0.03 mol/L and 0.06 mol/L were obtained
Solution.
3.2.17.2 calibration and indicator correction
In 3 500mL Erlenmeyer flasks, each add 50mL sulfuric acid - phosphoric acid mixed acid (3.2.9), heated to evaporate sulfuric acid smoke, slightly cold, add water
50mL, cooled to room temperature, were added chromium standard solution (the chromium content should be similar to the quality of chromium in the sample), diluted with water to.200mL, with
Ferrous ammonium sulfate standard titration solution (3.2.17.1) titration until the solution was light yellow, add 3 drops of benzene substituted anthranilic acid solution (3.2.14), followed by
Continued titration rose to bright green by the rose to the end. Read the volume (mL) of the ferrous ammonium sulfate standard titration solution consumed. Plus phase
The same amount of chromium standard solution, and then ammonium ferrous sulfate standard titration solution (3.2.17.1) titration until the bright red from rose to the end.
Both the consumption of ammonium ferrous sulfate standard titration solution volume difference, that is, 3 drops of benzene substituted anthranilate solution correction. Add this value
Into the titration of ferrous ammonium sulfate standard titration solution volume (mL), and then calculate. 3 parts of chromium standard solution consumed ferrous sulfate
Ammonium standard titration solution volume (mL) of the very poor, not more than 0.05mL, whichever is the average.
According to equation (1) Calculate the unit volume Ferrous ammonium sulfate standard titration solution is equivalent to the quality of chromium.
T = 犞 × 犮 犞 1
(1)
Where.
T --- unit volume ammonium ferrous sulfate standard titration solution equivalent to the quality of chromium in units of grams per milliliter (g/mL);
犞 --- Remove the volume of chromium standard solution, in milliliters (mL);
犞 1 --- titration consumed ammonium ferrous sulfate standard titration solution volume (including the indicator correction value) average, in milliliters
(ML);
犮 --- chromium standard solution concentration, in grams per milliliter (g/mL).
3.2.18 potassium permanganate solution preparation and calibration
3.2.18.1 Preparation
Weigh 0.48g, 0.95g or 1.9g potassium permanganate were placed in 1000mL beaker, dissolved in water and add 5mL ~ 10mL
Phosphoric acid (3.2.5), diluted with water to 1000mL, stored in a brown bottle, placed in the shade 6d ~ 10d, before use with a crucible filter
Filter after use.
3.2.18.2 Calibration
Pipette 25.00mL ferrous ammonium sulfate standard titration solution (3.2.17.1) 3 were placed in 250mL Erlenmeyer flask to the corresponding concentration
Degree of potassium permanganate solution titration to the solution was pink, did not disappear within 1min ~ 2min as the end point, three ammonium ferrous sulfate standard titration
Liquid potassium permanganate volume (mL) of the very poor, not more than 0.05mL, whichever is the average.
According to equation (2) Calcium permanganate solution equivalent to ammonium ferrous sulfate standard titration solution volume ratio.
K = 25.00 犞 2
(2)
Where.
K --- potassium permanganate solution equivalent to ammonium ferrous sulfate standard titration solution volume ratio;
犞 2 --- volume titration consumed potassium permanganate solution, in milliliters (mL);
25.00 --- remove ferrous ammonium sulfate standard titration solution volume, in milliliters (mL).
3.3 take sample
Take samples according to GB/T 20066 or appropriate national standards.
3.4 Analysis steps
3.4.1 sample volume
According to Table 1 Weigh the sample, accurate to 0.0001g.
Table 1
Chromium content (mass fraction) /% Weigh sample/g
0.10 ~ 2.00 2.00
> 2.00 ~ 10.00 2.00 ~ 0.50
> 10.00 ~ 35.00 0.50 ~ 0.15
Note. In the weighed sample containing tungsten, manganese content of less than 100mg control, or the end is not easy to identify.
3.4.2 Blank test
With the sample to do a blank test.
3.4.3 Determination
3.4.3.1 sample dissolution and treatment
3.4.3.1.1 General sample
The sample (3.4.1) placed in 500mL Erlenmeyer flask, add 50mL sulfuric acid - phosphoric acid mixed acid (3.2.9), heated until the sample completely dissolved.
3.4.3.1.2 sulfuric acid - phosphoric acid mixed acid is not easy to dissolve the sample
The sample (3.4.1) placed 500mL Erlenmeyer flask, add appropriate amount of hydrochloric acid (3.2.2) and nitric acid (3.2.4), heated to dissolve, plus
50mL sulfuric acid - phosphoric acid mixture (3.2.9).
3.4.3.1.3 Samples containing high silicon
The sample (3.4.1) was placed 500mL Erlenmeyer flask, add 50mL sulfuric acid - phosphoric acid mixed acid (3.2.9), heated until the sample is completely dissolved,
A few drops of hydrofluoric acid (3.2.8).
3.4.3.1.4 sample handling
To 3.4.3.1.1,3.4.3.1.2,3.4.3.1.3 test solution was added dropwise nitric acid (3.2.4) oxidation, until the intense effect after the stop , According to Table 2
Additional phosphoric acid (3.2.5), continue heating and evaporation to take sulfuric acid smoke. High-carbon, high-chromium, high-molybdenum samples of sulfuric acid smoke drip nitric acid (3.2.4) oxygen
To the solution is clear, carbides all destroyed so far.
Table 2
Specimens weighed sample
Additional Phosphoric Acid (3.2.5)
mL
Anhydrous sodium acetate (3.2.1)
Tungsten-free and Vanadium-free
Weigh the sample 2g 5 ~ 10 -
Weigh the sample is less than 2g but the sample containing carbide high 5 ~ 10 -
Tungsten does not contain vanadium
Weigh the sample containing less than 30mg tungsten 10 -
Weigh the sample containing tungsten more than 30mg ~ 100mg 20 -
Vanadium-free tungsten
Weigh the sample is less than 1g 10 10
Weigh the sample 1g ~ 2g 15 15
Weigh the sample is greater than 2g 20 20
Vanadium tungsten coexist
Weigh the sample containing less than 10mg tungsten 15 ~ 25 15 ~ 25
Weigh the sample containing tungsten is greater than 10mg ~ 100mg 25 ~ 30 25 ~ 30
3.4.3.2 Chromium oxide
The test solution obtained in 3.4.3.1.4, slightly cold, diluted with water to.200mL (pig iron sample precipitation, diluted with water to 100mL,
Medium-sized filter paper, washed with water 5 times to 6 times, and diluted to.200mL), add 5mL silver nitrate solution (3.2.10) [test solution containing
When the amount of chromium is greater than 50mg plus 10mL silver nitrate solution (3.2.10)], 20mL ammonium persulfate solution (3.2.9) (such as the test solution containing 50mg
Chromium, 40mg manganese plus 30mL), shake, boil until the solution is heated to a stable purple (such as low manganese content of the test solution can be added dropwise 2 drops ~
4 drops of manganese sulfate solution (3.2.13)〕, continue to boil 5min, remove, add 5mL hydrochloric acid (3.2.3), boiled to red disappear, if Ruoyin
High manganese content, add 5mL hydrochloric acid (3.2.3) did not completely decompose permanganate, the solution was red, then add 2mL ~ 3mL hydrochloric acid (3.2.3), cook
Boil 2min ~ 3min to completely decompose. Remove and cool to room temperature.
3.4.3.3 titration
3.4.3.3.1 Vanadium-free coupons
The 3.4.3.2 obtained test solution, first ferrous ammonium sulfate standard titration solution (3.2.17.1) titration until the solution was light yellow, add 3 drops of benzene
The anthranilic acid solution (3.2.14) continues titration until it turns from rose red to bright green.
3.4.3.3.2 Vanadium-containing specimens
3.4.3.3.2.1 potassium permanganate back titration method
3.4.3.2 obtained test solution, first with a suitable concentration of ammonium ferrous sulfate standard titration solution (3.2.17.1) titration to hexavalent chromium yellow
Before the color changes to bright green, add 5 drops of ferrous-o-phenanthroline solution (3.2.15) and continue titration until the solution shows a steady red color with excess
5mL, plus 5 drops of ferrous - o-phenanthroline solution (3.2.15) to a similar concentration of potassium permanganate solution (3.2.18) back to the initial red disappear
Loss, add anhydrous sodium acetate (3.2.1) according to Table 2, until sodium acetate dissolved, continue to use potassium permanganate solution (3.2.18) slowly titrated to light blue
(High chromium content is blue-green) as the end point.
Ferrous - o-phenanthroline solution to consume potassium permanganate solution (3.2.18) to be corrected according to the following method.
In the finished potassium permanganate equivalent to ammonium ferrous sulfate standard titration solution volume ratio of the two after the calibration solution, add 10 drops of Asia
Iron - o - phenanthroline solution (3.2.15), the other plus 20 drops, each with the same concentration of titration solution of potassium permanganate solution (3.2.18) titration,
The difference between the volumes consumed by both solutions of potassium permanganate (3.2.18) is the corrected value of 10 drops of ferrous-o-phenanthroline solution (3.2.15). This value
Should be subtracted from the volume (mL) of potassium permanganate solution consumed by excess ferrous ammonium sulfate standard titration solution.
3.4.3.3.2.2 Calculation of theoretical value
Titration according to 3.4.3.3.1 first, get the total amount of chromium and vanadium; then the theoretical value of the correction. 1% vanadium corresponds to 0.34% chromium.
Vanadium content can be GB/T 223.13, GB/T 223.14, GB/T 223.76 or GB/T 20125 provides for the operation of the determination,
Can also be measured by the appropriate international standard vanadium.
Note. When the chromium content of the solution is less than or equal to 10mg, with a concentration of 0.015mol/L ammonium ferrous sulfate solution titration; when the solution of chromium content in the
10mg ~ 25mg, with a concentration of 0.03mol/L ammonium ferrous sulfate solution titration; when the solution is greater than the content of chromium 25mg, the concentration
0.06mol/L ammonium ferrous sulfate solution titration.
3.5 Calculation Results
3.5.1 Vanadium-free samples
According to equation (3) calculate the chromium content in the sample Cr, expressed in terms of mass fraction.
Cr =
犞 3 × T
(3)
Where.
犞 3 --- titration consumed ammonium ferrous sulfate standard titration solution volume (including the indicator correction value), in milliliters (mL);
T --- unit volume ammonium ferrous sulfate standard titration solution equivalent to the quality of chromium in units of grams per milliliter (g/mL);
3.5.2 Vanadium-containing specimens
3.5.2.1 potassium permanganate back titration method
According to equation (4) calculate the chromium content in the sample Cr, expressed in mass fraction.
Cr =
(犞 4- 犞 5 × K) × T
(4)
Where.
犞 4 --- titration consumed ferrous ammonium sulfate standard titration solution volume, in milliliters (mL);
犞 5 --- Volume of ammonium permanganate solution consumed by excess ammonium ferrous sulfate standard titration solution minus the correction of ferrous-o-phenanthroline solution
After the value of the volume in milliliters (mL);
K --- potassium permanganate solution equivalent to ammonium ferrous sulfate standard titration solution volume ratio;
T --- ammonium ferrous sulfate standard titration solution of chromium titer, in grams per milliliter (g/mL);
3.5.2.2 theoretical value calculation method
According to equation (5) calculate the chromium content in the sample Cr, expressed in terms of mass fraction.
Cr =
犞 6 × T
(5)
Where.
犞 6 --- titration of chromium and vanadium total consumption volume of ammonium ferrous sulfate standard titration solution (including the indicator correction value), in milliwatts
Liter (mL);
T --- ammonium ferrous sulfate standard titration solution of chromium titer, in grams per milliliter (g/mL);
V --- vanadium mass fraction;
0.34 --- vanadium correction factor.
3.6 precision
Method One precision is selected in.2007 eleven levels by eight laboratories to conduct a joint test, each laboratory for each chromium
Level in accordance with the provisions of GB/T 6379.1 Determination of repeatability determined 3 times. The raw data reported by each laboratory (measured values) see
Appendix A (informative). The original data in accordance with GB/T 6379.2 for statistical analysis, precision in Table 3.
Table 3
The situation does not exceed 5% as a prerequisite;
Under reproducibility conditions, the absolute difference between the two independent test results obtained is not greater than the reproducibility limit (R) and greater than the reproducibility limit (R)
The case does not exceed 5% as a prerequisite.
4 method two potentiometric titration
4.1 principle
The sample is dissolved with a suitable acid, chromium is oxidized to chromium (VI) with ammonium persulfate in an acidic medium in the presence of silver sulfate,
Manganese (VII) is used to reduce chromium (VI) with ferrous ammonium sulfate standard solution.
Potentiometric titration, with the constant addition of ammonium ferrous sulfate standard solution, by measuring the potential changes to determine the equivalence point.
4.2 Reagents
Unless otherwise stated, only certified analytical reagents and distilled water or water of comparable purity are used in the analysis without oxidation or reduction
behavior.
4.2.1 Urea.
4.2.2 Perchloric acid, p approximately 1.67 g/mL.
4.2.3 Hydrofluoric acid, p approx. 1.15 g/mL.
4.2.4 Phosphoric acid, p approximately 1.69 g/mL.
4.2.5 ρ nitric acid is about 1.42g/mL.
4.2.6 hydrochloric acid, ρ about 1.19g/mL, diluted to 1 +1.
4.2.7 hydrochloric acid, ρ about 1.19g/mL, diluted to 1 +10.
4.2.8 sulfuric acid, ρ about 1.84g/mL, diluted to 1 +1.
4.2.9 sulfuric acid, ρ about 1.84g/mL, diluted to 1 +5.
4.2.10 sulfuric acid, ρ about 1.84g/mL, diluted to 1 +19.
4.2.11 silver sulfate solution, 5g/L.
4.2.12 Ammonium persulfate [(NH4) 2S2O8] solution, 500g/L, formulated before use.
4.2.13 Manganese sulfate [MnSO4 · H2O] solution, 4g/L.
4.2.14 Manganese sulfate [MnSO4 · H2O] solution, 100g/L.
4.2.15 potassium permanganate solution, 5g/L.
4.2.16 sodium nitrite solution, 3g/L, formulated before use.
4.2.17 Sulfamic Acid Solution [NH2SO3H], 100 g/L.
This solution can only stabilize for 1 week.
4.2.18 Ferrous ammonium sulfate standard solution, sulfuric acid medium, the solution 1mL equivalent to 2mg chromium.
4.2.18.1 solution preparation
Weigh 46g ammonium ferrous sulfate hexahydrate [Fe (NH4) 2 (SO4) 2 · 6H2O], dissolved in 500mL of water, was added 110mL sulfuric acid
(4.2.8), cool, dilute to 1000mL, mix well.
4.2.18.2 solution potential calibration (before use)
Measure 30.0mL potassium dichromate standard solution (4.2.19), transferred to 600mL beaker, add 45mL sulfuric acid (4.2.9), add water to
About 400 mL. Titrate according to the conditions specified in 4.5.3.3.1.
From formula (6) calculate the corresponding ferrous ammonium sulfate concentration 犮 1, expressed in milligrams per milliliter of chromium (mg).
犮 1 = 30.0 × 1.733 犞 7
(6)
Where.
犞 7 --- Calibrated volume of ammonium ferrous sulfate, in milliliters (mL);
30.0 --- measure the volume of potassium dichromate standard solution (4.2.19), in milliliters (mL);
1.733 --- 1mL potassium dichromate standard solution (4.2.19) chromium (VI) mass, in milligrams (mg).
4.2.19 potassium dichromate standard solution
4.9031 g (accurate to 0.0001 g) of potassium dichromate which had been previously dried at 150 ° C to a constant weight and cooled in a desiccator was weighed,
Water was dissolved and quantitatively transferred to 1000mL single standard volumetric flask, diluted with water to the mark, and mixed.
This standard solution 1mL contains 1.733mg of chromium.
4.3 Instruments
Ordinary experimental equipment and the following instruments.
Potentiometric titration apparatus. The difference in potential can be measured with a platinum-calomel electrode (see note).
Note. Platinum and other reference electrodes can also be used for the assay but the titration curve needs to be redone to determine the end point of the titration.
All glassware should be in line with GB 12805, GB 12806 or GB 12808 provisions of the A-level.
4.4 take samples
According to GB/T 20066 or appropriate national standards for steel samples.
4.5 Analysis steps
Warning. Perchloric acid evaporation may cause an explosion, usually in the presence of ammonia, nitrous oxide fumes or organic matter.
4.5.1 Sample
According to Table 4 Weigh the sample, accurate to 0.0001g.
Table 4
Chromium content (mas...
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